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Laptev Sea and East Siberian Sea landfast ice: Mechanisms of formation and variability of extent
No full textLandfast ice is a motionless continuous with the shore sea ice over. It forms seasonally in the majority of the Arctic coastal areas. Although it comprises a only small fraction of winter Arctic sea ice extent, it plays a significant role in the global climate system and is particularly important for coastal ecosystems and human activity. Along with the ongoing changes in the Arctic sea ice cover, the reduction of fast ice season and extent were reported in the majority of the Arctic marginal seas. A detail understanding of the mechanisms controlling fast ice development on a regional scale is important to predict future changes in fast ice cover and coastal environment. The main goal of this thesis is to investigate the variability of the fast ice extent in the Laptev and East Siberian seas and to find the mechanisms responsible for this variability.
Using operational sea ice charts produced at the Arctic and Antarctic Research Institute (Russia) we analyzed seasonal and interannual variability of fast ice extent in the southeastern Laptev Sea between 1999 and 2013 and in the East Siberian Seas between 1999 and 2015. We characterized seasonal fast ice development in these regions by identifying key events in the course of fast ice growth and decay. Analyzing the timing of the fast ice key events, we found a decrease in duration of fast ice season in both regions with a rate of 2.8~d/y in the Laptev Sea and 1.5~d/y in the East Siberian Sea. This changes are caused by both a later beginning and earlier end of fast ice season, which can be partially explained by long-term trends in the onset of freezeup and melt. The winter fast ice extent did not show any changes during the investigation period, however previous studies report on the reduction in winter fast area \citep{Yu2013}.
A time series of Synthetic Aperture Radar (SAR) imagery was used to investigate small-scale processes contributing to the advance of fast ice edge to its winter location in the southeaster
Existence, uniqueness, and breakdown of solutions for models of chemical reactions with hysteresis
No full textWe consider the fast reaction limit of the Keller--Rubinow model for Liesegang rings which was rigorously formulated by D. Hilhorst, R. van der Hout, M. Mimura, and I. Ohnishi in 2009; we shall refer to it as the HHMO-model in the following.
Using a combination of analytical and numerical methods, we demonstrate a mechanism which suggests that the solution of this model possesses an infinite number of precipitation regions, but these regions accumulate in a finite region of space-time. This is done by introducing modifications which simplify the HHMO-model. This simplified model is shown to be equivalent to solving a fixed point functional equation of integral type. Provided that the precipitation region is followed by non-precipitation region and vice versa, we prove that all those regions accumulate at a finite point.
Beyond the accumulation point, the solution can only be continued in a weak sense in which the precipitation indicator function takes fractional values and may be interpreted as a precipitation density function. We demonstrate the existence of that extended solution.
Its uniqueness is shown under the assumption that the precipitation attains fractional values only. The technique involves the theory of Volterra integral equation for weakly degenerate cordial kernel functions.
In separate chapter we present new results for those kernel functions.
Furthermore, numerical evidence suggests that the concentration function converges, in a well-defined sense in the long-time limit, to a self-similar solution for which an explicit expression is derived.
It is achieved when the precipitation functions is interchanged with self-similar scaling profile. That behaviour is proven after modifying the full HHMO-model according to numerical results, to be precise, the precipitation functions is assumed to converge strongly or weakly to the self-similar scaling profile.
Moreover, we establish several uniqueness theorems for the full model
New dyes for ocular surgery : synthesis and preclinical testing
No full textIn cases of vitreoretinal interface diseases, such as macular hole or macular pucker, the inner limiting membrane (ILM) or epiretinal membranes (ERM) need to be surgically removed. The challenging step in the surgery is the transparency of ILM and ERM that makes the membranes difficult to identify and to peel without risk of damaging the retina. Only a few vital dyes have been proposed to stain the ILM and ERM and no perfect dye is available that would stain the tissue of interest sufficiently, while being non-toxic and stable in aqueous solution. During cataract surgery a dye to stain outer part of a capsule of the lens is used when the red reflex from the fundus is absent. Dyes used for capsulorhexis need to be safe for corneal endothelial cells. Phototoxicity needs to be tested for dyes intended to be used in vitreoretinal surgery. A very strong source of light is present during the surgery, that can cause the dyes to become toxic while illuminated. A set-up for testing phototoxicity on a 96-well plate has been developed. New models for staining ability of dyes for ILM and ERM are suggested, as porcine eye was proved not reliable for those studies. Instead, a model for ILM and ERM was developed with good correlation to staining of human ILM and human ERM. Pig eyes can, however, serve as a useful model for capsule staining when cataract is induced in them.
A new dye for capsulorhexis is presented. No safe, green dye that would stain the capsule had been suggested before. The new dye is an alternative to the currently used Trypan Blue and provides as strong staining while being slightly less toxic to corneal endothelial cells.
Fourteen new dyes, that belong to the cyanine family, were synthesized and investigated for staining ability, toxicity, and stability in aqueous solution. Two of the new substances were found to stain the model for ILM in green, while being safe to retinal epithelial cells. Their stability in aqueous solution can be achieved with additives
What explains phytoplankton dynamics? An analysis of the Helgoland Roads Time Series data sets
No full textPhytoplankton is a diverse group of organisms that account for almost 50% of the global primary production. This thesis aims to investigate the role of environmental variables in structuring phytoplankton communities at Helgoland Roads, North Sea. It contains a detailed description of long-term changes in nutrients, calculates the phytoplankton-carrying capacity of the German Bight, and explores the response of phytoplankton diversity to environmental changes. Moreover, the importance of different biotic and abiotic factors in explaining the variability of phytoplankton abundance is discussed here. This thesis, for the first time, estimates the phytoplankton K of the German Bight, showing a high degree of variability over time. It also establishes a causal relationship between ecosystem variability and biodiversity; it explains the coexistence of the phytoplankton species in a system limited by multiple resources. In addition, this thesis establishes a pattern of seasonal phytoplankton dynamics in relation to biotic and abiotic factors. Overall, the results of this thesis will expand our understanding of the effect of long-term environmental changes on the dynamics of the phytoplankton community in the North Sea
Opto-electronics of thin-film silicon solar cells and color sensors
No full textOptical and electrical performances of silicon solar cells are investigated experimentally and numerically. The solar cells are based on nanoscale, multiscale and tiled textured surfaces. In the first part, the short circuit current density and energy conversion efficiency of multiscale textured solar cells are increased compared to nanoscale textured solar cells. This gain in the electrical parameters are achieved for both the amorphous and microcrystalline silicon materials. The short circuit current density of the simulated solar cells is further increased by optimizing the optical losses. In the second part, hexagonal tiled microcrystalline silicon solar cells exhibit record short circuit current densities and energy conversion efficiencies. Light trapping and microstructure of the fabricated and simulated hexagonal tiled solar cells are compared to square and triangular tiled solar cells. The triangular textured substrates are superior to the square and hexagonal textured substrates in terms of crack formations and light trapping. Finally, crack-free triangular textured solar cells exhibit increased short circuit current densities as compared to hexagonal and square textured solar cells, allowing to achieve short circuit current densities close to the light trapping limit.
Commonly, color image sensing is carried out by an array of color pixels. Each of the color pixels consist of at least three sensing elements in combination with optical filters for red, green and blue. Due to side-by-side arrangement of the filters the quantum efficiency of a color pixel is limited to 1/3. In order to increase the quantum efficiency an alternative sensor device is proposed and is studied using optical simulations. The proposed sensor uses silicon optical antennas to detect color information. The sensor allows for detecting the color information with quantum efficiencies approaching unity for both the microcrystalline and crystalline silicon materials
Large-scale production of high-value bioactive substances from microalgae
No full textA variety of bioactive substances have been extracted and identified from microalgae such as polyunsaturated fatty acids, polysaccharides, polypeptides, pigments as well as polyphenols. Although this topic is gaining increasing attention, mass production of microalgae-derived bioactive compounds is restricted by factors such as the low yield of algal biomass, the poor productivity of target compounds, immature extraction techniques, high capital and running costs, and insufficient knowledge in biosynthesis pathways. In this thesis, several critical obstacles in the large-scale production of bioactive compounds were addressed including the selection of appropriate algal species, the establishment of identification and purification methods, optimization of environmental conditions, and modification of photobioreactors. By a recently established high-resolution chromatography method, two fractions that showed antibacterial effects against Bacillus subtilis were eluted from Phaeodactylum tricornutum biomass, from which one was identified as pure polyunsaturated fatty acid – eicosapentaenoic acid, and the other designated as potential novel anti-bacterial compound(s) in Chapter 3. In Chapter 4, one benthic diatom, Cylindrotheca closterium, was selected from four tested species yielding the highest content of fucoxanthin and productivity. The optimal light condition, producing maximum fucoxanthin productivity and minimizing energy consumption, was predicted and validated. To better understand the metabolism of lipid accumulation in response to nitrogen starvation in diatoms and green algae, the lipidomes of the benthic marine diatom – C. closterium and the freshwater green alga – Scenedesmus sp. – were compared by an HPLC – coupled Micro-TOF mass spectrometric method in Chapter 5. In conclusions, the techniques developed in this thesis aimed to reveal the commercial feasibility of large-scale production of high-value bioactive substances and lipids from microalgae
Learning and Leadership in Organizations: A Group Process Perspective
No full textOrganizations are faced with a number of challenges for effectively managing their workforce, such as maintaining and developing employees’ knowledge against the background of demographic shifts, ensuring employees’ pro-organizational behavior, and conducting work in self-managed teams. Across four empirical chapters, the present dissertation investigates learning (studies 1 and 2) and leadership processes (studies 3 and 4) related to these organizational challenges, with an emphasis on the influence of the group context. Particularly, drawing from social identity theory and the information elaboration lens, studies 1 and 2 investigate processes and boundary conditions of knowledge development in age-diverse groups. In studies 3 and 4, I consider the group context when investigating leaders’ effect on followers’ pro-organizational behavior and the development of group members into informal leaders in self-managed teams. The studies showcase qualitative as well as quantitative approaches; they rely on multiple sources of data (i.e., supervisor/trainer/mentor narrative, employee ratings, information on team composition, behavioral data) as well as different forms of data collection (interviews, survey measures, experimental and field studies, interaction coding). The results were obtained using a range of analytical methods (qualitative content analysis, moderated meditation index, and micro-level interaction analysis). The findings have important implications for conceptualizing and designing learning in organizational groups in a way that promotes active sharing and integration of knowledge. Moreover, this thesis emphasizes the conceptual and empirical value of understanding leadership as a relational process coming into place through the interactions between leaders and followers. The results are also highly relevant for HRM practitioners who are in charge of training employees in diverse learning groups and responsible for selecting and developing leaders
The Involvement of Trace Amine-Associated Receptor 1 and Thyroid Hormone Transporters in Non-Classical Pathways of the Thyroid Gland Auto-Regulation
No full textThe thyroid gland is an endocrine organ responsible for producing thyroid hormones, which are essential for normal growth and development, and for maintaining functional homeostasis of different organ systems. The thyroid is known to be classically regulated by the hypothalamic-pituitary-thyroid (HPT) axis which, in short, involves hypothalamic release of thyrotropin-releasing hormone (TRH) in response to low levels of thyroid hormones in the circulation. Through positive feedback, the TRH signals to the pituitary to release thyroid stimulating hormone (TSH), which, in turn, binds and activates thyrocytes to release thyroid hormones. Replenishment of thyroid hormones in circulation then serves as a negative feedback to quench TRH and TSH release. Growing evidence, including the non-genomic effect of thyroid hormones (T3 and T4), the selective thyroid hormone transporters that regulate cellular thyroid hormone uptake and release (including in the thyrocytes), as well as the discovery of endogenous thyroid hormone derivatives, the thyronamines, and their physiological effects, collectively challenge the classical view on thyroid regulation. The implications of that is that more complex regulatory mechanisms might exist, that are capable modulating thyroid function, also at the level of the thyroid follicle itself – the functional unit of the thyroid gland. Such pathways may be independent of the HPT axis, and are collectively referred to as “thyroid auto-regulation”
Enhanced downstream bioprocessing of monoclonal antibodies utilizing biofouling resilient expanded bed chromatography
No full textIntegration and intensification in bioprocessing has a significant role in the development of cost-effective recovery and purification schemes. Expanded Bed Adsorption (EBA) is an integrated unit operation, which allows for simultaneous clarification, concentration, and partial purification -directly from a non-clarified feedstock. EBA technology, however, suffer from unwanted interactions between biomass components and the fluidized adsorbent. This phenomenon compromises dynamic binding capacity and overall process performance.
The main objective of this Thesis work was the optimization of EBA processing using surface-modified adsorbent beads. A detailed study on cell adhesion behavior of four different industrially relevant types of biomass on twenty-six different commonly occurring surfaces was conducted. This study resulted in deriving a “stickiness” factor for every type of biomass. In the next stage, a microplate method was developed for high throughput screening of cell-repellent-polymers. Experimental results, in combination with xDLVO-based interaction energy calculations allowed for the selection of three cell-repellent adsorbent systems. Process performance was validated using commercial affinity adsorbents for the purification of monoclonal antibodies (MAB) from Chinese Hamster Ovary (CHO) crude feedstock. Finally, MAB purification was performed employing PAA-coated and PMA-coated adsorbents at pilot scale. PMA can be proposed as an excellent cell-repellant polymer for application in EBA.
We extended our research into two more aspects: i) the modeling of the CHO cells transportation in EBA and ii) a detailed study on the effect of DNA binding on EBA adsorbents. These studies provided additional insights into the deterioration of the binding capacity of the adsorbent.
This work has added significant value for the advances of expanded bed adsorption. Polymer shielded adsorbents were successfully used for mAb purification, using high cell density CHO cell broth. Polymer shielding of the adsorbents was found to be effective in reducing biomass adhesion and also yielded higher dynamic binding capacities in the presence of cells
Interaction between Plant Phenolics and Bacteria-Structure, Identification, Bioactivity and Uptake
No full textPlant natural product is becoming the target of anti-infective research, and many groups have identified that phenolic compounds are possessing broad-spectrum antimicrobial activity. However, the scientific challenge in drug discovery is the isolation and identification of pure biologically active compounds. Nevertheless, the science of metabolomics offers the possibility to measure full secondary plant metabolomes with a limited experimental effort to allow identification of metabolome differences using statistical analysis of LC-MS data.
In this study, a series of uncharacterized Rhododendron plant extracts have been assayed and compared by principal component analysis (PCA) & multivariate statistical analysis (PLS-DA), thereby revealing identification of a single bioactive cannabinoid compound, which could be validated using activity-guided fractionation.
Moreover, using LC-MS in combination with statistical analysis (i.e., PCA and PLSDA), the Rhododendron species were found to be a rich source of polyphenols derivatives. Where, a total of sixty-nine hydroxycinnamic acid derivatives in the leaves of ninety-eight Rhododendron species were identified. Next, through a combination of phytochemical profiles with antimicrobial susceptibility and cytotoxicity, complemented by phylogenetic analyses, potentially antimicrobial active but non-cytotoxic compounds were identified.
Furthermore, it is known that the human diet consists of a large part of plant-derived products (like vegetables, fruits, tea, and coffee), which contain relatively high levels
of essential polyphenols. Gut microbiota often transforms them before absorption.
This transformation produces a series of chemically diverse gut floral metabolites with high bioactivity. It was much desirable to obtain quantitative information on the uptake of dietary polyphenols into gut microorganisms and to understand quantitatively the time scale of bacterial polyphenol uptake which is absent from the literature. Hence a novel mass spectrometry-based assay was introduced to determine intracellular concentrations of specific dietary polyphenols in selected gut microbes (Escherichia coli and Bifidobacterium bifidum). Additionally, this approach was extended to study the simultaneous uptake of phenolics from a model mixture of dietary phenolics and to assess the uptake of several phenolics into bacterial model (E. coli) from real food matrices with green tea and coffee as examples.
The thesis also addresses a brief determination of intracellular accumulation of antibiotics in gram-negative bacteria (E. coli and P. aeruginosa) using the phenolic uptake LC-MS based method, which may shed light on transport and efflux of antibiotics in and out of bacterial cells.
Finally, the developed analytical methods applied to the isolation and identification of antibacterial compounds from marine algae (Phaeodactylum tricornutum), where isolated EPA (Eicosapentaenoic acid) displayed an inhibitory effect against Bacillus subtilis and different potential pathogenic Vibrio species