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A robust, automated nudged elastic band method in internal coordinates
No full textIn this work, a robust and reliable implementation of the Nudged Elastic Band (NEB) method is developed and tested. It is a method for finding reaction paths and TS, which can be used to theoretically compute reaction barriers, allowing a theoretical understanding of kinetics experiments. It can also be used in mechanistic studies, for finding reaction mechanisms, or explore entire networks of
interconnected reactions. A short overview and comparison of methods for modeling reaction paths and finding transition states is provided, including the NEB method. The challenges of reaction path modeling and transition state finding are discussed, both in general
and in the particular case of the NEB method. The NEB method and its implementation are discussed in detail. Various issues and pitfalls when using the NEB method are addressed, and solutions proposed and implemented. The NEB implementation thus developed is tested on a reaction set for benchmarking, and used in kinetics studies on real-world systems. One of these systems is the FeMAN challenge, a series of reactions where theoretical chemistry groups are challenged to accurately predict barrier heights and experimentally measured rate constants. The other set of syste ms are mixtures of substituted benzyl alcohols with methyl glycolate in the gas phase, which form a number of possible dimers, which can interconvert through a network of reaction paths. The results for these systems are discussed in detail. The NEB implementation was able to find sensible reaction paths and approximate transition state geometries for many of these reactions with comparatively little human oversight, allowing a ’semiautomatic’ workflow. This work’s aim to make NEB more robust and reliable was a success, but there is still room for improvement. Remaining issues, and possible avenues for future research are discussed.2025-12-2
Study of Compact Multi-Planet Systems around M Dwarf Stars
No full textIn this thesis, the architecture and dynamics of two known compact multi-planet systems around M
dwarf stars were investigated, in particular L 98-59 and YZ Ceti. These two systems are among the
28 closest M dwarfs to the solar system with two or more planets. The proximity of these systems,
as well as their architecture, makes them prime targets for observations with the Radial Velocity
(RV) and transit method, as well as observations of planetary atmospheres with direct imaging
or transit spectroscopy. The study of these systems with focus on the precise determinations of
planetary and orbital parameters, planet-planet interactions, and dynamical stability yield important
information for testing and refining general planet formation and evolution theories. The studies
presented in this thesis focus on combining different methods for constraining the parameters of
the planetary systems. In addition to the study of the planets of the two systems, we also investigate
the stellar activity with Gaussian Processes (GP) modelling, exploration of the activity indicators
obtained from the stellar spectra and (in the case of YZ Ceti) photometric variability. These are
important features for the re-analysis of the RV data, since it reduces stellar activity signals and
allows for a better distinction between the planetary signals, the planet-planet interactions, and the
stellar signals.
In the analysis of L 98-59, we use the combination of RV (HARPS and ESPRESSO) and
transit (individual observations from HST and 21 sectors from TESS) data, and constraints from
dynamical stability models for a better estimation of the planetary masses (or minimum masses
for the non-transiting planets). The combination and simultaneous modelling of RV and transits
additionally leads to stronger constraints on the overall orbital and planetary parameters in this
system. We confirm planet L 98-59 f with a sin = 2.97 M⊕ and a period of = 23.069 d.
In addition, we find a planet candidate, L 98-59 ‘06’, with sin ‘06′ = 0.58 M⊕ and a period of
‘06′ = 1.736 15 d in the residuals of the RV data of the five planet model.
The planets in the YZ Ceti system are near a rare 3:2-3:2 resonance chain. The planets do not
show transits. However, there are 20 years of RV data available from HARPS, CARMENES and
ESPRESSO that we fit with a dynamic (Newtonian) orbit model. This dynamic analysis breaks the
degeneracy of mass and inclination inherent to the RV method, and further explores the nature of
the near Mean Motion Resonance (MMR) in this system. With this we are able to constrain the
true masses of the three orbiting planets to be = 0.83 M⊕, = 1.29 M⊕ and = 1.24 M⊕.
In the residuals of YZ Ceti we can not find any signals that could point towards further planets.
While we could not detect additional, long period or low-mass planets hidden in these systems,
the precise fits and the new candidate add to the understanding of these systems’ architectures
and contribute another step in the understanding and completeness of multi-planet systems. The
constraints presented in this work are comparable with other detailed studies of similar systems
(e.g. GJ 1061 – Dreizler et al. 2020, TOI-178 – Leleu et al. 2024, or Teegarden’s star – Dreizler
et al. 2024).2026-01-2
Limitations and accident-related duration of incapacity to work / of professional activity after spinal injury
No full textDie traumatische Wirbelköperfraktur ist eine häufige Verletzung in der Unfallchirurgie, die besonders Männer im arbeitsfähigen Alter betrifft. Es gibt bisher nur wenige Aussagen mit welcher Arbeitsunfähigkeitsdauer der Patient, der Kostenträger und auch der Arbeitgeber nach Wirbelkörperfraktur zu rechnen haben. Die Faktoren, die die Länge der Arbeitsunfähigkeit beeinflussen könnten, sind noch nicht ausreichend untersucht.
In dieser Arbeit erfolgte die retrospektive Datenerhebung aus anonymisierten orthopädischen / unfallchirurgischen Gutachten des überregionalen Instituts für Medizinische Begutachtung Kassel von 734 Patienten mit traumatischer Fraktur der Brust- und / oder Lendenwirbelsäule aus den Jahren 2005 bis 2017. Die Gutachten der 203 Patienten mit angegebener Dauer der Arbeitsunfähigkeit wurden zur Identifizierung möglicher Einflussfaktoren standardisiert ausgewertet und statistisch mittels MS Excel untersucht.
Die mediane Arbeitsunfähigkeitsdauer aller begutachteter Patienten mit erlangter Arbeitsfähigkeit bei Gutachtenerstellung betrug 183 Tage und damit 6,1 Monate (n=203). Es ließen sich eine Reihe statistisch signifikanter Einflussfaktoren (p <= 0,05) auf die Dauer der Arbeitsunfähigkeit nach Wirbelkörperfraktur ermitteln. Als prognostisch ungünstige Faktoren im Sinne einer längeren Arbeitsunfähigkeitsdauer konnten das Vorliegen einer Skoliose (+230 Tage, p=0,01, n=5), primär instabile Wirbelkörperfrakturen (+71 Tage, p=0,04, n=82), das Vorliegen einer Spinalkanalbeteiligung (+102 Tage, p=0,02, n=38) oder sensibler neurologischer Ausfallerscheinungen (+355 Tage, p<0,001, n=7) sowie das Vorhandensein eines Schädel-Hirn-Traumas (+92 Tage, p=0,02, n=50) identifiziert werden. Ebenso mit einer längeren Arbeitsunfähigkeitsdauer einhergehend zeigte sich die operative Therapie (+82 Tage, p=0,02, n=85). Als prognostisch günstige Faktoren im Sinne einer kürzeren Arbeitsunfähigkeitsdauer zeigten sich das Vorliegen einer Fraktur im BWS-Bereich (-74 Tage, p=0,03, n=76) und besonders einer Fraktur im Bereich der unteren BWS (-87 Tage, p=0,02, n=64).
Das der Arbeit zu Grunde liegende Patientenkollektiv stellt im Vergleich mit der Literatur eine repräsentative Gruppe von Patienten mit Wirbelkörperfraktur dar. Die Arbeitsunfähigkeitsdauer von median 183 Tagen lässt sich gut in die bisherigen Ergebnisse einfügen. Speziell die signifikanten Ergebnisse sollten als wegweisende Einflussfaktoren auf die Dauer der zu erwartenden Arbeitsunfähigkeit nach Wirbelkörperfraktur gewertet werden. Zudem sollten auch die nicht signifikant kürzeren Arbeitsunfähigkeitszeiten von Frauen, älteren Patienten, Selbstständigen und sitzend
arbeitenden Patienten Berücksichtigung finden. Zu ebenfalls nicht signifikant prognostisch ungünstigen Faktoren, die dennoch relevant erscheinen könnten, zählen: Ein High-Energy Trauma, motorische neurologische Ausfallerscheinungen durch die Wirbelkörperfraktur, das Vorhandensein von Begleitverletzungen sowie die Art der operativen Versorgung und das Vorliegen von Komplikationen postoperativ. Eher zu vernachlässigen sind das Vorliegen von somatischen oder psychischen Vorerkrankungen, die orthetische Versorgung bei konservativer Therapie und die Beschwerdeangabe und die Einnahme von Analgetika zum Gutachtenzeitpunkt sowie die Unterscheidung in Unfälle aus dem privaten und beruflichen Bereich.
Das Vorliegen einer Wirbelkörperfraktur und die daraus resultierende mediane Arbeitsunfähigkeitsdauer von über sechs Monaten hat eine große sozioökonomische Relevanz. Anhand dieser Arbeit konnten einige signifikante und nicht signifikante Einflussfaktoren auf die Arbeitsunfähigkeitsdauer ermittelt werden.The traumatic vertebral fracture is a common injury in trauma surgery, that is most often related to men in employable age. So far there are only a few statements regarding the duration of incapacity to work, which the patient, the cost bearer and the employers are having to expect. Influencing factors of the duration of incapacity to work are yet not enough examined. This paper is about the analysis of anonymized and retrospective data collection from orthopedic / trauma expert reports from the „Institut für Medizinische Begutachtung Kassel“ of 734 patients with traumatic fracture of the thoracic or / and lumbar spine from 2005 to 2017. In 203 cases there is a duration of incapacity to work documented. These expert reports have been analysed to identify influencing factors of the duration of incapacity to work. The statistical evaluation was made by MS Excel.
The median duration of incapacity to work of all patients, who returned to work, was 183 days / 6.1 month (n=203). Statistically significant (p <= 0.05) influencing factors for a longer duration of incapacity to work have been: Scoliosis (+230 days, p=0.01, n=5), unstable vertebral fractures (+71 days, p=0.04, n=82), involvement of the spinal canal (+102 days, p=0.02, n=38), sensitive neurological deficits (+355 days, p<0.001, n=7), trauma of the head (+92 days, p=0.02, n=50) and operative treatment (+82 days, p=0.02, n=85). Statistically significant influencing factors for a shorter duration of incapacity to work have been fractures in the thoracic spine (-74 days, p=0.03, n=76), especially in the lower thoracic spine (-87 days, p=0.02, n=64).
The patient collective with fractures of the thoracic and lumbar spine is representative compared to the literature research. The 183 days of duration of incapacity to work is comparatively to the few known durations.
Especially the statistically significant results should be graded influencing factors of the duration of incapacity to work after spinal injury. Graded as well should be following non-statistically significant results: Women, older patients and patients with independent or sedentary work have a shorter duration of incapacity to work. A longer duration of incapacity to work could be caused by: high-energy trauma, motor neurological deficits because of the spinal fracture, combined injuries, the kind of operative treatment and postoperative complications. Rather negligible are pre-existing conditions of the patient, orthosis during non-operative treatment, physical complaints of the patient and the use of painkillers as well as the differentiation between private accidents and accidents at work.
There is a high socio-economic relevance of fractures of the thoracic and lumbar spine and the long duration of incapacity to work for over six months. Some statistically significant and non-significant influencing factors of the duration of the incapacity to work have been identified by this paper.2025-07-1
Die Auswirkung verschiedener Cathepsin D Mutationen auf die zelluläre Autophagie
No full textDie Subtypen der Neuronalen Ceroidlipofuszinose (NCL) stellen kumulativ die häufigste Ursache einer Neurodegeneration im Kindes- und Jugendalter dar. Namensgebend für diese Gruppe der neuronalen Speichererkrankungen ist die progrediente intraneuronale Akkumulation von Lipofuszin, einem proteinhaltigen Speichermaterial unterschiedlicher biochemischer Zusammensetzung. In verschiedenen Tierspezies wurde beschrieben, dass Mutationen der lysosomalen Aspartatprotease Cathepsin D zur Rekapitulation eines NCL-typischen Phänotyps führten. In der Folge wurde ebenso in Fallberichten der gänzliche oder partielle katalytische Aktivitätsverlust von Cathepsin D als Ursache der NCL Typ 10 im Menschen identifiziert. Insbesondere zeigte sich u.a. eine veränderte posttranslationale Prozessierung einiger Cathepsin D-Mutanten, wobei Cathepsin D in seiner Funktion auf eine korrekte intrazelluläre Prozessierung seiner Prepro-Form (53 kDa) in die reife, intralysosomale Form (33 kDa, schweres Fragment) angewiesen ist. In Tiermodellen der Cathepsin D-Defizienz ergaben sich Hinweise auf verschiedene, dem neuronalen Phänotyp bei NCL Typ 10 zugrunde liegende biochemische Pathomechanismen, vorrangig eine Beeinträchtigung der zellulären Apoptose bzw. der zellulären Autophagie. Dabei erscheint aufgrund der Funktion von Cathepsin D als lysosomale Aspartatprotease eine Beeinträchtigung des autophagolysosomalen Systems wahrscheinlich. Bei Autophagie handelt es sich um einen intrazellulären, zwischen Spezies konservierten und mehrschrittigen Prozess der zellulären Proteinhomöostase und des Zellorganellenumsatzes. Zu degradierendes intrazelluläres Material wird hierbei von einer doppelten Zellmembran unter Bildung sog. Autophagosomen umschlossen, die mit Lysosomen zu sog. Autophagolysosomen fusionieren. In letzteren erfolgt die eigentliche (proteolytische) Degradation des Zellmaterials mit kontrollierter Freisetzung resultierender Makromoleküle. In ihrer Gesamtheit werden die einzelnen Schritte der Autophagie auch als autophagozytotischer Fluss (engl. autophagic flux) bezeichnet. Im Rahmen dieser Arbeit wurden verschiedene Cathepsin D-Mutanten in einem heterologen Expressisonssystem in primär Cathepsin D-defizienten murinen embryonalen Fibroblasten (MEF) durch Lipofektion mit dem Plasmid pEF3-zeo stabil exprimiert. Dabei handelte es sich um sieben vorbeschriebene und eine im Rahmen dieser Arbeit erstmals charakterisierte Mutation (p.K331del). Ziel war es, nach einer weiteren lentiviralen Transduktion der transfizierten, die Cathepsin D-Mutanten exprimierenden MEF zur Expression von Tandem-fluoreszentem LC3 (mCherry-GFP-LC3) die Auswirkungen der Mutationen auf die zelluläre Autophagie zu untersuchen. Dabei war von besonderem Interesse, ob durch Mutationen der lysosomalen Aspartatprotease Cathepsin D vorrangig die Degradationsphase der zellulären Autophagie in Autophagolysosomen beeinträchtigt ist. Hierbei stellte die Markierung von LC3 mit mCherry und GFP prinzipiell eine Methode dar, mit welcher der gesamte autophagozytotische Fluss abgebildet werden kann. Nach Transfektion der murinen embryonalen Fibroblasten (MEF) zeigte sich eine unterschiedliche posttranslationale Prozessierung der verschiedenen Cathepsin D-Mutanten. Fluoreszenzmikroskopisch zeigten vier der untersuchten Mutanten eine Kolokalisation mit dem lysosomalen Protein LAMP I (CD 107a), zwei ein nicht lysosomal lokalisiertes Fluoreszenzsignal für Cathepsin D und weitere zwei kein Fluoreszenzsignal für die lysosomale Protease. Nach Transduktion mit mCherry-GFP-LC3 erfolgte eine Induktion der nicht selektiven, zellulären Autophagie durch Nährstoffentzug mittels Kultivierung in Earle-Salze (EBSS, Earle’s balanced salt solution). Die Funktionalität der Methode wurde durch gleichzeitige Exposition gegenüber Bafilomycin A1, einem Autophagosomen-Lysosomen-Fusionshemmer, überprüft. Hier stellten sich erwartungsgemäß fluoreszenzmikroskopisch keine roten Signale, d.h. keine Autophagolysosomen, dar. Sowohl nach Autophagieinduktion durch Nährstoffentzug als auch nach einer sich daran anschließenden Kultivierungsphase in Standardkulturmedium zeigten mit dem Vektor pEF3-zeo ohne codierendes Insert transfizierte MEF und die mit den Cathepsin D-Mutanten transfizierten MEF im Median höhere Autophagolysosomenzahlen pro Zellfläche im Vergleich zu Cathepsin D-Wildtyp exprimierenden Zellen. Somit gelang im Rahmen dieser Arbeit der Nachweis eines gestörten autophagozytotischen Flusses, der möglicherweise durch eine verzögerte Rückbildungsdynamik der Autophagolysosomen für die untersuchten Cathepsin D-Mutanten in einem heterologen Expressionssystem in MEF verursacht wird. Eine genauere Lokalisation des Defektes innerhalb des autophagozytotischen Flusses für die untersuchten Cathepsin D-Mutanten ermöglicht für die NCL Typ 10 in der Zukunft potenziell die Entwicklung gezielterer, Autophagie-modulierender Therapien. Dies erscheint trotz der Tatsache, dass für Cathepsin D eine Machbarkeitsstudie des Enzymersatzes im Mausmodell existiert, im Sinne zukünftiger synergistischer Therapieansätze mit Enzymersatz und Autophagiemodulation relevant.The subtypes of neuronal ceroid lipofuscinosis (NCL) cumulatively represent the most common cause of neurodegeneration in children and adolescents. These disorders are characterized by progressive intraneuronal accumulation of lipofuscin, proteinaceous material of varying biochemical composition. In some animal species, mutations in the lysosomal aspartic protease cathepsin D have been described to lead to the recapitulation of the neuropathological hallmarks of NCL. Subsequently, total or partial loss of cathepsin D activity has likewise been identified in case reports as the cause of NCL type 10 in humans. In particular, defective posttranslational processing of cathepsin D was observed for some mutants, with cathepsin D relying for its function on proper intracellular processing from its prepro-form (53 kDa) into the mature intralysosomal form (33 kDa, heavy fragment). Animal models of cathepsin D deficiency revealed several possible biochemical pathomechanisms underlying neurodegeneration in NCL type 10, primarily impairment of autophagy and apoptosis. Due to the function of cathepsin D as lysosomal aspartate protease, a disruption of the autophagy-lysosome pathway appears likely. Autophagy represents an intracellular pathway of protein homeostasis and organelle turnover that is conserved among species and occurs in multiple steps. Intracellular material to be degraded is enclosed by a double cell membrane to form so-called autophagosomes which consecutively fuse with lysosomes to become autophagolysosomes. In the latter, the actual (proteolytic) degradation of the cell material takes place with controlled release of resulting macromolecules. In their entirety, the individual steps of cellular autophagy are also referred to as autophagic flux. In this study, several cathepsin D mutations were stably expressed in a heterologous expression system in primarily cathepsin D-deficient murine embryonic fibroblasts (MEF) by lipofection with plasmid vector pEF3-zeo. Among these were seven previously described mutations and one mutation that was characterized for the first time in this study (p.K331del). The aim was to investigate the effect of cathepsin D mutations on cellular autophagy after additional lentiviral transduction of the transfected MEF to coexpress tandem-fluorescent LC3 (mCherry-GFP-LC3). Of particular interest was whether mutations of the lysosomal aspartate protease cathepsin D primarily impair the autophagolysosomal degradation, i. e. the later steps within the autophagic flux. In this context, tandem fluorescent labelling of LC3 with mCherry and GFP provided a method by which the entire autophagic flux could be monitored. Transfection of the MEF revealed distinct posttranslational processing of the cathepsin D mutants. In fluorescence microscopy, four of the mutants showed colocalization with the lysosomal marker LAMP I (CD 107a), whereas two depicted a non-lysosomal fluorescent signal, and another two showed no fluorescent signal for cathepsin D at all. Lentiviral transduction with mCherry-GFP-LC3 of the transfected MEF was followed by induction of autophagy by cultivation under nutrient-deprived conditions in Earle’s balanced salt solution (EBSS). Functionality of the applied method was tested by simultaneous exposition to bafilomycin A1, an inhibitor of autophagosome lysosome fusion. As expected, no red fluorescent signals, i. e. no autophagolysosomes, presented themselves by fluorescent microscopy. After induction of autophagy by starvation as well as after nutrient deprivation followed by cultivation under nutrient-rich standard conditions, MEF that had been either transfected with cathepsin D mutants or with the vector pEF3-zeo without coding insert showed higher median numbers of autophagolysosomes per cell area when compared to cells expressing the cathepsin D wildtype. Thus, this work provided evidence of impaired autophagocytotic flux possibly caused by decelerated regression of autophagolysosomes for the cathepsin D mutants studied in a heterologous expression system in MEF. A more precise localization of the defect within the autophagic flux for the studied cathepsin D mutants will potentially allow the development of autophagy-modulating therapies for NCL type 10 in the future. This seems relevant in terms of future synergistic therapeutic approaches with enzyme replacement and autophagy modulation, despite the fact that a feasibility study of enzyme replacement exists for cathepsin D in a mouse model.2025-08-0
Small-scale Entrepreneurship and Informal Employment: Evidence from sub-Saharan Africa
No full textThis thesis investigates the livelihoods and constraints of small-scale entrepreneurs in sub-Saharan Africa through a series of empirical studies conducted in Uganda and Côte d’Ivoire. The four chapters provide complementary insights into the vulnerability, financial behaviour, and employment practices in small-scale entrepreneurship, offering a nuanced understanding of the challenges and potential policy levers to support more secure and productive self-employment.
The first chapter examines the limitations of the International Labour Organisation’s broad classification of own-account workers as inherently vulnerable by developing an empirically grounded measure of vulnerability based on income adequacy and volatility. Using a six-year panel of Ugandan micro-entrepreneurs, it reveals persistently high vulnerability rates, driven by intertemporal income fluctuations and limited upward mobility, underscoring the need for more context-sensitive criteria in identifying vulnerable populations.
The second chapter explores the role of savings in supporting business investment through a randomised control trial (RCT) of a behavioural commitment device in Kampala. The intervention, a goal-setting calendar rooted in mental contrasting techniques, had limited average impact but showed positive effects among specific subgroups, particularly those with lower saving constraints. The findings highlight the importance of intra-household dynamics and social obligations in shaping financial decision-making, challenging the assumption that self-control problems are the primary barriers to savings.
The third chapter evaluates a low-intensity, government-implemented business consulting programme for Ivorian Small and Medium Enterprises (SMEs). While the intervention did not significantly improve firm performance or management practices overall, it led to modest but meaningful improvements in employment quality—raising the incidence of minimum wage payments and formal contracts. The results suggest that even light-touch interventions can enhance job quality, especially when well-targeted.
The fourth chapter delves deeper into employment outcomes using matched employer-employee data. It confirms the improvements in wage levels and contract formalisation and finds evidence for firms selectively formalising key workers, likely to retain talent. These shifts occurred with minimal financial burden, suggesting that better regulatory awareness—not just enforcement—can enhance labour conditions.
Together, these studies contribute to our understanding of micro-entrepreneurship in low-income settings by examining both the vulnerabilities faced by entrepreneurs and the channels through which policy and behavioural interventions can affect firm behaviour and employment quality. The findings emphasise the need for targeted, context-aware support strategies that go beyond binary classifications of informality to foster decent work within the realities of African labour markets.2025-08-0
VAR Analysis of Heterogeneous Panel Data
No full textDie Vektor-Autoregression (VAR) ist ein zentrales Instrument der empirischen Makroökonomik und Ausgangpunkt vieler Erweiterungen der multivariaten Zeitreihenanalyse. So ermöglichen strukturelle VAR-Modelle, Kausalzusammenhänge in dynamischen Systemen zu identifizieren und damit die Effekte von politischen Interventionen zu quantifizieren. Panel-VAR-Modelle kombinieren Zeitreihen vieler Untersuchungseinheiten, wie z.B. Länder, um mit der größeren Datengrundlage präzisere Schätzungen zu erreichen. Die drei Paper der vorliegenden Dissertation greifen auf dieses Instrumentarium zurück.
Das erste Paper stellt das R-Paket pvars vor. Ziel des Pakets ist es, eine nahtlose Implementierung von VAR-Methoden für heterogene Paneldaten bereitzustellen und damit eine Lücke in den verfügbaren Softwarepaketen zu schließen. So bietet pvars Panel-Kointegrationsranktests, die Querschnittsabhängigkeiten in den Fehlertermen und Strukturbrüche in den deterministischen Termen berücksichtigen. Aufbauend auf diesen Spezifikationen können Panel-SVAR-Modelle mit gepoolten Kointegrationsvektoren geschätzt und durch verschiedene Panel-Verfahren identifiziert werden. Der Beitrag des Papers liegt in der Vorstellung der Methodik, ihrer modularen Implementierung in R und ihrer praktischen Anwendung. Zwei empirische Beispiele aus der Literatur werden Schritt für Schritt reproduziert, um Anwendern den Einstieg zu erleichtern und eigene Analysen zu ermöglichen.
Das zweite Paper greift die anhaltende wirtschaftspolitische Debatte um die Wachstumswirkung öffentlicher Investitionen – etwa im Kontext des Green New Deal – erneut auf. Ziel ist es, die umfangreiche empirische Literatur mithilfe eines neuen Paneldatensatzes für 23 OECD-Länder über den Zeitraum 1960–2019 systematisch zu überprüfen. Dazu wird ein heterogenes Panel-VAR-Modell verwendet, das das dynamische Panelmodel und das Vektor-Fehlerkorrekturmodel als zwei bisherige Ansätze kombiniert. Die empirischen Ergebnisse zeigen, dass zwei homogene Langfristbeziehungen im Panel bestehen und dass eine zeitlich abnehmende Produktivität ein wesentlicher Erklärungsfaktor für die uneinheitlichen und oft insignifikanten Impuls-Antwort-Funktionen auf Länderebene ist.
Das dritte Paper analysiert die Rüstungsdynamiken im arabisch-israelischen Konflikt von 1962 bis 2010 mithilfe von SVAR-Modellen. Im Unterschied zu früheren Arbeiten, die auf Granger-Kausalität in VAR-Modellen reduzierter Form setzen, verfolgt die Studie einen datengestützten Identifikationsansatz. Mittels der unabhängigen Komponentenanalyse werden zwei Schocktypen identifiziert: landesspezifische sowie regionale geopolitische Spannungen. Letztere erweisen sich als relevanter für die Erklärung der Rüstungsdynamiken in Israel, Ägypten, Jordanien und Syrien. Insbesondere für die Rivalität zwischen Israel und Ägypten werden reziproke Reaktionen und gegenseitige Verstärkungen nachgewiesen, die typische Muster eines Wettrüstens widerspiegeln.Vector-autoregressive (VAR) analysis is a central instrument of empirical macroeconomics and the starting point for numerous extensions of multivariate time series analysis. For example, structural VAR models allow to identify causal relationships in dynamic systems and thus to quantify the effects of political interventions. Panel VAR models combine time series of many survey units such as countries to increase the dataset and thus achieve more precise estimates. The three papers in this the dissertation draw on this toolkit.
The first paper introduces the R-package pvars. The aim of the package is to provide a seamless implementation of VAR methods for heterogeneous panel data, thus filling a gap in the available software packages. In particular, pvars provides panel cointegration rank tests that take into account cross-sectional dependencies in the error terms and structural breaks in the deterministic terms. Based on these specifications, panel SVAR models with pooled cointegration vectors can be estimated and identified by different panel methods. The paper’s contribution lies in presenting the methodology, its modular implementation in R, and the practical application: Two empirical examples from the literature are reproduced step by step and help users to get started and perform their own analyses.
The second paper revisits the long-lasting debate about whether public investment – for example in the context of the Green New Deal – promotes economic growth. The aim is to systematically revise the extensive empirical literature using a new panel dataset covering 23 OECD countries from 1960 to 2019. To this end, a heterogeneous panel VAR model is employed, which combines the dynamic panel model and the vector error correction model as two previous approaches. The empirical results show that two homogeneous long-run relationships exist within the panel and that the declining productivity over time is a key factor in explaining the puzzling and often insignificant impulse response functions at the country level.
The third paper analyzes the armament dynamics in the Arab-Israeli conflict between 1962 and 2010 using SVAR models. In contrast to earlier work that relied on Granger causality in reduced-form VAR models, this study takes a data-driven identification approach. Using independent component analysis, two types of shock are identified: country-specific and regional geopolitical tensions. The latter are shown to be more relevant for explaining the armament dynamics in Israel, Egypt, Jordan and Syria. Particularly for the rivalry between Israel and Egypt, reciprocal reactions and mutual reinforcements are found, which reflect typical patterns of an arms race.2025-10-0
How sustainable are sustainability standards? Impact of farm sustainability certifications on farmers' performance and environmental outcomes
No full textVoluntary Sustainability Standards (VSS) have emerged as a promising market-based response to global sustainability challenges within agricultural supply chains. By offering certifications for compliance with sustainability criteria, VSS aim to incentivize more responsible agricultural practices, especially in tropical commodity sectors such as coffee. Although the uptake of certification has grown substantially, particularly in the coffee sector, the effectiveness of these standards in delivering both economic and ecological benefits remains contested. Empirical evidence shows mixed outcomes, with
some studies reporting modest gains for farmers or improvements in sustainable practices, and others finding little or no impact, especially beyond the farm level or across both economic and environmental dimensions. Moreover, research has disproportionately focused on third-party certifications, leaving in-house standards largely understudied. This dissertation addresses these gaps by exploring whether VSS can simultaneously support farmer livelihoods and promote ecological sustainability, contributing to a better understanding of their role in shaping more equitable and resilient food systems.
The first essay of this dissertation examines the effect of Voluntary Sustainability Standards (VSS) on agricultural productivity and forest conservation among Rwandese coffee farmers. It relies on a stratified random sample of certified and non-certified farmers collected between November 2022 and January 2023 in Western and Southern provinces. While VSS aim to promote sustainability by establishing guidelines for improved agricultural practices and environmental protection, their effectiveness in enhancing coffee production while specifically mitigating forest degradation remains unclear. This essay first estimates the effect of certifications on productivity growth, considering its two main sources: technical efficiency and technical change. Additionally, it assesses whether VSS protect vegetation health and density at the landscape level, providing empirical evidence on broader environmental effects beyond individual farms. Finally, it explores the underlying pathways through
which certification influences conservation outcomes, distinguishing between productivity-driven land-sparing effects and regulatory mechanisms enforced by sustainability standards. This essay contributes to the broader debate on how market-based sustainability initiatives impact smallholder agricultural systems, highlighting opportunities to reconcile certification programs’ economic and environmental effects.
The second essay of this dissertation examines the economic and ecological effects of Voluntary Sustainability Standards (VSS), focusing on in-house certifications (e.g., Starbucks C.A.F.E. Practices) and third-party certifications (e.g., Rainforest Alliance, Fairtrade). It relies on a stratified random sample of certified and non-certified farmers surveyed between November 2022 and January 2023 in Western and Southern provinces and a subsample of farmers for ecological data collection. While VSS have been widely adopted as a sustainability tool in global agri-food supply chains, most research has focused on third-party certifications, leaving the impact of company-led (in-house) certifications largely unexplored. This essay addresses this gap by analyzing how in-house and third-party certifications affect the coffee plot’s economic performance (gross revenue, net revenue, costs, yield) and ecological outcomes (vegetation structure and animal diversity). It also examines whether different VSS schemes help balance economic and environmental trade-offs. This essay contributes to debates on corporate
responsibility in sustainable supply chains and informs policies on aligning certification programs with rural development and conservation efforts.
The third and final essay of this dissertation examines the relationship between VSS and farm household
resilience among coffee farmers in Rwanda. It moves beyond traditional outcome indicators to assess whether VSS can help farmers sustain consistently high levels of economic, dietary, and environmental
outcomes in the face of shocks. It relies on two rounds of a stratified random sample of certified and non-certified farmers collected between November 2022 and January 2023 and November 2023 and January 2024 in Western and Southern Province. While VSS aim to promote sustainability in agricultural supply chains, their effectiveness in long-term outcomes, such as preventing farmers from falling into poverty, poor diet quality, and environmental degradation following short-term disruptions, remains unclear. This study addresses this gap by analyzing whether VSS contribute to economic, dietary, and environmental resilience, offering insights into the discussion on the effectiveness of VSS as a rural development instrument and resilience-enhancing mechanism in smallholder farming systems.2025-08-0
Prognostic Value and Dynamic Changes of Plasma Biomarkers in Alzheimer’s Disease
No full textAs Alzheimer’s disease (AD) prevalence increases, identifying reliable biomarkers for diagnosis and monitoring is essential. This study investigates plasma biomarkers for tracking AD progression, specifically comparing rapid progressive Alzheimer’s dementia (rpAD) and non-rapid progressive Alzheimer’s dementia (non-rpAD). Biomarkers, including Tau, p-Tau 181, NfL, Aβ 1-42, Aβ 1-40, and the Aβ 42/40 ratio, were assessed for associations with disease stage, clinical progression, and cerebrospinal fluid (CSF) biomarkers. Longitudinal changes were analyzed to identify potential markers for distinguishing rpAD from non-rpAD and tracking disease dynamics over time.
Participants required to have AD-typical PET or CSF findings, an MMSE score below 30, and follow-up availability. Patients were classified as rpAD or non-rpAD based on an MMSE decline of six points within one year.
Plasma and CSF samples were collected, and biomarker concentrations were analyzed using Mann-Whitney U tests, logistic regression, and linear regression. Longitudinal biomarker changes were assessed using linear mixed-effects models.
In a cohort of 98 Alzheimer's patients, 23.5% exhibited rapid progression. At baseline, no significant differences were found in plasma biomarkers between rpAD and non-rpAD, although NfL showed a significant correlation with baseline MMSE (p=0.003). Plasma Aβ 1-40, Aβ 1-42, and CSF Aβ markers showed associations. Longitudinal analysis revealed significant increases in t-Tau (p=0.025), p-Tau 181 (p<0.001), Aβ 1-40 (p<0.001), and Aβ 1-42 (p<0.001) in the overall cohort. In rpAD, t-Tau, p-Tau 181, and Aβ 1-40 increased significantly (p=0.012, p=0.014, p=0.033), while NfL rose significantly in non-rpAD patients (p=0.005). No significant longitudinal changes were observed in Aβ 1-42 or Aβ 42/40 ratio between groups.
Our findings suggest that plasma biomarkers, particularly NfL, p-Tau 181, and Aβ 1-42, may serve as non-invasive indicators for monitoring AD progression, with potential for early diagnosis and disease tracking. While no significant differences were found between the rpAD and non-rpAD cohorts at baseline, longitudinal analysis revealed distinct biomarker dynamics, supporting the idea that tau biomarkers increase following rapid disease progression, while NfL may rise earlier. These biomarkers, particularly in plasma, hold promise for aiding diagnosis and tracking disease activity in Alzheimer’s disease. The observed correlation between plasma Aβ 1-42 and Aβ ratio with their cerebrospinal fluid counterparts further supports the potential of these biomarkers in reflecting pathological changes.2025-09-3
Recording and evaluating the impacts by beavers (Castor fiber) on German forests near watercourses
No full textDeutsche Bundesstiftung UmweltKlimawandel ist eines der meist diskutierten Umweltpolitischen Themen der letzten Jahrzehnte. Die Veränderungen, die hierbei beobachtet werden, haben enormen Einfluss auf die Ökosysteme und damit auch auf ihre Bewirtschaftung. Viele Wälder in Europa sind ein hocheffektiver Naturraum, das neben einem Lebensraum für viele Arten auch als Rohstofflieferant genutzt wird. Aufgrund von Klimaveränderungen, als auch damit einhergehenden Änderungen von biotischen Risiken, muss sich die Bewirtschaftung der Wälder verändern. Als biotische Faktoren müssen bei der Veränderung dieser Ökosysteme neben Insekten und deren Risiko, auch Wildtiere berücksichtigt werden. Gerade bei der Etablierung von Waldbeständen sind Wildtiere in Form von Nagetieren und Wiederkäuern ein Problem für die Forstwirtschaft. Durch selektiven Verbiss werden selten Bäume aus den Beständen verschwinden, und somit wird die Pflanzendiversität enorm beeinflusst. In den letzten Jahrzehnten hat sich nicht nur das Klima verändert, sondern auch die Fauna. Nachdem Biber noch vor 100 Jahren eher eine Seltenheit waren, hat sich die Art durch Unterschutzstellung, als auch Wiederansiedlungen so weit erholt, dass sie heute weite Teile ihres ursprünglichen Lebensraumes besiedelt. Durch die steigende Population, den selektiven Einfluss auf Waldbestände, als auch dem klimawandel-bedingten Änderungen, kommt es somit immer mehr zu Konflikten zwischen Forstwirtschaft und Wildtieren. Ziel dieser Arbeit ist es den Einfluss von Bibern auf bewirtschaftete Wälder in Deutschland besser zu verstehen und einen Beitrag zu liefern, um zukünftig besser den Biber in ein forstwirtschaftliches Management zu integrieren.
In der generellen Einleitung wird die Geschichte und die aufkommenden Probleme mit dem eurasischen Biber (Castor fiber) in Deutschland dargestellt. Hierbei wird auf das bisherige Wissen zu selektivem Verbiss, als auch Mensch-Wildtierkonflikten eingegangen. Kapitel 1 befasst sich dann zuerst mit der Analyse verschiedener Aufnahmeverfahren zur Erfassung des Bibereinflusses auf Waldbestände. In der Vergangenheit sind viele verschiedene Designs ausprobiert worden, jedoch ist nicht bekannt, ob diese vergleichbaren Resultate liefern, oder wie sich diese im Zeitaufwand unterscheiden. Um langfristig die Auswirkungen auf Waldbestände zu verstehen, muss gewusst werden, welches Verfahren einfach umsetzbar ist, aber trotzdem sich in den Ergebnissen nicht unterscheidet. Es sind vier unterschiedliche Aufnahmeflächen in zwei Untersuchungsgebieten getestet worden. Es zeigte sich, dass sich sowohl bei den Ergebnissen als auch dem zeitlichen Aufwand zwischen den Verfahren keine Unterschiede ergeben haben. Bei näherer Betrachtung der Resultate ergab sich zusätzlich, dass eine möglichst detaillierte Abdeckung der Untersuchungsgebiete notwendig ist, da aufgrund der kleinräumigen Diversität gewässernaher Standorte sonst schnell Informationen verloren gehen und sich die Ergebnisse zu stark voneinander unterscheiden.
Im zweiten Kapitel wird sich mit der Baumartenselektion von Bibern befasst. Hierbei steht im Fokus, dass zwar Schnitte sehr gut dokumentiert sind, allerdings eine weitere Auswirkung immer wieder mit dokumentiert wird, jedoch nie wissenschaftlich analysiert wurde. Die Ringelung von Bäumen scheint bei Bibern ebenfalls selektiv zu erfolgen und mit anderen Präferenzen als der Schnitt. Ebenfalls zeigte sich, dass neben Weichlaubhölzern auch weitere forstwirtschaftlich genutzte Baumarten (z.B. Buche) von Bibern präferiert genutzt werden. Eine Abhängigkeit vom Durchmesser und Abstand ist ebenfalls zu beobachten. Die vorgefundenen Ergebnisse wurden genutzt, um diese in Kapitel 3 zu integrieren. Ausgehend von den unterschiedlichen Selektionen bei den zwei Auswirkungen von Bibern wurde in einer deutschlandweiten Studie in 13 Untersuchungsgebieten der Bibereinfluss erfasst. Hierbei konnte n 12.694 Bäume aufgenommen und analysiert werden. Es zeigte sich eindeutig, dass es enorme Unterschiede zwischen der Selektion im Hinblick auf Schnitt und Ringelung gab. Während beim Schnitt viele Weichlaubhölzer bevorzugt genutzt werden, werden bei der Ringelung beispielsweise Nadelhölzer wie Tannen oder Lärchen präferiert genutzt. In einer Modellierung des Einflusses konnte festgestellt werden, dass diese Unterschiede maßgeblich beeinflusst sind von der Baumart und dem Durchmesser. In kleinen Durchmesserbereichen werden die Baumarten eher geschnitten, während mit steigenden Durchmessern das Risiko vor Ringelung stark zunimmt.
Kapitel 4 befasst sich mit den Mensch-Wildtierkonflikten. Da Biber immer mehr mit Menschen in Kontakt geraten steigen auch die Konflikte. Um zu erfassen, inwieweit sich diese bei verschiedenen Interessengruppen unterscheiden, wurde eine Umfrage durchgeführt. Hierbei zeigte sich, dass Landwirtschaft und Forstwirtschaft den Biber deutlich negativer betrachteten als die Allgemeine Bevölkerung. Ebenfalls wurde nach akzeptablen Biberhabitaten gefragt, welche sich nach den Ergebnissen nicht in der Natur wiederfinden lassen. Somit muss für eine Reduzierung der Mensch-Biber-Konflikte weiterhin an Managementmaßnahmen gearbeitet werden.
In der allgemeinen Diskussion werden die gesammelten Ergebnisse im Gesamtkontext diskutiert. Hierzu wird ein enormer Wert auf die praktischen Managementansätze für die Forstwirtschaft, aber auch für das Bibermanagement gelegt. Insgesamt zeigen die Ergebnisse dieser Arbeit Forschungslücken auf, die hiermit teilweise geschlossen werden konnten, aber auch Anreize für zukünftige Forschungen, um ein möglichst konfliktarmes Zusammenleben mit Bibern in Deutschland gewährleisten zu können.Climate change is one of the most discussed environmental policy issues of recent decades. The changes that are being observed have an enormous impact on ecosystems and therefore also on their management. Many forests in Europe are highly effective natural systems that are used not only as a habitat for many species but also as a source of wood. Due to climate change and the associated changes in biotic risks, the management of forests must change. In addition to insects and their risk, wild animals must also be considered as biotic factors when changing these ecosystems. Wild animals in the form of rodents and ruminants are a particular problem for forestry when establishing forest stands. Selective browsing can lead to the local disappearance of certain tree species, which has a huge impact on plant diversity. In recent decades, not only the climate has changed, but also the fauna. While beavers were considered rare in Central Europe just a century ago, legal protection and reintroduction efforts have led to a strong population recovery. Today, beavers once again inhabit large parts of their original range. Due to the increasing population, the selective impact on forest stands, and the changes caused by climate change are all contributing to rising conflicts between forestry and wildlife. The aim of this work is to better understand the influence of beavers on managed forests in Germany and to contribute to better integrating beavers into forestry management in the future.
In the general introduction, the history and emerging problems with the Eurasian beaver (Castor fiber) in Germany are presented. The previous knowledge on selective browsing and human-wildlife conflicts is discussed. Chapter 1 then begins by analysing various survey methods for recording the impact of beavers on forest stands. Although numerous designs have been tested in the past, it remains unclear whether they yield comparable results or differ significantly in terms of effort required. To understand the long-term effects on forest stands, it is important to know which method is easy to implement but does not differ in the results. Four different survey areas were tested in two study areas. Results showed no significant differences in data quality or time requirements among the methods. A closer look at the results also revealed that it is necessary to cover the study areas in as much detail as possible, as otherwise information is quickly lost due to the small-scale diversity of near-water sites and the results differ too greatly from one another.
Chapter 2 deals with the selection of tree species by beavers. The focus here is on the fact that although cutting is very well documented, another impact is repeatedly documented but has never been scientifically analysed. The stripping of trees also appears to be selective in beavers and with different preferences than cutting. It has also been shown that, in addition to softwoods, other tree species used in forestry (e.g. European beech) are also favoured by beavers. A dependence on diameter and distance can also be observed. These findings were then incorporated into Chapter 3. Based on the different selections for the two impacts of beavers, the impacts of beavers were recorded in a Germany-wide study in 13 study areas. In total 12.694 trees were recorded and analysed. It was clearly shown that there were enormous differences between the selection with regard to cutting and stripping. While many softwoods are favoured for cutting, conifers such as fir or larch are preferred for stripping. Modelling of the impacts showed that these differences are significantly influenced by the tree species and diameter. In small diameter ranges, the tree species are more likely to be cut, while the risk of stripping increases sharply with increasing diameters.
Chapter 4 addresses human-wildlife conflicts. As interactions between beavers and humans increase, so do potential conflicts. To explore how perceptions vary among different stakeholder groups, a survey was conducted. Results showed that agriculture and forestry viewed beavers much more negatively than the general public. Participants were also asked about acceptable beaver habitats, which, according to the results, cannot be found in nature. Management measures must therefore continue to be developed to mitigate human-beaver conflicts.
The general discussion integrates the findings of all chapters within a broader context. Special attention is given to practical management implications for both forest management and beaver conservation. Overall, the results of this work reveal gaps in research that have been partially filled, but also provide incentives for future research to ensure that coexistence with beavers in Germany is as conflict-free as possible.2025-08-0
Investigation of speech-related changes in excitability in the primary motor cortex in adults who stutter and control subjects using transcranial magnetic stimulation
No full textTranscranial magnetic stimulation reveals a lack of reduction of intracortical inhibition of the tongue primary motor cortex in adults who stutter as compared to fluent speakers:
Original neurogenic non-syndromic stuttering is a complex, multifactorial disease of the nervous system. It is characterized by involuntary speech dysfluencies, namely repetitions and prolongations of sounds and syllables as well as blockages. All these substantially complicate fluent speaking. Despite the high lifetime incidence of up to 8%, there are comparatively few studies which target the pathomechanisms of this disease.
One mechanism relates to the modulation of orofacial cortical excitability, elucidated with transcranial magnetic stimulation (TMS) shortly before speech onset. In previous studies, fluent speakers demonstrated a time-dependent increase of excitability, which was lacking in adults who stutter (AWS). It is plausible to infer a disruption in of speech-related movement planning and articulation.
Such an excitability increase (indicated by higher amplitudes of motor-evoked potentials, MEP) can be based on two distinct forms of intra-cortical modulation, namely reduced inhibition or increased facilitation.
To probe the current state of excitatory and inhibitory interneurons wihthin the primary motor cortex, we used established conditioning – test paired-TMS measures, namely short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF) at typical interstimulus intervals.
We investigated speech-related changes in cortical excitability in 15 adults who stutter and 14 fluently speaking control subjects in the context of a speaking task and focused in particular on the phase of preparation for a speech act.
We were able to show that the contralateral MEP amplitudes in the control group did increase immediately before the start of speech, in contrast to adults who stutter. The documented increase in MEP amplitude during speech preparation in fluent speakers could be attributed to a reduced intracortical inhibition (reduced SICI). In AWS, however, there was neither a decrease in SICI nor an increase in ICF.
The results of our study show that a modulation of excitability within the primary motor tongue representation during speech preparation is missing in adults who stutter.
We postulate that the lack of increase in excitability in the preparatory phase immediately before the start of speaking which was found in adults who stutter represents an abnormal initiation of movement programs, and that it can thus be associated with some typical speech disfluencies. Previous studies already linked SICI findings to a dysfunctional cortico-striato-thalamo-cortical loop. Our finding further strenghten and substantiate this link.
In summary, our study supports the increasingly recognized theory of dysfunction in the complex processes of preparation, control and execution of speech movements in adults who stutter.2025-03-1