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Iron sedimentation and the neodymium isotopic composition of Archean seawater as inferred from banded iron-formations
No full textThe neodymium (Nd) isotopic composition of ~3.0 Ga seawater is inferred from iron-formations (IF) from South Africa. Pongola Supergroup iron-formations display negative ªNd(t) values similar to local shale, suggesting Nd derived from continental crust dominated the isotopic composition of shallow seawater. In contrast, ªNd(t) in Pietersburg greenstone belt IF indicates seawater could possess more radiogenic ªNd(t) values of +1. The Pietersburg IF ªNd(t) data are interpreted as representing bulk Archean seawater not affected by local crustal Nd signatures. If bulk Archean seawater displayed ªNd(t) of +1, then hydrothermal alteration of mafic oceanic crust was the likely process for delivering radiogenic Nd to seawater. High temperature (T) fluid input to seawater between 2.5-3.8 Ga is supported by positive europium (Eu) anomalies in IFs, and the lack of negative cerium anomalies in any Archean IFs indicates that seawater was more reducing than modern seawater. Modern high-T fluids altering mafic oceanic crust possess both positive ªNd values and Eu anomalies, and it is possible that these reducing, Fe-rich fluids exerted a greater control on Archean seawater chemistry than is observed today. However, negative ªNd(t) values for the Pongola IF indicate that locally, shallow seawater could possess distinct Nd isotopic signatures, and the data are interpreted as reflecting isotopically distinct water masses in ~3.0 Ga world oceans, similar to modern oceans. The process(es) of IF deposition are investigated using Pongola Fe-rich shales, which suffered post-depositional mobility and extreme depletion of alkali metals and barium (Ba). The alkali metal and Ba behavior is best explained by significant concentrations of dissolved Fe2+ in sediment pore waters and/or bottom seawater, suggesting that precipitating Fe(III) minerals, either in the water column or at the sediment water interface, were not the dominant phases responsible for the deposition of the Fe-rich sediment
On self-organizing reservoirs and their hierarchies
No full textCurrent advances in reservoir computing have demonstrated that fixed random recurrent networks with only readouts trained often outperform fully-trained recurrent neural networks. While full supervised training of such networks is problematic, intuitively there should also be something better than a random network. In this contribution we investigate a different approach which is in between the two. We use reservoirs derived from recursive self-organizing maps that are trained in an unsupervised way and later tested by training supervised readouts. This approach enables us to train greedy unsupervised hierarchies of such dynamic reservoirs. We demonstrate in a rigorous way the advantage of using the self-organizing reservoirs over the traditional random ones and using hierarchies of such over single reservoirs with a synthetic handwriting-like temporal pattern recognition dataset
Investigations on the ecology of the marine centric diatom Paralia sulcata at Helgoland Roads, North Sea, Germany: Ecology of Paralia sulcata at Helgoland Roads
No full textResearch Questions: - What are the long-term trends and which environmental parameters influence the ecological niche of Paralia sulcata? (multivariate statistical analyses, field and laboratory experiments) - Does a genetically different population of Paralia sulcata occur at Helgoland Roads? (molecular fingerprint method) - How important is Paralia sulcata within the marine food web and as possible food source for grazers? (grazing experiments, meso- and microcosm) Topic of my thesis was the ecological role of Paralia sulcata at Helgoland Roads, North Sea. This species is a cosmopolitan marine diatom species which is common in the benthos and pelagic during winter around Helgoland. P. sulcata lives under a wide range of environmental conditions, but not much is known about its ecology. Many previous studies have been concerned with different environmental conditions and their influence on the occurrence of P. sulcata in marine and coastal areas, but often these studies provided contrasting results. Furthermore, the worldwide distribution and the wide range of adaptations to environmental parameters make it necessary to understand the current ecological characteristics of P. sulcata. One focus of my thesis was to investigate the autecological behaviour of P. sulcata in more detail with laboratory experiments and compare the results with a detailed two year field sampling campaign as well as the long-term data set provided at Helgoland. These results of the laboratory and field sampling data revealed different behaviours of P. sulcata during the seasons. Using a fingerprint method a high genetic diversity of different P. sulcata strains and a separation between January and September to December strains was detected. One possible explanation for the occurrence of P. sulcata especially in the summer period seemed to be the introduction of new clones adapted to warmer water temperatures. Furthermore, the increasing storm activity at Helgoland Roads leads to a mixing of the water column and therefore, to a mixing of the existing naturally highly diverse P. sulcata population. Additionally, the role of P. sulcata as food source in the marine food web was investigated during a mesocosm spring bloom experiment. The observed trend towards a less seasonal appearance leads to the conclusion that this diatom is now a baseline diatom occurring in the water column throughout the year
Algorithms, models, and measurements for sensing and secure transmission in cognitive radio
No full textCognitive radio is a novel approach for improving the utilization of radio spectrum. Spectrum sensing is one of the most important components of cognitive radio. This thesis concentrates on spectrum sensing and secure communication, allowing cognitive radio (CR) users to robustly identify unutilized spectrum and to use that spectrum securely, thus maximizing spectrum utilization without harmful interference to primary licensed users.
This thesis proposes a new Correlation-Sum (CorrSum) method is proposed and its performance is compared with existing methods. Collaborative sensing is discussed as an effort for mitigating challenges of spectrum sensing arising due to channel fading. Different fusion methods as well as decision statistic combining methods are analyzed and compared. Since the multinode shadowing correlation in real environments has an impact on the performance of collaborative sensing, an experimental characterization of the shadowing correlation is performed.
A tighter bound for the performance of correlation-based detection (CBD) methods is developed based on a signal with random correlation and Neyman-Pearson (NP)
detection under the assumption of correlation distribution information (CDI). Additionally, a measurement campaign is presented where radio frequency (RF) spectra in many bands of interest are measured throughout a large sub-urban environment, generating realistic models for the random signal correlation. The measurement-based model indicates limits on performance gains possible with correlation-based detection.
Finally, security issues in CR are discussed and a physical layer secure key generation method termed as reciprocal channel key generation (RCKG) is proposed. A new wideband indoor MIMO measurement campaign in the 2.51 GHz to 2.59 GHz band is presented, whose purpose is to study the number of available key bits in both line-of-sight (LOS) and non-line-of-sight (NLOS) environments
From individual to organization : knowledge sharing within firms and knowledge protection between firms
No full textThis dissertation aims to synthesize relevant theories on knowledge sharing and knowledge protection from multiple disciplines that advance our understanding of the factors that facilitate knowledge sharing within firms and impede imitation between firms. It consists of an introduction, conclusion, and three independent studies on different topics.
The first study investigated the antecedents to hierarchical knowledge sharing within organizations in China. The second one explored employees' preference for different knowledge sharing tools. The third study analyzed organizational strategies to protect key knowledge against counterfeiters. Quantitative design and qualitative method were applied in this research. Through regression modeling and between-subject design, the empirical findings of the study on a medium-sized Chinese company (N=860) revealed antecedents to employees' knowledge sharing with their supervisors. The identified independent variables that had direct effects were affect-based trust, power distance, and affect commitment. In an attempt to identify the determinants of employees' usage of different knowledge sharing tools, between-subject design helped to identify the key effects of openness to give and seek knowledge, trust, and role-breadth self-efficacy. Finally, the third study suggests a comprehensive anti-counterfeit strategy model aimed at helping companies to understand different sources of threats within the unique Chinese environment. This strategy model is aimed at examining and improving companies' existing corporate strategies against counterfeiting, and, lastly, it aims at developing and introducing new and effective approaches against counterfeiting. The model includes five different strategic perspectives, and implications for practice and suggestions for future research were drawn from the study findings
Flow Cytometry Based Screening System for Finding and Improving Bioindustrial Important Biocatalysts - Cytochrome P450 BM3
No full textDirected evolution presents one of the most common ways of tailoring biocatalysts for a certain application, especially when the information about the structure of biocatalyst is lacking. It consists of iterative cycles of diversity generation, on genetic level, and screening for the target property using a specific screening system. One of the bottlenecks of directed evolution experiment is the throughput of currently available screening systems. Recently, a new technology based on double emulsions and flow cytometry/FACS enabled screening for the enzyme activity with ultra high throughput (10[to the power]9 clones per round of directed evolution). In this work, we have optimized this technology for directed evolution of bacterial enzyme, Cytochrome P450 BM3
Lipid membranes on microstructured glass : Electrophysiological single channels recordings of reconstituted proteins
No full textChip based automated patch clamping is an attractive biophysical tool for studying ion channel proteins. Solvent-free planar lipid bilayers can be formed in an automated fashion by positioning and subsequent bursting of giant unilamellar lipid vesicles containing membrane proteins on micron-sized apertures in a borosilicate glass substrate. The use of proteoliposomes for bilayer formation on such chips allows for the direct recording of single channel activity without need for commonly difficult reconstitution of membrane protein after bilayer formation. This approach is specifically attractive for investigations of membrane proteins with less material and in particular channels which not accessible to patch clamp analysis like e.g. proteins from organelles or proteins from bacteria.
To validate a new technology which allows miniaturizing and automating the Patch-clamp technique, the biophysical and pharmacological characterization of different membrane proteins was performed. A wide variety of ion channels have been studied with this technique, for example potassium channels (KcsA, Kv1.2), sodium channels (NachBac) as well as other ligand-dependent (IP3 receptor) or mechanosensitive channels (MscL, TRP channels).
One of the main aims of my thesis was to acquire knowledge on antibiotic translocation through porins and transfer this into drug development and screening devices. OmpF porin plays an important role in permeation of antibiotics through the outer membrane of bacteria. We show data obtained with OmpF porin from Escherichia coli and discuss the characteristics of OmpF in borosilicate glass substrates compare with studies observed with black lipid membrane (BLM). Also, screening for influx of antibiotics through porins (OmpF, OmpC) was done to elucidate the uptake kinetics of antibiotics through porins
Site selection citeria and technical requirements for the offshore cultivation of blue mussles (Mytilus edulis L)
No full textThe aim of this study was to evaluate offshore areas in the German Bight (North Sea) to determine their suitability for cultivation of blue mussels (Mytilus edulis). A relocation of production off the coast offers a new perspective for shellfish farming, as a variety of factors including restrictions on the number of licenses, environmental protection issues and stakeholder conflicts have prevented further expansion in the intertidal and subtidal areas of the coastal sea. The development of the offshore wind farm operators, offers further the opportunity to co-use large marine areas with submerged culture systems for blue mussels. However, offshore production would entail much higher costs than the traditional on-bottom cultivation. Therefore biodiagnostic tools were used to analyse the overall health status of blue mussels grown in different areas of the North Sea. In addition to investigations on the extent of parasite infestation, bacteria, and virus and toxic algae concentrations, this information was used to determine site conditions to aid in the calculation of economic risk for potential mussel farmers. Besides the analysis of health-related parameters, fundamental technical requirements were improved and discussion on supervisional control and appropriate regulatory framework was initiated. The study was conducted using two designated near- and offshore locations for the cultivation of blue mussels. For two consecutive sampling seasons (2006 and 2007) both testing sites and three wild banks were sampled at monthly intervals, partly with the help of research vessels and scuba divers. The mussel samples were used to assess morphometric parameters, condition indices, infestation rates of micro and macro parasites, microbial loads, viruses and the concentrations of algae toxins. Mussels attached to the substrates were used to determine dislodgement force, growth rates, and size distributions. In addition frozen tissue samples were analysed for the membrane stability of lysosomes from the digestive gland to determine the status of mussel health from these locations
Dynamics of organo-mineral aggregates in two submarine canyons of the Portuguese western margin
No full textIn this work the dynamics of organo-mineral aggregates in submarine canyons were investigated, as were their role in the transport of organic matter and pollutants from the productive continental shelf to the deep sea floor, and the effect of this transport on the biological degradation of organic matter. Also addressed were the methodological problems present in the investigation of particle dynamics in the benthic boundary layer.
The work focuses on two large canyons of the Iberian Margin, with very distinct morphologies and hydrodynamic regimes. Although several studies have focused on the geology, hydrodynamics and sediment dynamics in submarine canyons, this work is one of the first to address the role of the two-layer nature of the sediment surface in the transport and fate of particulates in submarine canyons. This study brings forth new information on the role of organo-mineral aggregates as important components of the transport and preservation of organic matter in submarine canyons. It also identifies organo-mineral aggregates as preferential vector for transport of persistent organic pollutants. Additionally, this work shows the significant effect of physical variables on the resuspension of organo-mineral aggregates, and the bias that they bring to the current methodologies for its estimation
On homomorphisms of diagonal Lie algebras
No full textDiagonal Lie algebras are defined as direct limits of finite-dimensional Lie algebras under diagonal injective homomorphisms. An explicit description of the isomorphism classes of diagonal locally simple Lie algebras is given in the paper [A. A. Baranov, A. G. Zhilinskii, Diagonal direct limits of simple Lie algebras, Comm. Algebra, 27 (1998), 2749-2766]. The three finitary infinite-dimensional Lie algebras sl(1), so(1), and sp(1) are important special cases of diagonal locally simple Lie algebras. Many classical results have been extended to these three infinite-dimensional Lie algebras. In particular, in the paper [I. Dimitrov, I. Penkov, Locally semisimple and maximal subalgebras of the finitary Lie algebras gl(1), sl(1), so(1), and sp(1), J. Algebra 322 (2009), 2069-2081] all locally semisimple subalgebras of g $= sl(1), so(1), and sp(1) are described, and moreover all injective homomorphisms s ! g are described in terms of the action of s on the natural and the conatural g-modules. The present dissertation makes a substantial contribution to further extending these results to the class of diagonal locally simple Lie algebras.
In Chapter 3 all locally simple Lie subalgebras of any diagonal locally simple Lie algebra are described up to isomorphism. The main result of the dissertation, Theorem 3.1.11, provides a list of conditions under which there exists an injective homomorphism s ! g of a locally simple Lie algebra s into a diagonal locally simple Lie algebra g.
In Chapter 4, with Ivan Penkov, we study certain invariants of homomorphisms of diagonal locally simple Lie algebras. The ideas and partial results presented in this Chapter may lead to a description of such homomorphisms in the future