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Micromegas are parallel-plate gaseous detectors with micro-pattern readout structures that are able to measure precisely and efficiently at high particle rates. Their difference with respect to other gaseous detectors is that the space in which particles ionise the gas and create electrons is separated from the region in which these electrons are multiplied (or amplified) by a thin metallic mesh. In the ionisation region, typically a few mm thick, a moderate field of a few hundred V/cm is applied. The amplification region with a homogeneous electrical field of 40--50~kV/cm is only 100--150~$\upmu$m thick. The latter guarantees that the positive ions produced in the amplification process are rapidly evacuated and the possibility to build up space charge at high rate is reduced. Critical in micromegas detectors are sparks in the thin amplification region in the presence of the high electrical field. This problem was solved in 2011 by introducing a spark protection scheme. It consists of a layer of resistive strips on top of the readout strips, separated from the latter by a thin insulation layer.
Micromegas with the spark protection scheme were selected as instrumentation of the first ATLAS forward muon station (NSW) in the upgrade of the ATLAS detector for the operation of the Large Hadron Collider (LHC) at high luminosity (HL-LHC), expected for 2026.
The main subjects of this thesis are: the characterisation of the first micromegas quadruplet prototypes for the NSW detectors; the characterisation of the materials used in the spark-protection system; and the study of the influence of the mesh distance holders (pillars) on the detector performance.
The thesis starts with a brief introduction into the LHC and ATLAS projects, followed by a chapter that explains the reason for the upgrade of the ATLAS muon system and shows the layout of the NSW.
The first of the three main chapters covers the construction and the characterisation of the first two prototypes for the NSW detectors. These detectors comprise four detection layers and have the same mechanical structure as the NSW detectors. The mechanical precision as well as the homogeneity of the detector response are discussed. The latter has been measured using X-rays and cosmic rays. The spatial resolution that can be achieved with these detectors precision has been measured at the MAMI accelerator at Mainz with low-energy electrons. The chapter is completed by a section that describes the successful integration of a data acquisition system (DAQ) into the official ATLAS DAQ system that was required for an initially planned installation of one of the prototypes on the existing Small Wheel.
The next chapter presents a study of the influence of temperature and humidity changes on the resistive strips used in the spark protection system. In addition the long-term stability of the resistive material has been measured accumulating charge equivalent to 100 years of operation in the HL-LHC and exposing the samples to intense gamma irradiation equivalent to 10 years of HL-LHC operation.
The third part covers the impact of the mesh distance holders (pillars) on the performance of the detector. This study has been performed with a 10 x 10 cm$^2$ bulk-micromegas with two different pillar shapes. Both 5.9 keV gammas from a $^{55}$Fe and 8 keV X-rays from a Cu target were used. In this context also the electrostatic charge-up of the detector is discussed.
In the Appendices one finds a summary of the fundamental physics relevant for gaseous detectors as well as some supporting material for the topics covered in the main part of the thesis.
The abilities to comprehend and critically evaluate scientific texts and the various arguments stated in these texts are an important aspect of scientific literacy, but these competences are usually not formally taught to students. Previous research indicates that, although undergraduate students evaluate the claims and evidence they find in scientific
documents to some extent, these evaluations usually fail to meet normative standards. In addition, students’ use of source information for evaluation is often insufficient. The rise of the internet and the increased accessibility of information have yielded some additional challenges that highlight the importance of adequate training and instruction.The aim of the present work was to further examine introductory students’ competences to systematically and heuristically evaluate scientific information, to identify relevant strategies that are involved in a successful evaluation, and to use this knowledge to design appropriate interventions for fostering epistemic competences in university students.To this end, a number of computer-based studies, including both quantitative and qualitative data as well as experimental designs, were developed. The first two studies were designed to specify educational needs and to reveal helpful processing strategies that are required in different tasks and situations. Two expert-novice comparisons were developed, whereby the performance of German students of psychology (novices) was compared to the performance of scientists from the domain of psychology (experts) in a number of different tasks, such as systematic plausibility evaluations of informal arguments (Study 1) or heuristic evaluations of the credibility of multiple scientific documents (Study 2). A think-aloud procedure was used
to identify specific strategies that were applied in both groups during task completion, and that possibly mediated performance differences between students and scientists. In addition, relationships between different strategies and between strategy use and relevant conceptual knowledge was examined. Based on the results of the expert-novice comparisons, an intervention study, consisting of two training experiments, was constructed to foster some
competences that proved to be particularly deficient in the comparisons (Study 3). Study 1 examined introductory students’ abilities to accurately judge the plausibility of informal arguments according to normative standards, to recognise common argumentation fallacies, and to identify different structural components of arguments. The results from Study 1 indicate that many students, compared to scientists, lack relevant knowledge about the structure of arguments, and that normatively accurate evaluations of their plausibility seem to be challenging in this group. Often, common argumentation fallacies were not identified correctly. Importantly, these deficits were partly mediated by differences in strategy use: It was especially difficult for students to pay sufficient attention to the relationship between argument components when forming their judgements. Moreover, they frequently relied on their intuition or opinion as a criterion for evaluation, whereas scientists predominantly determined quality of arguments based on their internal consistency.
In addition to students’ evaluation of the plausibility of informal arguments, Study 2 examined introductory students’ competences to evaluate the credibility of multiple scientific texts, and to use source characteristics for evaluation. The results show that students struggled not only to judge the plausibility of arguments correctly, but also to heuristically judge the credibility of science texts, and these deficits were fully mediated by their insufficient use of source information. In contrast, scientists were able to apply different strategies in a flexible manner. When the conditions for evaluation did not allow systematic processing (i.e. time limit), they primarily used source characteristics for their evaluations. However, when
systematic evaluations were possible (i.e. no time limit), they used more sophisticated normative criteria for their evaluations, such as paying attention to the internal consistency of arguments (cf. Study 1). Results also showed that students, in contrast to experts, lacked relevant knowledge about different publication types, and this was related to their ability to correctly determine document credibility. The results from the expert-novice comparisons also suggest that the competences assessed in both tasks might develop as a result of a more fundamental form of scientific literacy and discipline expertise. Performances in all tasks were positively related. On the basis of these results, two training experiments were developed that aimed at fostering university students’ competences to understand and evaluate informal arguments (Study 3). Experiment 1 describes an intervention approach in which students were familiarised with the formal structure of arguments based on Toulmin’s (1958) argumentation model. The performance of the experimental group to identify the structural components of this model was compared to the performance of a control group in which speed reading skills were practiced, using a pre-post-follow-up design. Results show that the training was successful for improving the comprehension of more complex arguments and relational aspects between key components in the posttest, compared to the control group. Moreover, an interaction effect was found with study performance. High achieving students with above average grades profited the most from the training intervention. Experiment 2 showed that
training in plausibility, normative criteria of argument evaluation, and argumentation fallacies improved students’ abilities to evaluate the plausibility of arguments and, in addition, their competences to recognise structural components of arguments, compared to a speed-reading control group. These results have important implications for education and practice, which will be discussed in detail in this dissertation.
The present thesis comprises synthesis and stoichiometric model reactions of well-defined NHC-stabilized copper(I) complexes (NHC = N-heterocyclic carbene) in order to understand their basic reactivity in borylation and cross-coupling reactions. This also includes the investigations of the reactivity of the ligands used (NHCs and CaaCs = cyclic alkyl(amino)carbenes) with the substrates, i.e. diboron(4) esters and arylboronates, which are addressed in the second part of the thesis.
The plant cuticle is a continuous extracellular protective layer covering the outermost surfaces of higher plants that are in contact with the surrounding atmosphere. The primary function of the cuticular lipid membrane, which is mainly composed of biopolymer cutin and cuticular waxes, is to protect the plant organs against uncontrolled water loss. The chemical composition and the biophysical properties of cuticular waxes affect the rate of water diffusion across the cuticle. Fruit transpiration plays an important role in the development and the maintenance of fruit quality. The fruit has been suggested to present better dehydration stress tolerance than the leaf. However, the differences in transpiration and the chemical composition of cuticular waxes between fruit and leaf have yet to be comprehensively investigated.
The present study aims to investigate the water permeability and cuticular wax composition of fruit and leaf cuticles of a wide range of plant species and to elucidate the different roles of the cuticular wax components in the transpiration barrier. To address these objectives, fruit and leaf samples from 17 species were investigated. The cuticular transpiration of intact fruits and astomatous adaxial leaf surfaces and the minimum leaf conductance obtained by leaf drying curves for intact leaves were gravimetrically determined for a variety of plant species. The chemical composition of cuticular waxes of fruits and leaves was thoroughly analysed by gas chromatography with flame ionization and mass spectrometry.
The water permeability of fruits ranged from 3.7 x 10-5 m s-1 (Prunus domestica subsp. syriaca) to 37.4 x 10-5 m s-1 (Coffea arabica), whereas permeability for leaves varied between 1.6 x 10-5 m s-1 (Cornus officinalis) and 4.5 x 10-5 m s-1 (Prunus domestica subsp. syriaca (L.)). The interspecies range of water permeability of fruits was significantly higher than that of leaves. Chemical analyses of the cuticular waxes demonstrated that fatty acids, primary alcohols, n-alkanes, aldehydes and alkyl esters were the predominant very-long-chain aliphatic compound classes of fruit and leaf surfaces. Sterols, such as β-sitosterol and campesterol, and triterpenoids, such as oleanolic acid, ursolic acid, α-amyrin and ß-amyrin, were the major cyclic compound classes in the cuticular wax membrane.
The amount and composition of cuticular waxes of both fruits and leaves varied at an intraspecific level. There were no significant correlations between the total cuticular wax load or the individual cuticular wax composition and the water permeability of fruits or leaves independently or together. After combining the fruit and leaf data set, a significant correlation between the average chain length of very-long-chain aliphatic compounds and permeabilities was detected, i.e. the longer the average chain length, the lower the water permeability.
Interestingly, n-Nonacosane (C29) was abundantly detected in fruit waxes of Rosaceae species. These fruits exhibited a relatively low transpiration level, which was very close to their leaf cuticular permeability. The present study suggests that the lower cuticular permeability of leaves, in comparison to that of fruits, may be attributed to the longer average chain length of aliphatic compounds. The accumulation of total wax, triterpenoids and aliphatic compounds may not contribute to the transpiration barrier directly. The present results are highly consistent with the previous model assumptions for the cuticular structure and transport barrier. Furthermore, this comparative study on leaf and fruit cuticles provides further insights linking the cuticular wax chemistry to the physiological properties of the plant cuticle.
This dissertation is concerned with the empirical investigation of the link between globalization and labor market outcomes as well as the determinants of governmental redistribution, with a special focus on the effects of culture and diversity on the welfare state. In recent years, globalization has been criticized for adverse structural effects, e.g. increasing employment volatility and higher inequality.
Following the introduction, the second chapter investigates the relationship between growing import penetration and manufacturing employment growth in 12 OECD countries between 1995 and 2011, accounting for various model specifications, different measures of import penetration, and alternative estimation strategies. The application of the latest version of the World Input-Output Database (WIOD), which has only recently become available, enables measurement of the effect of increases in imported intermediates according to their country of origin. The findings emphasize a weak positive overall impact of growing trade on manufacturing employment. However, while intermediate inputs from China and the new EU members are substitutes for manufacturing employment in highly developed countries, imports from the EU-27 complement domestic manufacturing production. The three-level mixed model utilized implies that the hierarchical structure of the data plays only a minor role, and controlling for endogeneity leaves the results unchanged.
The findings point to ambiguous effects of globalization on labor market outcomes which increase the demand for equalizing public policies. Accordingly, the following chapter examines the relationship between income inequality and redistribution, accounting for the shape of the income distribution, different development levels, and subjective perceptions. Cross-national inequality datasets that have become available only recently allow for the assessment of the link for various sample compositions and several model specifications. The empirical results confirm the Meltzer-Richard hypothesis, but suggest that the relationship between market inequality and redistribution is even stronger when using perceived inequality measures. The findings emphasize a decisive role of the middle class, while also identifying a negative impact of top incomes. The Meltzer-Richard effect is less pronounced in developing economies with less sophisticated political rights, illustrating that it is the political channel through which higher inequality translates into more redistribution.
Chapter (4) extends the framework developed in the preceding chapter by studying the effects of culture and diversity on governmental redistribution for a large sample of countries. To disentangle culture from institutions, the analysis employs regional instruments as well as data on linguistic differences, the frequency of blood types, and the prevalence of the pathogen Toxoplasma Gondii. Redistribution is higher in countries with (1) loose family ties and individualistic attitudes, (2) a high prevalence of trust and tolerance, (3) low acceptance of unequally distributed power and obedience, and (4) a prevalent belief that success is the result of luck and connections. Apart from their direct effects, these traits also exert an indirect impact by influencing the transmission of inequality to redistribution. Finally, the findings indicate that redistribution and diversity in terms of culture, ethnic groups, and religion stand in a non-linear relationship, where moderate levels of diversity impede redistribution and higher levels offset the generally negative effect.
Purpose: Early identification of aggressive disease could improve decision-support in pancreatic neuroendocrine tumor (pNET) patients prior to peptide receptor radionuclide therapy (PRRT). The prognostic value of intratumoral textural features (TF) determined by baseline somatostatin receptor (SSTR)-PET before PRRT was analyzed.
Procedures: 31 patients with G1/G2 pNET were enrolled (G2, n=23/31). Prior to PRRT with [\(^{177}\)Lu]DOTATATE (mean, 3.6 cycles), baseline SSTR-PET/CT was performed. By segmentation of 162 (median per patient, 5) metastases, intratumoral TF were computed. The impact of conventional PET parameters (SUV\(_{mean/max}\)), imaging-based TF as well as clinical parameters (Ki67, CgA) for prediction of both progression-free (PFS) and overall survival (OS) after PRRT was evaluated.
Results: Within a median follow-up of 3.7y, tumor progression was detected in 21 patients (median, 1.5y) and 13/31 deceased (median, 1.9y). In ROC analysis, the TF Entropy, reflecting derangement on a voxel-by-voxel level, demonstrated predictive capability for OS (cutoff=6.7, AUC=0.71, p=0.02). Of note, increasing Entropy could predict a longer survival (>6.7, OS=2.5y, 17/31), whereas less voxel-based derangement portended inferior outcome (<6.7, OS=1.9y, 14/31). These findings were supported in a G2 subanalysis (>6.9, OS=2.8y, 9/23 vs. <6.9, OS=1.9y, 14/23). Kaplan-Meier analysis revealed a significant distinction between high- and low-risk groups using Entropy (n=31, p<0.05). For those patients below the ROC-derived threshold, the relative risk of death after PRRT was 2.73 (n=31, p=0.04). Ki67 was negatively associated with PFS (p=0.002); however, SUVmean/max failed in prognostication (n.s.).
Conclusions: In contrast to conventional PET parameters, assessment of intratumoral heterogeneity demonstrated superior prognostic performance in pNET patients undergoing PRRT. This novel PET-based strategy of outcome prediction prior to PRRT might be useful for patient risk stratification.
Both prostate-specific membrane antigen (PSMA)- and somatostatin receptor (SSTR)-targeted positron emission tomography (PET) imaging agents for staging and restaging of prostate carcinoma or neuroendocrine tumors, respectively, are seeing rapidly expanding use. In addition to diagnostic applications, both classes of radiotracers can be used to triage patients for theranostic endoradiotherapy. While interpreting PSMA- or SSTR-targeted PET/computed tomography (CT) scans, the reader has to be aware of certain pitfalls. Adding to the complexity of the interpretation of those imaging agents, both normal biodistribution, and also false-positive and -negative findings differ between PSMA- and SSTR-targeted PET radiotracers. Herein summarized under the umbrella term molecular imaging reporting and data systems (MI-RADS), two novel RADS classifications for PSMA- and SSTR-targeted PET imaging are described (PSMA- and SSTR-RADS). Both framework systems may contribute to increase the level of a reader’s confidence and to navigate the imaging interpreter through indeterminate lesions, so that appropriate workup for equivocal findings can be pursued. Notably, PSMA- and SSTR-RADS are structured in a reciprocal fashion, i.e. if the reader is familiar with one system, the other system can readily be applied as well. In the present review we will discuss the most common pitfalls on PSMA- and SSTR-targeted PET/CT, briefly introduce PSMA- and SSTR-RADS, and define a future role of the umbrella framework MI-RADS compared to other harmonization systems.
Background: \(^{18}\)F-N-[3-bromo-4-(3-fluoro-propoxy)-benzyl]-guanidine (\(^{18}\)F-LMI1195) is a new class of PET tracer designed for sympathetic nervous imaging of the heart. The favorable image quality with high and specific neural uptake has been previously demonstrated in animals and humans, but intracellular behavior is not yet fully understood. The aim of the present study is to verify whether it is taken up in storage vesicles and released in company with vesicle turnover.
Results: Both vesicle-rich (PC12) and vesicle-poor (SK-N-SH) norepinephrine-expressing cell lines were used for in vitro tracer uptake studies. After 2 h of \(^{18}\)F-LMI1195 preloading into both cell lines, effects of stimulants for storage vesicle turnover (high concentration KCl (100 mM) or reserpine treatment) were measured at 10, 20, and 30 min. \(^{131}\)I-meta-iodobenzylguanidine (\(^{131}\)I-MIBG) served as a reference. Both high concentration KCl and reserpine enhanced \(^{18}\)F-LMI1195 washout from PC12 cells, while tracer retention remained stable in the SK-N-SH cells. After 30 min of treatment, 18F-LMI1195 releasing index (percentage of tracer released from cells) from vesicle-rich PC12 cells achieved significant differences compared to cells without treatment condition. In contrast, such effect could not be observed using vesicle-poor SK-N-SH cell lines. Similar tracer kinetics after KCl or reserpine treatment were also observed using 131I-MIBG. In case of KCl exposure, Ca\(^{2+}\)-free buffer with the calcium chelator, ethylenediaminetetracetic acid (EDTA), could suppress the tracer washout from PC12 cells. This finding is consistent with the tracer release being mediated by Ca\(^{2+}\) influx resulting from membrane depolarization.
Conclusions: Analogous to \(^{131}\)I-MIBG, the current in vitro tracer uptake study confirmed that \(^{131}\)F-LMI1195 is also stored in vesicles in PC12 cells and released along with vesicle turnover. Understanding the basic kinetics of \(^{18}\)FLMI1195 at a subcellular level is important for the design of clinical imaging protocols and imaging interpretation.