Améliorer notre compréhension des mécanismes de transport/transfert de charges et de stockage de charges dans les films d'oxyde métallique semi-conducteur mésoporeux transparents (fonctionnalisés ou non par des chromophores redox-actifs) dans des électrolytes aqueux est d'une importance fondamentale pour le développement et l'optimisation d'une large gamme de dispositifs de production ou de stockage d'énergie éco-compatibles et/ou éco-durables (cellules solaires à colorants, batteries, photoélectrolyseurs, ….). Dans ce but, des films de TiO2 semi-conducteur mésoporeux préparés par dépôt sous incidence rasante (GLAD-TiO2) ont été sélectionnés pour leur grande surface spécifique, leur morphologie bien contrôlée, leur transparence élevée dans le visible et leur semiconductivité bien définie qui peut être facilement ajustée par l’application d’un potentiel externe, autorisant ainsi leur caractérisation aisée par spectroélectrochimie en temps réel. Nous avons d'abord étudié le transfert et transport de charges dans des électrodes GLAD-ITO et GLAD-TiO2 fonctionnalisées par une porphyrine de manganèse redox-active jouant à la fois le rôle de chromophore et de catalyseur. Nous avons démontré que la réponse électrochimique des électrodes ainsi modifiées, enregistrée en l'absence ou en présence du substrat O2, dépend fortement de la conductivité du film mésoporeux. En utilisant la voltamétrie cyclique couplée à la spectroscopie d'absorption UV-visible, nous avons pu extraire des informations clés telles que la vitesse du transfert d'électrons hétérogène entre le chromophore redox immobilisé et le matériau semi-conducteur, et aussi pu rationaliser le comportement électrochimique spécifique obtenu sur un film GLAD-TiO2 modifié par la porphyrine en condition catalytique. En parallèle, nous avons développé un procédé de fonctionnalisation de ces films d'oxyde métallique mésoporeux (en l’occurrence des films GLAD-ITO) par électrogreffage de sels d'aryldiazonium générés in situ, permettant d'obtenir des électrodes fonctionnalisées avec un taux de recouvrement surfacique élevé et une stabilité dans le temps particulièrement bonne en conditions hydrolytiques. Nous avons également étudié le stockage de charges au sein d’électrodes GLAD-TiO2 dans divers électrolytes aqueux. Nous avons notamment démontré pour la première fois qu’une insertion rapide, massive et réversible de protons peut être effectuée dans des films de TiO2 nanostructurés amorphes immergés dans un tampon aqueux neutre, le donneur de protons étant alors la forme acide faible du tampon. Nous avons également démontré que ce processus de stockage d’électrons couplé à l’insertion de protons peut se produire sur toute la gamme de pH et pour un vaste panel d'acides faibles organiques ou inorganiques, mais aussi de complexes aqueux d'ions métalliques multivalents, à condition que le potentiel appliqué et le pKa de l'acide faible soient correctement ajustés. / Better understanding of the mechanisms of charge transport/transfer and charge storage in transparent mesoporous semiconductive metal oxide films (either functionalized or not by redox-active chromophores) in aqueous electrolytes is of fundamental importance for the development and optimization of a wide range of safe, eco-compatible and sustainable energy producing or energy storage devices (e.g., dye-sensitized solar cells, batteries, photoelectrocatalytic cells, …). To address this question, mesoporous semiconductive TiO2 films prepared by glancing angle deposition (GLAD-TiO2) were selected for their unique high surface area, well-controlled morphology, high transparency in the visible, and well-defined semiconductivity that can be easily adjusted through an external bias, allowing thus their characterization by real-time spectroelectrochemistry. We first investigated charge transfer/transport at GLAD-ITO and GLAD-TiO2 electrodes functionalized by a redox-active manganese porphyrin that can play both the role of chromophore and catalyst. We demonstrate that the electrochemical response of the modified electrodes, recorded either in the absence or presence of O2 as substrate, is strongly dependent on the mesoporous film conductivity. By using cyclic voltammetry coupled to UV-visible absorption spectroscopy, we were able to recover some key information such as the heterogeneous electron transfer rate between the immobilized redox-active dye and the semiconductive material, and also to rationalize the specific electrochemical behavior obtained at a porphyrin-modified GLAD TiO2 film under catalytic turnover. In parallel, we developed a new functionalization procedure of mesoporous metal oxide films (GLAD-ITO in the present case) by electrografting of in-situ generated aryldiazonium salts, allowing for modified electrodes characterized by both a high surface coverage and a particularly good stability over time under hydrolytic conditions. Also, we investigated charge storage at GLAD-TiO2 electrodes under various aqueous electrolytic conditions. We notably evidenced for the first time that fast, massive, and reversible insertion of protons can occur in amorphous nanostructured TiO2 films immersed in near neutral aqueous buffer, with the proton donor being the weak acid form of the buffer but not water. We also demonstrated that this proton-coupled electron charge storage process can occur over the entire range of pH and for a wide range of organic or inorganic weak acids, but also of multivalent metal ion aquo complexes, as long as the applied potential and pKa of weak acid are properly adjusted.

The diploma thesis "Digital Marketing Strategies - Combination of Digital Media Channels" examines how the three telecom operators dominating the Czech market - T-Mobile Czech Republic, O2 Czech Republic and Vodafone Czech Republic - use the digital media channels within the communication with the customers. More specifically, it identifies and describes which channels do the companies involve into their marketing communication, how do they use them and why they have integrated them into the communication strategy. It also examines how the companies interconnect these digital media channels and how the channels can be combined to form an effective digital media strategy. By using the method of case study the companies ' digital marketing activities were examined. It was found that each company uses for its marketing communication the similar set of digital media channels, but the usage is different across the companies studied. Based on these findings I have identified three specific strategies - Diversified Content Strategy, Interactive Channel Strategy and Standardized Content Strategy. Each of the strategies has its advantages and disadvantages, which have been described and the strategies were compared. The findings also indicate that it is better to study the digital media channels as a whole,...

With the progress of high alloy steelmaking processes, it is essential to minimize the loss of valuable metals, like chromium and vanadium during the decarburization process, from both economic as well as environmental view points. One unique technique to realize this aim, used in the present work, is the decarburization of high alloy steel grades using oxygen with CO2 in order to reduce the partial pressure of oxygen. In the present work, the investigation on the oxidation of iron-chromium and iron-vanadium molten alloys under CO2-O2 mixtures was carried out and presented in this dissertation. For oxidation study on Fe-Cr molten alloy with CO2-O2 mixtures, on the basis of thermodynamic analysis, energy balance calculation and modeling results, experimental validation in laboratory was carried out, and later on, the oxidation kinetics of Fe-Cr and Fe-Cr-C melts under controlled partial pressure of oxygen was investigated. Thermodynamics calculation and energy balance estimation demonstrated that, it is possible to use CO2 or CO2-O2 mixtures as decarburizers during EAF process and high initial carbon contents in the steel can be adopted at the beginning in order to reduce the cost. A generic model has been developed to describe the overall process kinetics prevailing in metallurgical reactors containing liquid metal and gas bubbles. This model is general and can be extended further to consider any gas liquid reactions in any chemical engineering reactor, and especially the metallurgical ones, like AOD. In the present dissertation, the model is applied in predicting the evolution of Cr and C contents in a Fe-C-Cr melt during injection of different O2-CO2 mixtures. The related simulation results illustrated that CO2 is efficient in Cr retention. In order to verify the modeling results, 1kg induction furnace experiments were carried out in the present laboratory. The results indicated that the predictions of the model are in good agreement with the experimental results. Meanwhile, the experimental results indicated that the Cr-losses can be significantly lowered by replacing the oxygen with CO2 in the injected gas, specifically for Fe-Cr-C melts with carbon levels higher than about 0.8 mass%. Subsequently, the oxidation kinetics of Fe-Cr and Fe-Cr-C melts was investigated under different CO2-O2 mixtures. It is indicated that, the oxidation rate is controlled by the chemical reaction at the initial stage and the reaction rate can be expressed as  at the Cr range of 11-21 mass% in the Fe-Cr melt. For oxidation study on Fe-V liquid alloy, the investigation of the oxidation kinetics was carried out under CO2-O2 mixtures, which is followed by the study on thermodynamic properties of vanadium containing slags. During oxidation of Fe-V melt, in the case of alloys with vanadium contents exceeding 10 mass%, there exists an incubation period before the chemical reactions prevail the process. In addition, the ‘incubation time’ increased with the increase of temperature and the vanadium content, whereas it decreased with the increase of oxygen partial pressure in the oxidant gas. High-temperature mass spectrometric method was used to determine the activity of the vanadium oxide in CaO-MgO-Al2O3-SiO2-V2O3 slags, whereas, the oxidation states of vanadium in the CaO-MgO-Al2O3-SiO2-VOxslag system was studied by XANES method. The results indicated that, higher basicities stabilize higher vanadium oxidation state, whereas, higher temperature stabilizes lower vanadium oxidation state. The present work, which was carried out within the ECO-STEELMAKING project funded by MISTRA via Jernkontoret is expected to lead to implementation of some modifications in high alloy steel production based on fundamental concepts towards more environment-friendly steel processing. / <p>QC20100628</p>

A galvanic cell converts chemical energy into electrical energy. Devices that carry out these conversions are called batteries. In batteries, generally the chemical components are contained within the device itself. If the reactants are supplied from an external source as they are consumed, the device is called a fuel cell. A fuel cell converts chemical energy into electrical energy as long as the chemicals are supplied from external reserves. The working principle of a metal-air battery involves the principles of both batteries and fuel cells. The anode of a metal-air cell is stored inside the cell, whereas O2 for the air-electrode is supplied from either atmosphere or a tank. There are several metal-air batteries available academically, which include Zn-air, Alair, Fe-air, Mg-air, Ca-air, Li-air and Na-air batteries. So far, only Zn-air battery is successfully commercialized. Li-air battery is attractive compared to other metal-air batteries because of its high theoretical energy density (11140 Wh kg-1). The energy density of Li-air battery is 3 - 5 times greater than state-of-art Li-ion battery. Li-air (or Li-O2) battery comprises Li-metal as the anode and a porous cathode. The cathode and the anode are separated by a suitable separator soaked in an organic electrolyte. Atmospheric air can enter the battery through the porous cathode. Out of the mixture of gases present in the air, only O2 is electrochemically active. For optimization purpose, most of researchers use pure O2 gas instead of air. Li-air battery is not commercialized till now because of several issues associated with it. The issues include: (i) sluggish kinetics of O2 electrode reaction, (ii) decomposition of the electrolyte during charge-discharge cycling, (iii) formation of Li dendrites, (iv) contamination by moisture, etc. Among these scientific and technical problems related to Li-O2 cell system, studies on rechargeable O2 electrode with fast kinetics of oxygen reduction reaction (ORR) during the cell discharge and oxygen evolution reaction (OER) during charge in non-aqueous electrolytes are important. In non-aqueous electrolytes, the 1-electron reduction of O2 to form superoxide (O2 -) is known to occur as the first step. (ii) Subsequently, superoxide undergoes reduction to peroxide (O2 2-) and then to oxide (O2-). The kinetics of ORR is slow in non-aqueous electrolytes. Furthermore, the reaction needs to be reversible for rechargeable Li-air batteries. In order to realize fast kinetics, a suitable catalyst is essential. The catalyst should be bifunctional for both of ORR and OER in rechargeable battery applications. Noble metal particles have been rarely investigated as catalysts for O2 electrode of Li-O2 cells. Graphene has two-dimensional planar structure with sp2 bonded carbon atoms. It has become an important electrode material owing to its high electronic conductivity and large surface area. It has been investigated for applications such as supercapacitors, Li-ion batteries, and fuel cells. Catalyst nanoparticles prepared and anchored to graphene sheets are expected to sustain discrete existence without undergoing agglomeration and therefore they possess a high catalytic stability for long term experiments as well as applications. In this context, it is intended to explore the catalytic activity of noble metal nanoparticles dispersed on reduced graphene oxide (RGO) for O2 electrode of Li-O2 cells. While a majority of the investigations reported in the thesis involves noble metal and alloy particles dispersed on RGO sheets, results on polypyrrole-RGO composite and also magnesium cobalt silicate for Li-O2 system are included. A chapter on electrochemical impedance analysis of LiMn2O4, a cathode material of Li-ion batteries, is also presented in the thesis. Introduction on electrochemical energy storage systems, in particular on Li-O2 system is provided in the 1st Chapter of the thesis. Synthesis of Ag nanoparticles anchored to RGO and catalytic activity are presented in the 2nd Chapter. Ag-RGO is prepared by insitu reduction of Ag+ ions and graphene oxide in aqueous phase by ethylene glycol as the reducing agent. The product is characterized by powder XRD, UV-VIS, IR, Raman, AFM, XPS, SEM and TEM studies. The SEM images show the layered morphology of graphene and TEM images confirm the presence of Ag nanoparticles of average diameter less than 5 nm anchored to RGO (Fig. 1a). Ag-RGO is investigated for ORR in alkaline (1 M KOH), neutral (1 M K2SO4) and non-aqueous 0.1 M tetrabutyl ammonium perchlorate in dimethyl sulphoxide (TBAP-DMSO) electrolytes. The ORR follows 4e- reduction in aqueous and 1e- reduction pathway in non-aqueous electrolytes. Li-O2 cells are assembled with Ag-RGO as (iii) Fig. 1. (a) TEM image of Ag-RGO and (b) charge-discharge voltage profiles of Li-O2 (Ag-RGO) cells. oxygen electrode catalyst in non-aqueous electrolyte (1 M LiPF6-DMSO) and subjected to charge-discharge cycling at several current densities. The discharge capacity values obtained are 11950 (11.29), 9340 (5.00), and 2780 mAh g-1 (2.47 mAh cm-2) when discharged at 0.2, 0.5, 0.8 mA cm-2, respectively (Fig. 1b). Powder XRD studies of discharged electrodes indicate the formation of Li2O2 and Li2O during the cell discharge. In addition to these studies, Na-O2 cells are also assembled with Ag-RGO in non-aqueous electrolyte. It is concluded that the chemistry Li-O2 and Na-O2 cells are similar except for the capacity values. Metal nanoparticles of Au, Pd and Ir are decorated on RGO sheets by reduction of metal ions on graphene oxide by NaBH4. Au-RGO, Pd-RGO and Ir-RGO are characterized by various physicochemical techniques. Particle size of metal nanoparticles ranges from 2 to Fig.2. Charge-discharge voltage profiles Li-O2(RGO) (i) and Li-O2(Au-RGO) (ii) cells at current density 0.3 mA cm-2. 0 2500 5000 7500 10000 12500 15000 10 nm on graphene sheets. All samples are studied for ORR in aqueous and non-aqueous electrolytes by cyclic voltammetry and rotating disk electrode experiments. Li-O2 cells are assembled in 1 M LiPF6-DMSO and discharge capacity values obtained are 3344, 8192 and 11449 mAh g-1 with Au-RGO, Pd-RGO and Ir-RGO, respectively, at 0.2 mA cm-2 current density. The results of these studies are described in Chapter 3. Synthesis and electrochemical activity of Pt-based alloy nanoparticles (Pt3Ni, Pt3Co and Pt3Fe) on RGO are presented in Chapter 4. The Pt3Ni alloy particles are prepared by simultaneous reduction of Pt4+, Ni2+ and graphene oxide by hydrazine in ethylene glycol medium. Pt3Co-RGO and Pt3Fe-RGO are also prepared similar to Pt3Ni-RGO. Formation of alloys is confirmed with XRD studies. O2 reduction reaction on Pt-alloys in non-aqueous electrolyte follows 1e- reduction to O2 -. RDE results show that Pt3Ni-RGO is a better catalyst than Pt for O2 reduction (Fig. 3). Li-O2 cells are assembled with all samples and subjected to Fig. 3. Linear sweep voltammograms of Pt3Ni-RGO, Pt3Co-RGO and Pt3Fe-RGO in 0.1 M TBAPDMSO with 1600 rpm at 10 mV s-1 scan rate. The area of GC electrode was 0.0314 cm2 with a catalyst mass of 200 μg. charge-discharge cycling at several current densities. The initial discharge capacity values obtained are 14128, 5000 and 10500 mAh g-1 with Pt3Ni-RGO, Pt3Co-RGO and Pt3Fe-RGO, respectively, as the air electrode catalysts. Polypyrrole (PPY) is an attractive conducting polymer with advantages such as high electronic conductivity and electrochemical stability. A combination of advantages of graphene and PPY composite are explained in the Chapter 5. PPY is grown on already synthesized RGO sheets by oxidative polymerization of pyrrole in an acidic PY composite is characterized by XRD and Raman spectroscopy studies. Li-O2 cells are assembled in non-aqueous electrolyte and subjected for charge-discharge cycling at different current densities. The discharge capacity value of Li-O2(PPY-RGO) cell is 3358 mAh g-1 Fig. 4. (a) Discharge-charge performance of Li-O2(PPY-RGO) cell with a current density of 0.2 mA cm-2 limiting to a capacity of 1000 mAh g-1 and (b) variation of cut-off voltages on cycling. (3.94 mAh cm-2) in the first cycle. Li-O2(PPY-RGO) cell delivers 3.7 times greater discharge capacity than Li-O2(RGO) cell. Cycling stability of Li-O2 (PPY-RGO) cell is investigated by charge-discharge cycling by limiting the capacity to 1000 mAh g-1, and the cell voltage at the end of discharge and at the end of charge are found constant at 2.75 and 4.10 V, respectively (Fig. 4 a, b). This study shows that PPY-RGO is stable in Li-O2 cells. Electrochemical impedance study shows that charge-transfer resistant is 500 Ω for freshly assembled Li- O2(PPY-RGO) cell and it decreases to 200 Ω after 1st discharge. Synthesis of magnesium cobalt silicate and its electrochemical activity are presented in Chapter 6. MgCoSiO4 is synthesized by mixed solvothermal approach and characterized by various physicochemical techniques. Cubic shaped MgCoSiO4 is investigated for oxygen evolution reaction (OER) activity in alkaline and neutral media. The current values at 0.95 versus SHE are 43, 0.18, 16 mA cm-2 on MgCoSiO4, bare carbon paper and Pt foil electrodes, respectively (Fig. 5), indicating that MgCoSiO4 is a good catalyst for OER. The onset potential for OER is 0.68 V versus SHE on MgCoSiO4 in 1 M KOH. OER activity on MgCoSiO4 is also studied in K2SO4 and phosphate buffer electrolytes. The results indicate good catalytic activity of MgCoSiO4 in neutral electrolytes also. The catalytic activity of Fig. 5. Cyclic voltammograms of bare carbon paper (i), Pt foil (ii), MgCoSiO4 coated carbon (iii) electrodes in 1 M KOH (sweep rate = 5 mV s-1, loading level = 1.15 mg, area = 0.5 cm-2). MgCoSiO4 towards ORR in aqueous and non-aqueous electrolytes is studied by RDE experiments. Li-O2 cells are assembled with bifunctional MgCoSiO4 catalyst in 1 M LiPF6- DMSO electrolyte and the discharge capacity values obtained are 7721 (8.27), 2510 (1.66) and 1053 mAh g-1 (0.92 mAh cm-2) when discharged at 0.3, 0.5 and 0.8 mA cm-2 current densities, respectively. Electrochemical impedance spectroscopy (EIS) measurements of LiMn2O4 electrode are carried out at different temperatures from -10 to 50 0C and in the potential range from 3.50 to 4.30 V, and the data are analysed in Chapter 7. In the EIS spectra recorded over the frequency range from 100 kHz to 0.01 Hz at different temperatures, there are two semicircles present in the Nyquist plot (Fig. 6a). But in 3.90 to 4.10 V versus Li/Li+(1M) potential range at low temperatures (-10 to 15 oC) range, another semicircle also appears (Fig. 6b). Impedance parameters such as solution resistant (Rs), charge-transfer resistance (Rct), doublelayer capacitance (Cdl), electronic resistance (Re) and Warburg impedance (WR), etc., are obtained by analysis of the EIS data. The variations of resistances with temperature are analysed by Arrhenius-like relationships and the apparent activation energies of the corresponding transport properties are evaluated. The values of activation energy for chargetransfer process are 0.37, 0.30 and 0.42 eV, at 3.50, 3.90 and 4.10 V versus Li/Li+(1M), respectively. The chemical diffusion coefficient of Li+ ions into LiMn2O4 calculated from EIS data. The values of diffusion coefficient calculated are in the range of 2.50 x 10-12 - 4.10 Fig. 6. Nyquist plot of impedance study of Li/LiMn2O4 cell at 3.50 V (a) and 3.90 V (b) at -10 0C. Details of the above studies are described in the thesis.

There was a fame time for silicon in condensed matter physics, then the graphene era came and now topological insulators are gaining lot of attention, but magnetism in condensed matter physics has remained always fascinating starting from the ancient days up to now and it will remain as one of the core topic in basic or applied physics. The improvement in the modern techniques allows one to explore magnetism in different length scales as well as in different time scales. As an effect of the improvement in experimental techniques, different magnetic anomalies are unearthed. As a result theories are getting refined and the area of magnetism progresses. From the material point of view, oxides carry the most diverse nature in condensed matter starting from high temperature superconductivity (HTS), colossal magnetoresistance, metal insulator transition etc. to ferromagnetism (FM), anti-ferromagnetism (AFM), spin glass (SG) and so on. Among this list, SG and HTS are one of the least understood topics in magnetism till today. A large research community is involved in understanding the underlying physics behind these two, especially in transition metal oxides. It has drawn attention not only due to fundamental aspects but also due to various applications in day to day life. This thesis is an attempt to understand these two phenomena in transition metal oxides. As the title of this thesis suggest, it is all about magnetic and magneto-transport properties of certain transition metal oxide (crystalline) addressing the interplay between two competing order parameters to understand the underlying physics behind it from an experimental point of view. We have studied two different kinds of competing interactions: (i) the FM/AFM interplay either in bulk or at the interface of the two layers in thin films; (ii) the interplay between FM and superconductivity (SC) in superconductor (S)/ferromagnet (F) heterostructures. Basically both of these two kinds lead to non-equilibrium phenomena in these oxides. One of such competition is between FM and AFM leading to slow dynamics (glassy physics). Disorder and frustrations are the key ingredients for such slow dynamics. The spin frustration arises either due to geometry or due to competing interactions. For example, in a triangular antiferromagnet due to the triangular geometry spins gets frustrated. Now, if it prevails spin disorder as well then it satisfies both the criteria for a spin glass and hence it gives birth to glassiness. Another kind of competition is the interplay among SC and FM. It is known that SC and FM are two antagonistic quantum phenomena thus in a single material SC (singlet pairing) and FM does not co-exist. However one can realize this by making F/S heterostructures and observe the battle between these two competing order parameters. The spin polarized quasiparticle injection from F creates non equilibrium spin density inside S and thereby suppressing the order parameter of S. Also by choosing an appropriate ferromagnet the vortex motion inside S can be arrested to certain extent which can enhance the critical current density of S. Thus FM/SC interplay has become an alternative way to look at the high temperature superconductivity. This thesis is categorized into nine chapters. The summary of each chapter is as follows: Chapter: 1 contains certain concepts of magnetism and superconductivity which is useful to understand the topics and experiments described in this thesis. Chapter: 2 gives the underlying principles of the various experimental techniques used in this thesis. Chapter: 3 describes the magnetic properties of successfully synthesized five compositions of LixNi(2-x)O2 (0.67<x<0.99) which has five distinct ground states namely antiferromagnet (AF), spin glass (SG), cluster glass (CG), re-entrant spin glass (RSG) and ferromagnet (FM). The SG and CG ground state has been well described by the frequency dependent peak shift. From the power-law divergence of critical slowing down the estimated value of relaxation time indicates the presence of interacting macro spins (spin cluster) rather than individual spins in certain LixNi(2-x)O2 samples possessing CG ground state which is also supported by the Arrhenius law. The shift in the spin freezing temperature with the application of dc field obeys Almeida-Thouless line. It also exhibits memory effect which is generic to the slow dynamics. The remnant magnetization relaxation follows logarithmic decay. Interestingly, the sample having RSG ground state shows memory effect up-to 50K and behaves like a FM above that temperature. FC-ZFC M(T) curve shows a splitting at the ordering temperature. The critical analysis across the ferromagnetic-paramagnetic phase transition yields a self-consistent γ, β and δ value and the spin-spin interaction in this material follows long range mean field model. The critical exponents obey Widom scaling law: δ = 1 + γ β −1. The universality class of the scaling relations is also verified where the scaled m and scaled h collapses into two branches. Finally the magnetic phase diagram illustrates a vivid picture of the gradual evolution of ferromagnetism in LixNi(2-x)O2 through a glassy state. As a concluding remark, we think, the present study of glassy physics in magnetic insulator/semiconductor sets an example to compare them with the conventional metallic spin glass system. Chapter: 4 exhibits the results of the structural, magnetic and transport measurements to elucidate some of the most striking unusual physical responses of bulk SrRuO3. Two set of polycrystalline SrRuO3 samples with unique ordering temperature have been synthesized. In one case, we have taken the stoichiometric weight ratio of precursors that eventually resulted in Ru-deficient SrRuO3(SROD). In the other case, we have taken extra 2% wt. RuO2 deliberately to form stoichiometric SrRuO3(SRO). Both the samples are found to crystallize in orthorhombic crystal structure with Pnma space group. The low temperature magnetization is found to be well described by the Bloch T3/2 law and the magnetization near Tc is found to follow the scaling law; M~(Tc-T)β with β=0.35 and β=0.30 for SRO and SROD respectively, apparently showing the 3D Ising behaviour. This aspect will be elaborated in the next chapter. The magnetic ac susceptibility study exhibits a broad hump far below the ferromagnetic ordering temperature and the frequency dependence of this hump position exhibits the characteristics of multiple relaxations. Most strikingly, we notice a low temperature glassy magnetic behaviour clearly demonstrated by the time dependent memory effect. This is very surprising and unlikely to happen in systems, which have itinerant ferromagnetic character. However, we conjecture that slow domain growth and spin canting could be the cause for such effect. The transport study evidences a crossover from Fermi liquid (FL) to non-Fermi liquid (NFL) behaviour around 40 K and a slope change in dρ/dT vs. T plot in the vicinity of that temperature. Astonishingly, we observe two distinct dips (one around ferromagnetic ordering temperature and the other far below the ferromagnetic ordering temperature) in the temperature dependent MR response. In addition, we also observe the signature of an unusual dip in the temperature dependent coercive field towards low temperature side. The emergence of such unusual magnetic and transport response is strongly believed to be connected with hidden magnetic interactions. Our effort on neutron diffraction study has been able to trace the cause of such cryptic magnetic interaction. The findings of neutron diffraction study evidence the change in the unit cell lattice parameters around 75 K and that could be the central cause behind such anomalous low temperature magnetic responses. It also demonstrates that the octahedral tilt freezes around the FM transition and has a minimum around the low temperature glass transition temperature. Most remarkably we observe a decline in the total integrated magnetic intensity towards the low temperature side indicating the presence of antiferromagnetic like interaction in SrRuO3. Chapter: 5 resolves the ambiguity in determining the crritical exponents in SrRuO3. Most remarkably, the application of scaling law in the FC magnetization leads a systematic change in the values of critical exponent with the measuring field in SRO. The β value changes from 0 to o.44 to to 0.29 (corresponds to mean field to Ising) with the increase in the measurement field from 10 to 2500 Oe. However, the H→0 extrapolation fields β=0.5. In order to substantiate the actual nature, the critical behavior is studied across the phase transition from the M-H isotherms. The critical analysis yields a self-consistent β, γ and δ values and the spin-spin interaction follows long range mean field δ=γ β model 1+. The critical exponents also obey Widom scaling law: δ = 1 + γ β-1 The universality class of the scaling relations is verified where the scaled m and scaled h collapses into two branches. We have also found that Ru deficiency does not affect the nature of the spin-spin interaction (though ferromagnetism gets reduced). Further the directional dependence of the critical exponent reflects the isotropic nature of the magnetic interaction. In other words the spin-spin interaction found to be: i) three dimensional, ii) long range, iii) mean field type and iv) isotropic in SrRuO3. We have also found magnetocaloric effect (calculated from the M-H isotherms) that across the phase transition. The specific heat measurements find sharp jump at the ferromagnetic transition due to the magnetic contribution of the specific heat. Chapter: 6 describes the magnetism at the SrRuO3 (SRO)/LaAlO3 (LAO) interface where SRO is an itinerant ferromagnet (FM) and LAO is non-magnetic (NM) (rather diamagnetic). Most surprisingly SRO/LAO exhibits pronounced exchange bias (EB) effect realized by observing a shift in the field cooled M-H hysteresis. Further investigation results an increasing trend of the strength of the EB with the decreases in the thickness of ferromagnetic layer. This system also displays the training effect which essentially confirms that this effect is due to EB. EB arises due to the uncompensated spins at the FM/AFM interface hence the EB effect in SRO/LAO system is unconventional. However, the origin of such AFM interaction (responsible for EB effect in FM/NM system) at SRO/LAO interface is realized and explained through the temperature dependence of the EB effect. Further, we have extensively investigated EB effect in other analogous ferromagnets, FM/FM bilayers and FM/FM superlattices. We found that La0.7Sr0.3MnO3 (LSMO) grown on LAO exhibits the signature of EB. In contrast to that La0.5Sr0.5CoO3 (LSCO) does not show any signature of EB. All the bilayers (LSMO/SRO, LSMO/LSCO and LSCO/SRO) exhibit EB and have similar kind of temperature dependence. In order to gain more insight we have grown a (LSMO/SRO)8 superlattice and observed a complex magnetic behaviour. It exhibits partial inverted magnetic hysteresis. But the system shows EB effect characterized by the shift in the FC hysteresis and training effect. All these observations essentially demonstrate that the magnetic nature of various ferromagnetisms at the interfaces can be changed by choosing a proper partner (acts like adding perturbations into one of those system which lies close to the instability region). Chapter: 7 presents the magneto-transport properties of three SRO films grown on LAO (100) of thicknesses of 12, 24 and 48 nm are studied extensively. For a one to one comparison one of the sample is also grown on STO(100). The coercivity vs. temperature in SRO(48 nm)/LAO exhibits a plateau at ~40 K. The dR/dT exhibits the low temperature hump in all the samples which very much replicates with the bulk scenario that we observed in SRO. Most strikingly the 12 nm SRO sample exhibits NFL behaviour throughout the temperature range of measurement (10-150 K). Our careful investigation reveals a cross-over from FL to NFL in all SRO thin films. The cross-over temperature increases with the increase in thickness and eventually shifts towards the bulk cross-over value. It is apt to remind that in bulk SRO we have demonstrated (by employing temperature dependent neutron diffraction) that there is a presence of antiferromagnetic like interaction at low temperature giving birth to glassiness in bulk SRO. Further, an attempt is made to understand the low temperature magneto-transport anomaly by looking into the spin fluctuation through the low frequency 1/f noise measurements. It conveys a message that there are two types of magnetic ordering present in SRO giving rise to two peaks in the temperature dependence of the relative variance. Application of magnetic field suppresses both the peaks in the relative variance. This certainly indicates that the origin of such peak is caused by the spin fluctuations and thereby it is of magnetic origin. Further we have looked into the Hall effect of a structured (Hall patterned) SRO thin film and observed regular Hall effect (RHE) as well as anomalous Hall effect (AHE) in it. Most remarkably the temperature dependence of the RHE coefficient changes its sign close to the ferromagnetic transition temperature of SRO. This implies a change of the type of the carrier as the temperature is varied. Based on these results, the carrier concentration of SRO as a function of temperature is determined. Chapter: 8 is about the magnetic and magnetotransport studies on the successfully grown high quality S/F heterostructures. The oxygen content plays a vital role in superconductivity of oxide materials thus for studying FM/SC interplay in oxides we have discussed how to achieve a high quality sample (oxygen stoichiometric). We have observed a great influence of a FM in suppressing the superconductivity in YBa2Cu3O(7-δ) (YBCO) in FM/SC heterostructures. The analysis of the out of plane M-H hysteresis reveals a significant reduction of the critical fields (HC1 and HC2) of the SC (in SRO/YBCO bilayer) which might have a great significance to understand the superconductivity in a better way (from both the perspectives: theory and experiments). Most remarkably we have found 40% enhancement of the critical current density of YBCO in SRO/YBCO bilayer. We have demonstrated that in order to see the effect of spin polarizes quasiparticle (SPQP) injection into YBCO, one should not apply more than 20mA current since Joule heating contribution wins over pair breaking effect. The SPQP injection from SRO into YBCO exhibits pair breaking effect as the TC (of the SC) shift follows I2/3 law. The resistive transitions under various applied magnetic fields and the field dependence of the activation energy confirms that the vortices are in the 2D regimes (it follows power law, U0~Hα withα=0.5) in SRO/YBCO. To get a better insight into the FM/SC interplay we have looked into two of the FM/YBCO combinations (LSCO/YBCO and LSMO/YBCO). We observe that the degree of the spin polarizations of the FMs scales with the suppression of superconductivity in YBCO which means more the spin polarization more is the suppression. We have also found out that spin polarization is not the sole parameter in suppressing superconductivity in SRO/YBCO bilayers. It also depends upon the state of magnetization of the ferromagnet. Further, we observed a significant reduction (one order) of the activation energy in LSCO/YBCO compared to SRO/YBCO which clearly indicates that the vortex dynamics might depend on other aspects as well (of the FM). It also reveals the formation of decoupled pancake vortices (pure 2D regime) in LSCO/YBCO and LSMO/YBCO bilayers whereas in case of YBCO and SRO/YBCO it is of 2D coupled type. Chapter: 9 summarizes the whole work presented in this thesis. It also discusses about few research problems which one need to look at in future.

In this diploma thesis I constructed generally usable program for processing economical data through mathematical methods of linear regression in Maple system. Program is used for trend dependency analysis of examined quantities. Via multi-stage algorithmization and implementation of information criterion I created interactive form with user-friendly interface with possibility of straight data import from office suite applications. Functionality of this program is verified on example with specific data collection.

Tesis por compendio / La presente tesis doctoral, titulada "Contribution to the modelling of the light field distribution within Synechocystis sp. PCC 6803 cultures and its influence on cellular photosynthesis processes", engloba diversos trabajos cuyo objetivo es avanzar en la compresión de la distribución lumínica en cultivos de cianobacterias y en los efectos de la luz sobre los mecanismos fotosintéticos de dichos microorganismos. Se trata, en definitiva, de otro paso hacia la integración de modelos matemáticos sobre la fotosíntesis a nivel celular y a escala de cultivo. En primer lugar, para comprender cómo se comporta un cultivo de bacterias fotosintéticas, es fundamental predecir la distribución del campo de luz a lo largo del perfil del biorreactor, tanto a nivel de intensidad total, como respecto a su distribución de flujo de fotones. La distribución de longitudes de onda presente en el medio es importante puesto que muchos procesos de la fotosíntesis están regulados por ciertas longitudes de onda y, por tanto, están modulados por la distribución espectral - el color - de la luz. Aprovechando las propiedades inherentes ópticas del cultivo, se desarrolló un modelo matemático basado en el concepto de campo auto-consistente. Este algoritmo, bautizado en la correspondiente publicación como Auto-consistent Field Approximation Algorithm (AFA), proporciona una predicción del campo lumínico, incluyendo la evolución espectral del mismo a lo largo del camino óptico, para cultivos aclimatados a distintos valores de radiación. Dicha investigación se publicó en la revista Algal Research mediante el artículo titulado "Light distribution and spectral composition within cultures of micro-algae: Quantitative modelling of the light field in photobioreactors", en el que se valida el algoritmo con datos experimentales de dos cepas de estudio de la cianobacteria Synechocystis. Si bien los resultados fueron satisfactorios, el empleo de la ley de Lambert-Beer con un valor constante de atenuación no permite modelizar la parte del campo de luz con menor intensidad, donde el coeficiente de atenuación deja de ser constante y el comportamiento se desvía del exponencial. Por ello, se decidió modelizar el campo de luz con una función que generaliza el caso exponencial mediante el uso de cálculo fraccionario. Se empleó una función de Mittag-Leffler que cumplía con los requisitos formales y ofrecía un ajuste de los datos mejor al obtenido mediante la ley de Lambert-Beer. Como un hallazgo notable, se determinó que el valor de dicho parámetro, que caracteriza la función de Mittag-Leffler, era el mismo para los datos empíricos de las dos cepas estudiadas. Este trabajo se publicó en la contribución llamada "Estimation of the light field inside photosynthetic microorganism cultures through Mittag-Leffler functions at depleted light conditions" en la revista Journal of Quantitative Spectroscopy & Radiative Transfer. Después se procedió a utilizar sendos trabajos de investigación para calcular el campo de luz en un cultivo de Synechocystis y relacionarlo con su productividad máxima. En concreto se ha estudiado, como indicador del rendimiento de la fotosíntesis, la producción de oxígeno y los mecanismos respiratorios asociados a distintas intensidades de luz. Esta investigación está en su fase final y se está ultimando la escritura del artículo para enviarlo a una revista científica próximamente. Dicho manuscrito se titula "Experimental characterisation of Synechocystis sp. PCC 6803 cultures productivity up on light conditions". Finalmente, se está desarrollando una cuarta contribución titulada "Individual pigment contribution to overall in vivo absorption in Synechocystis sp. PCC 6803 cells". Esta investigación estudia la cantidad de luz absorbida por los cromóforos de Synechocystis en función del tipo de iluminación utilizada y calcula la concentración de pigmentos presentes en la célula. / The present doctoral thesis, entitled "Contribution to the modelling of the light field distribution within Synechocystis sp PCC 6803 cultures and its influence on cellular photosynthesis processes", includes several works whose objective is to advance in the understanding of the light distribution in cyanobacterial cultures and in the effects of light on the photosynthetic mechanisms of these microorganisms. It is, ultimately, another step towards the integration of mathematical models on photosynthesis at the cellular level and at the scale of culture. First, to understand how a culture of photosynthetic bacteria behaves, it is essential to predict the distribution of the light field along the bioreactor profile, both at the level of total intensity and with respect to its photon flux distribution. The distribution of wavelengths present in the medium is important since many processes of photosynthesis are regulated by certain wavelengths and are therefore modulated by the spectral distribution - the colour - of the light. Taking advantage of the inherent optical properties of the culture, a mathematical model based on the self-consistent field concept was developed. This algorithm, named in the corresponding publication as Auto-consistent Field Approximation Algorithm (AFA), provides an estimation of the light field, including the spectral evolution thereof along the optical path-length, for acclimated cultures to different radiation values. This research was published in the journal Algal Research through the article entitled "Light distribution and spectral composition within cultures of micro-algae: Quantitative modelling of the light field in photobioreactors", in which the algorithm is validated with experimental data of two strains of study of the cyanobacterium Synechocystis. Although the results were satisfactory, the use of the Lambert-Beer Law with a constant attenuation value, cannot correctly model the part of the light field with less intensity, where the attenuation coefficient ceases to be constant and the behaviour deviates from the exponential. Therefore, it was decided to model the light field with a function that generalizes the exponential case through the use of fractional calculus. A Mittag-Leffler function was used that fulfilled the formal requirements and offered a better data fit than that obtained with the Lambert-Beer law. As a remarkable finding, it was determined that the value of this parameter, which characterises the Mittag-Leffler function, was the same for the empirical data of both studied strains. This work was published in the contribution called "Estimation of the light field in photosynthetic microorganism cultures through Mittag-Leffler functions at depleted light conditions" in the journal Journal of Quantitative Spectroscopy & Radiative Transfer. Thereafter we proceeded to use both research works to calculate the light field within Synechocystis cultures and relate it to its maximum productivity. Specifically, it has been studied, as an indicator of the performance of photosynthesis, the production of oxygen and the associated respiratory mechanisms under different light intensities. This research is in its final phase and the writing of the article is being finalised to submit it to a scientific journal soon. This manuscript is entitled "Experimental characterization of Synechocystis sp. PCC 6803 cultures productivity up on light conditions". Finally, a fourth contribution entitled "Individual pigment contribution to overall in vivo absorption in Synechocystis sp. PCC 6803 cells" is under development. This research studies the amount of light absorbed by Synechocystis chromophores according to the type of employed illumination and calculates the concentration of pigments present in the cell. / La present tesi doctoral, titulada "Contribution to the modelling of the light field distribution within Synechocystis sp. PCC 6803 cultures and its influence on cellular photosynthesis processes", engloba diversos treballs l'objectiu dels quals és avançar en la compressió de la distribució lumínica en cultius de cianobacteris i en els efectes de la llum sobre els mecanismes fotosintètics d'aquests microorganismes. Llavors, es tracta en definitiva d'un altre pas cap a la integració de models matemàtics sobre la fotosíntesi a nivell cel·lular i a escala de cultiu. En primer lloc, per a comprendre com es comporta un cultiu de bacteris fotosintètics, és fonamental predir la distribució del camp de llum al llarg del perfil del bioreactor, tant a nivell d'intensitat total, com pel que fa a la seua distribució de flux de fotons. La distribució de longituds d'ona present en el medi és important ja que molts processos de la fotosíntesi estan regulats per certes longituds d'ona i, per tant, estan modulats per la distribució espectral - el color - de la llum. Aprofitant les propietats inherents òptiques del cultiu, es va desenvolupar un model matemàtic basat en el concepte de camp auto-consistent. Aquest algoritme, batejat en la corresponent publicació com Auto-consistent Field Approximation Algorithm (AFA), proporciona una predicció del camp lumínic, incloent l'evolució espectral del mateix al llarg del camí òptic, per a cultius aclimatats a diferents valors de radiació. Aquesta investigació es va publicar a la revista Algal Research mitjançant l'article titulat "Light distribution and espectral composition within cultures of micro-algae: Quantitative modelling of the light field in photobioreactors", en què es valida l'algoritme amb dades experimentals de dues soques d'estudi de la cianobacteri Synechocystis. Si bé els resultats van ser satisfactoris, l'ús de la llei de Lambert-Beer amb un valor constant d'atenuació no permet modelitzar la part del camp de llum amb menys intensitat, on el coeficient d'atenuació deixa de ser constant i el comportament es desvia del exponencial. Per això, es va decidir modelitzar el camp de llum amb una funció que generalitza el cas exponencial mitjançant l'ús de càlcul fraccionari. Es va emprar una funció de Mittag-Leffler que complia amb els requisits formals i oferia un ajust de les dades millor a l'obtingut mitjançant la llei de Lambert-Beer. Com una troballa notable, es va determinar que el valor d'aquest paràmetre, que caracteritza la funció de Mittag-Leffler, era el mateix per a les dades empíriques de les dues soques estudiades. Aquest treball es va publicar en la contribució anomenada "Estimation of the light field inside Photosynthetic microorganisme cultures through Mittag-Leffler functions at depleted light conditions" a la revista Journal of Quantitative Spectroscopy & Radiative Transfer. Després, es va procedir a utilitzar sengles treballs d'investigació per calcular el camp de llum en un cultiu de Synechocystis i relacionar-lo amb la seua productivitat màxima. En concret s'ha estudiat, com a indicador del rendiment de la fotosíntesi, la producció d'oxigen i els mecanismes respiratoris associats a diferents intensitats de llum. Aquesta investigació està en la seua fase final i s'està ultimant l'escriptura de l'article per enviar-lo a una revista científica pròximament. Dit manuscrit es titula "Experimental characterisation of Synechocystis sp. PCC 6803 cultures productivity up on light conditions". Finalment, s'està desenvolupant una quarta contribució titulada "Individual pigment contribution to overall in vivo absorption in Synechocystis sp. PCC 6803 cells". Aquesta recerca estudia la quantitat de llum absorbida pels cromòfors de Synechocystis en funció del tipus d'il·luminació utilitzada i calcula la concentració de pigments presents en la cèl·lula. / Fuente Herraiz, D. (2018). Contribution to the modelling of the light field distribution within Synechocystis sp. PCC 6803 cultures and its influence on cellular photosynthesis processes [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/106362 / Compendio

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A radio frequency (rf) quadrupole instrument, currently known as an Isobar Separator for Anions (ISA), has been integrated into an Accelerator Mass Spectrometry (AMS) system to facilitate anion–gas reactions before the tandem accelerator. An AMS Cs+ sputter source provided > 15 keV ions that were decelerated in the prototype ISA to < 20 eV for reaction in a single collision cell and re-accelerated for AMS analysis. Reaction based isobar suppression capabilities were assessed for smaller AMS systems and a new technique for gas–phase reaction studies was developed. Isobar suppression of 36S– and 12C3– for 36Cl analysis, and YF3– and ZrF3– for 90Sr analysis were studied in NO2 with deceleration to < 12 eV. Observed attenuation cross sections, σ [x 10^–15 cm^2], were σ(S– + NO2) = 6.6, σ(C3– + NO2) = 4.2, σ(YF3– + NO2) = 7.6, σ(ZrF3– + NO2) = 19. With 8 mTorr NO2, relative attenuations of S–/Cl– ~ 10^–6, C3–/Cl– ~ 10^–7, YF3–/SrF3– ~ 5 x 10^–5 and ZrF3–/SrF3– ~ 4 x 10^–6 were observed with Cl– ~ 30% and SrF3– > 90% transmission. Current isobar attenuation limits with < 1.75 MV accelerator terminal voltage and ppm impurity levels were calculated to be 36S–/Cl– ~ 4 x 10^–16, 12C3–/Cl– ~ 1.2 x 10^–16, 90YF3–/SrF3– ~ 10^–15 and 90ZrF3–/SrF3– ~ 10^–16. Using 1.75 MV, four 36Cl reference standards in the range 4 x 10^–13 < 36Cl/Cl < 4 x 10^–11 were analyzed with 8 mTorr NO2. The measured 36Cl/Cl ratios plotted very well against the accepted values. A sample impurity content S/Cl < 6 x 10^–5 was measured and a background level of 36S–/Cl < 9 x 10^–15 was determined. Useful currents of a wide variety of anions are produced in AMS sputter sources and molecules can be identified relatively unambiguously by stripping fragments from tandem accelerators. Reactions involving YF3–, ZrF3–, S– and SO– + NO2 in the ISA analyzed by AMS are described, and some interesting reactants are identified.

A radio frequency (rf) quadrupole instrument, currently known as an Isobar Separator for Anions (ISA), has been integrated into an Accelerator Mass Spectrometry (AMS) system to facilitate anion–gas reactions before the tandem accelerator. An AMS Cs+ sputter source provided > 15 keV ions that were decelerated in the prototype ISA to < 20 eV for reaction in a single collision cell and re-accelerated for AMS analysis. Reaction based isobar suppression capabilities were assessed for smaller AMS systems and a new technique for gas–phase reaction studies was developed. Isobar suppression of 36S– and 12C3– for 36Cl analysis, and YF3– and ZrF3– for 90Sr analysis were studied in NO2 with deceleration to < 12 eV. Observed attenuation cross sections, σ [x 10^–15 cm^2], were σ(S– + NO2) = 6.6, σ(C3– + NO2) = 4.2, σ(YF3– + NO2) = 7.6, σ(ZrF3– + NO2) = 19. With 8 mTorr NO2, relative attenuations of S–/Cl– ~ 10^–6, C3–/Cl– ~ 10^–7, YF3–/SrF3– ~ 5 x 10^–5 and ZrF3–/SrF3– ~ 4 x 10^–6 were observed with Cl– ~ 30% and SrF3– > 90% transmission. Current isobar attenuation limits with < 1.75 MV accelerator terminal voltage and ppm impurity levels were calculated to be 36S–/Cl– ~ 4 x 10^–16, 12C3–/Cl– ~ 1.2 x 10^–16, 90YF3–/SrF3– ~ 10^–15 and 90ZrF3–/SrF3– ~ 10^–16. Using 1.75 MV, four 36Cl reference standards in the range 4 x 10^–13 < 36Cl/Cl < 4 x 10^–11 were analyzed with 8 mTorr NO2. The measured 36Cl/Cl ratios plotted very well against the accepted values. A sample impurity content S/Cl < 6 x 10^–5 was measured and a background level of 36S–/Cl < 9 x 10^–15 was determined. Useful currents of a wide variety of anions are produced in AMS sputter sources and molecules can be identified relatively unambiguously by stripping fragments from tandem accelerators. Reactions involving YF3–, ZrF3–, S– and SO– + NO2 in the ISA analyzed by AMS are described, and some interesting reactants are identified.