Publication Server of Constructor University Library
Not a member yet
858 research outputs found
Sort by
Femtosecond Time-Resolved Four-Wave Mixing Applied to the Investigation of Excited State Dynamics
No full textLaser spectroscopy in the frequency domain has, very early, developed into a powerful tool for the analysis of structural properties of molecules. The development of ultrafast lasers added a new dimension to conventional spectroscopy by rendering time resolved measurements possible. The high time resolution offered by picosecond and femtosecond laser pulses enabled the real time observation of extremely fast processes, such as vibrations and rotations of molecules. With pulses of duration about 100 fs, it is now possible to monitor processes such as internal conversion, vibrational relaxation, and many other processes occurring in the excited electronic states which leads to reactive or energy transfer pathways. The work presented in this thesis focuses on the study of molecular dynamics in these excited electronic states using timeresolved four-wave mixing (FWM) techniques. It is demonstrated that, by combining the FWM process with an excitation pulse, it is possible to study molecular dynamics in the excited states of gaseous and condensed phase samples. The advantages of the four-wave mixing technique over the commonly used time-resolved fluorescence and pump-probe techniques are also discussed. The pump-FWM method is applied to simple molecules in the gas phase as well as to complex molecular systems where internal conversion processes dominate the ultrafast dynamics. The thesis also presents preliminary studies on the effect of the surface enhancement effect of the nonlinear optical process coherent anti-Stokes Raman scattering (CARS) in presence of colloidal metal particles
Cold-Water Corals. Distribution of fauna and responses to environmental perturbation
No full textOver the last decade, the importance of Cold-Water Coral (CWC) reefs as hotspots of elevated biodiversity on the European continental margin has become firmly established in scientific literature. Reefs are formed predominantly by the calcium carbonate skeletons of successive generations of Scleractinian corals such as Lophelia pertusa (Linnaeus, 1758). This skeletal structure often forms complex 3D structures which can provide a host of habitat niches for other fauna. Advances in remote sensing techniques has led to the location of a large number of reef structures, commonly in regions with elevated flow or productivity, such as on the Norwegian margin. Often these reefs are associated with high commercial fish stocks, and structural damage to reef ecosystems from fishing activity has led to progressively more CWC reefs being closed to fishing by various national legislations. The oil and gas industry also operates in regions and at depths where extensive reef structures can are found, and there is a level of concern over the potential negative impact this industry may have on these ecosystems.
The variation in faunal composition across and between reefs has only been investigated in a few studies to date. Likewise, the fundamental functioning of some of the key ecosystem species, such as Lophelia pertusa, is not well understood. In this thesis a selection of techniques were used to fill some of these knowledge gaps.
A novel method was developed utilising machine-learning algorithms to swiftly and semiautomatically quantify percentage coverage of substrate by living coral polyps. The system was used to assess live coral coverage across a trawl damaged region of the Tisler reef, Norway. The machine-learning algorithm method performed as accurately as a human in quantifying coverage (using standard methodologies), but in considerably less time.
Distribution of a selection of fauna across and between Norwegian reefs was investigated using a large dataset collected as part of the Hotspot Research on the Margin of European Seas (HERMES) project. Previously unreported distribution patterns were observed on a variety of spatial scales for a number of the species investigated.
Laboratory work was conducted to determine the degree to which flow velocity related to net zooplankton capture rates by Lophelia pertusa. The investigation clearly indicated that a significantly higher capture rate was attainable under 0.025 m s-1 than 0.05 m s-1 flow velocity, a surprising result given the high flow velocities often prevalent at reef locations.
Additional laboratory investigations subjecting Lophelia pertusa polyps to doses of various anthropogenic materials (waste from drilling operations, trawl resuspended sediments) were conducted, with results indicating a general resilience of the species to particle exposure
A Study on the Impact of Nonlinear Characteristics of LEDs on Optical OFDM
No full textRecently, indoor OW communication systems based on LEDs as light sources and OFDM as a modulation technique have gained significant attention. For instance, in VLC, in addition to lightening capabilities of white LEDs, they can be modulated to achieve high-speed wireless data transmission. However, only little research has been done in this area, and many open questions exist such as the performance of O-OFDM systems in the presence of LED nonlinearities.
The time domain OFDM signal exhibits a random-like variations. Therefore, special attention must be paid to its sensitivity to nonlinearities. This thesis analyzes the performance of indoor OW systems based on OFDM in the presence LED nonlinearities, i.e. amplitude and clipping distortions. The distortion analysis shows that LED nonlinearities can drastically degrade system performance. As a consequence, a linearization technique is proposed. A digital pre-distorter is applied to compensate for LED nonlinearities. It is found that the degradation can greatly be mitigated by using the proposed predistortion technique.
In a practical system, the OFDM signal is forcibly clipped at the LED TOV and purposely clipped prior to the LED modulation for voltage levels above the saturation voltage. The OFDM pre-conditioning prior to the LED modulation is to ensure that the LED chip does not overheat. Therefore, there is a need to describe the nonlinear behavior of an LED with a model that fits the LED measured transfer function and to level off at both extremes to represent the TOV at one end and the saturation voltage at the other end. A model offering the desired "S-shaped" curve is proposed.
Analytical methodologies to evaluate error probability of uncompensated O-OFDM system and compensated O-OFDM system are proposed. A comparison with Monte Carlo simulation results are carried out. The simulation curves and the analytical curves show a close match in terms of SER
Towards Autonomous Navigation for Robots with 3D Sensors
No full textThis thesis contributes to mobile robot autonomous navigation at different levels. Different methods for 3D sensing are discussed. In particular, we evaluate a time-of-flight range camera. We develop a method to detect and heuristically correct the most inhibitive error source, wrap-around of range measurements.
We show several 3D point cloud datasets gathered with the 3D sensors presented in the preceding chapter. The datasets represent a wide variety of real-world and set-up scenes, indoors and outdoors, underwater and land, and small scale and large scale.
We present a robust and fast short-range obstacle detection algorithm. It is based on the Hough transform for planes in 3D point clouds. The method allows a mobile robot to reliably detect the drivability of the terrain it faces. Experiments with two types of sensors on data from indoors and outdoors demonstrated the algorithm's performance. The processing time typically lies between 5 and 50 ms per frame.
We develop the Patch Map data-structure for memory efficient 3D mapping based on planar surfaces extracted from 3D point cloud data. We survey and benchmark different methods of generating planar patches from a point cloud segmented into planar regions. We benchmark various collision detection methods with various roadmap algorithms on synthetic data to find out the most efficient ones.
We thoroughly test the Patch Map data-structure developed in the preceding chapter on real-world data. We perform both roadmap generation with PRM and RRT and way finding from start to goal, based on RRT. We compare our approach to the established methods of trimeshes and point clouds and find that it performs an order of magnitude faster on 3D LRF data and also considerably better on sonar data. We also show that this speed advantage does not come at the cost of loss of precision
A bilateral model system for the molecular investigation of diatom-bacteria interactions
No full textDiatom blooms are frequently terminated by aggregation of algae and subsequent sedimentation in form of marine snow. Transparent exopolymer particles (TEP) are produced by phytoplankton or bacteria and play an important role in aggregate formation. This study was aimed at analyzing the interactions between bacteria and phytoplankton and their influences on TEP formation, aggregation dynamics, and sedimentation of phytoplankton.
For this, an in vitro model system consisting of the diatom Thalassiosira weissflogii and the marine Gammaproteobacterium Marinobacter adhaerens sp. nov. HP15 was established and was analyzed in rolling tank experiments. From the results it could be concluded, that interaction of M. adhaerens with T. weissflogii increased aggregate formation and particle sinking. Detailed investigation of this interaction revealed differences in the response of T. weissflogii, towards bacteria, namely diatom growth and exopolymer production. A careful interpretation of these results suggested a close and specific interaction of HP15 with the diatom in a mutualistic relationship. The type of interaction shifted to commensalism during nutrient stress conditions. Depending on the nature of M. adhaerens - T. weissflogii interactions the extent and quality of algal exudation in form of TEP dramatically changed and consequently influenced aggregate formation.
Another part of this thesis focused on the chemotaxonomic and genomic characterization of M. adhaerens as the bacterial counterpart of the established model system. In this context the bacterial genome sequence was determined and a genetic system for molecular work has been established. A site-directed deletion mutation of the flagellin-encoding gene fliC of HP15 was generated and confirmed the suitability of M. adhaerens as a genetically accessible model organism.
With this bilateral model system being generated, a species-specific interaction can now be intensively and mechanistically studied in depth
American Travel Narratives of the Orient (1830-1870) : a study in the nineteenth century latent orientalism
No full textThis dissertation seeks to examine the rise of interest in American travel narratives and increasing Orientalist representations on direct encounter with the Orient within the following six immediately popular and influential narratives David Porters Constantinople and Its Environs by an American (1835), Nathaniel P. Willis Pencillings by the Way (1836), John Lloyd Stephens Incidents of Travel in Egypt, Arabia Petrea, and the Holy Land (1837), and Incidents of Travel in Greece, Turkey, Russia, and Poland (1838), Bayard Taylors The Land of the Saracen, or Pictures of Palestine, Asia Minor, Sicily and Spain (1854), and Mark Twains Traveling with the Innocents Abroad, or the New Pilgrims Progress. The study traces 19th century American exceptionalist discourses in these narratives via categories of latent Orientalism and argue for a by no means uniform but an indigenous 19th century latent American Orientalism prevalent in these six texts. The analysis also draws on the substantial influence of the journey narrative both as a motif and as a genre in the 19th century American literary scene and its historically embedded impact. The work treats the discursive preferences of the authors as conscious strategies or subliminal reflexes in the national identity formation processes that these narratives partake in
Visualization of Gender in the Turkish Press : A Comparative Analysis of Six Turkish Newspapers
No full textThis study analyses the female and the male visuals in six Turkish newspapers representing different socio-political positions. Visual representations shape the ways people perceive the world and they signify the social fabric. Changes in the visualization of the females in particular indicate societal changes taking place. Various previous studies on Turkish press focused either on the question of underrepresentation of women or on a comparative analysis of the religious and secular press with respect to the representation of women based on textual material. Turkish newspapers are very rich in terms of visual material and in terms of the visual depiction of women. The study argues that the exclusion of visuals from such analyses creates a serious shortcoming. Thus, this study aims to expand the previous research with the incorporation of visual analysis. Secondly, as is the case in previous research, approaching secular and religious press as two separate and distinct camps tends to obscure both the similarities between religious and secular newspapers and the differences within secular and within religious newspapers with respect to the depiction of women. Therefore this study aims not only to look at the differences between secular and religious newspapers in Turkey but also at the differences within them in terms of the visual representation of women. In methodological terms quantitative visual content analysis and qualitative iconological and semiological analyses are employed to analyze the characteristics and meanings of the visuals. In theoretical terms selected approaches towards modernity, media, gender and visual communication inform the study
Development of a mechanistic understanding of element incorporation into biogenic carbonate (foraminifera)
No full textThe trace element composition of calcitic foraminiferal tests has become an important tool by which paleoceanographers reconstruct past oceanic conditions. On timescales much shorter than their residence time, the elements strontium and magnesium occur in seawater with nearly constant ratios to calcium. Variation in Sr/Ca and Mg/Ca in benthic foraminiferal tests can then be explained as a function of environmental parameters that control their incorporation into the tests. For benthic foraminifers, temperature appears to be the dominant parameter controlling the incorporation of Mg, however, a better understanding of the possible impact of other parameters such as pH or [CO32-], and salinity is needed to increase the accuracy of element ratio proxies. My thesis aimed to optimise these reconstructions by developing a mechanistic understanding of the biotic processes that control divalent cation concentration in biogenic carbonate. Towards this goal the benthic foraminifer Ammonia tepida was cultured under three different salinities (20, 33 and 40) and two different pCO2 conditions (230 and 1900ppm), both sets of experiment were run at two different temperatures (10 and 15°C). Weights and elemental composition were determined. Results indicate that both Mg and Sr incorporation are enhanced with increasing temperatures and increasing salinity. Changes in [CO32-] or total dissolved inorganic carbon do not affect the Mg partitioning coefficient. On the contrary, Sr incorporation is enhanced under increasing [CO32-]. Shell weights decrease with decreasing [CO32-], and increase with decreasing temperature. To extend this mechanistic understanding to planktonic foraminifers, a calibration based on field specimen of Globigerinoides sacculifer was developed. This allowed us to evaluate agreement between observed and predicted δ18Ow as a function of Mg/Ca temperature and δ18Oc, and to test the robustness of SSS reconstructions for the Atlantic Ocean
Directed Evolution of Bacillus gibsonii Alkaline Protease towards Washing Applications: a Study of Protein Adaptation
No full textB. gibsonii Alkaline Protease (BgAP) is a recently described subtilisin with activity and stability properties suitable for applications in washing detergents, having a significant decrease of activity at low temperatures. To improve BgAP activity at 15°C, directed evolution was used using SeSaM mutagenesis method. A parallel screening towards improved protein stability and further recombination yielded variant 39IC1+N253D with a half time at 60°C more than 200 times that of WT BgAP. Recombination of both sets of amino acid substitutions resulted in variant 39IC1 MutIII with 1.5 times the specific activity and 100 times the half life at 60°C of the WT BgAP. Analysis of the introduced amino acid substitutions revealed no substitutions close to the active site, and activity related ones were non-charged to non-charged of the large to small type whereas those related with improved thermal stability introduced negative charged residues in loop areas, and increasing ionic and hydrogen bonds interactions. To further study protein adaptation, the psychrophilic subtilisin S41 from the Antarctic bacillus TA41, and two variants with two and seven amino acid substitutions were studied using Molecular Dynamics simulation at 283K and 363K. Essential dynamics analysis evidenced that the most important collective motions, especially at 363K, differ in distribution and intensity for each protein. At high temperature and for the thermo labile wild type, selective amplification of a subset of the low temperature largest collective motions was observed. The thermostable variants showed a different pattern of the collective motions at 363K from those at 283K. These results support the hypothesis that these amino acid substitutions, rather than improving the global stability of the variants by increasing its rigidity, selectively activate collective fluxional modes. A better understanding of this process can open alternative strategies to design proteins with improved thermal stability
Reservoir Self-Control for Achieving Invariance Against Slow Input Distortions
No full textA method is presented for immunizing an Echo State Network against slow, task-irrelevant variation in its input. The main idea is to extract some principal components of the smoothed reservoir dynamics, and augment the reservoir with a feedback controller which attempts to pull these components to zero. This leads to a "homeostatic" self-stabilization of the reservoir dynamics. A proof-of-principle case study is presented where the network has to predict a two-mode input signal which is subjected to a large-amplitude, slow variation in offset. With the controller in place, this task is solved with exactly the same quality as in a condition where the input is undistorted. Furthermore, the action of the controller can be “compiled into” the reservoir, by recomputing reservoir weights such that the controlled network dynamics is recovered without the controller switched on. One thus finally obtains a reservoir whose internal dynamics are largely invariant against slow distortion in the input