Iron spin crossovers at high pressures and temperatures and their effects on materials relevant tot he Earth’s lower mantle and core
- Iron is the most abundant element by mass in the Earth. The iron content and its spin or oxidation state have a major influence on the physical properties of the main phases in the Earth’s interior. Therefore it is of vast importance to understand the behavior of iron in mineral phases at the temperature and pressure conditions of the Earth’s interior. This cumulative thesis investigates Fe spin crossovers in iron-containing magnesium aluminum silicates, iron-bearing silicate glasses, the iron carbide Fe3C and the effect of Fe spin crossovers on the Fe/Mg partitioning between perovskite and ferropericlase in pyrolitic model system of the Earth’s lower mantle. The goal is first to understand the nature of the Fe spin crossover in respect to its oxidation state and second to estimate the consequences of their occurrence to processes and the structure in the Earth. Central tools in these studies are laser heated diamond anvil cells, to reach the pressure and temperature conditions of the Earth’s interior, Mössbauer spectroscopy, which is a sensitive probe for detecting structural and spin changes in Fe-bearing materials, and analytical transmission electron microscopy, as a probe of chemistry and oxidation state on the nm-scale. In this cumulative thesis I present the results of five research articles. For the analysis of conventional and recently developed synchrotron energy domain Mössbauer spectra the computer program MossA is introduced, which builds the basis for the analysis and interpretation of the results for the other studies. Based on synchrotron Mössbauer spectroscopy and electrical conductivity measurements of Fe-bearing silicate aluminum perovskite it is shown that Fe3+ occupies the dodecahedral A-site of the perovskite structure and remains in the high-spin state throughout the pressure and temperature conditions of the Earth’s lower mantle. Furthermore, a study on the electronic behavior of Fe in a Fe2+-rich aluminous silicate glass and a Fe3+-rich sodium silicate glass infers that no sharp high spin to low spin crossover occurs in silicate melts in the Earth’s lower mantle. This result excludes the possibility of negatively buoyant melts in the lower mantle in an early magma ocean solely due to strong preferential partitioning of iron into the melt phase, which would be induced by a Fe low-spin bearing melt. New insights into to decoupled partitioning behavior of Fe2+ and Fe3+ between the two dominant phases of the Earth’s lower mantle, perovskite and ferropericlase, are presented. The intermediate spin to low spin crossover of Fe2+ in perovskite at about 110 GPa seems to have a strong effect on partitioning and oxidation state of Fe. It leads to a change of the partitioning behavior of Fe between perovskite and ferropericlase and induces a reduction of Fe3+ to Fe2+ in perovskite. Finally, a Mössbauer spectroscopic and single-crystal x-ray diffraction study of Fe3C reveals a two-stage loss of magnetism in Fe3C at high pressures at room temperature: a ferro- to paramagnetic transition around 8-10 GPa and a para- to nonmagnetic transition at about 22 GPa.
Wage Policy in a Global World
- This thesis contains an extended literature review and three essays on the interaction of globalization and wage policy, employment, income distribution and welfare. A specific focus lies thereby on the role of trade unions as one major labor market institution. A brief introductory chapter motivates the general topic before an extended literature review highlights main findings from previous studies.
The first essay sets up a multi-sector general oligopolistic equilibrium trade model in which all firms face wage claims of firm-level unions. By accounting for productivity differences across industries, the model features income inequality along multiple lines, including inequality between firm owners and workers as well as within these two groups of agents, and involuntary unemployment. This setting is used to study the impact of trade liberalization on key macroeconomic performance measures. In particular, the study shows that a movement from autarky to free trade with a fully symmetric partner country lowers union wage claims and therefore stimulates employment and raises welfare. Whether firms can extract a larger share of rents in the open economy depends on the competitive environment in the product market. Furthermore, the distribution of profit income becomes more equal when a country opens up to trade with a fully symmetric trading partner. It is also shown how country size differences and technological dissimilarity of trading partners affect the results from the analysis.
The second essay also builds upon the framework of general oligopolistic equilibrium with two countries that, however, differ in the centralization of union wage setting. Being interested in the consequences of openness, this study shows that, in the short-run, trade increases welfare and employment in both locations, and it raises income of capital owners as well as workers. In the long run, capital outflows from the country with the more centralized wage setting generate winners and losers and make the two countries more dissimilar in terms of unemployment and welfare. Decentralization of wage setting can successfully prevent capital outflow and the export of jobs.
The third and final essay is of an empirical nature and investigates the role of wages as a potential driving force for German export activity. In the past 15 years Germany has been characterized by a strong export activity while at the same time initiating structural reforms on the labor market. It is often argued that German firms and plants are particularly successful in exporting since they are very competitive internationally. By computing unit labor costs as a measure of international competitiveness based on OECD STAN data and the IAB establishment panel this study investigates the role of unit labor costs for the decision to export. The results show that (i) German plants’ export intensity is positively correlated with competitiveness and (ii) that the relationship is spuriously driven by a non-industry specific common time trend. The study furthermore applies a corner solution model that allows to disentangle the total effect into its effect at the extensive and intensive margin of trade. Results indicate a positive and significant effect of competitiveness at both margins but the effect turns out insignificant before the introduction of the Euro.
Domänenspezifische Evaluation und Optimierung von Datenstandards und Infrastrukturen
- In den letzten Jahren und Jahrzehnten ist die Menge der Daten, die in wissenschaftlichen Projekten erhoben wird, exorbitant gestiegen. Mit diesem gestiegenen Datenaufkommen geht eine Zunahme der Anforderungen an die Datenspeicherung und den Datenaustausch einher. Dazu wurden in den letzten Jahrzehnten Infrastrukturen entwickelt, welche diese Aufgaben für eine bestimmte Domäne übernehmen. Insbesondere in der Domäne der Lebenswissenschaften sind sogenannte Megascience-Plattformen entstanden, welche für den globalen Datenaustausch verantwortlich sind. Ein wesentliches Merkmal dieser Infrastrukturen sind die unterstützten Datenstandards. Um die Eignung eines Datenstandards oder einer Infrastruktur in einer Domäne zu bestimmen, werden generische Evaluationssysteme benötigt. Auf Basis der Evaluation mit diesen Systemen ist es möglich, Schwachstellen in Infrastrukturen und Datenmodellen zu erkennen und diese Mängel zu beseitigen. Grundlage hierfür ist die Strukturierung der Anwendungsdomäne in Prozessen.
In dieser Arbeit werden die Themenbereiche der Datenstandards und Infrastrukturen in der Anwendungsdomäne der Biodiversitätsinformatik getrennt untersucht. Im ersten Teil der Arbeit werden Datenstandards betrachtet. Ausgangspunkt sind die Datenstandards, da diese den Datenaustausch in einer Infrastruktur limitieren. Dazu wird ein generisches Evaluationssystem für Datenstandards entwickelt, domänenspezifisch angepasst und auf Standards der Biodiversitätsinformatik angewendet. Kern des Frameworks ist die Vollständigkeitsanalyse mit der 'Process Oriented Schema Evaluation' (POSE), welche die Basis des Frameworks bildet. Dabei konnte keiner der untersuchten Datenstandards die Anforderungen der Biodiversitätsinformatik vollständig erfüllen. Auf Basis dieser Erkenntnisse wurde mit der 'Process Oriented Data Schema Language' (PODSL) mit PODSL-Biodiv ein flexibles Datenmodell für die Datenspeicherung in der Biodiversität entwickelt.
Der zweite Teil der Arbeit behandelt Infrastrukturen. Dazu wird zunächst mit dem 'Infrastructure Evaluation Framework' (IEF) ein Evaluationssystem für Infrastrukturen auf der Grundlage von Prozessen entwickelt und auf die wichtigsten Infrastrukturen in der Biodiversitätsinformatik angewendet. Dabei ist für die Qualität einer Infrastruktur neben der technischen Umsetzung auch deren Organisation dieser maßgeblich. Im Rahmen der Evaluation konnte ermittelt werden, dass die Infrastruktur der 'Global Biodiversity Information Facility' (GBIF) als wichtigste Infrastruktur der Biodiversitätsinformatik die Kriterien an die Funktionalität einer Infrastruktur nicht vollständig erfüllen kann. Mit BDEI wird ein Konzept zur Weiterentwicklung von GBIF vorgestellt, um diese Mängel zu beseitigen.
Measurement of elastic properties of silicates at realistic mantle pressures
- Measurements of seismic wave travel times through the Earth’s interior provide one of the few sources of information on the properties of deep mantle rocks. These travel times can be interpreted in terms of their implications for the mineralogy, chemistry and temperature of the mantle if they can be compared with models determined from laboratory measurements for the elastic properties of mantle minerals at high pressures and temperatures. In this study MHz ultrasonic measurements have been used to determine the velocities of P and S acoustic waves in mantle minerals at mantle conditions. These results are used to constrain the properties of the mantle through comparison with seismic data.
Subduction zones exhibit faster seismic wave velocities compared to the surrounding mantle due to the recycling of relatively cold oceanic lithosphere. In certain subduction zones, however, a 5-10 km thick low velocity layer (LVL) has been inferred to exist along the top surface of the subducting slab at depths of up to 250 km. Shear-wave velocities, in particular, within these layers have been estimated as up to 10% slower than in the surrounding mantle. High-pressure ultrasonic interferometric measurements were performed to gain insight into the elastic properties of lawsonite [CaAl2(Si2O7)(OH)2.H2O], a hydrous mineral phase stabilized under cold subduction zone conditions. It was found that lawsonite has an unusually low shear modulus at high pressure and its formation in subducted oceanic crust can explain some seismic evidence for LVL at depths exceeding 100 km. To approach estimated LVL velocities requires lawsonite to form in the subducting crust as a result of a fluid influx due to the breakdown of other hydrous minerals such as serpentine. The formation of lawsonite additionally lowers seismic velocities because it forms at the expense of garnet, a mineral with relatively fast seismic velocities. LVL observations may therefore be used to place constraints on the amount of H2O subducted into the deep mantle.
Chemical heterogeneities in the transition zone are potentially developed through the subduction of basaltic oceanic crust and lithospheric ultramafic mantle. The mineralogy of these lithologies in the transition zone will mainly differ in terms of the proportion and chemistry of garnet. Garnets formed from originally basaltic and ultramafic compositions will differ in the proportions of Ca, Fe and majoritic component, with the former being richer in all components except majorite. Most models use partial derivatives of elastic properties with respect to composition to determine the elastic properties of complex garnet compositions in the mantle. In this study the effect of chemical variations on seismic wave velocities of garnets up to transition zone conditions have been intensively studied by examining the effects of Ca, Fe and majoritic substitutions on the elasticity of pyrope. In addition, complex multicomponent garnet compositions, expected to form from both subducted basaltic material and typical ultramafic mantle at transition zone conditions, have been studied. The results indicate that elastic properties of multicomponent garnets can be quite reliably interpolated from the end member properties, with an accuracy that is generally within the experimental uncertainties. No evidence was found that large excess properties exist that cause non-linear contributions to multicomponent elastic properties for the mineral garnet. Deviation between the two calculated mantle models, pyrolitic and MORB, is about 3% for both VP and VS, with the modelled slab composition being slower. Within the uncertainties of the seismic data therefore a pyrolite mantle composition is quite consistent with velocities at the base of the transition zone. Relatively low temperatures and olivine-rich nature of the stagnant slab support that there would be few grounds to argue that significant accumulation of MORB composition material may occur at the base of the transition zone.
Ultrasonic interferometry measurements in conjunction with in situ X-ray techniques have been used to measure compressional and shear wave velocities and densities of MgSiO3 perovskite (Mg-Pv) and perovskite ((Mg, Fe)-Pv) in the multianvil at pressures up to 25 GPa and temperatures to 1200 K. Data for Mg-Pv are consistent with previous studies and the (Mg, Fe)-Pv sample has almost identical shear properties to Mg-Pv. The adiabatic bulk modulus, Ks, for (Mg, Fe)-Pv, however, is found to be substantially lower than Mg-Pv, with a refined value of 236 GPa and a pressure derivative of 4.7. It is proposed that this low KS value results from a change in the elasticity of Fe-bearing perovskite at low pressures <30 GPa.
High temperatures measurements of VP and VS of and perovskite samples lead to the conclusion that the substitution of Mg by Fe seems to have a consistent effect on Ks, strongly lowering it in both Al and Al-free perovskites while it does not have any noticeable effect on the shear elastic properties. By substituting Al into the Si octahedral site, the rigidity of this framework is being reduced which clearly has an influence on the shear modulus G. G of the Al-bearing perovskites is obviously controlled by the Al content in the structure. Seismic observations indicate low visibility of underside PP reflections from the 660 km discontinuity. Seismologists have used this in the past to argue that the P velocity contrast at the discontinuity is much lower than would be expected from seismic reference models. The data collected on Fe-Al perovskite in this study provide excellent support for this argument as model calculations based on these data show very little contrast in Vp at 660 km depth. Instead, the model derived in this study indicates that much of the change in P velocity between the transition zone and lower mantle occurs over a much broader depth, 200km, interval and is mainly attributed to the transformation of garnet to perovskite. A major conclusion therefore is that a sharp 660 km discontinuity reflection should be visible in S but not P wave seismic data. The model calculation for VS is in a good agreement with the seismic reference models up to depths as great as 1071 km, while VP remains 3 to 4% lower at lower mantle conditions. The extrapolations of pressure and temperature dependences significantly out of the ranges over that they were measured may well explain this discrepancy however.
Describing Charge Transfer in Extended Donor-Acceptor Systems with Density Functional Theory
- It is a long-standing problem of (time-dependent) density functional theory ((TD)DFT) that traditional functionals severely underestimate charge transfer (CT) excitations. In particular, the theoretical description of donor-acceptor (DA) systems is plagued by this shortcoming. DA systems are frequently used as light absorbing components in organic photovoltaic devices. The lowest electronic excitation in these molecules is usually influenced by CT.
In order to support the systematic development of new DA systems that are needed to improve the efficiency of organic solar cells it is a prerequisite for theory to reliably predict the electronic properties of this system class.
We demonstrate that the tuned range-separated hybrid (RSH) approach predicts these excitations in accordance with experiment. The approach can be regarded as an implicitly defined density functional within the generalized Kohn-Sham (GKS) scheme of DFT. Its main ingredient is the range-separation parameter that determines the splitting between long- and short-range exchange. It is obtained from first principles by enforcing the ionization potential theorem of GKS theory.
We consider DA systems of various sizes that are composed of thiophene as donor and benzothiadiazole or naphthalene diimide as acceptor. We show how the optical and electronic properties can be tailored by changing the conjugation length and the arrangement of the donor and acceptor components. We also address the downsides that accompany the use of tuned RSH functionals. Due to the way the approach is implicitly defined anew for each system it is not size consistent. By calculating ground state properties of atoms and diatomic molecules we report size consistency errors and demonstrate consequences of the size consistency violation, e.g., the incorrect prediction of binding energies.
In order to reliably predict CT excitations within the Kohn Sham scheme of DFT the exchange correlation potential approximation has to incorporate particle number discontinuities. A candidate potential with the necessary features is the Becke-Johnson potential that is based on semi-local ingredients and is therefore computationally attractive for the treatment of very large systems. We show, however, that the potential cannot be applied in TDDFT because it is not a functional derivative and violates the zero-force theorem. We discuss a procedure on the basis of density path integrals that transforms the BJ potential into a functional derivative of a corresponding energy expression.
Diffusion of proteins inside crowded structures generated using microemulsions
- Microemulsions are thermodynamically stable mixtures of water, oil and surfactant. In the case of microemulsions based on sugar surfactants a cosurfactant as an additional component is necessary, most often a short-chain alcohol. In this thesis mainly pure surfactants are used. The focus is on n-nonyl-ß-d-maltosid and n-dodecyl-ß-d-maltosid as model systems for microemulsions based on technical grade surfactants. Depending on the ratio of the components microemulsion form different structures. In the bicontinuous phase continuous oil and water domains are present separated by a surfactant/co-surfactant film. At higher surfactant amounts the bicontinuous structure passes over to a droplet phase. The size of these structures is in the scale of up to 100nm, therefore microemulsions look transparent for the human eye. Bicontinuous microemulsions are a promising carrier medium for decontamination applications. Chemical warfare agents are mainly lipophilic, in contrast degradation agents are hydrophilic. A microemulsion is able to solubilize lipophilic and hydrophilic molecules. At the interface the warfare agent is close to the degradation agent and can be eliminated. The protein diisopropyl-fluorophosphatase (DFPase) is a promising candidate for decontamination applications and is able to degrade different warfare agents. Therefore, the knowledge of the dynamics and properties of enzymes inside a bicontinuous structure is of big importance. In this thesis different microemulsion systems based on C9G2 or C12G2, water, cyclohexane and 1-pentanol are systematically characterized by X-ray and neutron scattering experiments. By using an improved Green Fluorescent Protein (GFP+) as a counterpart of DFPase with a similar size, the diffusion inside a microemulsion can be studied with the fluorescence correlation spectroscopy (FCS) method. Here, fluorescent impurities in the used components are a problem. By the choice of a suitable concentration of GFP+ and regarding the dynamics of the microemulsion structure, it could be shown that the protein is able to move inside the microemulsion structure. Hence, microemulsions are interesting model systems to produce crowding effects in a controlled way. This is probably the most important result of this thesis. In the C9G2 system a bicontinuous phase is present. At small oil/water ratios o/w with a high water amount big water domains exist with length scales of approximately 10nm, which allows protein diffusion. With increasing oil/water ratio the protein diffusion is more and more hindered. This results in an increase of the diffusion time and a decrease of the anomalous diffusion exponent. At even higher oil/water ratios the diffusion of the protein is nearly identical with the microemulsion dynamics. The length scales are too small to allow protein diffusion, therefore it is stuck in the structure. The C12G2 system shows an oil-in-water droplet phase which also hinders the GFP+ diffusion due to crowding effects. For small oil/water ratios nearly free diffusion is present, at o/w = 0.3 - 0.5 the diffusion is hindered, the anomalous diffusion exponent decreases. At o/w = 0.6 the protein diffusion reflects the microemulsion dynamics. Again at higher values of o/w, GFP+ is stuck in the structure because of the high oil fraction. Two microemulsion systems with different structures were studied, which allow protein diffusion due to their length scales. These results are related to applications: For the formulation of decontamination media the knowledge of the dynamics of the decontaminating protein is of importance. Moreover, pure surfactants can be easily replaced by technical grade surfactants. This enables cheap systems for a production-scale. Furthermore, the situation in living cells can be simulated by a microemulsion structure, where a confined diffusion is present as well. Additional neutron spin echo experiments emphasize the complexity when studying a microemulsion system based on four components. The contrast matching procedure, which is necessary when protein dynamics inside the microemulsion are investigated, is very difficult and requires a high amount of surfactant.
New Trust Region SQP Methods for Continuous and Integer Optimization
- In this thesis new algorithms are presented that address nonlinear optimization problems. The algorithms belong to the class of sequential quadratic programming (SQP) methods. Two problem formulations that arise frequently in real-world applications are considered. Both have in common that functions are nonlinear and the formulations contain equality and inequality constraints. For the one class of problems the domain of all variables is R. These problems are called nonlinear programming (NLP) problems. Many applications also require that some of the featured variables are restricted to the domain Z. Problems with additional integer variables are called mixed-integer nonlinear programs (MINLP) and are also considered here.
This work is motivated by the advancement of an algorithm for solving MINLPs that was first discussed by Exler and Schittkowski (2007). The algorithm adapts concepts of SQP methods to mixed-integer nonlinear optimization. The new approach replaces the continuous quadratic problems by mixed-integer quadratic problems. The aim is to profit from the fast local convergence properties of SQP methods at least with respect to the continuous variables when integer variables remain fixed. Two new versions of the underlying algorithm of Exler and Schittkowski are presented.
It is well-known that SQP methods might not converge for any arbitrary starting point. To obtain global convergence, techniques of trust region methods are employed by the new algorithms. The first version of an algorithm for MINLPs presented in this thesis employs the Linf-penalty function as merit function. Applying this penalty function might lead to a slow convergence. The so-called Maratos effect requires the reduction of the step length so that fast convergence is lost. Hence, safeguards have to be added. The presented algorithm calculates additional second order correction (SOC) steps. Calculating SOC steps is a frequently used approach to obtain fast local convergence. There also exist other techniques. The SOC steps require additional function evaluations. Frequently, function values of mixed-integer problems arising in the field of engineering are evaluated by running time-consuming simulation tools, where a single function evaluation can take minutes or even hours. Thus, the goal of the development of an efficient method has to be that the number of needed function evaluations is as small as possible.
For that reason the investigation of methods that obtain fast local convergence without calculating SOC steps is the key aspect of this thesis. As a fundamental theory is available for NLPs, whereas MINLPs lack in most of these concepts, the main part of this thesis presents and analyzes a new trust region SQP algorithm addressing NLPs. The algorithm proposed here avoids the calculation of SOC steps by using an augmented Lagrangian function as merit function. In trust region methods a differentiable merit function, such as an augmented Lagrangian function, was employed in the past for equality constrained problems. Methods that also treat inequality constraints, transform these constraints into equality constraints. The new algorithm does not reformulate the underlying problem.
The proposed algorithm for NLPs is described in detail. The global and local convergence properties of the new algorithm are investigated. Under suitable assumptions it is shown that for any arbitrary starting point the sequence of generated iterates contains at least one accumulation point that is a Karush-Kuhn-Tucker point of the underlying NLP. Under certain conditions fast local convergence is proved, as full SQP steps will be accepted close to a solution. Thus, no additional SOC steps are required.
Due to the insight that is gained by the development of the algorithm for NLPs, an additional version of the algorithm for MINLPs can be stated. The second algorithm also enhances the algorithm of Exler and Schittkowski (2007), but does not calculate SOC steps anymore and the extra function evaluations are avoided.
All presented algorithms are implemented in FORTRAN and completely documented. The code is evaluated on a set of almost 500 test problems. Numerical results show the good performance of the new algorithms. The numerical tests of the algorithm for NLPs indicate that the theoretical convergence results hold in practice. Moreover, the efficiency of the second algorithm for MINLPs that does not calculate SOC steps has improved compared to the first version with SOC steps
Design, Synthesis and Application of Cylindrical Polymer Brushes: From Nanostructures to Advanced Materials
- This thesis focuses on the design, synthesis and application of cylindrical polymer brushes (CPBs). Herein, we investigated the scission behavior of polyelectrolyte CPBs on different surfaces, developed novel synthetic pathways for well-defined CPBs via reversible addition-fragmentation chain transfer (RAFT) polymerization, designed and prepared complex functional CPBs for light-harvesting and energy transfer, and utilized CPBs as templates for the synthesis of novel one-dimensional (1D) organic/inorganic hybrid nanostructures.
The ‘grafting-from’ approach was chosen as the general method to synthesize well-defined CPBs with various chemical and structural compositions. The linear polymer backbones (polyinitiators) were obtained by anionic polymerization or RAFT polymerization, whereas the side chains were grafted by atom transfer radical polymerization (ATRP) or RAFT polymerization. The obtained CPBs possess a narrow molecular weight distribution in both the backbone and the side chains.
The polymer backbone of core-shell CPBs consisting of a poly(oligo(ethylene glycol) methyl ether methacrylate) (POEGMA) core block and a poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) shell block was ruptured upon drying on solid surfaces, when suf-ficient Coulombic interactions between the shell block and the surface were formed. We controlled this scission behavior by tuning the surface interactions through switching the surface nature, shell quaternization, varying pH, or adding multivalent counterions. This study demonstrates that core-shell CPBs serve as a tool to directly compare the weak intermolecular forces with the strong carbon-carbon covalent bonds.
A novel ‘grafting-from’ approach was developed to overcome the challenges of synthesizing well-defined CPBs from a linear polymer backbone with a high density of RAFT functionalities. In this so-called “CTA-shuttled” R-group approach, a certain amount of low-molecular-weight chain transfer agent (CTA) was added to the polymerization system, serving as shuttles to transfer active radicals among the individual growing CPBs. Well-defined CPBs with polystyrene or poly(tert-butyl acrylate) branches and core-shell CPBs with polystyrene-block-poly(N-isopropylacrylamide) branches were synthesized, with the molecular weight distribution much narrower than that from the conventional R-group approach. Monte Carlo simulations confirmed that the advantage of the “CTA-shuttled” R-group approach consists in the release of the active radicals from the trapping CPB systems.
Imitating the natural “energy cascade” architecture, we developed single-molecular, rod-like nano-light harvesters (NLHs) on the basis of CPBs. Herein, a number of block copolymer side chains carrying light absorbing antennae groups (9,9-diethylfluorene, energy donors) were tethered to a linear polymer backbone containing emitting groups (anthracene, energy acceptors). These NLHs provide very efficient energy absorption and energy transfer from antennae to energy acceptors. Furthermore, we were able to manipulate the efficiency of energy transfer by tuning the distance between energy donors and energy acceptors in physical and/or chemical ways. This CPB-based NLH architecture presents a novel concept to design light harvesting materials and can readily be transplanted to any other applications in photoelectronic devices.
Core-shell CPBs with a poly(acrylic acid) (PAA) core block and a PDMAEMA shell block were employed as templates for the preparation of various rare-earth metal cations (Ln3+) incorporated silica hybrid nanoparticles (NPs). A tight chelation of Ln3+ ions in the PAA core and a crosslinked silica layer deposited on the shell provide a very stable encapsulation of Ln3+ ions within the hybrid NPs and thus a high biocompatibility. The silica hybrid NPs obtain unique and diverse properties from the incorporated Ln3+ ions, such as visible photoluminescence, paramagnetic behavior, and a longitudinal relaxation time (T1) shortening effect. This novel template-directed approach succeeds in combining different functional centers via loading in-situ mixed Ln3+ ions into individual CPBs resulting in multicomponent hybrid NPs, which possess both visible photoluminescence and T1 contrast enhancement and can thus be applied as multimodal bioimaging probes.
Taxonomical use of floral scent data in apomictic taxa of Hieracium and Sorbus derived from hybridization
- Scent investigations are mainly carried out in the context of the ecological function of scent components for pollinator attraction, to study their geographical variability or their evolution. In contrast, profiles of inflorescence scent compounds were rarely used for phylogenetic analyses and taxonomy. So far no investigations are available that focus on scent of apomictic plant groups and its value for the taxonomy of these groups. Apomicts produce fertile seeds without pollination. Overall, apomixis occurs scattered over the whole Angiosperm tree in early as well as late branching families. Rosaceae and Asteraceae are particularly rich in apomictic taxa. In these families genera such as Hieracium and Sorbus contribute a lot to local species biodiversity in Central Europe because of their high number of apomictic species and taxa, which are often endemic. Most members of these genera built up polyploid microspecies swarms initiated by hybridization events. The reticulate structure of these taxon complexes leads to taxonomic difficulties that can not be solved by morphology alone. Therefore, molecular or chemical markers are needed to investigate the parentage of such taxa and their collective species membership.
An important starting point of this research was the finding that artificial hybrids of Citrus produce a combination of the leaf and peel volatiles of their parents. This led to the hypothesis that natural hybrids might likewise produce scent patterns combined of the volatiles of their parents. Inflorescence scents were investigated from 64 mainly Bavarian taxa of the genus Hieracium (Subgenus Pilosella and Subgenus Hieracium). In Sorbus (Rosaceae) we focussed on three taxa of the S. latifolia agg., endemic to Northern Bavaria, S. adeana, S. cordigastensis and S. franconica and their parental species from the S. aria aggregate (agg.), as well as S. torminalis. Samples were collected with dynamic headspace method. Substances were identified by gas chromatography coupled to mass spectrometry (GC-MS). Scent data were evaluated by using various cluster methods. In Hieracium, additional reticulation analyses were applied that trace conflicting signals in a phylogram which can be interpreted as hybridizations between the taxa involved.
In Sorbus additional AFLP (Amplified Fragment Length Polymorphism) analyses were carried out from the populations and individuals that were studied for scent and genetic and scent data were correlated.
In Hieracium, the inflorescense scent consisted mainly of sesquiterpenes, monoterpenes, aliphatics and aromatics. In the flower scent of Sorbus besides these substances also nitrogene-containing substances were found.
In Hieracium (both subgenera) as well as in Sorbus, taxa of hybrid origin showed a mixed scent pattern compared with the parental taxa. In many cases, the parental taxa that had been suggested by morphological investigations or revealed by genetic investigations could be confirmed by scent. In general, scent patterns correlate well with morphological or genetical groupings, both in Hieracium and in Sorbus. Reticulate scent analyses in Hieracium showed that some taxa are probably derived from more than two ancestors. Scent data reflected even taxonomic patterns on a higher level, i.e. the sectional level.
The AFLP study revealed that the selected members of the Sorbus latifolia agg. are genetically clearly differentiated and mostly of clonal structure. They are more closely related to S. aria than to S. torminalis. The S. aria agg. has a complex structure. Besides S. aria s.str. and S. pannonica there are also intermediate plants with affinity (aff.) to either the one or the other of these taxa. S. cordigastensis was derived from intermediates aff. S. aria s.str., and both S. adeana and S. franconica derived from intermediates aff. S. pannonica or S. pannonica itself.
Floral scent of the same Sorbus taxa was investigated and compared with AFLP data on individual as well as on population level. Correlation analysis revealed a very high correlation between scent and AFLP data on individual and population level.
Overall, this work shows that in two unrelated plant complexes, Hieracium and Sorbus, which both harbour a high number of apomictic species derived by hybridization, scent is of high taxonomical value. The main reason for this correlation may be that most taxa in the investigated groups possess mixed scent patterns from their parents or progenitors because they are of hybrid origin. In addition, intraspecific variability of scent patterns is low within apomictic taxa due to their clonality, simplifying the taxonomic use of scent data. Furthermore, the role of pollinator mediated selection of scent is reduced because of apomixis.
Jahresbericht der Universitätsbibliothek Bayreuth
- Jahresbericht der Universitätsbibliothek Bayreuth - Berichtsjahr 2012