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Improving Point Cloud Quality for Mobile Laser Scanning
No full textThis thesis deals with mobile laser scanning and the complex challenges that it poses to data processing, calibration and registration. New approaches to storing, searching and displaying point cloud data as well as algorithms for calibrating mobile laser scanners and registering laser scans are presented and discussed. Novel methods are tested on state of the art mobile laser scanning systems and are examined in detail. Irma3D, an autonomous mobile laser scanning platform has been developed for the purpose of experimentation. This work is the result of several years of research in robotics and laser scanning. It is the accumulation of many journal articles and conference papers that have been reviewed by peers in the field of computer science, robotics, artificial intelligence and surveying
Phytochemical Characterization of Stevia rebaudiana
No full textStevia rebaudiana (Bertoni) is from the Asteraceae family of plants with significant economic value due to its high content of natural zero calorie steviol glycoside sweeteners in its leaves. The leaves contain ent-kaurene glycosides, comprising stevioside, rebaudioside A, B, C, D, E, F and dulcoside A. Rebaudioside A and stevioside are the most abundant diterpene glycosides (steviol glycosides) in the leaves.
The phytochemical characterization of stevia leaves is playing an important role in a future EU consumption of stevia as a novel food. For this purpose, the chemical composition of stevia (phenols and steviol glycosides detailed, with lipids and proteins in representative cases) was studied and methods have been developed for quantitative and qualitative analysis. Stevia leaves cultivated in more than ten locations inside and outside of Europe with seven different varieties, corresponding to total of 166 stevia samples, were extracted and their chemical composition was profiled and quantified by LC-MS for steviol glycosides and polyphenols (chlorogenic acids and flavonoids). Profiling, identification and quantification of terpenoids and lipids were achieved by using GC, GC-MS and MALDI-TOF techniques. In addition, protein extraction and analysis was carried out to identify potentially allergenic proteins in stevia leaves. Protein separation and isolation was achieved with 2-dimensional electrophoresis (2DE) and MALDI-TOF MS analysis was performed for the identification of individual proteins.
Furthermore, as stevia may cultivated within various regions of the EU with different soil and climatic conditions it is important to know whether an EU-common specification will be achieved and how stevia leaves from regions outside EU can be distinguished on a scientific basis. For this purpose, principal component analysis (PCA) was performed based on the LC-MS dataset of stevia phenols. In addition, effect of growth origin and variety on stevia secondary metabolite profile was analyzed statistically by ANOVA (analysis of variance)
Positioning using terrestrial wireless systems
No full textThe Global Positioning System (GPS) is a satellite-based location system, which is widely used for location determination, navigation and time synchronization. Because GPS signals are transmitted at relatively low power levels and over great distances, the received GPS signal is relatively weak. Moreover, inside buildings or in urban canyons, the GPS signals are further attenuated by walls, roofs and other objects. Thus, the reception of GPS signals is not reliable in indoor or obstructed environments.
An accurate and reliable indoor positioning system is critical to provide navigation support to first responders in emergency scenarios as well as to minimize the rescue time of injured personnel. Moreover, Location Based Services (LBS) drive the development of indoor positioning techniques, mainly due to the need to provide service continuity inside buildings. Location based services are typically used with mobile devices in pedestrian mode for applications such as locationbased advertising, people or pet tracking and friend-finder functionality. All these applications require continuous, seamless and ubiquitous positioning, which GPS is not capable of delivering.
In the last ten years several techniques have been proposed to solve the problem of indoor positioning. Some depend on the presence of a known network of base stations such as Wireless Local Area Networks (WLANs) access points, Bluetooth nodes or digital television towers. Other short-range technologies depend on specialized transceivers specifically designed for positioning e.g. GPS pseudolites and repeaters, active Radio Frequency Identification (RFID) or Ultra-Wide Band (UWB). However, no single positioning technology is able to provide high availability and precision. For this reason, the trend is toward hybrid solutions, i.e. the combination of different positioning methods. The seamless cooperation between different technologies is required in order to provide location capability whenever a clear view of the sky is obstructed.
While dead-reckoning is not a standalone positioning technology (it needs a known start reference position) it is the most promising option when other infrastructure based solutions, such as GPS, are not available. The principle of operation is based on the ability to accurately measure the velocity vector i.e. both the amplitude (speed) and direction, starting from a known reference point. An accurate starting point can be assumed from a standalone positioning technology such as GPS, and the direction of movement can also be obtained with fidelity using a combination of magnetometers and gyroscopes. In order to determine the walking speed and thus the displacement compared to the reference position, accelerometers together with statistical models of the human walk are used to detect steps and to estimate the step length. However, these step-length estimators require user calibration and fail in practice when the user is moving with an irregular posture like crawling, sliding on a slippery surface, using the fast walking lane in an airport, riding a bicycle or skateboarding.
This dissertation proposes a novel speed estimation method for pedestrian dead-reckoning, which is based on the coherence time of wideband terrestrial wireless systems. In the proposed method, the coherence time is defined as the time required for the envelope correlation coefficient of a wideband frequency-selective channel frequency response vector to drop below a certain threshold value.
The effect of the several channel propagation conditions, such as signal-to-noise ratio, the direction-of-arrival of the line-of-sight component and Rician factor, is investigated on the performance of the proposed method.
Moreover, a proof-of-concept hardware demonstrator is realized and several experimental measurement campaigns are conducted to verify the performance of the proposed algorithm under real-world indoor conditions.
Experimental results indicate that speed estimation errors lead to an average positioning uncertainty of 1:1% of the total traveled distance with a standard deviation of 2:4% from the average. Moreover, there is a probability of 97% that the absolute positioning uncertainty will be less 4.5% of the traveled distance.
It is demonstrated that the proposed speed estimation method outperforms traditional pedestrian dead-reckoning systems, which are based on step length estimators. In addition, the proposed algorithm does not require user calibration and it is not based on a particular type of movement because it solely measures the absolute speed of the moving antenna
Characterization of complex mixtures of the light shredder waste fraction and caramelization processes by mass spectrometry
No full textThe analysis of complex mixtures is one of the most challenging areas of analytical chemistry. Within this thesis the composition of two complex mixtures of environmental and food origin, such as the light shredder waste fraction and caramel was studied, respectively. In the last few decades, the light shredder waste fraction has attracted much interest due to the scarcity of space and the toxicological properties of some of its contaminants. In this work, gas chromatography with a flame ionization detector (FID) as well as coupled to mass spectrometry with electron impact (EI) and atmospheric pressure chemical ionization (APCI) has been applied to study the composition of the light shredder waste fraction focusing on non-volatile hydrocarbons. GC-APCI with a time of flight mass analyzer was utilized for the first time in order to determine heavy hydrocarbons of n-alkanes standard and the light shredder waste fraction. Adducts, such as [(M-3H)+H2O]+ and [M-H]+ were found to be the most abundant ions up to n-nonadecane (C19H40) and for higher hydrocarbons established by APCI, respectively. In the second part of this thesis, the composition of caramel, one of the mankind'Engineering and Sciences well-known dietary materials, obtained by the heating of carbohydrates, have been studied. Caramel formed by heating of glucose, fructose, galactose, mannose as well as disaccharides, such as sucrose, lactose and maltose using a conceptually novel combination of mass spectrometric techniques have yielded for the first time an unprecedented account of its chemical composition. The analytical strategy employed uses high-resolution mass spectrometry to identify the most abundant molecular formulas followed by a van Krevelen and Kendrick analysis. A resulting structural hypothesis was further substantiated using targeted LC-tandem MS experiments. The caramelization products include oligomers with up to six carbohydrate units produced through an unselective glycosidic bond formation, dehydration products of oligomers losing up to eight water molecules, hydration products of sugar oligomers, disproportionation and aromatic products. In addition, the molecular formulas of compounds responsible for a brown color of caramel were also proposed. The investigation of thermal decomposition products of pure starch and cellulose as model systems followed by the investigation of bread obtained under comparable conditions has been performed. Commercial caramel products and caramel colors (E 150) were compared with studied carbohydrates. Furthermore, understanding of the composition of roasted coffee beans has been improved by the examination of their carbohydrates fraction
Thermoelectrical properties of Graphene
No full textThis study aims to analyze the electrical conductivity properties and thermopower of monolayer and bilayer graphene.
After an experimental and theoretical introduction to the effect of thermopower in graphene, we aim to explain the divergence between experiment and theory for thermopower in bilayer graphene in the first part of this work. Several approaches are presented; an extended Mott normalism, diagrammatic calculations in the linear response framework and Boltzmann equation calculations. A comparison of these approaches is provided. These approaches take into account both the diffusion of the electrons as well as electron phonon interaction with a particular focus on the phonon drag component. Within these calculations the detailed analysis of the phonon bath turns out to be of key importance. Therefore, the contribution of phonon-phonon interaction, phonon-boundary interaction and phonon-impurity interaction is examined in detail. Furthermore, the results are compared to competing theories such as the balance equations theory, as well as to other systems, and finally to experimental results.
In the second part the quantum corrections to the conductivity and the thermopower in monolayer graphene are studied numerically and analytically. First, we use the recursive Green’s function method to numerically calculate the conductivity and the thermopower of graphene. For conductivity, we obtain changes between weak antilocalization to weak localization as a function of the system’s parameters, namely the correlation strength of the impurities, the width and concentration of the impurities and the Fermi energy of the system. In addition, we find an increase of the quantum correction to the thermopower, and thereby magneto thermopower, which depends on the same parameters weak localization corrections to the conductivity. We analytically reproduce the known results for the conductivity, linking them to the same parameters that we tuned in the numerical calculation
Time Resolved Spectroscopy in the Nearfield and Farfield: Probing Ultrafast Molecular Dynamics and Subwavelength Resolution Imaging
No full textThe vibrations of nuclei, formation and breaking of chemical bonds and biological transformations that happen on a time scale of picoseconds to femtoseconds can be captured using nonlinear spectroscopic techniques employing ultrafast laser pulses. The high peak power of the femtosecond pulses can induce a nonlinear polarization efficiently, which in turn acts as the source of the signal, which contains dynamical information. The combination of multiple laser pulses can be used to monitor the evolution of the molecules. The thesis discusses the pump-probe technique and the four-wave mixing process, coherent anti-Stokes Raman scattering (CARS). These techniques are applied to monitor exciton dynamics in organic semiconductor thin films and vibrational dynamics. Time resolved CARS experiments in Bromine vapor is presented, which show the potential of this technique to probe vibrational dynamics in both ground and excited state potential energy surfaces. The dynamical information obtained could be used to generate chemical specific contrast for non-invasive imaging. The investigation of the influence of the nanostructuring of materials on the ultrafast photo-induced dynamics is of considerable interest. The scanning near-field imaging technique can be integrated with nonlinear spectroscopic techniques to improve spatial and axial resolution of the images. Additionally, the dynamics can be probed down to nano-scale dimension. The thesis shows the proof of principle examples for this combination, in order to obtain exciton map and vibrational contrast images with sub-wavelength resolution
Synthesis and Characterization of Multinuclear Manganese-Containing Polyoxotungstates for Homogeneous Water-Oxidation Catalysis
No full textPolyoxometalates are anionic, nano-sized metal-oxygen clusters of early transition metals in high oxidation states such as Mo6+, W6+, and V5+. The structural and compositional versatility of polyoxometalates is remarkable and is complemented by other tunable properties such as high stability, solubility and redox activity. Such properties render polyoxometalates highly desirable for catalytic studies such as homogeneous water-oxidation catalysis. Our group was able for the past thirteen years to synthesize a variety of polyanions containing multinuclear transition metal centers and clusters in acidic aqueous media. In particular, manganese-containing heteropolyoxotungstates are of special interest owed to the discovery of the active center responsible for the production of molecular oxygen from water in Photosystem II. The tetranuclear manganese oxygen-evolving center has motivated numerous attempts directed towards mimicking its structural or functional properties by designing a variety of manganese organic-based complexes. However have only resulted in poor activity being affected by thermal and oxidative degradation, unlike the robustness of polyoxometalates making them ideal frameworks for developing novel artificial photosystems.
Along these guidelines inspired by nature, the reaction of [MnIII8MnIV4O12(CH3COO)16(H2O)4] with [A-α-PW9O34]9- in a 1:2 molar ratio in aqueous, acidic medium resulted in a trimanganese(III)-containing, sandwich-type 18-tungsto-2-phosphate [MnIII3(H2O)5(A-α-PW9O34)2]9-. The polyanion crystallizes as a mixed potassium/cesium/guanidinium salt in the triclinic space group P-1, with cell parameters a = 13.1718(19) Å, b = 16.505(2) Å, c = 22.842(4) Å, α = 104.141(7)°, β = 106.267(8)°, γ = 101.369(6)°, V = 4430.6(12) Å3, and Z = 2. The polyanion comprises two [A-α-PW9O34]9- Keggin fragments linked via three MnIII ions, two of which are 6-ccordinated and one is 5-coordinated. The obtained polyanion salt was further characterized by IR, TGA, elemental analysis and magnetic measurements in the solid state. Electrochemical studies showed that the polyanion is both stable in solution and interesting for the elaboration of a water oxidation electrocatalyst, due to its MnIII oxidation wave governed by a mixed adsorption-diffusion regime, accompanied by electrode activation.
Five other manganese-containing Keggin-based tungstosilicates [MnII3(OH)3(H2O)3(A-α-SiW9O34)]7-, [MnIII3(OH)3(H2O)3(A-α-SiW9O34)]4-, [MnIII3(OH)3(H2O)3(A-β-SiW9O34)]4-, [MnIII3MnIVO3(CH3COO)3(A-α-SiW9O34)]6-, and [MnIII3MnIVO3(CH3COO)3(A-β-SiW9O34)]6- were also synthesized in aqueous medium by interaction of [A-α-SiW9O34]10- or [A-β-SiW9O34H]9- with either MnCl2·4H2O or [MnIII8MnIV4O12(CH3COO)16(H2O)4] under various reaction conditions. The obtained salts of these polyanions were further characterized in the solid state by IR, TGA, elemental analysis and magnetic studies, as well as in solution by electrochemistry. The tetranuclear manganese-containing 9-tungstosilicate, with its mixed-valence [MnIII3MnIVO3(CH3COO)3]4+ manganese assembly reminiscent of the oxygen evolving complex in Photosystem II, revealed high activity in photo-induced water splitting reactions. These results were further supported by several analytical techniques such as FT-IR, UV-Vis, electrochemical and conductiometric titration experiments. Additionally, in a similar fashion, the interaction of the same manganese coordination complex however with 9-tungstoarsenate(V) [A-α-AsVW9O34]9-, resulted into a novel mixed-valent decamanaganese-containing 36-tungsto-4aresenate(V) [MnIII6MnIV4O4(OH)12(H2O)12(A-β-AsVW9O34)4]22-, which might show interesting magnetic properties and photocatalytic activity in water-splitting due to the structurally appealing and electrocatalytically active [MnIII6MnIV4O4(OH)12(H2O)12]14+ core stabilized within the tungstoarsenate framework
Novel strategies for the purification of biomolecules by affinity chromatography: Ceramic fluorapatite binding peptides for the development of self-assembled systems and ligand-less adsorbents
No full textA key issue related to bioprocessing technology is product recovery and purification i.e. the so-called downstream processing, which still remains a daunting task in the life science industry. Affinity chromatography is the most efficient method known for highly selective sequestration of (bio) products. This technique exploits the recognition ability of certain chemical structures or “ligands” for the species being targeted within a feedstock. Such ligands are normally covalently coupled to a solid support (“beads”). This traditional immobilization process, however, may present several drawbacks such as ligand inactivation and leakage, high expense, and environmental burden. To overcome such limitations, the present work has focused on the development of two completely new approaches, as follows: a) The fabrication of self-assembling affinity adsorbent beads, and b) The implementation of ligand-less affinity systems. As a first step to materialize the concepts proposed above, peptides with the ability to bind to ceramic fluorapatite beads (CFT) were discovered by screening binding-peptides out the diversity created utilizing either biological or synthetic peptide libraries. The fabrication of affinity adsorbent beads for the purification of total human immunoglobin G (hIgG) was attempted. The peptide construct pIC, composed of a hIgG-specific peptide ligand pLI, HWRGWV, and a CFT-specific peptide tag pTC, KPRSVSG (F5-4), was immobilized on CFT beads by self-assemblage without the need of any chemical procedure. The hIgG-binding capacity of the self-functionalized CFT beads increased as a function of the conjugate density on the surface of the adsorbent. The approach regarding the use of CFT-specific peptides as tags for the purification of recombinant proteins was investigated by fusing CBPs at the C terminus of enhanced green fluorescent protein (eGFP). The resulting fusion protein was expressed in Escherichia coli strain BL-21, and the clarified crude extract was subjected to CFT column chromatography. The yield and purity of the isolated protein were over 90%. This work demonstrates the potential of material binding peptides in the development of novel, and highly selective, adsorbents for chromatography and allied techniques
Coupled Methane Hydrate Formation and Fluid Transport in Marine Sediments : Numerical Modelling and Case Studies
No full textThe quantification of organic carbon stored in gas hydrates and the prediction of the consequences of global warming on the release of greenhouse gases from hydrate fields are challenging. Several models exist to predict the hydrate saturation in vertical sediment profiles based on the supply and transport of organic carbon.
This work describes the development and the application of a multi-dimensional numerical reactive transport model, coupling fluid flow and sediment transport in sub-seafloor hydrate fields with the changes of the hydraulic sediment properties during the precipitation of methane hydrate. The involved biogeochemical processes are modelled using a segregated solver based on the Finite Volume Method with adaptive time stepping. One of the challenges that is solved with this formulation is the accurate mass conservation of components transported across the boundary of hydrate stability. This approach was validated with pore water chlorinity data from the Blake Ridge hydrate field.
After an analysis of the sensitivity of the predicted hydrate saturation on parameters influencing the methane budget, particularly on the Darcy flow rate, the work focusses on the significance of lateral fluid transport for observable deviations from the hydrate abundance. The pore-scale formation of hydrate crystals that reduce the effective porosity is parameterised by the Kozeny-Carman and the tubes-in-series porosity-permeability relationships. We investigate the difference between the predicted hydrate saturations and related chlorinity anomalies according to both paramerisations in scenarios where a hydrate layer is limited laterally by shallow waterdepth or by sediments inhibiting hydrate formation. The results show that the effect is most significant when the less chlorine pore water, formed by hydrate dissociation at the base of the hydrate stability, is advected laterally into an area of inhibited hydrate formation
Human Perception in Using Projection Methods for Multidimensional Data Visualization
No full textThis thesis presents experimental results associated with the human factors aspects of visualizing multidimensional data. Visual exploration of multidimensional data typically requires projection onto lower-dimensional representations. A large number of possible projections has been proposed in the recent years. The analysis of multidimensional data has been studied in various research areas for many years and different quality measures have been introduced to help in the interpretation of sets of points in a multidimensional space. Different measures deliver different visual metrics to evaluate the best views of multidimensional datasets that do not necessarily match the expectations of human perception. This thesis contributes toward this goal by providing some perceptual guidelines through investigating different projections. Learning more about the effectiveness of projection layouts from a user’s perspective is an important step towards consolidating their role in supporting visual analytics tasks. Such tasks often involve detecting and correlating clusters. This thesis supports discovering certain characteristics that change the visual attention and cognitive process for finding clusters, patterns, outliers, and relationships. The main approach consists of three major steps according to three fundamental parts of the visualization pipeline: Data preparation, Mapping, and Rendering. The visualization pipeline describes the (step-wise) process of creating visual representations of data. A good visualization guides the observers’ attention to the relevant aspects of the representation. To achieve this aim, correlations and connections between human perception and different visualization steps are investigated.
At the first stage, the supporting visual analytics tasks are found through understanding the data set and learning more about domain-specific issues. This helps to improve decision process when making decisions becomes hard for selecting from alternative multidimensional data representations. In the second stage of our study, projection methods representative of different approaches are considered that generate different layouts of multidimensional data in a lower-dimensional visual space.
Mapping or geometry extraction is the main core of the visualization process. In the case of high-dimensional data, dimension reduction techniques such as projections are applied to map the input space to a 2D or 3D visual space. Many layout strategies have been proposed addressing different objectives that are targeted at distinct domains and applications. The resulting projected information is typically displayed in form of 2D scatter plots. The user’s perspective such as the role of visual attention and cognitive processing for a respective layout and task has not been addressed much. It is the goal of this work to investigate, how characteristics in the layout affect the cognitive process during task completion. Eye trackers are an effective means to capture visual attention over time. An eye tracker is used in a user study, where users have been asked to perform typical analysis tasks for projected multidimensional data such as relation seeking, behavior comparison, and pattern identification. Those tasks often involve detecting and correlating clusters. To understand the role of point density within clusters, cluster sizes, and cluster shapes, synthetic 2D scatter plots were created where properties could be manipulated manually. How changing various parameters affect the visual attention pattern has been investigated. The insight obtained from synthetic data is transferred to investigate the decision making with real-world data. Some conclusions on how different projection methods support or hinder decision-making leading to respective guidelines are drawn. In addition, this thesis shows that a 3D visual space can increase the performance of common visual analysis tasks due to a higher projection precision. The findings are backed up with a user study. However, 3D projections typically are displayed on a 2D screen which may impede the correct perception of the third dimension. This thesis presents a study that investigates the effect of stereoscopic environments when used for the visual analysis of multi-dimensional data after projection into a 3D visual space. Finally, through the last stage, visually encoding data clusters in a 3D setup as the form of enclosing surfaces or hulls are compared to scatter plots to evaluate the suitability of these methods for the visual analysis tasks. Efficient analysis of multi-dimensional data in order to understand the relationships between information hidden in huge data sets is essential. Our results offer interesting insight on the use of projection layouts in data visualization tasks and provide a departing point for further systematic investigations