Complex patterns arise in many extended nonlinear nonequilibrium systems in physics, chemistry and biology. Information extraction from these complex patterns is a challenge and has been a main subject of research for many years. We study patterns in Rayleigh-Benard convection (RBC) acquired from our laboratory experiments to develop new characterization techniques for complex spatio-temporal patterns. Computational homology, a new topological characterization technique, is applied to the experimental data to investigate dynamics by quantifying convective patterns in a unique way. The homology analysis is used to detect symmetry breakings between hot and cold flows as a function of thermal driving in experiments, where other conventional techniques, e.g., curvature and wave-number distribution, failed to reveal this asymmetry. Furthermore, quantitative information is acquired from the outputs of homology to identify different spatio-temporal states. We use this information to obtain a reduced dynamical description of spatio-temporal chaos to investigate extensivity and physical boundary effects in RBC. The results from homological analysis are also compared to other dimensionality reduction techniques such as Karhunen-Loeve decomposition and Fourier analysis.

The knowledge of geometry of molecular complexes formed via molecular association in solution through weak interactions is always important to understand the origin of stability and function of an array of molecules, supramolecular assemblies, and macromolecular networks. Simple 1:1 molecular complexes are very useful in this regard as they provide a model to understand both the nature of these interactions and their structural implications. Several weak noncovalent forces from long range (van der Waal’s, electrostatic, induction, dispersion) to short range (charge transfer) govern the geometry, that is, relative orientation of the two molecules in such a complex. On one hand, we find 1:1 electron donor acceptor (EDA) complexes such as naphthalene-tetracyanobenzene, hexamethylbenzene-chloranil etc. which stack parallel or in slipped parallel geometry in their crystals. On the other, benzene dimer has been found to stabilize in T shaped geometry in all its three physical states. In this thesis, I focus on 1:1 EDA complexes in solution. A good volume of literature is available which deals with the optical studies on the formation of such complexes. It has been suggested that the nature of the intermolecular interactions stabilizing these complexes in the gas phase or in their crystals is modified by the presence of solvent-solute interactions in solution thus bringing in difference in the solution geometry. However, the existing experimental techniques, both optical and magnetic, are unable to determine the exact geometries of 1:1 EDA complexes in solution. This opens an opportunity to probe their geometry in solution. The quadratic nonlinearity or first hyperpolarizability (β) of a molecule is a measure of the change in dipole moment (or polarization) in the second order of the applied electrical field and thus has a purely electronic origin. It is a tensorial property and can be resolved in components along the three dimensions. The number of β components and the nonlinear optical anisotropies in a typical donor-acceptor type dipolar molecule, defined as (equation) (where1, 2, 3 axes define the molecular frame, 1 being the direction along the principal axis of symmetry and pointing from the acceptor toward the donor), are determined by the symmetry /structure of the molecule. It has been shown theoretically that the 1:1 EDA complexes possess large hyperpolarizabilities. In the case of pNA dimers calculation revealed that the geometry of the dimer and its symmetry is important for obtaining the correct estimate of β from its tensorial components. Therefore, it should be possible to use the values of tensorial β components to construct the unknown geometry of such complexes. Experimentally macroscopic depolarization ratios (D and D′) in the laboratory fixed frame (XYZ, X being the direction of polarization and Z the direction of propagation of the incident light), are measured from the polarization resolved intensities of second harmonic scattering from molecules in solution using the hyper-Rayleigh scattering technique. The depolarization ratios are correlated to the anisotropy parameters, u and v through a co-ordinate transformation. In this thesis I, have first, characterized the quadratic nonlinear optical property of a variety of 1:1 electron donor acceptor complexes and used the values of u and v obtained from depolarized hyper-Rayleigh scattering to deduce their geometry in solution. Chapter 1 provides an introduction to the 1:1 electron donor acceptor complexes, their relevance to chemistry and biology. It also contains an introduction to nonlinear optical processes in molecules. The objective of the present work and scope of the investigation carried out in this thesis is presented in this chapter. Chapter 2 describes the details of the experimental polarization resolved HRS technique. The geometrical model adopted for the analysis of the HRS data has also been introduced and the method of analysis has been described in detail in this chapter. Chapter 3 presents the measurement of β values of two series of 1:1 EDA complexes of variously substituted methylbenzenes donors with tetrachloro-p-benzoquinone (CHL) and dicyanodichloro-p-benzoquinone (DDQ) acceptors at 1064 nm. In agreement with recent theoretical results we find large first hyperpolarizabilities for these complexes. The β values are greater than that of the typical push-pull molecule p-nitroaniline (pNA). We also find that in general β decreases with decrease in the donor strength. Chapter 4 presents the β values for the two series of EDA complexes of CHL and DDQ acceptors at 1907 nm. The values of β are less in magnitude at 1907 nm than that at 1064 nm which is due to the dispersion effect in β. In Chapter 5 and 6, it is described how depolarized hyper-Rayleigh scattering can be utilized to probe geometries of 1:1 complexes in solution. Chapter 5 concentrates mainly on 1:1 EDA complexes of CHL and DDQ and TCNB (tetracyanobenzene), while chapter 6 contains examples of other 1:1 molecular complexes where the noncovalent interactions are much weaker, such as in benzene-naphthalene, benzene-methoxybenzene, benzene-hexafluorobenzene and benzene-chlorobenzene pairs. We find the geometry of 1:1 EDA complexes in solution in terms of tilt angle (θ) and twist angle (ϕ) between the donor and acceptor pairs. The angle θ varies from 29°-47° for different pairs of EDA complexes, while ϕ varies within 34° and 38°. We find that the geometry of 1:1 EDA complexes in solution is different (twisted and tilted cofacial and twisted ‘V’) from those in the crystalline or gaseous states (cofacial), if known. We find that both benzene-naphthalene and benzene-chlorobenzene pairs assume twisted ‘T’ shape geometry with θ = 82° and 85°, respectively, and φ = 38°, while benzene-hexafluorobenzene assumes a twisted ‘V’ shape. A strong solvent effect is seen in the geometry of the benzene- methoxybenzene complex. The tilt angle is 55° when chloroform is used as a solvent and it is 82° without chloroform. Chapter 7 is the concluding chapter where the main work done in this thesis is summarized and future directions are presented.

In verfahrenstechnischen Anlagen der Flüssig-Flüssig-Stoffübertragung kommt es an der Phasengrenze zwischen den nicht mischbaren Flüssigphasen häufig zur Ausbildung hydrodynamischer Instabilitäten. Sie sind mit komplexen Geschwindigkeitsfeldern in den Flüssigphasen, insbesondere in den grenzschichtnahen Regionen verbunden und führen zu einem starken Anstieg der pro Zeiteinheit übertragenen Stoffmenge. Die Lösung der Diffusionsgleichung reicht in diesem Fall zur Vorausberechnung des für Auslegungszwecke bedeutsamen Stoffdurchgangskoeffizienten nicht mehr aus. Chemische Reaktionen stellen Quellen oder Senken von Wärme und Stoff dar, die das Auftreten von Instabilitäten begünstigen und die mathematische Beschreibung zusätzlich erschweren. Im Rahmen der vorliegenden Arbeit wurden experimentelle und numerische Untersuchungen zum Flüssig-Flüssig-Stoffübergang in einem vertikalen Kapillarspalt durchgeführt. Reaktionsfreie Stoffübergänge und solche mit einer exothermen chemischen Reaktion an der Phasengrenze zeigten eine große Vielfalt von Konvektionsstrukturen, wie Rollzellen, Thermiken und das doppeldiffusive Fingerregime. Die Visualisierung der Transportvorgänge erfolgte durch das Schattenschlierenverfahren. Die Beobachtungen wurden hinsichtlich geometrischer Eigenschaften von Konvektionsstrukturen sowie deren zeitlicher Änderung ausgewertet. Dazu zählten insbesondere das Längenwachstum von Thermiken und horizontale Wellenlängen von Fingerstrukturen. Zur mathematischen Beschreibung der Phänomene im Kapillarspalt wurde ein Modell entwickelt, welches auf den gekoppelten, zweidimensionalen Transportgleichungen von Impuls, Wärme und Stoff beruht. Es berücksichtigt dichte- und grenzflächenspannungsgetriebene Instabilitätsmechanismen sowie die besonderen Durchströmungseigenschaften des Kapillarspalts. Die Phasengrenze wurde als eben angenommen. Die Lösung der Modellgleichungen erfolgt auf numerischem Wege durch ein Computerprogramm. Das Modell ist in der Lage, die beobachteten Instabilitätsphänomene qualitativ richtig wiederzugeben. Mit Hilfe von Simulationsrechnungen konnte der Mechanismus aufgeklärt werden, der zum schnelleren Rückgang des Stoffdurchgangskoeffizienten im Rollzellenregime der rein grenzflächenspannungsgetrieben Instabilität im Vergleich zum Vorgang mit überlagerter Dichtekonvektion führt. Des Weiteren gelang der Nachweis des doppeldiffusiven Fingerregimes beim Stoffübergang mit exothermer Grenzflächenreaktion. Die berechnete Erhöhung des Stoffdurchgangskoeffizienten stimmt mit Angaben in experimentellen Arbeiten anderer Autoren überein.

L'absorption d'une impulsion laser crée un échauffement localisé suivi d'une brusque dilatation. Dès lors, un champ acoustique de plusieurs dizaines de gigahertz peut être généré. Cette méthode optique sans contact et non destructive possède des applications en micro-électronique pour la caractérisation de structures nanométriques, mais également dans des domaines plus fondamentaux. Jusqu'à présent, la dimension latérale de la tache focale des impulsions laser était très grande devant l'épaisseur des films considérés. Dès lors, la génération était unidimensionnelle et seules des ondes acoustiques planes pouvaient être engendrées. Récemment, l'utilisation de sources laser focalisées a permis de générer par diffraction des champs acoustiques tridimensionnels (3D). <br /><br />Lorsque des impulsions d'une durée inférieure à la picoseconde sont employées dans les métaux, une approche macroscopique n'est plus suffisante. Il est alors nécessaire d'expliciter les évolutions microscopiques impliquées dans le processus de génération. Ainsi, une méthode semi-analytique basée sur un modèle à deux températures 3D est développée dans la première partie de ce mémoire afin de décrire les phénomènes électroniques. En se propageant, l'onde acoustique divergente module l'indice optique en temps et en espace par couplage élasto-optique. La propagation de la lumière est alors perturbée, et sa mesure permet de caractériser la propagation acoustique. Dans la seconde partie de ce mémoire, l'interaction 3D de l'impulsion laser gaussienne avec le champ acoustique diffracté est donc modélisée.

Ce mémoire analyse le phénomène de convection turbulente dans diverses cellules de Rayleigh-Bénard remplies d'hélium gazeux et liquide. Une des spécificités de cette étude est sa mise en oeuvre en environnement cryogénique, afin de bénéficier de conditions expérimentales optimales, tant en terme de contrôle thermique qu'en terme de plage de variation des paramètres de contrôle : les Nombres de Prandtl (Pr) et de Rayleigh. Ce dernier est en particulier exploré sur plus de 11 décades. Trois contributions principales se dégagent de cette étude. Tout d'abord, la mise en évidence d'un effet de conduction déterminant dû à la paroi latérale. Négligé dans les travaux antérieurs, cet effet est étudié expérimentalement puis modélisé. Il permet de lever certaines incohérences apparues dans des publications de références. En outre, le ré-examen de publications antérieures conforte l'idée que le Nombre de Nusselt (Nu) dépend du Nombre de Rayleigh suivant une loi de puissance d'exposant supérieur à 0,3, plutôt que 2/7 par exemple. La deuxième contribution porte sur l'influence du Nombre de Prandtl, analysée sur une décade et demie (0,7

Dans ce travail, nous avons abordé le phénomène de la Convection Thermique Turbulente sous des angles nouveaux et innovants. <br /><br />Le premier système que nous abordons expérimentalement est un Canal Vertical dit Infini au sein duquel règne un gradient de température moyen constant. Le flux de masse dans ce canal est nul. L'image qui se dégage de nos mesures est celle d'un écoulement majoritairement inertiel, où les coefficients dissipatifs (la viscosité en l'occurrence) n'interviennent que pour fixer une longueur de cohérence L. Cette longueur est celle sur laquelle les panaches thermiques peuvent êtres considérés comme en « chute libre ». Le transport horizontal (d'impulsion et de chaleur) est entièrement dû aux fluctuations. La « longueur de mélange » associée est petite devant la largeur du canal. Par contre, le transport de chaleur vertical est dû à des structures cohérentes, les panaches. <br />Ces panaches, nous les retrouvons dans une étude Lagrangienne de l'écoulement au centre d'une cellule de Rayleigh Bénard. La sonde est une sphère de 2 cm de diamètre qui a la même densité que le fluide que nous utilisons, équipée de thermomètres et d'un émetteur radio. Elle est transportée par les panaches, ce qui nous permet une étude statistique de ceux-ci.

Advances in digital signal processing (DSP) and computing technology have resulted in the emergence of increasingly adaptive radar systems. It is clear that the Electronic Attack (EA), or jamming, of such radar systems is expected to become a more difficult task. The reason for this research was to address the issue of jamming adaptive radar systems. This required consideration of adaptive jamming systems and the development of a methodology for outlining the features of such a system is proposed as the key contribution of this thesis. For the first time, game-based optimization methods have been applied to a maritime counter-surveillance/counter-targeting scenario involving conventional, as well as so-called ‘smart’ noise jamming.Conventional noise jamming methods feature prominently in the origins of radar electronic warfare, and are still widely implemented. They have been well studied, and are important for comparisons with coherent jamming techniques.Moreover, noise jamming is more readily applied with limited information support and is therefore germane to the problem of jamming adaptive radars; during theearly stages when the jammer tries to learn about the radar’s parameters and its own optimal actions.A radar and a jammer were considered as informed opponents ‘playing’ in a non-cooperative two-player, zero-sum game. The effects of jamming on the target detection performance of a radar using Constant False Alarm Rate (CFAR)processing were analyzed using a game theoretic approach for three cases: (1) Ungated Range Noise (URN), (2) Range-Gated Noise (RGN) and (3) False-Target (FT) jamming.Assuming a Swerling type II target in the presence of Rayleigh-distributed clutter, utility functions were described for Cell-Averaging (CA) and Order Statistic (OS) CFAR processors and the three cases of jamming. The analyses included optimizations of these utility functions, subject to certain constraints, with respectto control variables (strategies) in the jammer, such as jammer power and spatial extent of jamming, and control variables in the radar, such as threshold parameter and reference window size. The utility functions were evaluated over the players’ strategy sets and the resulting matrix-form games were solved for the optimal or ‘best response’ strategies of both the jammer and the radar.

The title of the thesis: The Identification of Substances in Real Samples Using Portable Raman Spectrometer The portable Raman spectrometer Ahura First Defender is a device designated for identifying unrecognized solid and liquid substances. The aim of this diploma thesis was to test the efficiency of the portable Raman spectrometer First Defender and to draw up a draft of the methodology for its manipulation. The objects of the investigation were the accuracy of results and collection of findings coming out of measuring tests using the device mentioned above. The introduction part briefly describes problems of chemical monitoring within Fire Rescue Service of the Czech Republic. As a partly solution of the problems could be the use of the portable spectrometer First Defender. Further are described problems of sampling and possibilities of sample detection through means of chemical reconnaissance. As next, there is described the device itself including the principle of Raman effect that allows the device to identify unrecognized solid and liquid chemical substances. The practical part explains the procedure and the way of applied measuring tests when using the device. The results are summarized in charts and the percentage of successful performed tests analyzed in charts. Findings concerning the manipulation with the device, methods for sample modification and the influence of sample matrix on the identification of selected chemicals in observed samples are introduced in the discussion. Professional knowledge and experience were used to draw up guidelines for the identification of substances in real samples conceived as general informational source describing procedures, rules, and recommendations. Upon all outcomes and findings, there was confirmed the hypothesis of greatly beneficial using Raman spectrometer in Fire Protection Units when identifying unknown substances at places of intervention at the end of the thesis.

In a nuclear fuel cask, the heat generating spent fuel rods are packed in a housing and the resulting bundle is placed inside a cask of thick outer shell made of materials like lead or concrete. The cask presents a wide variation in geometrical dimensions ranging from the diameter of the rods to the diameter of the cask. To make the problem tractable, first the heat generating rod bundle alone is considered for analysis and the effective thermal conductance of the bundle is correlated in terms of the relevant parameters. In the second part, the bundle is represented as a solid of equivalent thermal conductance and the attention is focused on the modelling of the cask. The first part, dealing with the effective thermal conductance is solved using Fluent software, considering coupled conduction, natural convection and surface radiation in the heat generating rod bundle encased in a hexagonal sheath. Helium, argon, air and nitrogen are considered as working media inside the bundle. A correlation is obtained for the critical Rayleigh number which signifies the onset of natural convection. A correlation is also developed for the effective thermal conductance of the bundle, considering all the modes of transport, in terms of the maximum temperature in the rod bundle, pitch-to-diameter ratio, bundle dimension (or number of rods), heat generation rate and the sheath temperature. The correlation covers pitch-to-diameter ratios in the range 1.1-2, number of rods ranging from 19 to 217 and the heat generation rates encountered in practical applications. The second part deals with the heat transfer modeling of the cask with the bundle represented as a solid of effective (or equivalent) thermal conductance. The mathematical model describes two-dimensional conjugate natural convection and its interaction with surface radiation in the cask. Both Boussinesq and non-Boussinesq formulations have been considered for convection. Numerical solutions are obtained on a staggered mesh with a pressure correction method using a custom-made Fortran code. The surface radiation is coupled to the conduction and convection at the solid-fluid interfaces. Steady-state results are obtained using time-marching. Results for various quantities of interest, namely, the flow and temperature distributions, Nusselt numbers, and interface temperatures, are presented. The Grashof number based on the volumetric heat generation and gap width is varied from 105 to 5 ×109. The emissivities of the interfaces are varied from 0.2-0.8 for the radiative calculations. The solid-to-fluid thermal conductivity ratio for the inner cylinder is varied in the range 5-20 in the parametric studies. Simulations are also performed with thermal conductivity calculated in an iterative manner from bundle parameters. The dimensionless outer wall conductivity ratio is chosen to correspond to cask walls made of lead or concrete. The dimensionless thickness (with respect to gap width) of the outer shell is in the range of 0.0825-1, while the inner cylinder dimensionless radius is 0.2. Air is the working medium in the cask for which the Prandtl number is 0.71. Correlations are obtained for the average temperatures and Nusselt numbers at the inner interface in terms of the parameters. The radiation heat transfer is found to contribute significantly to the heat dissipation.

Nous étudions dans cette thèse le problème de la stabilité d'une goutte à l'état sphérique. La goutte est soumise à forçage qui s'exerce à sa surface de manière purement radiale. Deux configurations sont envisagées : lorsque le forçage est oscillant (avec ou sans une composante constante) et lorsque le forçage est constant. Pour ce faire, nous avons utilisé un code de simulation numérique tridimensionnel pour les écoulements multiphasique incompressibles massivement parallélisé. Le solver combine les méthodes eulériennes et lagrangiennes pour le traitement de la dynamique de l'interface. Le premier problème correspond à l'analogue de l'instabilité de Faraday en présence d'une interface sphérique. Nous avons réalisé une étude de stabilité linéaire en utilisant une décomposition spatiale sur une base d'harmonique sphérique et une généralisation de l'analyse de Floquet de Kumar and Tuckerman (1994) d'une interface plane. Les régions d'instabilités permettent de déterminer le mode sphérique le plus instable. Le mode prédit par la théorie linéaire correspond à celui obtenu à l'aide des simulations numériques. Le second problème est celui d'un forçage radial constant à l'interface de la goutte. En orientant la force dans le sens du gradient de densité, le problème est similaire à l'instabilité de Rayleigh-Taylor en géométrie sphérique. Nous présentons les résultats préliminaires de nos simulations à très haute résolution pour des petits nombres d'onde sur une sphère en tenant compte de la tension de surface durant les premières phases de l'instabilités. La phase turbulente n'est pas abordée. Pour de grand nombre d'onde, nous avons suivi l'évolution de différent motifs de la condition initiale jusque dans la phase non-linéaire. Un troisième problème est considéré pour un forçage horizontal d'une interface plane. Nous avons reproduit à l'aide de notre solver numérique les expériences de Yoshikawa and Wesfreid (2011b). L'interface entre deux fluides stablement stratifiés avec un fort contraste de viscosité est soumise à un cisaillement oscillant horizontal et oscillant . Le problème est celui de l'instabilité de Kelvin-Helmholtz oscillant. Les simulations numériques reproduisent avec succès la croissance et l'évolution de l'interface. nous distinguons deux régimes où l'interface adopte un comportement qualitativement différent dont un nouvel état à saturation est mis en évidence. Nous avons obtenu que pour ce nouvel état l'interface se déstabilise via une première bifurcation fourche supercritique. Cet état semble subir une seconde bifurcation lorsque la fréquence de forçage dépasse un second seuil avec une transition sous-critique, où deux états existent pour les mêmes paramètres de forçages. / We consider in this thesis the stability problem of a spherical drop subjected to a radial bulk force for two different configurations consisting of an oscillating (with or without a constant component) and a constant force. To do so, we use a full three-dimensional parallel front-tracking code for incompressible multiphase flow to calculate the interface motion. The first configuration consist to the spherical analogue of the Faraday instability. We linearize the governing equations about the state of rest and decompose deformations of the interface as spherical harmonics. Generalizing the Kumar & Tuckerman (1994) Floquet procedure to a spherical interface, we present a linear stability analysis for the appearance of standing waves. The most unstable spherical mode at onset predicted by the linear theory agrees with full three-dimensional nonlinear numerical simulations. The second configuration consists to the spherical analogue of the Rayleigh-Taylor instability when the force is oriented from the heavier to the lighter fluid. We performed numerical simulations for both high and low spherical modenumbers and followed their evolutions up to the nonlinear stage. Finally, we consider a plane interface subjected to an horizontal oscillatory forcing which is called the oscillatory Kelvin-Helmholtz instability. We consider the experimental configuration proposed by Yoshikawa and Wesfreid (2011b) for stably stratified fluids with a high viscosity contrast. Numerical simulations reproduce succesfully the growth and the evolution of the interface. We distinguish a new regime for the interface saturation which was not observed by the original experiment. We obtained a subcritical transition between the two different regimes.