31325 research outputs found
Sort by
Intrinsic Water Transport in Moisture-Capturing Hydrogels
Get PDFMoisture-capturing hydrogels have emerged as attractive sorbent materials capable of converting ambient humidity into liquid water. Recent works have demonstrated exceptional water capture capabilities of hydrogels while simultaneously exploring different strategies to accelerate water capture and release. However, on the material level, an understanding of the intrinsic transport properties of moisture-capturing hydrogels is currently missing, which hinders their rational design. In this work, we combine absorption and desorption experiments of macroscopic hydrogel samples in pure vapor with models of water diffusion in the hydrogels to demonstrate the first measurements of the intrinsic water diffusion coefficient in hydrogel–salt composites. Based on these insights, we pattern hydrogels with micropores to significantly decrease the required absorption and desorption times by 19% and 72%, respectively, while reducing the total water capacity of the hydrogel by only 4%. Thereby, we provide an effective strategy toward hydrogel material optimization, with a particular significance in pure-vapor environments.Schweizerischer Nationalfonds zur F?rderung der Wissenschaftlichen Forschung
10.13039/501100001711Peer Reviewe
Evaluating the origin of Cynodontia (Synapsida, Therapsida) using 3D–Imaging Technologies
No full textComputertomographie (CT) ist eine nicht-destruktive bildgebende Methode, die in den letzten Jahren häufig bei fossilen Wirbeltierschädeln angewendet wird und Paläontologen ermöglicht bisher unbekannte interne Schädelmerkmale zu untersuchen. Letztere sind bedeutend um die Gehör- und Gehirnevolution, Gesichtsinnervation, den Zahnwechsel und den Ursprung von Endothermie entlang der Stammlinie der Säugetiere (Synapsida) zu verdeutlichen. Obwohl interne Schädelmerkmale in den letzten Jahren bei zahlreichen Therapsiden beschrieben wurden, sind sie bisher von der Wissenschaft weitestgehend vernachlässigt worden, verglichen mit den gut erforschten äußeren craniodentalen Merkmalen bei Synapsiden und wurden daher in phylogenetischen Analysen überwiegend vernachlässigt. In dieser Doktorarbeit stelle ich eine Neubewertung der der Phylogenie der Eutheriodontier (die Synapsidengruppe bestehend aus Cynodontia+Therocephalia) und eine Beurteilung der Merkmalsevolution innerhalb dieser Gruppe bereit. Der Ursprung der Cynodontier, die Ahnen der Säugetiere, stellt einen der bedeutendsten, bisher ungelösten Probleme in der Evolution der Therapsiden dar. Es ist bekannt, dass die Cynodontier am engsten mit den Therocephaliern verwandt sind, jedoch sind die genauen Verwandtschaftsverhältnisse bisher nicht eindeutig geklärt. Obwohl eine wesentliche Dichotomie in der abgeleiteten triassischen Subklade Eucynodontia in der Phylogenie der Cynodontia gut unterstützt wird, bleiben die Verwandtschaftsverhältnisse basalerer Cynodontier derzeit ungelöst. Anhand von CT Daten, die anhand eines ausgiebigen Datensatzes von Exemplaren der am frühesten bekannten (oberpermischen und untertriassischen) Cynodontier, sowie einiger ausgewählter Therocephalier und höherer (mitteltriassischer) Cynodontier (Eucynodontia) gewonnen wurden, konnte ich neue interne Schädelmerkmale dieser Tiere beschreiben. Diese Daten wurden anschließend in einem neuen, umfassenden phylogenetischen Datensatz dieser Gruppe integriert.Computed tomography (CT) is a non-destructive imaging technique that has been widely used on fossil vertebrate crania in recent years and allowed paleontologists to investigate previously-obscure endocranial data. The latter have been instrumental in elucidating patterns of ear and brain evolution, facial innervation, tooth replacement and the origin of endothermy along the mammalian stem lineage (Synapsida). Although endocranial characters have been described for various synapsids in recent years, they remain understudied compared to the well-known external craniodental features in synapsids and have been largely ignored in phylogenetic analyses. In this thesis, I provide a re-evaluation of the phylogeny of Eutheriodontia (the synapsid subclade consisting of Cynodontia+Therocephalia) and an assessment of character evolution within the group. The origin of cynodonts, the group ancestral to (and including) mammals, is one of the major outstanding problems in therapsid evolution. It is well-established that cynodonts are most closely related to Therocephalia among the major synapsid groups, but the exact nature of this relationship is uncertain. Furthermore, although a fundamental dichotomy in the derived Triassic subclade Eucynodontia is well-supported in cynodont phylogeny, the relationships of more stemward cynodonts are currently unresolved. Using CT data derived from extensive sampling of the earliest known (late Permian and Early Triassic) cynodonts and selected exemplars of therocephalians and later (Middle Triassic onwards) cynodonts (eucynodonts), I described novel aspects of the endocranial anatomy of these animals. These data were incorporated into a new, taxonomically comprehensive phylogenetic dataset of the group
Essays on Labor Economics, Dynamic Decision Making and the Role of Gender
Get PDFDas Thema dieser Arbeit ist die Heterogenität der Arbeitsmarktresultate über den Lebenszyklus und über die Geschlechter hinweg. Die Dissertation besteht aus drei unabhängigen Forschungsarbeiten (Kapitel 2-4), die sich auf komplementäre Aspekte der übergeordneten Forschungsfrage konzentrieren: Wie bestimmen Erwerbsentscheidungen das Einkommen und welche Rolle spielt die Geschlechtskomponente? Kapitel 1 führt in das Thema Lohn- und Geschlechtergefälle ein und wie diese mit Erwerbsentscheidungen zusammenhängen. Kapitel 2 analysiert Daten des Deutschen Sozio-oekonomischen Panels und der Innovationsstichprobe des Panels und untersucht die Rolle von verzerrten Erwartungen. Es setzt falsche Vorstellungen über die Arbeitsmarktvergütung von Teilzeitarbeitsjahren mit der Neigung von Frauen zur Teilnahme an Teilzeitbeschäftigung und den daraus resultierenden Einkommensverlusten aus der Beschäftigung in Beziehung. Kapitel 3 fügt die Dimension der Karriereentwicklung hinzu. Es zeigt auf, dass Arbeitserfahrung in Teilzeitbeschäftigung im Vergleich zu Vollzeitbeschäftigung mit geringeren Aufstiegsschancen einhergeht, und dass Beförderungen wichtige Quellen für Lohnsteigerungen sind. Zusammengenommen zeigt die Analyse, dass geringere Löhne durch Teilzeiterfahrung zwei Hauptkomponenten haben – einen erschwerten Karriereaufstieg in höher bezahlte Karrierestufen und ein stagnierendes Lohnwachstum unabhängig von der Karrierestufe. Das letzte Kapitel ergänzt die Diskussion über Lösungen für eine seit langem bestehende Herausforderung in der empirischen Arbeitsökonomie - die Selektionsverzerrung bei Löhnen. Es steuert einen neuartigen nicht-parametrischen Schätzer der von Selektionseffekten bereinigten kumulativen Verteilungslohnfunktion bei. In diesem Kapitel wird anhand von administrativen Daten aus Deutschland gezeigt, wie der Schätzer zur Schätzung einer selektionskorrigierten Verteilung der geschlechtsspezifischen Lohnunterschiede eingesetzt werden kann.The topic of this thesis is the heterogeneity in labor market outcomes over the life cycle and across gender. The thesis comprises three independent research papers (Chapters 2-4), which focus on complementary aspects of the overreaching research question: how do employment choices determine earnings, and what role does the gender component play? Chapter 1 introduces the topic of wage and gender gaps and how these stand related to employment choices. Chapter 2 analyzes data from the German Socio-Economic Panel and the Panel's Innovation Sample and investigates the role of biases in beliefs. It relates misperceptions about the labor market remuneration of years spent working part-time to the women's propensity to engage in part-time employment and the consequent earnings losses. Chapter 3 adds the dimension of career development. It posits that part-time penalties in experience accumulation decrease the chances of being promoted and that promotions are important sources of wage growth. In sum, the analysis shows that part-time wage penalties have two key components - hampered career progression to higher-paying career levels and stagnating wage growth regardless of career level. The final chapter adds to the discussion on solutions to a longstanding challenge in empirical labor economics posed by the selection bias in wages observed by econometricians. It contributes a novel non-parametric estimator of the selection-free cumulative distribution wage function. This chapter leverages administrative data records from Germany to show how the estimator can be applied in estimating a selection-corrected distribution of gender wage gaps
Increasing Safety: A Survey of Open Greenspace Usage during and after the Pandemic in Belgrade, Serbia
Get PDFCOVID-19 has severely affected almost every aspect of our everyday lives, especially the use of open greenspace (OGS) in urban settings, which has proven to have a significant role in increasing overall public health and well-being. Hence, the restricted usage of these spaces should be reconsidered. This research aims to analyze the sensitive nature of OGS usage (1) during the pandemic from the perspective of users’ perceived safety and (2) after the pandemic to assess the possible long-term effects. Additionally, this research proposed that location-tracking mobile applications could lead to an increased frequency of OGS visits. The methodology contains detailed background research and two surveys. One survey was conducted during the pandemic in 2020 (sample size n = 412) and was repeated post-pandemic in 2024 (sample n = 451). The 2020 questionnaire A includes questions about the duration, frequency, and activities of OGS usage while focusing on the perceived safety and possibilities of monitoring OGS visits using mobile apps. The 2024 survey represents the continuation of the 2020 survey, focusing on the post-pandemic state of OGS. The statistical analysis is separated into a descriptive data analysis, various χ2 independence tests and a machine learning safety prediction. The results indicate how COVID-19 could affect OGS usage and how app-related physical safety enhancements during the pandemic cannot be statistically distinguished from those in the post-pandemic period. Although the interest in location-tracking mobile applications has statistically decreased in 2024, the majority of the total 863 participants stated that applications could increase their feeling of perceived safety. The added value of this research is that it considers age and gender roles in analyzing OGS usage in the context of a pandemic.This research received no external funding.Peer Reviewe
A Flexible and Efficient Approach to Missing Transverse Momentum Reconstruction
Get PDFThe article processing charge was funded by the Open Access Publication Fund of Humboldt-Universität zu Berlin.Missing transverse momentum is a crucial observable for physics at hadron colliders, being the only constraint on the kinematics of “invisible” objects such as neutrinos and hypothetical dark matter particles. Computing missing transverse momentum at the highest possible precision, particularly in experiments at the energy frontier, can be a challenging procedure due to ambiguities in the distribution of energy and momentum between many reconstructed particle candidates. This paper describes a novel solution for efficiently encoding information required for the computation of missing transverse momentum given arbitrary selection criteria for the constituent reconstructed objects. Pileup suppression using information from both the calorimeter and the inner detector is an integral component of the reconstruction procedure. Energy calibration and systematic variations are naturally supported. Following this strategy, the ATLAS Collaboration has been able to optimise the use of missing transverse momentum in diverse analyses throughout Runs 2 and 3 of the Large Hadron Collider and for future analyses.Peer Reviewe
Quantifying intra‐ and inter‐annual dynamics of river‐floodplain connectivity and wetland inundation with remote sensing and wavelet analysis
Get PDFWe used imagery from remote sensing (FORCE Time Series Analysis submodule (combining Landsat and Sentinel-2 imagery) to derive spatially distributed times series (8 years) of NDWI data to infer patterns of floodplain inundation and river-floodplain connectivity in two contrasting polders in the Lower Oder Valley National Park. The upstream Polder A (14.4 km2) was extensively flooded for prolonged periods most winters. Wavelet analysis showed that this strong seasonality was primarily driven by winter water levels in the river Oder that could enter and leave the polder through two opened floodgates. Subsequent drainage was slow and aided by a pumping station. Inundation of the downstream Polder 10 (17.7km2) was lower and had less marked seasonality. This reflected the impact of flood attenuation by storage in Polder A upstream, but also the greater connectivity (via 10 floodgates) to the Oder and a functional network of channels, which facilitated rapid drainage after flood peaks. In Polder A, secondary periods of transient inundation could also occur in response to local intense summer rainfall. Wavelet analysis also showed that groundwater recharge in and around Polder A is primarily induced by floodwater, whilst Polder 10 also reflects the influence of local rainfall-driven recharge. The flood regimes of the two polders showed marked inter-annual variation, largely dependent on flows from the upper Oder catchment. Understanding these patterns and processes of inundation is important for both managing flows and sustaining valuable wetland habitats within the National Park. Given projected climate change in eastern Europe and possible management alterations to the flow regime of the Oder, the potential implications for these habitats needs urgent attention.Leibnitz Association GermanyChina Scholarship Council
http://dx.doi.org/10.13039/501100004543Einstein Stiftung Berlin
http://dx.doi.org/10.13039/501100006188Berlin University Alliance
http://dx.doi.org/10.13039/501100021727Peer Reviewe
Jevakuacija i zhizn' za rubezhom: istorii ukrainskih bezhenok
No full textС началом войны в Украине многие люди покинули свои дома и нашли убежище в других странах. Интервьюируемые беженцы осознают, что эвакуация – это лишь одна часть более широкого процесса, многие их родные по-прежнему остаются в зоне боевых действий. Используя мотивный анализ, мы смотрим, в каких аспектах проявляется эмоциональность, стараясь зафиксировать память о недавних трагических событиях.With the onset of the war in Ukraine, many people fled their homes and sought refuge in other countries. Interviewed refugees are aware that evacuation is just one part of a broader process, as many of their relatives remain in the conflict zone. Employing a motivational analysis, we ex-amine the emotional aspects, endeavoring to document the memory of recent tragic events
Bacterial Chaperone Domain Insertions Convert Human FKBP12 into an Excellent Protein-Folding Catalyst—A Structural and Functional Analysis
Get PDFMany folding enzymes use separate domains for the binding of substrate proteins and for the catalysis of slow folding reactions such as prolyl isomerization. FKBP12 is a small prolyl isomerase without a chaperone domain. Its folding activity is low, but it could be increased by inserting the chaperone domain from the homolog SlyD of E. coli near the prolyl isomerase active site. We inserted two other chaperone domains into human FKBP12: the chaperone domain of SlpA from E. coli, and the chaperone domain of SlyD from Thermococcus sp. Both stabilized FKBP12 and greatly increased its folding activity. The insertion of these chaperone domains had no influence on the FKBP12 and the chaperone domain structure, as revealed by two crystal structures of the chimeric proteins. The relative domain orientations differ in the two crystal structures, presumably representing snapshots of a more open and a more closed conformation. Together with crystal structures from SlyD-like proteins, they suggest a path for how substrate proteins might be transferred from the chaperone domain to the prolyl isomerase domain.Fonds der Chemischen Industrie and the Deutsche ForschungsgemeinschaftPeer Reviewe
The Tempo-spatial Conflicts of Platform Mediation
Get PDFDie aktuellen Debatten im Feld der Digitalen Geographie und der Arbeitsgeographie zeigen, dass digitale Plattformen nicht neutrale Vermittelnde von digitalen Interaktionsmöglichkeiten sind, die in einem entfernten digitalen Cyberspace operieren. Stattdessen beruht die Funktionalität digitaler Plattformen auf zeitintensiven Arbeitspraktiken, die von den Nutzenden der Plattform zwischen digitalen und sozial-materiellen Räumen durchgeführt und von den Plattformunternehmen gesteuert werden.
Vor diesem Hintergrund besteht das übergeordnete Forschungsziel der Dissertation darin, die Räume und die Zeitlichkeit zu erforschen, die von dem Plattformunternehmen und den Nutzenden gemeinsam, aber dennoch konfliktreich konstruiert werden. Es wird eine Perspektive auf die Produktion von plattformvermittelten Zeiträumen und deren Friktionen herausgearbeitet. Die alltägliche Aushandlung von digitalen Zeit-Räumen wird als Zeit-Raum-Reibung entwickelt.
Um die plattformgestützte Vermittlung von Zeit und Raum und ihre Reibungen empirisch aufzuarbeiten, kommt das Instrumentarium einer digitalen Ethnographie zum Einsatz. Dieser Ansatz ermöglicht die detailreiche Untersuchung der Wechselbeziehung von Plattformoberflächen, Nutzungspraktiken und Erfahrungen in einem spezifischen Fall. Es wird die Arbeit selbständiger Berliner Modeunternehmer:innen analysiert, die zwischen Offline-Räumen und der digitalen Plattform Instagram erfolgt.
Die Dissertation unterstreicht die Verbindung von Perspektiven der Digitalen Geographie und der Arbeitsgeographie. So können kritische Einblicke in die tägliche Arbeit, die Aushandlungen und die Machtverhältnisse gewonnen werden, die der Ausgestaltung von Zeit und Raum im digitalen Kapitalismus zugrunde liegen. Schließlich zeigt die Dissertation, wie qualitative Online- und Offline-Methoden miteinander verschränkt werden können, um eine detaillierte, fallspezifische Analyse der Produktion digital vermittelter Zeiträume und ihrer Aushandlungsprozesse offenzulegen.Current digital and labor geography debates reveal that daily spaces represent a web of interconnected online and offline spaces. This implies that not only has the web become platformized, but work practices and daily tempo-spatial relations have also been structured by the spaces of digital platforms and their models of value capture. Therefore, digital platforms are not merely asset-light matchmakers operating in distant digital cyberspace. They are deeply embedded in the fabric of daily life.
The dissertation aims to uncover the platform mediation of time and space and its frictions. The concept of platform-mediated timespace suggests that platform interfaces, human practices, and socio-material relations intricately and seamlessly shape the configuration of space and the perception of time. Platform-mediated time and space are negotiated and contested between platform capitalism and platform labor. This contested production of digitally mediated timespace is defined as timespace friction.
Methodologically, a digital ethnography is employed to investigate the interplay between platform interfaces, user practices, and experiences in a specific case of platform mediation. The study analyzes independent fashion entrepreneurs in Berlin who work between offline spaces and the digital platform Instagram.
Against this backdrop, the dissertation urges the field of digital geography to move beyond notions of augmented digital space. Instead, in combination with a labor geography perspective, it suggests gaining more critical insights into the daily work, negotiations, and power relations underlying the creation of platform-mediated timespace in digital capitalism.
Finally, the dissertation advocates for the application of mediated methods in researching mediated timespaces. It demonstrates how a detailed, case-specific digital ethnography can provide insights into the production of digitally mediated spacetime and its struggles
Tail Risk Protection via reproducible data-adaptive strategies
Get PDFDie Dissertation untersucht das Potenzial von Machine-Learning-Methoden zur Verwaltung von Schwanzrisiken in nicht-stationären und hochdimensionalen Umgebungen. Dazu vergleichen wir auf robuste Weise datenabhängige Ansätze aus parametrischer oder nicht-parametrischer Statistik mit datenadaptiven Methoden. Da datengetriebene Methoden reproduzierbar sein müssen, um Vertrauen und Transparenz zu gewährleisten, schlagen wir zunächst eine neue Plattform namens Quantinar vor, die einen neuen Standard für wissenschaftliche Veröffentlichungen setzen soll. Im zweiten Kapitel werden parametrische, lokale parametrische und nicht-parametrische Methoden verglichen, um eine dynamische Handelsstrategie für den Schutz vor Schwanzrisiken in Bitcoin zu entwickeln. Das dritte Kapitel präsentiert die Portfolio-Allokationsmethode NMFRB, die durch eine Dimensionsreduktionstechnik hohe Dimensionen bewältigt. Im Vergleich zu klassischen Machine-Learning-Methoden zeigt NMFRB in zwei Universen überlegene risikobereinigte Renditen. Das letzte Kapitel kombiniert bisherige Ansätze zu einer Schwanzrisikoschutzstrategie für Portfolios. Die erweiterte NMFRB berücksichtigt Schwanzrisikomaße, behandelt nicht-lineare Beziehungen zwischen Vermögenswerten während Schwanzereignissen und entwickelt eine dynamische Schwanzrisikoschutzstrategie unter Berücksichtigung der Nicht-Stationarität der Vermögensrenditen. Die vorgestellte Strategie reduziert erfolgreich große Drawdowns und übertrifft andere moderne Schwanzrisikoschutzstrategien wie die Value-at-Risk-Spread-Strategie. Die Ergebnisse werden durch verschiedene Data-Snooping-Tests überprüft.This dissertation shows the potential of machine learning methods for managing tail risk in a non-stationary and high-dimensional setting. For this, we compare in a robust manner data-dependent approaches from parametric or non-parametric statistics with data-adaptive methods. As these methods need to be reproducible to ensure trust and transparency, we start by proposing a new platform called Quantinar, which aims to set a new standard for academic publications. In the second chapter, we dive into the core subject of this thesis which compares various parametric, local parametric, and non-parametric methods to create a dynamic trading strategy that protects against tail risk in Bitcoin cryptocurrency. In the third chapter, we propose a new portfolio allocation method, called NMFRB, that deals with high dimensions thanks to a dimension reduction technique, convex Non-negative Matrix Factorization. This technique allows us to find latent interpretable portfolios that are diversified out-of-sample. We show in two universes that the proposed method outperforms other classical machine learning-based methods such as Hierarchical Risk Parity (HRP) concerning risk-adjusted returns. We also test the robustness of our results via Monte Carlo simulation. Finally, the last chapter combines our previous approaches to develop a tail-risk protection strategy for portfolios: we extend the NMFRB to tail-risk measures, we address the non-linear relationships between assets during tail events by developing a specific non-linear latent factor model, finally, we develop a dynamic tail risk protection strategy that deals with the non-stationarity of asset returns using classical econometrics models. We show that our strategy is successful at reducing large drawdowns and outperforms other modern tail-risk protection strategies such as the Value-at-Risk-spread strategy. We verify our findings by performing various data snooping tests