Dissertations / Theses on the topic 'Surface processes'

Numerical experiments were completed examining the variability of key aspects of the Martian dust cycle and investigating their importance in predicting conditions for spacecraft atmospheric descent and landing. The dust cycle - lifting, transportation and deposition - is a significant Martian climate cycle. The geographical and temporal variation in dust lifting processes were investigated using a Martian Global Circulation Model. The geographical representation of Martian dust lifting by wind stress was used to explore the experimental impact of changes in model resolution. It was found that increasing the resolution improved the model's geographical representation of observed dust lifting regions, such as resolving important storm-forming regions in the northern hemisphere. This improvement was unanticipated in the case of changes in vertical resolution, and the horizontal resolution work identified an important length scale for dust lifting (of the order of 100 kilometres). The temporal variation of a dust lifting process was investigated through experiments focusing on the diurnal variability of Martian dust devils (small-scale convective vortices). This research compared results with published lander and rover observations and found that dust devils were more active during morning hours than anticipated, suggesting that the generally accepted description of dust devil behaviour on Mars is incomplete. Predictions were made of the atmospheric and near-surface environment encountered by the ESA ExoMars Schiaparelli landing module. The experiments produced a reasonable representation of atmospheric quantities along the descent trajectory and were able to generate similar low-altitude wind fields to those reported by the spacecraft. The global-scale model also out-performed a higher resolution mesoscale model. These findings are significant in the field of Martian climate modelling, are important for the planning of Martian dust devil observation campaigns and future missions to the planet`s surface, and will also be relevant to researchers operating atmospheric models for other planetary bodies.

L'incision des rivières est un processus clé contrôlant l'érosion des paysages. L'efficacité de l'incision est principalement influencée par le climat et par l'érodibilité. La possibilité de mesurer in-situ l'érodibilité avec un marteau de Schmidt (R) est évaluée pour Taiwan, les grès d'Annot et la zone de faille de St Clement. Les résultats suggèrent un fort contrôle de R par les propriétés équivalentes. Un modèle basé sur la théorie des milieux équivalents, est appliqué à une zone de faille avec une résolution inégalée (750 mesures, 25 mesures par mètre carré). Le modèle permet de corréler avec succès la densité de fracture et R. Ces résultats démontrent empiriquement que l'érodibilité est sensible à la densité et à la nature des fractures. Par ailleurs, plusieurs outils numériques sont développés. Un formalisme 1D d'évolution des paysages avec une approche stochastique est proposée ainsi qu'un nouvel algorithme de remaillage appelé Surface Lagrangian Remeshing permettant d'inclure l'érosion dans les codes numériques 2D aux éléments finis. Le modèle est appliqué à l'évolution post-orogénique des chaînes de montagnes. Les taux observés de décroissance topographique et de diminution du rapport de l'élévation de surface sur l'épaisseur de racine crustale sont reproduit. Ce nouveau modèle met en évidence le contrôle du climat et de l'érodibilité sur la décroissance topographique, et de la rhéologie lithosphérique sur la persévérance des racines crustales
River incision is a key process controlling landscapes evolution. Efficiency of incision is mainly influenced by climate and soil erodibility. The possibility of measuring erodibility in-situ with a Schmidt hammer (R) is evaluated for Taiwan, the Annot sandstones and the fault zone of St Clement. The results suggest a strong control of R by rocks effective properties. A model based on the theory of equivalent media, is applied to a fault zone with unmatched resolution (750 measures, 25 steps per square meter). The model successfully correlates the density of fractures and R. These results empirically demonstrate that erodibility is sensitive to the density and nature of fractures. Ln addition, several numerical tools are developed. A 1D formalism of landscape evolution with a stochastic approach is proposed as weIl as a new remeshing algorithm called Surface Lagrangian Remeshing, dedicated to erosion in 2D numerical codes with finite elements. The model is applied to the post-orogenic evolution of mountain ranges. The observed rates of topographie decay and decrease of the ratio of surface elevation to crustal root thickness are reproduced. This new model highlights the control of climate and erodibility on the decay of topography, and lithospheric rheology on the perseverance of crustal roots

Understanding the impacts of surface microtopography on hydrologic processes is critical. The objectives of this thesis research are: (1) to evaluate the effects of DEM resolution on microtopographic characteristics, hydrologic connectivity, and modeling of hydrologic processes; and (2) to assess the influences of multiple rainfall events on surface and subsurface hydrologic processes with the use of a puddle-to-puddle (P2P) modeling system. The change in DEM resolution has a significant effect on how surface microtopography is depicted, which in turn alters the hydrologic response of a topographic surface. The smoothing of reduced DEM resolution tends to enhance hydrologic connectivity, reduce the depression storage and infiltration, and increase surface runoff. Temporal rainfall distribution results in spatio-temporal variations in soil water dynamics, depression storage, infiltration, hydrologic connectivity, and surface runoff. The reduction in ponding time and infiltration, and the enhancement of hydrologic connectivity further caused earlier and greater surface runoff generation.

Various processes that participate in ion beam surface modification are studied using phenomenological, analytical and first principle models. The processes that are modelled phenomenologically include preferential sputtering, radiation-damage induced migration and second phase precipitation. The models are based on numerical solutions of the transport equation and include the processes of ion collection, sputtering, lattice dilation or accommodation and diffusion as well. The model for preferential sputtering takes into account the depletion of the preferentially sputtered element at the surface and the atomic transport process that results from the concentration gradients caused by the depletion. Results are presented for the case of Ta implantation into Fe. ln the radiation-damage induced migration the flux of the solute atoms is coupled to the concentration gradient of the continuously introduced defects. Examples of implantation of Sn into Fe and N into Fe are modeled to demonstrate the influence of radiation-damage induced migration. The precipitation of second phases during irradiation is modelled using thermodynamic considerations but with solubility values under irradiation obtained from experiment. In the model the solute atoms in excess of the solubility limit are assumed to precipitate out. Calculations are presented for the case of N implantation into Nb. Using first principle calculation for binary collisions in solids a computer simulation code was developed to study the collisional mixing occurring during high fluence ion implantation. It is based on the Monte Carlo code TRIM, and is capable of updating the target composition as the implantation process proceeds to high fluences. The physical basis for the dynamic simulation as well as a detailed analysis on the statistics required for obtaining the profiles with a given accuracy are presented. Vectorized results in a high computational efficiency. The predicted collisional broadening of the implantation profiles is presented for Ar bombardment into a Sn-Fe target as well as Ti implantation into C-Fe. The results are compared to those of the diffusion approximation. A semi-empiricaI model based on an analytical evaluation of ion mixing at low temperatures was developed taking into account collisional mixing and thermal spike effects, as well as the thermal spike shape. The ion beam mixing parameter for the thermal spike is derived as being proportional to different powers of the damage parameter, i.e. the damage energy scaled by the cohesive energy of the matrix, dependent on the thermal spike shape and point defect density in the thermal spike regions. Three different regions of ion beam induced mixing were recognized according to different density levels of the damage parameter. An experiment was conducted to determine the effect of chemical or thermodynamic factors in the migration of C in the presence of Fe and Ti atoms. A marker layer of C in a Fe-Ti matrix was ion beam mixed using Ar. The large mixing effect is tentatively attributed to a favorable heat of mixing values.
Ph. D.

Satellite-based remotely sensed data were used to estimate regional-scale surface energy fluxes and a water deficit index of a semi-arid heterogeneous region in southeast Arizona. Spectral reflectance and radiometric temperature of the surface, derived from the digital counts of TM bands of LANDSAT-5 satellite, were used for this purpose. These reflectance and temperature, along with conventional meteorological information of the region, were used as inputs to numerical models which estimate surface energy fluxes. Point-based meteorological data of the region were spatially extrapolated over a grid of 120 m X 120 m so that it could be used with the spatially continuous remotely sensed data. The water deficit index (WDI) was estimated using surface temperature and a spectral vegetation index, "soil adjusted vegetation index" (SAVI). The surface fluxes were net radiation flux, sensible heat flux, soil heat flux and latent heat flux. Measured values obtained from the meteorological flux measurement (METFLUX) stations in the study area were compared with the modeled fluxes. Latent heat flux (LE) was the most important one to estimate in the scope of this study. The method of spatially extrapolating the point-based meteorological information and combining with the remotely sensed data produced good estimation of LE for the region, with a mean absolute difference (MAD) of 65 W/m² over a range of 67 to 196 W/m² . Also it was found that the numerical models that were previously used to estimate daily LE values from a region using mid-day remotely sensed data (mostly from NOAAAVHRR) can also be used with the mid-morning remotely sensed data (from LANDSAT). Out of the two models tested for this purpose (`Seguin-Itier' and 'Jackson' models), one was found to need some modification so that it could use mid-morning remotely sensed data as inputs. The other was found to be useable as it is, without any modification. Outputs from both models compared well with the measured fluxes from the METFLUX stations. In an effort of estimating the water deficit of the different biomes of the region, WDI of the biomes were estimated. The main goal of this effort was to be able to monitor the surface hydrologic conditions of the region using remotely sensed vegetation and surface information, and minimum ground data. Good estimation of the water deficit condition of the area were obtained by this method. This method was found to be sensitive to a few of the ground information such as wind speed and leaf area index (LAI). It was also found that if the required ground data were correctly estimated, this method could be used as an operational procedure for monitoring the vegetation water stress of the biomes and hence for better management of the region.

This PhD thesis reports the use the emerging surface-sensitive optical technique of localized surface plasmon resonance (LSPR) to characterize the interaction of relevant classes of biomolecules, e.g. peptides, proteins, lipids and DNA strands, at solid-liquid interfaces, with an emphasis on deciphering kinetics and pathways of dynamic adsorption processes. LSPR-based biosensor exploits the high sensitivity of the plasmon frequency to refractive index changes confined to 5-30 nanometers around the metal nanoparticles deposited on the sensor surface to monitor in situ and in real time the interaction of unlabeled biological molecules skipping the misleading contribution from the bulk of solution affecting conventional optical technique, e.g. SPR and OWLS. In the present dissertation the advantages of applying this powerful technique are thoroughly demonstrated by investigating four case studies concerning relevant aspects for the biointerfaces science. The case of study 1 will involve the adsorption kinetics of single and binary solution of proteins onto model hydrophilic and hydrophobic surfaces. The analysis of the adsorption kinetics reveals that competitive adsorption occurs, at physiological pH 7.4 and relatively high ionic strength (NaCl 0.1 M), favoring the heavier protein (fibronectin, in our case), which is shown to adsorb faster and in larger amount than the lighter one (human serum albumin, in our case). The case of study 2 will discuss the DNA hybridization process for binary solutions of respectively perfectly matching (PM) and single base mismatching (MM) 93-mer ssDNA from KRAS codon 12, with a surface tethered probe complementary to the PM sequence. Sensitivity down to obtaining down to 10 nM and 13 nM, respectively for PM and MM were obtained, showing that the hybridization process occurs at a lower rate for MM with respect to PM target. The competitive hybridization was accounted for by an inhibition model, where the non-complementary sequences kinetically hinder the hybridization of the perfect matching sequences, owing to their above mentioned affinity constant differences for the same probe. The case of study 3 will cover the kinetics of phospholipid vesicle adsorption on silicon oxide surfaces as function of pH. Two different regimes have been observed for acidic and basic conditions. At low pH, vesicles adsorption showed one-step exponential kinetics. Moreover, no significantly variation of the adsorption rate was observed over the investigated pH range 3-6, suggesting the process is controlled by Van der Waals interactions and steric forces. At high pH, vesicles adsorb showing two-step kinetic. Furthermore, it was observed that the rate of the first step slows down linearly with the increasing of pH, suggesting that the process is primarily driven by vesicle-surface electrostatic repulsion. The case of study 4 will report preliminary results from the study of pH stimuli-responsive smart surfaces, formed by gold nanodisks array of an LSPR sensor chip decorated with Trichogin GA IV and two of its positively-charged analogs, i.e. Lipo-Lys and L20, in which four and eight Lysines positive charged residues have been introduced respectively. The surface-bound peptides exhibit reversible and rapid switching between conformations and can withstand several cycles of swelling and collapsing with no significant loss from the surfaces. Overall, the results here reported demonstrated the great potential of LSPR technique as a unique tool to monitor specific and non-specific biomolecular interactions at interfaces in application fields ranging from biosensing to materials science.

The optimization of metallic solid surfaces is one of the greatest industrial challenges about surface engineering. Surface hardening treatments are applied to improve the wear resistance of parts without affecting the more tough and soft core of the treated substrates. This doctoral work is focused on the study of gaseous multistage oxynitrocarburizing treatments for low carbon steels and hard-anodizing processes applied on aluminum HPDC components. There is still a lack of knowledge both in literature and in industry about these treatments. The aim of this work is to investigate the microstructural evolution during gaseous multistage oxynitrocarburizing treatments and the impact of the substrate’s characteristics on the hard-anodic layer, respectively. It is important to understand the impact of the process parameters and the substrate’s microstructure on the respective resulting layers; in this way, it is possible to improve the scientific knowledge and therefore to understand the basics for following replications in an industrial context. A wide-ranging view of the whole thermochemical and hard-anodizing processes has been provided by a review of the literature and several treatments replicated in an industrial plant.
L’ottimizzazione delle performance di superfici metalliche è una delle sfide industriali più avvincenti nell’ambito dell’ingegneria delle superfici. I trattamenti di indurimento superficiale sono quei processi sviluppati per incrementare la durezza e resistenza a usura superficiali di componenti senza però peggiorare la tenacità che presentano a cuore. Questo lavoro di dottorato è focalizzato sullo studio sia di trattamenti multistadio di ossinitrocarburazione applicati a substrati in acciaio basso legato, sia di trattamenti di anodizzazione dura applicati a componenti pressocolati in lega di alluminio. Attualmente vi sono ancora importanti lacune riguardo queste specifiche tipologie di trattamenti, sia in letteratura che nel mondo industriale. L’obiettivo di questo lavoro è approfondire sia l’evoluzione microstrutturale durante un trattamento multistadio di ossinitrocarburazione applicato a un substrato ferroso, sia come le caratteristiche microstrutturali di un substrato in lega di alluminio impattano sul film di ossido anodico duro. L’obiettivo finale è quello di ampliare il sapere scientifico e, quindi, gettare le basi per poter poi replicare con successo su scala industriale quanto studiato in laboratorio. Un’accurata revisione della letteratura e una serie di trattamenti replicati in impianti industriali ha portato a una visione ad ampio spettro su questi trattamenti termochimici e di ossidazione anodica dura.

Ever since Halley (1686) superimposed onto a map of land forms. the direction of trade winds and monsoons between and near the tropics and attempted to assign them a physical cause. homo-sapiens has attempted to develop procedures which quantify the level of change in a spatial process. or assess the relationship between associated spatially measured variables. Most spatial data. whether it be originally point. linear or areal in nature. can be converted by a suitable procedure into a continuous form and plotted as an isarithmic map i.e. points of equal height are joined. Once in that form it may be regarded as a statistical surface in which height varies over area in much the same way as the terrain varies on topographic maps. Particularly in environmental statistics. the underlying shape of the surface is unknown. and hence the use of non-parametric techniques is wholly appropriate. For most applications. the location of data points is beyond the control of the map-maker hence the analyst must cope with irregularly spaced data points. A variety of possible techniques for describing a surface are given in chapter two, with attention focusing on the methodology surrounding kernel density estimation. Once a surface has been produced to describe a set of data. a decision concerning the number of contours and how they should be selected has to be taken. When comparing two sets of data. it is imperative that the contours selected are chosen using the same criteria. A data based procedure is developed in chapter three which ensures comparability of the surfaces and hence spurious conclusions are not reached as a result of inconsistencies between surfaces. Contained within this chapter is a discussion of issues which relate to other aspects of how a contour should be drawn to minimise the potential for inaccuracies in the swface fitting methodology. Chapter four focuses on a whole wealth of techniques which are currently available for comparing surfaces. These range from the simplest method of overlaying two maps and visually comparing them to more involved techniques which require intensive numerical computation. It is the formalisation of the former of these techniques which forms the basis of the methodology developed in the following two chapters to discern whether change/association has materialised between variables.One means of quantifying change between two surfaces, represented as a contoured surface, is in terms of the transformation which would be required for the two surfaces to be matched. Mathematically, transformations are described in terms of rotation, translation and scalar change. Chapter five provides a geometrical interpretation of the three transformations in terms of area, perimeter, orientation and the centre of gravity of the contour of interest and their associated properties. Although grid resolution is fundamentally a secondary level of smoothing, this aspect of surface fitting has generally been ignored. However to ensure consistency across surfaces, it is necessary to decide firstly, whether data sets of different sizes should be depicted using different mesh resolutions and secondly, how fine a resolution provides optimal results, both in terms of execution time and inherent surface variability. This aspect is examined with particular reference to the geometric descriptors used to quantify change. The question of random noise contained within a measurement process has been ignored in the analysis to this point. However in practice, some form of noise will always be contained within a process. Quantifying the level of noise attributable to a process can prove difficult since the scientist may be over optimistic in his evaluation of the noise level. In developing a suitable set of test statistics, four situations were examined, firstly when no noise was present and then for three levels of noise, the upper bounds of which were 5, 15 and 25%. Based on these statistics, a series of hypothesis tests were developed to look at the question of change for individual contour levels Le. local analysis. or alternatively for a whole surface by combining the statistics and effectively performing a multivariate test. A number of problems are associated with the methodology. These difficulties are discussed and various remedial measures are proposed. The theoretical derivation of the test statistic, both in the absence and presence of random noise, has proved mathematically to be extremely complex, with a number of stringent assumptions required to enable the theoretical distribution to be derived. A major simulation study was subsequently undertaken to develop the empirical probability distribution function for the various statistics defining change for the four levels of noise. Also for each of the statistics, the resultant power of the test was examined.The remaining chapter explicitly examines two case studies and how the methodology developed in the preceding two chapters may be implemented. The first example cited raises the question, 'Has a seasonal temperature change resulted during the fifty year span, 1930 to 1980, within the contiguous United States of America?' The data base was provided by the United States Historical Climatology Network (HCN) Serial Temperature and Precipitation Data, Quinlan et al (1987). The second problem examines whether there is an association between background radiation levels, within three regions of the south-west England, and the location of various fonns of leukaemia or whether case location is a product of the population distribution. Differences between this example and the previous illustration materialise in terms of the spatial resolution of the data; the leukaemia data are defined as punctual data points and are extremely sparse; the population distribution is defined as areal regions; with the radiation data being of a more continuous format. The methodology developed required modification, but aside of this a preliminary set of conclusions were reached.

La millora de la productivitat i la qualitat són indubtablement dues de les principals exigències del sector productiu modern i factors clau per la competitivitat i la supervivència. Dins aquest sector,la fabricació per arrancada de material juga encara avui en dia un paper protagonista tot i l'aparició de noves tècniques de conformat per addició.Indústries com l'aeronàutica, l'automobilística,la del motlle o l'energètica, depenen en bona part de les prestacions de les màquines-eina. Aquesta Tesi aborda dos aspectes rellevants quan es tracta de millorar de la productivitat i la qualitat del sector productiu: el problema del fimbrament, més conegut per la denominació anglosaxona chatter,i la monitorització de la rugositat superficial en el mecanitzat a alta velocitat.
Productivity and quality improvement are undoubtedly two of the main demands of the
modern manufacturing sector and key factors for competitiveness and survival. Within this sector, material removal processes play, still nowadays, a principal role despite the emergence of additive manufacturing techniques. Industries such as aerospace, automotive, molds and dies or energy largely depend on machine tools performance for improved productivity and quality. This Thesis is focused on two important aspects when it comes to improving productivity and quality of the manufacturing sector: chatter problem, and surface roughness monitoring in high speed milling.

The purpose of this study was to apply vibrations to the workpiece during surface grinding in order to improve the performance of the process. In addition to this, further necessary parameters were examined and analysed. A first step was to design the vibrating rig and after a number of different designs the most suitable model was selected for the conduction of the preliminary studies. However, a novel-improved system was designed and manufactured in order to undertake the full volume of experimental work. A number of simulations including stress and modal analysis were carried out and all the static and dynamic characteristics of the rigs were identified. Moreover, the exact dynamic behaviour of the rigs - including their natural frequencies - was established though real experiments. Sweep - sine and impact tests were employed in order to identify these dynamic parameters and the results were compared to those of simulation with the intention to detect the amount of error between these techniques. The rigs were vibrated at their resonant frequencies in order to achieve high values of amplitude with low voltage input. The static and dynamic characteristics of the grinding machine tool were identified. Similar methods such as sweep-sine test were employed in order to find the natural frequency of the machine tool's spindle unit. Static and dynamic stiffness of the machine tool's spindle unit as well as its compliance were identified. The preliminary studies showed an improvement in surface quality of the workpiece as well as a small reduction in cutting forces. This reduction was getting bigger with the increase of depth of cut. The main body of experimental work followed and showed that for 25 urn depths of cut, the vibration-assisted method could decrease up to 22.5 % the tangential forces. Furthermore, the effect of vibration was getting more noticeable at higher wheelspeeds and workspeeds. At those speeds the reduction in workpiece surface roughness reached 12.6%. Moreover, it was found that the application of vibration increased the material removal rate, reduced the cutting forces, increased the G-ratio and produced lower values of wheel wear compared to conventional grinding. Finally, an innovative closed-loop vibration control system was used for the process which could control the amplitude and the frequency of vibration in the actual grinding cycle. This I A Abstract system managed to control the applied values of vibration amplitude at resonant or near resonant frequencies. It was found that for higher depths of cut the closed-loop vibration control reduced the normal forces by 19% compared to open-loop control and 21 % compared to conventional grinding. Furthermore, the closed-loop control system performed better in terms of workpiece surface quality when grinding mild steel compared to conventional grinding and open-loop vibration control.

This PhD thesis is about understanding some aspects of the dynamics of the ocean surface mixed layer by means of satellite Sea Surface Temperature (SST) measurements. The focus is on surface density fronts which are used as a measure of the dynamical activity at the meso- and submesoscale. A review of the current knowledge on the non-linear physical mechanisms that occur in the vicinity of fronts is presented in Chapter 2. Chapter 3 characterizes the ability of two algorithms for detecting fronts of various sizes and strengths that are embedded in a complex turbulent flow and sampled on noisy two-dimensional images. Chapter 4 explores and compares the performances of several new multi-sensor Level-4 SST products in resolving the small scale gradients. These Group for High Resolution Sea Surface Temperature (GHRSST) data sets offer an unprecedented spatial and temporal SST coverage. Their production however involves a variable and partially unknown level of smoothing which “hides” some of the small scale variability. In Chapter 5, a robust, flexible, automatic and optimized Matlab-based methodology for detecting fronts on SST images and calculating a frontal index is presented. A basic frontal index capturing the frontal length and strength is exploited to quantify the spatial scales present in the various Level-4 SST products. More advanced frontal indexes based on physical oceanography results by others are constructed in order to estimate vertical exchanges occurring at fronts from their signature on the SST. These new frontal indexes, which characterize fronts according to their dynamical significance, allow the quantification of the upwelling, subduction and restratification associated with frontal submesoscale processes. Finally, the spatial and temporal variability of ocean fronts is explored in order to determine their sensitivity to climatic signals.