La combustion stratifiée, qui consiste à brûler un mélange carburant/oxydant inhomogène, et la combustion diluée, consistant à ajouter une quantité limitée de gaz brûlés, sont deux technologies utilisées dans les moteurs à piston pour réduire leur consommation. Cette thèse est dédiée à l’étude de l’allumage dans ces deux types de milieux en régimes laminaire et turbulent. Un nouveau schéma cinétique pour la combustion propane/air a été dérivé et combiné à deux approches de modélisation différentes : la chimie complexe et une approche de chimie tabulée de type FPI. Dans le cas laminaire, les deux approches de modélisation donnent des résultats similaires et un modèle simple a mis en évidence l’importance de la dynamique des gaz frais et des gaz brûlés sur le développement du noyau. Dans le cas turbulent, plusieurs techniques d’analyse ont montré la dépendance de la vitesse absolue de la flamme au champ de vitesse moyen et la décorrélation des fluctuations locales de richesse. / Stratified combustion, which consists in burning an inhomogeneous fuel/air mixture, and diluted combustion, which consists in adding a limited quantity of burnt gases, are two technologies used in internal combustion engines to reduce fuel consumption. This Ph.D is devoted to the study of ignition in these two types of combustion in laminar and turbulent regimes. A new kinetic scheme for propane/air combustion has been derived and combined to two modeling approaches: finite-rate chemistry and an FPI tabulated chemistry approach. In the laminar case, both approaches give similar results and a simplified model has highlighted the importance of fresh and burnt gases dynamics on the kernel development. In the turbulent case, several techniques of analysis have shown the dependency of absolute flame speed on the mean fluid velocity and the lack of correlation to the local equivalence ratio.

<p>In Chapter 2, an experiment has been developed to investigate the passive pre-chamber jet ignition process in gasoline engine configurations and low-load operating conditions. The apparatus adopted a modified 4-cylinder 2.0L gasoline engine to enable single-cylinder operation. To reduce the complexity, the piston position was fixed at a predefined position relative to the top dead center (TDC) to simulate thermodynamic conditions at ignition and injection timings. High-speed Infrared (IR) imaging was applied to visualize the jet penetration and ignition process inside the main cylinder and to investigate the cyclic spatial variability. Two passive pre-chambers with different total nozzle areas and numbers of nozzles were used. In addition, the pre-chamber volume and pressure at ignition timing were varied to examine their effect on jet ignition performance. Misfire behavior was observed in the main chamber of all test cases, and the results suggested that the main cause is a high Residual Mass Fraction (RMF) in the pre-chamber affecting the subsequent cycle. A larger total nozzle area, smaller volume, higher pressure, and fuel-lean operation tended to mitigate the misfire behavior. For a test case with a spark pressure of 6 bar, a reduced cyclic variability in terms of coefficient of variation peak cylinder pressure (COVPmax) from 10.03% to 7.38% and combustion phasing variation from 81 crank angle degree (CAD) to 12 CAD were observed with increasing pre-chamber volume-to-area (V/A) ratio from 59.37 m to 103.11 m, but slightly higher misfire frequency was observed, from 46.67% to 50.00%, suggesting an accurate combination of pre-chamber design parameters is needed to improve overall performance at low-load operation.</p> <p>In Chapter 3, it examines the influence of passive pre-chamber nozzle diameter and dilution level on jet formation and engine performance. Utilizing a modified constant-volume gasoline direct injection engine with an optically-accessible piston, we tested three passive pre-chambers with nozzle diameters of 1.2, 1.4, and 1.6 mm, while nitrogen dilution varied from 0 to 20%. With the help of high-speed imaging, we captured pre-chamber jet formations and subsequent flame propagation within the main chamber. Our novel findings reveal that asymmetric temporal and spatial jet formation patterns arising from pre-chambers significantly impact engine performance. The larger nozzle diameter pre-chambers exhibited the least variation in jet formation due to their improved scavenging and main mixture filling processes, but had the slowest jet velocity and lowest jet penetration depth. At no dilution condition, the 1.2 mm-PC demonstrated superior performance attributed to higher pressure build-up in the pre-chamber, resulting in accelerated jet velocity and increased jet penetration depth. However, at high dilution condition, the 1.6 mm-PC performed better, highlighting the importance of scavenging and symmetry jet formation. This study emphasizes the importance of carefully selecting the pre-chamber nozzle diameter, based on the engine's operating conditions, to achieve an optimal and balanced configuration that can improve both jet formation and jet characteristics, as well as scavenging.</p> <p>In Chapter 4, it investigates the influence of passive pre-chamber nozzle diameter on jet ignition and subsequent main chamber combustion under varying load conditions and dilution levels using a constant-volume optical gasoline direct injection engine. The results reveal that as the load decreases, both fuel availability and flow conditions deteriorate, leading to delayed and inferior jet characteristics that affect main chamber ignition and combustion processes. In high and medium load conditions without dilution, the smallest nozzle diameter pre-chamber (1.2mm-PC) shows improved jet ignition and main combustion due to earlier jet ejection, enhanced penetration, and intensified jet. This is facilitated by the smaller nozzle diameter enabling faster and higher pre-chamber pressurization. Conversely, under low load conditions, the largest nozzle diameter pre-chamber (1.6mm-PC) performs better, likely due to improved scavenging and reduced residual levels, resulting in less compromised pre-chamber combustion and subsequent jet characteristics. The nozzle diameter also has a significant impact on cycle-to-cycle variations, with smaller diameters enhancing jet ignition performance but increasing variability. The effect of external residuals (dilution) on jet ignition performance varies depending on the nozzle diameter, with the 1.6mm-PC exhibiting less degradation and demonstrating earlier jet ejection and CA50 timing compared to smaller nozzle diameter pre-chambers at higher dilution conditions. The improved scavenging and relatively lower residual levels in the larger nozzle diameter pre-chamber contribute to its increased resistance to dilution and potential extension of dilution tolerance.</p> <p>In Chapter 5, it presents an analysis of the effects of pre-chamber nozzle orientation on dilution tolerance in a constant-volume optical engine. Using a combination of experimental and numerical methodologies, we provide novel insights into how variations in nozzle number, orientation, and size influence combustion performance under different dilution conditions. The findings reveal that an increase in the number of nozzles, for a fixed A/V ratio, tends to enhance ignition performance and stability across a range of dilution scenarios, primarily due to an increase in ignition points and a larger ignition surface area. Meanwhile, swirling pre-chambers, despite their potential to boost initial combustion performance at no dilution condition, may limit dilution tolerance due to the complexity of their internal flow dynamics and increased heat loss through nozzle surfaces. Furthermore, pre-chambers combining swirling and straight nozzle orientations fail to synergize the benefits of each type, and instead, exacerbate challenges such as heat loss, flame quenching, and unfavorable flow dynamics. These findings emphasize the complexity and nuanced trade-offs involved in optimizing pre-chamber design for improved dilution tolerance and suggest potential directions for future research in this area.</p> <p>In Chapter 6, it investigates the behavior of pre-chamber knock in comparison to traditional spark ignition engine knock, using a modified constant-volume gasoline engine with an optically-accessible piston. The aim is to provide a deeper understanding of pre-chamber knock combustion and its potential for mitigating knock. Five passive pre-chambers with different nozzle diameters, volumes, and nozzle numbers were tested, and nitrogen dilution was varied from 0 to 10%. The stochastic nature of knock behavior necessitates the use of statistical methods, leading to the proposal of a high-frequency band-pass filter (37-43 kHz) as an alternative pre-chamber knock metric. Pre-chamber knock combustion was found to exhibit fewer strong knock cycles compared to SI engines, indicating its potential for mitigating knock intensity. High-speed images revealed pre-chamber knock primarily occurs near the liner, where end-gas knock is typically exhibited. The study identified that increasing pre-chamber nozzle diameter resulted in a larger dispersion of knock cycles and more severe knock intensity, likely due to shorter jet penetration depth requiring more time for end-gas consumption. Strategies for mitigating knock in pre-chamber combustion systems include reducing the pre-chamber volume for a fixed A/V ratio and increasing dilution level. The results of this study offer valuable insights for developing effective knock mitigation approaches in pre-chamber combustion systems, contributing to the advancement of more efficient and reliable engines.</p> <p>In Chapter 7, a numerical investigation of different premixed gaseous injection strategies was performed to understand their impact on the scavenging and mixture formation of an air-fuel premixed pre-chamber with high exhaust gas recirculation (EGR) operations. EGR dilution is effective for reducing coolant heat loss, pumping work at throttled conditions, and mitigates knock at high-load conditions, thus increasing engine efficiency. To further extend the EGR limit of an air-fuel premixed pre-chamber engine, the effects of different injection strategies (including timing, duration, pressure, pre-chamber volume, and hardware) on the EGR level, trap efficiency, and parasitic loss were determined. Regardless of injection duration and upstream pressure, injecting too early not only increased the amount of the injected premixed gas leaking into the main chamber but also was inefficient in reducing the EGR level in the pre-chamber. To reduce the EGR level in the pre-chamber to a level where successful ignition and combustion of the pre-chamber mixture is possible, the injection timing should be delayed to be close to the ignition timing. A premixed air-fuel injection is thus proposed to reduce the time required for air-fuel mixing in the pre-chamber. With a delayed end of injection (EOI), both leakage amount and EGR level were reduced compared to the cases with earlier injection timings. The results show that an injection with 15 bar upstream pressure, 20 CA duration, EOI of −20 CAD aTDC (ignition timing), and with guided injection hardware for the base pre-chamber volume resulted in about 0.17% air compression parasitic loss, over a 94% trap efficiency, at the same time maintaining the mean EGR level in the pre-chamber below 20%, ensuring good pre-chamber combustion. With a 50% increase in pre-chamber volume from the base case, the parasitic loss increased by 65% (from 0.17% to 0.28% loss), indicating a problem with a larger pre-chamber with a separate air valve and injector.</p>

Thermometry measurements were carried out using planar laser induced phosphorescence in conjunction with thermographic phosphors in heated turbulent jets and laminar flames in order to further develop the technique for usage in flames. Two dimensional thermometry measurements are essential to improve the understanding of combustion processes, as temperature governs soot pyrolysis, leading to soot formation. Two particular thermographic phosphors, BAM and YAG:Dy were tested and compared and it was found that they were unsuitable for gas phase flame thermometry measurements. Soot volume fraction measurements were carried out using planar two colour laser induced incandescence in gaseous and liquid fuel flames. The gas fuel flames were diluted with nitrogen, carbon dioxide and hydrogen individually and then with nitrogen and hydrogen together, as well as carbon dioxide and hydrogen together, separately. Results revealed the dilution effects of the gases on the soot formation process, where increasing nitrogen percentage in the flow decreased SVF, carbon dioxide reduced it further and hydrogen showed no marked difference. Biodiesels were compared with each other and with diesel in a wick burner in order to analyse their compositional effects on soot. Biodiesel composition was measured using gas chromatography. The sooting tendencies of the biodiesels were as expected, fuels with a longer average carbon chain length and a higher degree of unsaturation were found to produce more soot than shorter, more saturated fuels. Diesel was sootier than all of the biofuels tested, due to containing aromatics and a lower oxygen content. A pilot study was also done, where the performance and emissions of biofuels and biofuel-diesel blends were tested in a gas turbine engine, in order to relate the investigation to real world situations.

<p>When establishing a groundwater protection area it is of great interest to be able to estimate the transit time of the groundwater from different places of the aquifer to the withdrawal well. These estimates can be uncertain due to heterogeneities in the aquifer. As a part of the work to develop methods for a more certain delineation of protection areas, a tracer test was performed in an esker located 25 kilometres NW of the town Uppsala.</p><p>The purpose of this master thesis was to perform, describe and evaluate the tracer test. Travel times from the tracer test should then enable comparison against stochastic simulated travel times of the groundwater in the area.</p><p>Three dyes (rhodamine WT, uranine and naphtionate) and a salt (NaBr) were used in the tracer test. The tracers were injected in four different wells located 25 meters from a pumping well. The pumping well was pumped at a rate of 1.7 L/s and water samples were collected from the pumped water. The calculated mass recovery was large for bromide (101 %) but considerably lower for the dyes rhodamine WT (70 %), uranine (61 %) and Naphthionate (19 %). The low mass recovery for the dyes is probably due to degradation and maybe also adsorption.</p><p>An analytical solution to the advection – dispersion equation in one dimension for radial converging flow was used for the interpretation of the breakthrough curves. Smallest and largest transit time that was received from the model fitting was 1,9 days and 5,1 days respectively and without exception large longitudinal dispersivities (9-35 m). Point dilution tests were performed in the injection wells in order to determine the ground water flow at these wells. The tests gave information about the magnitude of the ground water flow, differences between the wells and the flow change at pumping.</p><p>Travel times were estimated from the received breakthrough curves and the travel time distributions can be used for comparison against stochastic simulated travel times of the groundwater.</p> / <p>Vid utformningen av skyddsområden för grundvattentäkter är det av stor vikt att kunna uppskatta grundvattnets transporttid (uppehållstid) från olika partier av akviferen till uttagsplatsen. Dessa bedömningar har en tendens att bli osäkra på grund av heterogeniteter i akviferen. Som ett led i arbetet att utveckla metoder för en säkrare avgränsning av skyddsområden genomfördes ett spårämnesförsök i en isälvsavlagring (Järlåsaåsen) belägen cirka 2,5 mil nordväst om Uppsala.</p><p>Syftet med examensarbetet var att genomföra, beskriva och utvärdera spårämnesförsöket. Bestämda transporttider från spårämnesförsöket skulle sedan kunna användas för jämförelse med stokastiskt simulerade transporttider för grundvattnet i området.</p><p>Tre färgspårämnen (rhodamin WT, uranin och naphtionat) och ett salt (NaBr) användes vid spårämnesförsöken. Spårämnena injicerades i fyra olika grundvattenrör belägna 25 meter från en uttagsbrunn. Pumpflödet ur uttagsbrunnen var 1,7 L/s och med en automatprovtagare togs vattenprover från det uppumpade vattnet. Resultatet från massbalansberäkningarna visade på att all injicerad bromid återfanns i uttagsbrunnen, men andelen återfunnen spårämnesmassa var betydligt lägre för färgspårämnena rhodamin WT (70 %), uranin (61 %) och naphtionat (19 %). Den låga andelen återfunnen massa beror troligtvis främst på nedbrytning och kanske även på adsorption.</p><p>En analytisk lösning till advektions- dispersionsekvationen i en dimension för radiellt konvergerande strömning användes vid utvärderingen av genombrottskurvorna. En minsta och största uppehållstid på 1,9 dygn respektive 5,1 dygn och överlag oväntat stora dispersiviteter (9 – 35 m) erhölls från kurvanpassningen. Den första ankomsttiden till uttagsbrunnen hade ett minsta och största värde på 3,8 respektive 13 timmar. Utspädningsförsök genomfördes också för att bestämma storleken på flödet vid injektionsrören. Dessa försök gav en bild av flödets storlek, skillnader mellan de olika injektionsrören och flödets förändring vid pumpning.</p><p>De bestämda transporttiderna visar på relativt stora tidsskillnader och ett heterogent försöksområde. Transporttidsfördelningarna utgör också ett underlag för en jämförelse mot stokastiskt simulerade transporttider av grundvattnet.</p>

<p>In order to examine the usefulness of the multi breath helium dilution method (MB) it was compared to the single breath helium dilution method (SB) and body plethysmography (BP). Residual volume (RV), total lung capacity (TLC) and vital capacity (VC) were measured in seventeen subjects with obstructive (11) or restrictive (6) lung disease and four normal subjects.</p><p>With information from professional literature and current periodicals, advantages and disadvantages with all three methods were compared. ANOVA and Student's t-test were performed on the measurement results.</p><p>The results of the statistical tests tell us there are differences among the methods in the group of obstructive patients. They also reveal a notable difference between the MB and SB methods when measuring the same parameter. In addition, it was noted that none of the existing sets of prediction equations fulfill the requirements established on high quality lung function testing.</p><p>Although a thorough evaluation of the reproducibility of the method is still required, it appears to be a viable alternative to body plethysmography. We claim that measuring the above mentioned static lung volumes with only the single breath helium dilution method cannot be considered a satisfactory practice.</p>

The goal of this elaborate work was to describe the most often medication misconducts, errors and risks during the intravenous drug administration and dilution in the field of primary care in the Intensive Care Unit - ICU. My interest was to find out about local ICU's standards and regulations and to survey how knowledgeable nursing stuff is towards medication hazard regulation and its affect. The first theoretical part concentrates on conception of IV drug administration and dilution. It charts and shows the situation at the current time. Empirical section of my elaborate work shows findings based upon questionnaire. It serves the purpose of hypothesis verification and confirms the goals of my study. Obtained information should be a foundation for future processing and utilization standards regulation or recommendation how to safely administrate intravenous drugs.

The newly discovered iron based superconductors have captivated the attention of the scientific community due to the unusual mechanism behind their superconductivity and their promise as the next generation high temperature superconductors. After a century of superconductor research, the physical mechanism behind high temperature superconductivity is still not understood. These new materials bring renewed hope in elucidating the pairing mechanism responsible with high temperature superconductors and achieving the ultimate goal of the field, room temperature superconductivity. Consequently, a deeper understanding of the intriguing properties of iron based materials is essential. A great deal about the pairing mechanism of Cooper electron pairs can be inferred from the symmetry of their pairing wave function or order parameter. One of the most involved probes for studying the pairing symmetry is the London penetration depth. The low temperature behavior of London penetration depth in superconductors is directly related to the density of states and provides a powerful tool for investigating low-lying quasiparticle energy and, for this very reason, can give valuable hints on superconducting gap symmetry. The work presented focuses on investigating the pairing symmetry in the Fe1+y(Te1−xSex) system using a radio-frequency tunnel diode oscillator (TDO) technique for precise measurements of the temperature dependence of their in-plane penetration depth. The TDO technique, based on an original concept involving the use of planar inductors in an novel configuration, was implemented on a dilution refrigerator to investigate a significant number of single crystal samples, with nominal Se concentrations of 36%, 40%, 43% and 45% respectively, down to temperatures as low as 50 mK. A systematic study together with a comprehensive analysis regarding the order parameter symmetry in the Fe1+y(Te1−xSex) system is presented. In many cases we found that London penetration depth shows an upturn below at low temperatures, indicative of a paramagnetic-type contribution. Also the low-temperature behavior of penetration depth is best described by a quadratic power law with no systematic dependence on the Se concentration. Most importantly, in the limit of T → 0, in some samples we observed a narrow region of linear temperature dependence, suggestive of nodes in the superconducting gap of Fe1+y(Te1−xSex).

O fósforo (P) é um elemento altamente demandado pela agricultura mundial para produção de alimentos. Os solos de regiões tropicais apresentam baixo teor de P disponível às plantas, devido à escassez natural herdada do material de origem e predominância de processos de fixação, sendo necessário o suprimento deste nutriente via adubação. Os fertilizantes fosfatados solúveis utilizados apresentam baixo aproveitamento devido a reações que se iniciam desde a interface solo-grânulo até o trajeto difusivo do P no solo. Pesquisas têm abordado sobre o potencial do silício (Si) em competir por sítios de adsorção de P no solo, tornando este nutriente mais disponível às plantas e aumentando o aproveitamento dos adubos fosfatados. Visando desenvolver estratégias para melhorar a eficiência agronômica do fosfato monoamônio (MAP) os objetivos deste trabalho foram: a) construir um dispositivo para granular fertilizante em pequenas quantidades, b) avaliar a difusão e disponibilidade do P a partir dos fertilizantes produzidos, em dois solos de característica textural e capacidade máxima de adsorção de P contrastantes e c) avaliar a eficiência agronômica e o aproveitamento do P dos fertilizantes propostos neste estudo em conjunto com o superfosfato orgânico-complexado (SOC) e o MAP, por meio da técnica isotópica com 32P. Foram conduzidos quatro experimentos no Laboratório de Fertilidade do Solo do Centro de Energia Nuclear na Agricultura (CENA-USP), Piracicaba - SP. Os solos utilizados nos ensaios foram classificados como Latossolo Vermelho-Amarelo distrófico (LVAd) e Latossolo Vermelho distrófico (LVd). Conduzidos simultaneamente, o primeiro e segundo experimentos constituíram de estudo da difusão do P por meio da incubação dos fertilizantes em placa de petri preenchidas com cada um dos solos, montados em delineamento inteiramente casualizado, compostos por 11 tratamentos (9 fertilizantes com diferentes proporções P-Si (1-9 a 9-1) no grânulo mais o MAP e o tratamento controle) e cinco repetições. O terceiro e quarto experimentos foram instalados em casa de vegetação com a cultura do milho cultivada nos dois tipos de solo, num delineamento inteiramente casualizado, em esquema fatorial 5x4, sendo cinco fertilizantes fosfatados dentre os quais três foram selecionados no estudo de incubação (proporções P-Si no grânulo: 2-8, 6-4 e 8-2) o SOC e o MAP, aplicados em quatro doses de P (0, 30, 60, 90 mg kg-1). Foi possível construir o granulador projetado, e com uso deste produzir os fertilizantes propostos. No estudo de incubação, observou-se que a presença de Si no grânulo do fertilizante fosfatado alterou o pH do solo ao redor dos grânulo e a difusão e disponibilidade do P em ambos os solos estudados. O P difundiu-se poucos centímetros no solo, ficando restrito às primeiras secções em torno do ponto de aplicação do fertilizante. No experimento em casa de vegetação, observou-se que o fertilizante contendo a maior quantidade de Si no grânulo proporcionou maiores valores de P acumulado, P na planta proveniente do fertilizante e aproveitamento do P do fertilizante, bem como melhores índices de eficiência agronômica relativa em relação ao MAP. O SOC proporcionou os menores resultados em todos os parâmetros avaliados / Phosphorus (P) is a highly demanded element for world agriculture for food production. Tropical soils present low level of this nutrient in phyto-available form due to natural inherited shortage of source material and predominance of fixation processes, requiring the supply of this nutrient via fertilization. The soluble phosphate fertilizers used have low utilization by plants due to reactions that start from the soil-granule interface to the P diffusive path in the soil. Research has addressed on the silicon (Si) potential to compete for P adsorption sites in the soil, making this nutrient more available to plants and increasing the use of fertilizer P. In order to develop strategies to increase the agronomic efficiency of monoammonium phosphate (MAP) the objectives of this study were: a) to build a device for the production of granulated fertilizer in small quantities b) assess the diffusion and availability of P from the fertilizer produced in two contrasting textural characteristics and maximum P adsorption capacity and c) evaluate the agronomic efficiency and utilization of P from fertilizers proposed in this study compared with the organic-complexed superphosphate (OCS) and MAP by 32P isotope technique. Four experiments were conducted at the Soil Fertility Laboratory of Center for Nuclear Energy in Agriculture (CENA-USP), Piracicaba SP, Brazil. The soils used in the experiments were classified as Oxisol and Haplortox collected from the surface layers. The first and second experiments, conducted simultaneously, constituted the fertilizer incubation study in petri dishes in a completely randomized design with 11 treatments (9 fertilizer with different P- Si proportions (1-9 to 9-1) in the granule, plus the MAP and the control) and five replicates. The third and fourth experiments were conducted in a greenhouse with corn grown in the two types of soil in a completely randomized 5x4 factorial design, with five phosphate fertilizer among which three were selected in the study of incubation (proportions P-Si in the granule: 2-8, 6-4 and 8-2), OCS and MAP applied in four rates of P (0, 30, 60, 90 mg kg-1). It was possible to build the projected granulator, and use this to produce the proposed fertilizer. In the study of incubation, it was observed that the presence of Si in phosphate fertilizer granule changed the pH of the soil around the granules and the diffusion of P in both soils. The P diffused few centimeters in both soils, being restricted to the first sections around the applied granule. It was observed that, in the greenhouse experiment, in both soils, the fertilizer containing the highest amount of Si in the granule provided the highest plant accumulated P values, P in the plant derived from fertilizer and of fertilizer P utilization and best relative agronomic efficiency rate in relation to MAP and the OCS. The OCS gave the lowest results in all parameters

O estudo do sistema antiferromagnético diluído K2Fe1-xInxCl5.H2O com a finalidade de se estudar efeitos de campos aleatórios, mostrou o aparecimento de uma magnetização remanente (Mr) quando o composto é resfriado sujeito a um campo magnético externo. Esta magnetização remanente surge ao longo do eixo de fácil magnetização, abaixo de TN, para campos tão baixos quanto alguns mOe. A presença deste efeito foi observada também em outros compostos como por exemplo no Rb2Fe1-xInxCl5.H2O. A origem de Mr está provavelmente associada à presença de domínios antiferromagnéticos que se formam mesmo em campos muito baixos, e cujas paredes são presas por íons não magnéticos e defeitos. No caso do composto com rubídio, as paredes se encontram aparentemente menos presas, podendo levar a outros efeitos como a observação de fenômenos de relaxação magnética quando o campo em que a amostra é resfriada é retirado abaixo de TN. É sugerido neste trabalho que a magnetização remanente está provavelmente armazenada nas paredes de domínio formadas, já que o comportamento de Mr não segue aquele observado para a sub-rede antiferromagnética. Estudamos também o efeito da diluição na transição entre as fases antiferromagnética e spin-flop. Observamos a presença de uma histerese para o caso dos compostos K2Fe1-xInxCl5.H2O, além de um alargamento da transição. A presença destes efeitos está provavelmente associada à presença de uma fase mista onde as fases antiferromagnética e spin-flop coexistem em uma estrutura de domínios. No caso dos compostos Rb2Fe1-xInxCl5.H2O, de uma modo geral é observado apenas um alargamento da transição, sem o aparecimento de histerese. Neste caso, é possível a existência de uma fase intermediária induzida por campos aleatórios, similar àquela proposta por Aharony. As medidas de calor específico realizadas com e sem campo magnético externo aplicado no sistema (Nd1-xSmx)2CuO4 mostrou em todos os casos a presença de um máximo. Através do estudo do comportamento deste máximo, observamos a presença de duas regiões de diluição de comportamento distinto. Para x > 0.7, o comportamento é aquele observado para um sistema antiferromagnético simples diluído. A aplicação de campo neste caso, leva a uma pequena diminuição na temperatura em que o máximo ocorre. Para x < 0.7 temos que o efeito dominante é o mesmo que aquele observado para o caso do Nd2CuO4. O comportamento do Nd2CuO4 não é o de um antiferromagneto simples, já que as interações entre as sub-redes de Cu e de Nd levam a um “splitting" do estado de energia fundamental da sub-rede de Nd, e consequentemente a um comportamento do tipo Schottky no calor específico. / Magnetization measurements performed on diluted antiferromagnetic compounds K2Fe1-xInxCl5.H2O in order to study the Random Fields Ising Model revealed the existence of a remnant magnetization (Mr) when the sample is cooled below TN in an applied axial magnetic field. This remnant magnetization along the easy axis direction is observed in magnetic fields as low as a few mOe. Other diluted compounds, like Rb2Fe1-xInxCl5.H2O, also show the same behavior. The origin of this remnant magnetization is probably related to the presence of low field antiferromagnetic domains, which walls are pinned by non-magnetic ions and defects. For the Rb-based compound, the walls are probably not strongly pinned. In this case, when the field is turned off bellow TN relaxation effects are sometimes observed. It is suggested in this work that the remnant magnetization is stored in the domain walls, since the Mr behavior is quite different from the one observed for the antiferromagnetic sublattice. We have also studied the dilution effect in the spin-flop transition. It is possible to observe the presence of an anomalous widening and a hysteresis in the transition region for the K2Fe1-xInxCl5.H2O compound. These effects are probably related to the presence of a mixed intermediate phase, where the spin-flop and the antiferromagnetic phase coexist in a domain structure. For the Rb2Fe1-xInxCl5.H2O compound, it is usually observed just a widening of the transition, without hysteresis. In this case it is possible the existence of a random fields induced intermediate phase, similar to the one proposed by Aharony. Specific heat measurements performed with and without applied fields in samples of (Nd1-xSmx)2CuO4 showed the presence of a maximum at low temperatures in all samples studied. The Sm concentration (x) dependence of the temperature of this maximum showed two regions with different behavior. For x > 0.7, the specific heat curve is similar to the one observed in ordinary diluted antiferromagnetic compounds. The temperature of the maximum decreases with increasing applied magnetic field. On the other hand, for x < 0.7, the effect is similar to the one observed for the pristine Nd2CuO4. The Nd2CuO4 behavior is not the one observed in ordinary antiferromagnets, since the Nd-Cu interaction causes a splitting of the ground state level of the Nd sublattice and, consequently, a Schottky like behavior in the specific heat measurements.

Sérios problemas ambientais têm origem em processos de combustão incompletos. Entre os produtos indesejados está a fuligem, considerada como um dos principais fatores da mudança climática observada nos último anos. Desta forma, ferramentas para diagnóstico da emissão de material particulado se fazem necessárias. Com o advento do laser, o desenvolvimento de técnicas óticas não intrusivas teve início. Dentre elas, destaca-se a técnica denominada incandescência induzida por laser (laser induced incandescence – LII), a qual pode gerar resultados resolvidos no espaço para a fração volumétrica de fuligem. Neste contexto, este trabalho apresenta um estudo experimental sobre a produção de fuligem em duas situações: na primeira, foram estudadas chamas laminares pré-misturadas de etileno e ar aplicando-se a técnica LII. Os resultados foram calibrados a partir da fração volumétrica de fuligem média empregando a técnica de extinção de luz, obtendo-se, então, resultados quantitativos espacialmente resolvidos da fração volumétrica de fuligem. A utilização de diferentes gases no escoamento anular também foi avaliada. A segunda situação abordada envolve o estudo de chamas laminares não pré-misturadas utilizando o gás natural como combustível. O impacto da diluição de inertes em diferentes proporções sobre a fração volumétrica de fuligem em diversas alturas da chama foi estudado por meio da técnica LII. Os resultados obtidos foram comparados à outros resultados presentes na literatura e servirão como validação de futuros modelos de formação de fuligem. / Serious environmental problems are assigned to incomplete combustion processes. Among the unwanted products, soot can be related as an important factor of climate changes observed in the last years. Thus, particulate material emissions diagnostic tools are necessary. Due the laser advent, the development of non-intrusive optical techniques was possible. One of the most importante technique is the laser induced incandescence, LII, which can generate spatially and temporally resolved results of soot volume fraction. In this context, an experimental study regarding the soot production was developed in two different situations: in the first one, premixed laminar flames of ethylene and air were investigated by applying the LII technique. The results were calibrated through the average of soot volume fraction results obtained by the light extinction technique. Therefore, it was possible to obtain quantitative results of spatially resolved soot volume fraction. Different gases employment at the annular flow were also evaluated. The second situation studied involves the analysis of natural gas laminar non-premixed flames. The impact of different inert gas dilution ratio on the soot volume fraction at different heights of the flame was evaluated by the LII technique. The results were compared to other authors and will serve as validation for future soot formation models.