Refine
Has Fulltext
- yes (72) (remove)
Year of publication
- 2015 (72) (remove)
Document Type
- Doctoral Thesis (72) (remove)
Language
- English (72) (remove)
Is part of the Bibliography
- yes (72)
Keywords
- Klimawandel (3)
- climate change (3)
- Arbeitsgedächtnis (2)
- Erosion (2)
- Geschäftsprozessmanagement (2)
- Modellierung (2)
- Nanopartikel (2)
- Psycholinguistik (2)
- Satzverarbeitung (2)
- Seesedimente (2)
Institute
- Institut für Geowissenschaften (23)
- Institut für Physik und Astronomie (15)
- Institut für Biochemie und Biologie (6)
- Department Linguistik (4)
- Institut für Umweltwissenschaften und Geographie (4)
- Hasso-Plattner-Institut für Digital Engineering gGmbH (3)
- Institut für Chemie (3)
- Institut für Ernährungswissenschaft (3)
- Institut für Mathematik (3)
- Sozialwissenschaften (2)
The main focus of the present thesis was to investigate the stabilization ability of poly(ionic liquid)s (PILs) in several examples as well as develop novel chemical structures and synthetic routes of PILs. The performed research can be specifically divided into three parts that include synthesis and application of hybrid material composed of PIL and cellulose nanofibers (CNFs), thiazolium-containing PILs, and main-chain imidazolium-type PILs.
In the first chapter, a vinylimidazolium-type IL was polymerized in water in the presence of CNFs resulting in the in situ electrostatic grafting of polymeric chains onto the surface of CNFs. The synthesized hybrid material merged advantages of its two components, that is, superior mechanical strength of CNFs and anion dependent solution properties of PILs. In contrast to unmodified CNFs, the hybrid could be stabilized and processed in organic solvents enabling its application as reinforcing agent for porous polyelectrolyte membranes.
In the second part, PILs and ionic polymers containing two types of thiazolium repeating units were synthesized. Such polymers displayed counterion dependent thermal stability and solubility in organic solvents of various dielectric constants. This new class of PILs was tested as stabilizers and phase transfer agents for carbon nanotubes in aqueous and organic media, and as binder materials to disperse electroactive powders and carbon additives in solid electrode in lithium-ion batteries. The incorporation of S and N atoms into the polymeric structures make such PILs also potential precursors for S, N - co-doped carbons.
In the last chapter, reactants originating from biomass were successfully harnessed to synthesize main-chain imidazolium-type PILs. An imidazolium-type diester IL obtained via a modified Debus-Radziszewski reaction underwent transesterification with diol in a polycondensation reaction. This yielded a polyester-type PIL which CO2 sorption properties were investigated. In the next step, the modified Debus-Radziszewski reaction was further applied to synthesize main-chain PILs according to a convenient, one-step protocol, using water as a green solvent and simple organic molecules as reagents. Depending on the structure of the employed diamine, the synthesized PILs after anion exchange showed superior thermal stability with unusually high carbonization yields.
Overall, the outcome of these studies will actively contribute to the current research on PILs by introducing novel PIL chemical structures, improved synthetic routes, and new examples of stabilized materials. The synthesis of main-chain imidazolium-type PILs by a modified Debus-Radziszewski reaction is of a special interest for the future work on porous ionic liquid networks as well as colloidal PIL nanoparticles.
The lives of more than 1/6 th of the world population is directly affected by the caprices of the South Asian summer monsoon rainfall. India receives around 78 % of the annual precipitation during the June-September months, the summer monsoon season of South Asia. But, the monsoon circulation is not consistent throughout the entire summer season. Episodes of heavy rainfall (active periods) and low rainfall (break periods) are inherent to the intraseasonal variability of the South Asian summer monsoon. Extended breaks or long-lasting dryness can result in droughts and hence trigger crop failures and in turn famines. Furthermore, India's electricity generation from renewable sources (wind and hydro-power), which is increasingly important in order to satisfy the rapidly rising demand for energy, is highly reliant on the prevailing meteorology. The major drought years 2002 and 2009 for the Indian summer monsoon during the last decades, which are results of the occurrence of multiple extended breaks, emphasise exemplary that the understanding of the monsoon system and its intraseasonal variation is of greatest importance. Although, numerous studies based on observations, reanalysis data and global model simulations have been carried out with the focus on monsoon active and break phases over India, the understanding of the monsoon intraseasonal variability is only in the infancy stage. Regional climate models could benefit the comprehension of monsoon breaks by its resolution advantage.
This study investigates moist dynamical processes that initiate and maintain breaks during the South Asian summer monsoon using the atmospheric regional climate model HIRHAM5 at a horizontal resolution of 25 km forced by the ECMWF ERA Interim reanalysis for the period 1979-2012. By calculating moisture and moist static energy budgets the various competing mechanisms leading to extended breaks are quantitatively estimated. Advection of dry air from the deserts of western Asia towards central India is the dominant moist dynamical process in initiating extended break conditions over South Asia. Once initiated, the extended breaks are maintained due to many competing mechanisms: (i) the anomalous easterlies at the southern flank of this anticyclonic anomaly weaken the low-level cross-equatorial jet and thus the moisture transport into the monsoon region, (ii) differential radiative heating over the continental and the oceanic tropical convergence zone induces a local Hadley circulation with anomalous rising over the equatorial Indian Ocean and descent over central India, and (iii) a cyclonic response to positive rainfall anomalies over the near-equatorial Indian Ocean amplifies the anomalous easterlies over India and hence contributes to the low-level divergence over central India.
A sensitivity experiment that mimics a scenario of higher atmospheric aerosol concentrations over South Asia addresses a current issue of large uncertainty: the role aerosols play in suppressing monsoon rainfall and hence in triggering breaks. To study the indirect aerosol effects the cloud droplet number concentration was increased to imitate the aerosol's function as cloud condensation nuclei. The sensitivity experiment with altered microphysical cloud properties shows a reduction in the summer monsoon precipitation together with a weakening of the South Asian summer monsoon. Several physical mechanisms are proposed to be responsible for the suppressed monsoon rainfall: (i) according to the first indirect radiative forcing the increase in the number of cloud droplets causes an increase in the cloud reflectivity of solar radiation, leading to a climate cooling over India which in turn reduces the hydrological cycle, (ii) a stabilisation of the troposphere induced by a differential cooling between the surface and the upper troposphere over central India inhibits the growth of deep convective rain clouds, (iii) an increase of the amount of low and mid-level clouds together with a decrease in high-level cloud amount amplify the surface cooling and hence the atmospheric stability, and (iv) dynamical changes of the monsoon manifested as a anomalous anticyclonic circulation over India reduce the moisture transport into the monsoon region. The study suggests that the changes in the total precipitation, which are dominated by changes in the convective precipitation, mainly result from the indirect radiative forcing. Suppression of rainfall due to the direct microphysical effect is found to be negligible over India. Break statistics of the polluted cloud scenario indicate an increase in the occurrence of short breaks (3 days), while the frequency of extended breaks (> 7 days) is clearly not affected. This disproves the hypothesis that more and smaller cloud droplets, caused by a high load of atmospheric aerosols trigger long drought conditions over central India.
This thesis contains three experimental studies addressing the interplay between deformation and the mineral reaction between natural calcite and magnesite. The solid-solid mineral reaction between the two carbonates causes the formation of a magnesio-calcite precursor layer and a dolomite reaction rim in every experiment at isostatic annealing and deformation conditions.
CHAPTER 1 briefly introduces general aspects concerning mineral reactions in nature and diffusion pathways for mass transport. Moreover, results of previous laboratory studies on the influence of deformation on mineral reactions are summarized. In addition, the main goals of this study are pointed out.
In CHAPTER 2, the reaction between calcite and magnesite single crystals is examined at isostatic annealing conditions. Time series performed at a fixed temperature revealed a diffusion-controlled dolomite rim growth. Two microstructural domains could be identified characterized by palisade-shaped dolomite grains growing into the magnesite and granular dolomite growing towards calcite. A model was provided for the dolomite rim growth based on the counter-diffusion of CaO and MgO. All reaction products exhibited a characteristic crystallographic relationship with respect to the calcite reactant. Moreover, kinetic parameters of the mineral reaction were determined out of a temperature series at a fixed time. The main goal of the isostatic test series was to gain information about the microstructure evolution, kinetic parameters, chemical composition and texture development of the reaction products. The results were used as a reference to quantify the influence of deformation on the mineral reaction.
CHAPTER 3 deals with the influence of non-isostatic deformation on dolomite and magnesio-calcite layer production between calcite and magnesite single crystals. Deformation was achieved by triaxial compression and by torsion. Triaxial compression up to 38 MPa axial stress at a fixed time showed no significant influence of stress and strain on dolomite formation. Time series conducted at a fixed stress yield no change in growth rates for dolomite and magnesio-calcite at low strains. Slightly larger magnesio-calcite growth rates were observed at strains above >0.1. High strains at similar stresses were caused by the activation of additional glide systems in the calcite single crystal and more mobile dislocations in the magnesio-calcite grains, providing fast diffusion pathways. In torsion experiments a gradual decrease in dolomite and magnesio-calcite layer thickness was observed at a critical shear strain. During deformation, crystallographic orientations of reaction products rearranged with respect to the external framework. A direct effect of the mineral reaction on deformation could not be recognized due to the relatively small reaction product widths.
In CHAPTER 4, the influence of starting material microfabrics and the presence of water on the reaction kinetics was evaluated. In these experimental series polycrystalline material was in contact with single crystals or two polycrystalline materials were used as reactants. Isostatic annealing resulted in different dolomite and magnesio-calcite layer thicknesses, depending on starting material microfabrics. The reaction progress at the magnesite interface was faster with smaller magnesite grain size, because grain boundaries provided fast pathways for diffusion and multiple nucleation sites for dolomite formation. Deformation by triaxial compression and torsion yield lower dolomite rim thicknesses compared to annealed samples for the same time. This was caused by grain coarsening of polycrystalline magnesite during deformation. In contrast, magnesio-calcite layers tended to be larger during deformation, which triggered enhanced diffusion along grain boundaries. The presence of excess water had no significant influence on the reaction kinetics, at least if the reactants were single crystals.
In CHAPTER 5 general conclusions about the interplay between deformation and the mineral reaction in the carbonate system are presented.
Finally, CHAPTER 6 highlights possible future work in the carbonate system based on the results of this study.
Most of the baryonic matter in the Universe resides in a diffuse gaseous phase in-between galaxies consisting mostly of hydrogen and helium. This intergalactic medium (IGM) is distributed in large-scale filaments as part of the overall cosmic web. The luminous extragalactic objects that we can observe today, such as galaxies and quasars, are surrounded by the IGM in the most dense regions within the cosmic web. The radiation of these objects contributes to the so-called ultraviolet background (UVB) which keeps the IGM highly ionized ever since the epoch of reionization.
Measuring the amount of absorption due to intergalactic neutral hydrogen (HI) against extragalactic background sources is a very useful tool to constrain the energy input of ionizing sources into the IGM. Observations suggest that the HI Lyman-alpha effective optical depth, τ_eff, decreases with decreasing redshift, which is primarily due to the expansion of the Universe. However, some studies find a smaller value of the effective optical depth than expected at the specific redshift z~3.2, possibly related to the complete reionization of helium in the IGM and a hardening of the UVB. The detection and possible cause of a decrease in τ_eff at z~3.2 is controversially debated in the literature and the observed features need further explanation.
To better understand the properties of the mean absorption at high redshift and to provide an answer for whether the detection of a τ_eff feature is real we study 13 high-resolution, high signal-to-noise ratio quasar spectra observed with the Ultraviolet and Visual Echelle Spectrograph (UVES) at the Very Large Telescope (VLT). The redshift evolution of the effective optical depth, τ_eff(z), is measured in the redshift range 2.7≤z≤3.6. The influence of metal absorption features is removed by performing a comprehensive absorption-line-fitting procedure.
In the first part of the thesis, a line-parameter analysis of the column density, N, and Doppler parameter, b, of ≈7500 individually fitted absorption lines is performed. The results are in good agreement with findings from previous surveys.
The second (main) part of this thesis deals with the analysis of the redshift evolution of the effective optical depth. The τ_eff measurements vary around the empirical power law τ_eff(z)~(1+z)^(γ+1) with γ=2.09±0.52. The same analysis as for the observed spectra is performed on synthetic absorption spectra. From a comparison between observed and synthetic spectral data it can be inferred that the uncertainties of the τ_eff values are likely underestimated and that the scatter is probably caused by high-column-density absorbers with column densities in the range 15≤logN≤17. In the real Universe, such absorbers are rarely observed, however. Hence, the difference in τ_eff from different observational data sets and absorption studies is most likely caused by cosmic variance. If, alternatively, the disagreement between such data is a result of an too optimistic estimate of the (systematic) errors, it is also possible that all τ_eff measurements agree with a smooth evolution within the investigated redshift range. To explore in detail the different analysis techniques of previous studies an extensive literature comparison to the results of this work is presented in this thesis.
Although a final explanation for the occurrence of the τ_eff deviation in different studies at z~3.2 cannot be given here, our study, which represents the most detailed line-fitting analysis of its kind performed at the investigated redshifts so far, represents another important benchmark for the characterization of the HI Ly-alpha effective optical depth at high redshift and its indicated unusual behavior at z~3.2.
The promotion of self-employment as part of active labor market policies is considered to be one of the most important unemployment support schemes in Germany. Against this background the main part of this thesis contributes to the evaluation of start-up support schemes within ALMP. Chapter 2 and 4 focus on the evaluation of the New Start-up Subsidy (NSUS, Gründungszuschuss) in its first version (from 2006 to the end of 2011). The chapters offer an advancement of the evaluation of start-up subsidies in Germany, and are based on a novel data set of administrative data from the Federal Employment Agency that was enriched with information from a telephone survey. Chapter 2 provides a thorough descriptive analysis of the NSUS that consists of two parts. First, the participant structure of the program is compared with the one of two former programs. In a second step, the study conducts an in-depth characterization of the participants of the NSUS focusing on founding motives, the level of start-up capital and equity used as well as the sectoral distribution of the new business. Furthermore, the business survival, income situation of founders and job creation by the new businesses is analyzed during a period of 19 months after start-up. The contribution of Chapter 4 is to introduce a new explorative data set that allows comparing subsidized start-ups out of unemployment with non-subsidized business start-ups that were founded by individuals who were not unemployed at the time of start-up. Because previous evaluation studies commonly used eligible non-participants amongst the unemployed as control group to assess the labor market effects of the start-up subsidies, the corresponding results hence referred to the effectiveness of the ALMP measure, but could not address the question whether the subsidy leads to similarly successful and innovative businesses compared to non-subsidized businesses. An assessment of this economic/growth aspect is also important, since the subsidy might induce negative effects that may outweigh the positive effects from an ALMP perspective. The main results of Chapter 4 indicate that subsidized founders seem to have no shortages in terms of formal education, but exhibit less employment and industry-specific experience, and are less likely to benefit from intergenerational transmission of start-ups. Moreover, the study finds evidence that necessity start-ups are over-represented among subsidized business founders, which suggests disadvantages in terms of business preparation due to possible time restrictions right before start-up. Finally, the study also detects more capital constraints among the unemployed, both in terms of the availability of personal equity and access to loans. With respect to potential differences between both groups in terms of business development over time, the results indicate that subsidized start-ups out of unemployment face higher business survival rates 19 months after start-up. However, they lag behind regular business founders in terms of income, business growth, and innovation. The arduous data collection process for start-up activities of non-subsidized founders for Chapter 4 made apparent that Germany is missing a central reporting system for business formations. Additionally, the different start-up reporting systems that do exist exhibit substantial discrepancies in data processing procedures, and therefore also in absolute numbers concerning the overall start-up activity. Chapter 3 is therefore placed in front of Chapter 4 and has the aim to provide a comprehensive review of the most important German start-up reporting systems. The second part of the thesis consists of Chapter 5 which contributes to the literature on determinants of job search behavior of the unemployed individuals by analyzing the effectiveness of internet search with regard to search behavior of unemployed individuals and subsequent job quality. The third and final part of the thesis outlines why the German labor market reacted in a very mild fashion to the Great Recession 2008/09, especially compared to other countries. Chapter 6 describes current economic trends of the labor market in light of general trends in the European Union, and reveals some of the main associated challenges. Thereafter, recent reforms of the main institutional settings of the labor market which influence labor supply are analyzed. Finally, based on the status quo of these institutional settings, the chapter gives a brief overview of strategies to adequately combat the challenges in terms of labor supply and to ensure economic growth in the future.
The Brazilian Cerrado is recognised as one of the most threatened biomes in the world, as the region has experienced a striking change from natural vegetation to intense cash crop production. The impacts of rapid agricultural expansion on soil and water resources are still poorly understood in the region. Therefore, the overall aim of the thesis is to improve our understanding of the ecohydrological processes causing water and soil degradation in the Brazilian Cerrado.
I first present a metaanalysis to provide quantitative evidence and identifying the main impacts of soil and water alterations resulting from land use change. Second, field studies were conducted to (i) examine the effects of land use change on soils of natural cerrado transformed to common croplands and pasture and (ii) indicate how agricultural production affects water quality across a meso-scale catchment. Third, the ecohydrological process-based model SWAT was tested with simple scenario analyses to gain insight into the impacts of land use and climate change on the water cycling in the upper São Lourenço catchment which experienced decreasing discharges in the last 40 years.
Soil and water quality parameters from different land uses were extracted from 89 soil and 18 water studies in different regions across the Cerrado. Significant effects on pH, bulk density and available P and K for croplands and less-pronounced effects on pastures were evident. Soil total N did not differ between land uses because most of the cropland sites were N-fixing soybean cultivations, which are not artificially fertilized with N. By contrast, water quality studies showed N enrichment in agricultural catchments, indicating fertilizer impacts and potential susceptibility to eutrophication. Regardless of the land use, P is widely absent because of the high-fixing capacities of deeply weathered soils and the filtering capacity of riparian vegetation. Pesticides, however, were consistently detected throughout the entire aquatic system. In several case studies, extremely high-peak concentrations exceeded Brazilian and EU water quality limits, which pose serious health risks.
My field study revealed that land conversion caused a significant reduction in infiltration rates near the soil surface of pasture (–96 %) and croplands (–90 % to –93 %). Soil aggregate stability was significantly reduced in croplands than in cerrado and pasture. Soybean crops had extremely high extractable P (80 mg kg–1), whereas pasture N levels declined. A snapshot water sampling showed strong seasonality in water quality parameters. Higher temperature, oxi-reduction potential (ORP), NO2–, and very low oxygen concentrations (<5 mg•l–1) and saturation (<60 %) were recorded during the rainy season. By contrast, remarkably high PO43– concentrations (up to 0.8 mg•l–1) were measured during the dry season. Water quality parameters were affected by agricultural activities at all sampled sub-catchments across the catchment, regardless of stream characteristic. Direct NO3– leaching appeared to play a minor role; however, water quality is affected by topsoil fertiliser inputs with impact on small low order streams and larger rivers. Land conversion leaving cropland soils more susceptible to surface erosion by increased overland flow events.
In a third study, the field data were used to parameterise SWAT. The model was tested with different input data and calibrated in SWAT-CUP using the SUFI-2 algorithm. The model was judged reliable to simulate the water balance in the Cerrado. A complete cerrado, pasture and cropland cover was used to analyse the impact of land use on water cycling as well as climate change projections (2039–2058) according to the projections of the RCP 8.5 scenario. The actual evapotranspiration (ET) for the cropland scenario was higher compared to the cerrado cover (+100 mm a–1). Land use change scenarios confirmed that deforestation caused higher annual ET rates explaining partly the trend of decreased streamflow. Taking all climate change scenarios into account, the most likely effect is a prolongation of the dry season (by about one month), with higher peak flows in the rainy season. Consequently, potential threats for crop production with lower soil moisture and increased erosion and sediment transport during the rainy season are likely and should be considered in adaption plans.
From the three studies of the thesis I conclude that land use intensification is likely to seriously limit the Cerrado’s future regarding both agricultural productivity and ecosystem stability. Because only limited data are available for the vast biome, we recommend further field studies to understand the interaction between terrestrial and aquatic systems. This thesis may serve as a valuable database for integrated modelling to investigate the impact of land use and climate change on soil and water resources and to test and develop mitigation measures for the Cerrado in the future.
This PhD thesis is essentially a collection of six sequential articles on dynamics of accountability in the reformed employment and welfare administration in different countries. The first article examines how recent changes in the governance of employment services in three European countries (Denmark, Germany and Norway) have influenced accountability relationships from a very wide-ranging perspective. It starts from the overall assumption in the literature that accountability relationships are becoming more numerous and complex, and that these changes may lead to multiple accountability disorder. The article explores these assumptions by analyzing the different actors involved and the information requested in the new governance arrangements in all three countries. It concludes that the considerable changes in organizational arrangements and more managerial information demanded and provided have led to more shared forms of accountability. Nevertheless, a clear development towards less political or administrative accountability could not be observed.
The second article analyzes how the structure and development of reform processes affect accountability relationships and via what mechanisms. It is distinguished between an instrumental perspective and an institutional perspective and each of these perspectives takes a different view on the link between reforms and concrete action and results. By taking the welfare reforms in Norway and Germany as an example, it is shown that the reform outcomes in both countries are the result of a complex process of powering, puzzling and institutional constraints where different situational interpretations of problems, interests and administrative legacies had to be balanced. Accountability thus results not from a single process of environmental necessity or strategic choice, but from a dynamic interplay between different actors and institutional spheres.
The third article then covers a specific instrument of public sector reforms, i.e. the increasing use of performance management. The article discusses the challenges and ambiguities between performance management and different forms of accountability based on the cases of the reformed welfare administration in Norway and Germany. The findings are that the introduction of performance management creates new accountability structures which influence service delivery, but not necessarily in the direction expected by reform agents. Observed unintended consequences include target fixation, the displacement of political accountability and the predominance of control aspects of accountability.
The fourth article analyzes the accountability implications of the increasingly marketized models of welfare governance. It has often been argued that relocating powers and discretion to private contractors involve a trade-off between democratic accountability and efficiency. However, there is limited empirical evidence of how contracting out shapes accountability or is shaped by alternative democratic or administrative forms of accountability. Along these lines the article examines employment service accountability in the era of contracting out in Germany, Denmark and Great Britain. It is found that market accountability instruments are complementary instruments, not substitutes. The findings highlight the importance of administrative and political instruments in legitimizing marketized service provision and shed light on the processes that lead to the development of a hybrid accountability model.
The fifth and sixth articles focus on the diagonal accountability relationships between public agencies, supreme audit institutions (SAI) and parental ministry or parliament.
The fifth article examines the evolving role of SAIs in Denmark, Germany and Norway focusing particularly on their contribution to public accountability and their ambivalent relationship with some aspects of public sector reform in the welfare sector. The article analyzes how SAIs assess New Public Management inspired reforms in the welfare sector in the three countries. The analysis shows that all three SAIs have taken on an evaluative role when judging New Public Management instruments. At the same time their emphasis on legality and compliance can be at odds with some of the operating principles introduced by New Public Management reforms.
The sixth article focuses on the auditing activities of the German SAI in the field of labor market administration as a single in-depth case study. The purpose is to analyze how SAIs gain impact in diagonal accountability settings. The results show that the direct relationship between auditor and auditee based on cooperation and trust is of outstanding importance for SAIs to give effect to their recommendations. However, if an SAI has to rely on actors of diagonal accountability, it is in a vulnerable position as it might lose control over the interpretation of its results.
The size and morphology control of precipitated solid particles is a major economic issue for numerous industries. For instance, it is interesting for the nuclear industry, concerning the recovery of radioactive species from used nuclear fuel.
The precipitates features, which are a key parameter from the post-precipitate processing, depend on the process local mixing conditions. So far, the relationship between precipitation features and hydrodynamic conditions have not been investigated.
In this study, a new experimental configuration consisting of coalescing drops is set to investigate the link between reactive crystallization and hydrodynamics. Two configurations of aqueous drops are examined. The first one corresponds to high contact angle drops (>90°) in oil, as a model system for flowing drops, the second one correspond to sessile drops in air with low contact angle (<25°). In both cases, one reactive is dissolved in each drop, namely oxalic acid and cerium nitrate. When both drops get into contact, they may coalesce; the dissolved species mix and react to produce insoluble cerium oxalate. The precipitates features and effect on hydrodynamics are investigated depending on the solvent. In the case of sessile drops in air, the surface tension difference between the drops generates a gradient which induces a Marangoni flow from the low surface tension drop over the high surface tension drop. By setting the surface tension difference between the two drops and thus the Marangoni flow, the hydrodynamics conditions during the drop coalescence could be modified. Diols/water mixtures are used as solvent, in order to fix the surface tension difference between the liquids of both drops regardless from the reactant concentration. More precisely, the used diols, 1,2-propanediol and 1,3-propanediol, are isomer with identical density and close viscosity. By keeping the water volume fraction constant and playing with the 1,2-propanediol and 1,3-propanediol volume fractions of the solvents, the mixtures surface tensions differ up to 10 mN/m for identical/constant reactant concentration, density and viscosity. 3 precipitation behaviors were identified for the coalescence of water/diols/recatants drops depending on the oxalic excess. The corresponding precipitates patterns are visualized by optical microscopy and the precipitates are characterized by confocal microscopy SEM, XRD and SAXS measurements. In the intermediate oxalic excess regime, formation of periodic patterns can be observed. These patterns consist in alternating cerium oxalate precipitates with distinct morphologies, namely needles and “microflowers”. Such periodic fringes can be explained by a feedback mechanism between convection, reaction and the diffusion.
This dissertation investigates the working memory mechanism subserving human sentence processing and its relative contribution to processing difficulty as compared to syntactic prediction. Within the last decades, evidence for a content-addressable memory system underlying human cognition in general has accumulated (e.g., Anderson et al., 2004). In sentence processing research, it has been proposed that this general content-addressable architecture is also used for language processing (e.g., McElree, 2000).
Although there is a growing body of evidence from various kinds of linguistic dependencies that is consistent with a general content-addressable memory subserving sentence processing (e.g., McElree et al., 2003; VanDyke2006), the case of reflexive-antecedent dependencies has challenged this view. It has been proposed that in the processing of reflexive-antecedent dependencies, a syntactic-structure based memory access is used rather than cue-based retrieval within a content-addressable framework (e.g., Sturt, 2003).
Two eye-tracking experiments on Chinese reflexives were designed to tease apart accounts assuming a syntactic-structure based memory access mechanism from cue-based retrieval (implemented in ACT-R as proposed by Lewis and Vasishth (2005).
In both experiments, interference effects were observed from noun phrases which syntactically do not qualify as the reflexive's antecedent but match the animacy requirement the reflexive imposes on its antecedent. These results are interpreted as evidence against a purely syntactic-structure based memory access. However, the exact pattern of effects observed in the data is only partially compatible with the Lewis and Vasishth cue-based parsing model.
Therefore, an extension of the Lewis and Vasishth model is proposed. Two principles are added to the original model, namely 'cue confusion' and 'distractor prominence'.
Although interference effects are generally interpreted in favor of a content-addressable memory architecture, an alternative explanation for interference effects in reflexive processing has been proposed which, crucially, might reconcile interference effects with a structure-based account.
It has been argued that interference effects do not necessarily reflect cue-based retrieval interference in a content-addressable memory but might equally well be accounted for by interference effects which have already occurred at the moment of encoding the antecedent in memory (Dillon, 2011).
Three experiments (eye-tracking and self-paced reading) on German reflexives and Swedish possessives were designed to tease apart cue-based retrieval interference from encoding interference. The results of all three experiments suggest that there is no evidence that encoding interference affects the retrieval of a reflexive's antecedent.
Taken together, these findings suggest that the processing of reflexives can be explained with the same cue-based retrieval mechanism that has been invoked to explain syntactic dependency resolution in a range of other structures. This supports the view that the language processing system is located within a general cognitive architecture, with a general-purpose content-addressable working memory system operating on linguistic expressions.
Finally, two experiments (self-paced reading and eye-tracking) using Chinese relative clauses were conducted to determine the relative contribution to sentence processing difficulty of working-memory processes as compared to syntactic prediction during incremental parsing.
Chinese has the cross-linguistically rare property of being a language with subject-verb-object word order and pre-nominal relative clauses. This property leads to opposing predictions of expectation-based
accounts and memory-based accounts with respect to the relative processing difficulty of subject vs. object relatives.
Previous studies showed contradictory results, which has been attributed to different kinds local ambiguities confounding the materials (Lin and Bever, 2011). The two experiments presented are the first to compare Chinese relatives clauses in syntactically unambiguous contexts.
The results of both experiments were consistent with the predictions of the expectation-based account of sentence processing but not with the memory-based account. From these findings, I conclude that any theory of human sentence processing needs to take into account the power of predictive processes unfolding in the human mind.
The main goal of this cumulative thesis is the derivation of surface emissivity data in the infrared from radiance measurements of Venus. Since these data are diagnostic of the chemical composition and grain size of the surface material, they can help to improve knowledge of the planet’s geology. Spectrally resolved images of nightside emissions in the range 1.0-5.1 μm were recently acquired by the InfraRed Mapping channel of the Visible and InfraRed Thermal Imaging Spectrometer (VIRTIS-M-IR) aboard ESA’s Venus EXpress (VEX). Surface and deep atmospheric thermal emissions in this spectral range are strongly obscured by the extremely opaque atmosphere, but three narrow spectral windows at 1.02, 1.10, and 1.18 μm allow the sounding of the surface. Additional windows between 1.3 and 2.6 μm provide information on atmospheric parameters that is required to interpret the surface signals. Quantitative data on surface and atmosphere can be retrieved from the measured spectra by comparing them to simulated spectra. A numerical radiative transfer model is used in this work to simulate the observable radiation as a function of atmospheric, surface, and instrumental parameters. It is a line-by-line model taking into account thermal emissions by surface and atmosphere as well as absorption and multiple scattering by gases and clouds. The VIRTIS-M-IR measurements are first preprocessed to obtain an optimal data basis for the subsequent steps. In this process, a detailed detector responsivity analysis enables the optimization of the data consistency. The measurement data have a relatively low spectral information content, and different parameter vectors can describe the same measured spectrum equally well. A usual method to regularize the retrieval of the wanted parameters from a measured spectrum is to take into account a priori mean values and standard deviations of the parameters to be retrieved. This decreases the probability to obtain unreasonable parameter values. The multi-spectrum retrieval algorithm MSR is developed to additionally consider physically realistic spatial and temporal a priori correlations between retrieval parameters describing different measurements. Neglecting geologic activity, MSR also allows the retrieval of an emissivity map as a parameter vector that is common to several spectrally resolved images that cover the same surface target. Even applying MSR, it is difficult to obtain reliable emissivity maps in absolute values. A detailed retrieval error analysis based on synthetic spectra reveals that this is mainly due to interferences from parameters that cannot be derived from the spectra themselves, but that have to be set to assumed values to enable the radiative transfer simulations. The MSR retrieval of emissivity maps relative to a fixed emissivity is shown to effectively avoid most emissivity retrieval errors. Relative emissivity maps at 1.02, 1.10, and 1.18 μm are finally derived from many VIRTIS-M-IR measurements that cover a surface target at Themis Regio. They are interpreted as spatial variations relative to an assumed emissivity mean of the target. It is verified that the maps are largely independent of the choice of many interfering parameters as well as the utilized measurement data set. These are the first Venus IR emissivity data maps based on a consistent application of a full radiative transfer simulation and a retrieval algorithm that respects a priori information. The maps are sufficiently reliable for future geologic interpretations.