University of Kaiserslautern
KLUEDO Publication Server of University of Kaiserslautern-Landau (RPTU)Not a member yet
6017 research outputs found
Sort by
Die (Ohn-)Macht der institutionellen Unternehmung
Get PDFDie Gesellschaft befindet sich im kontinuierlichen Wandel. Dennoch fehlt bisher ein tiefergehendes Verständnis darüber, wie dieser entsteht. Als Erklärungsansatz führen Neoinstitutionalist*innen vor diesem Hintergrund das Konzept des institutionellen Unternehmer*innentums an. Die Forschungen hierzu unterteilen sich zum einen in eine akteur*innenzentrierte Perspektive, welche die Bestrebungen einzelner Akteur*innen fokussiert, und zum anderen in eine prozesszentrierte Sichtweise, welche Wandel als kollektiven Prozess inkrementeller Veränderungen durch viele Akteur*innen betrachtet. Durch die überwiegend isolierte Betrachtung beider Forschungsströmungen bleibt die Frage nach der (Ohn-)Macht einzelner institutioneller Unternehmer*innen, diesen Wandel zu beeinflussen jedoch unbeantwortet.
Um beide Perspektiven miteinander zu kombinieren, wurde die Einführung einer auf künstlicher Intelligenz basierenden Wissensmanagementlösung in das organisationale Feld des technischen Kundenservices über einen Beobachtungszeitraum von über 30 Jahren rekonstruiert und mithilfe einer temporal-bracketing-Strategie in Phasen relativer Kontinuität unterteilt. Innerhalb dieser Phasen konnten durch teilnehmende Beobachtungen, semi-strukturierte Interviews und die Analyse von Sekundärdaten sowohl prozess- als auch akteur*innenzentrierte Einflüsse auf den Wandel identifiziert und kontextualisiert werden.
Aus einer akteur*innenzentrierten Sichtweise konnten so insgesamt fünf Freiheitsgrade institutionellen Unternehmer*innentums abgeleitet werden. Aus der prozess-zentrierten Perspektive konnte zudem die Koexistenz von Diffusions- und Übersetzungsprozessen bei der Ausbreitung der Institution im organisationalen Feld nachgewiesen und aufgezeigt werden, dass das Verhältnis beider Ausbreitungsprozesse zueinander die Geschwindigkeit der Ausbreitung beeinflussen kann. Abschließend entwickelt die vorliegende Arbeit einen konzeptionellen Rahmen zur Beurteilung der (Ohn-)Macht institutionellen Unternehmer*innentums in Form eines Wechselspiels von Anpassung an das organisationale Feld und Gestaltung dieses Feldes durch institutionelle Unternehmer*innen und führt so beide Forschungsströmungen zusammen
Majority English of Heritage Speakers
Get PDFThis dissertation focuses on heritage speakers - bilinguals who grow up speaking two languages: the language of their family, or the heritage language, and the main language of the larger society, or the majority language. We examine the majority language English of German, Greek, Russian and Turkish HSs in the USA and compare it to the English of monolingually-raised English speakers. The main conclusions are that heritage speakers exhibit a significant number of similarities in their majority English compared to monolingually-raised English speakers. The few observed differences do not point to qualitative shifts in the use of English by heritage speakers, but rather to slight quantitative dissimilarities in the frequencies of selected phenomena across registers. Overall, we concluded that heritage language maintenance did not have long-term negative consequences for the majority language of heritage speakers in our sample
Heterogeneous single-site catalysts based on multi-component metal-organic frameworks (MOFs) for sustainable oxidation reactions in the liquid phase
Get PDFMetal-organic frameworks (MOFs) have gained increasing attention in the last four decades due to their versatility and unique properties. They are often used as catalysts because they combine advantageous properties of both heterogeneous and homogeneous catalysts. Noble metals are very active in catalysis, but they are expensive, sometimes toxic to the environment and very rare. Therefore, the demand for the substitution of noble metals by commonly available metals such as iron or cobalt is of interest. The complexity and versatility of MOF materials is further enhanced by the use of mixed-linker and mixed-metal approaches or post-synthetic modification reactions.
The aim of this PhD project was to synthesize and characterize MOF-based catalysts which contain Co and Fe and to test the resulting materials in the liquid phase oxidation reaction of alcohols. In the first part of this work, mixed-metal CPO-27(Co,Fe) with three different metal ratios and two different spatial distributions were prepared. The spatial distributions of the metals were either statistically distributed or a core-shell orientation. The resulting catalysts were characterized by powder X-ray diffraction, thermogravimetric analysis and ICP-OES analysis. The results confirmed that the catalysts were highly porous, corresponded to the CPO 27 structure and that the amounts of metals were close to the desired ratios. The materials were then tested in oxidation reactions of benzyl alcohol and 1-phenylethanol. For the parameter optimization, the highly active monometallic CPO-27(Co) catalyst was used and parameters such as temperature and the amount of catalyst, substrate or oxidant (air) were investigated. Bimetallic CPO-27(Co,Fe) catalysts were then tested with the optimized parameters and both conversion and selectivity were compared to the monometallic CPO 27(Co) reference. In general, the rare and expensive cobalt can be partially replaced by cheap but inactive iron without affecting the catalytic activity and in some cases, the distribution of the metals in the MOF lattice have an effect on the catalytic performance.
In the second part of this work, the previously synthesized CPO-27(Co,Fe) catalysts were thermally decomposed in an inert atmosphere to obtain metal species which are encapsulated in a porous carbonaceous matrix via the so called MOF-mediated synthesis. The decomposition was expected to result in unique materials that could not be synthesized by any other route. The resulting materials were characterized by powder X-ray diffraction, N2 physisorption and ICP-OES analysis. The characterization revealed differences between materials prepared from statistically distributed and core-shell-structured CPO-27(Co,Fe). These catalysts were also tested in the oxidation of benzyl alcohol and compared not only within this series but also with the CPO-27 precursors, showing that in some cases the thermally decomposed materials were even more catalytically active than their MOF precursors.
In the last part of this thesis, Co,Fe DUT-5-based catalysts with core-shell structure and statistical distribution, respectively, were synthesized. The first step was to prepare a DUT-5-based framework. For the statistically distributed material, 4,4'-biphenyldicarboxylate, 2,2' bipyridine-5,5'-dicarboxylate and 2-amino-4,4'-biphenyldicarboxylate linkers were mixed with an aluminum salt precursor. The 2,2'-bipyridine-5,5'-dicarboxylate linkers were then used to directly immobilize cobalt ions. The amine-functionalized linkers were post-synthetically modified with salicylaldehyde and the resulting chelating groups were finally used for the immobilization of iron ions. The core-shell backbone consisted of 4,4'-biphenyldicarboxylate and 2,2'-bipyridine-5,5'-dicarboxylate in the core. The first shell contained only unfunctionalized 4,4' biphenyldicarboxylate and the outer shell consisted of a mixture of 2 amino-4,4'-biphenyldicarboxylate and 4,4'-biphenyldicarboxylate linkers. The post-synthetic reactions were then performed analogously to the statistically distributed materials: (1) cobalt immobilization at the bipyridine linkers, (2) insertion of chelating groups at the amine linkers and (3) iron immobilization. All materials were thoroughly characterized after each synthesis step using powder X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, N2 physisorption and ICP-OES analysis. The linker ratios were calculated by 1H NMR of diluted samples. The results confirmed the formation of a porous material with a DUT-5 structure, but the spatial distribution could not be confirmed unambiguously by the methods used. Both materials were tested, together with a monometallic DUT-5 BPyDC(Co) reference, in oxidation reactions cinnamyl alcohol. The results showed significant differences between the statistically distributed and core-shell catalysts, providing evidence for the difference in spatial orientations and the symergistic effects of the two metals.
In summary, novel MOF materials containing Co and Fe were synthesized, characterized and tested in oxidation reactions of primary and secondary alcohols under aerobic conditions. The results confirmed that in some cases a part of rare cobalt could be replaced by cheap and widely available iron without decreasing the catalytic activity and selectivity. In addition, the spatial distribution of the metals can have a direct and massive influence on the catalytic properties and therefore, a thorough characterization is a very important part of the synthesis process
MitoTraP: Compromised mitochondria trap mitoribosomal precursor proteins in the intermembrane space
Get PDFMost mitochondrial proteins are synthesized in the cytosol and subsequently have to be imported into mitochondria. An N-terminal mitochondrial targeting signal (MTS) guides these mitochondrial precursor proteins into the matrix. However, 25% of all mitoribosomal proteins (MRPs) do not have a typical MTS but use an internal targeting information instead. In this study, the model protein Mrp17 (bS6m) was used to investigate the import pathway of such a protein without a typical MTS. Despite its internal targeting signal, Mrp17 still is efficiently imported via the typical presequence pathway into the mitochondrial matrix. Like other matrix proteins, the translocation of Mrp17 depends on the TOM and TIM23 complex. Surprisingly, Mrp17 has a different energy dependency for the translocation compared to other matrix proteins. On one side, Mrp17 is highly dependent on the membrane potential which is built at the inner membrane by the respiratory chain. On the other side, the import motor with its core component the ATP-dependent mtHsp70 is not needed for the translocation of Mrp17 across the OM and is only needed to pass the inner membrane. This differs from other matrix proteins, which accumulate in the cytosol if the import motor is defective. Thereby low ATP levels, depletion of the import motor, or inhibition of the ATP synthase traps Mrp17 but also other MRPs in the intermembrane space (IMS). This Mitochondrial Triage of Precursor proteins (MitoTraP) is not simply the result of a general translocation block at the level of the inner membrane. Rather, MitoTraP specifically directs a defined subgroup of matrix proteins into the IMS, most of which are constituents of the mitochondrial ribosome. Due to the lack of rRNA in the IMS trapped MRPs will likely be degraded. Since non-imported Mrp17 interacts with assembly factors of the 90S pre-ribosome in the nucleolus, MitoTrap presumably acts as a safeguard mechanism by separating MRPs from the cytosolic ribosomal assembly machinery
VoroCrack3d: An annotated semi-synthetic 3d image data set of cracked concrete
Get PDFSustainability is an important topic in the field of materials science and civil engineering. In particular, concrete, as a building material, needs to be of high quality to ensure its durability. Damage and failure processes such as cracks in concrete can be evaluated non-destructively by micro-computed tomography. Cracks can be detected in the images, for example via edge-detection filters or machine learning models. To study the goodness, robustness, and generalizability of these methods, annotated 3d image data are of fundamental importance. However, data acquisition and, in particular, its annotation is often tedious and error-prone. To overcome data shortage, realistic data can be synthesized. The data set described in this article addresses the lack of freely available annotated 3d images of cracked concrete. To this end, seven concrete samples without cracks were scanned via micro-computed tomography. Realizations of a dedicated stochastic geometry model are discretized to binary images and morphologically transformed to mimic real crack structures. These are superimposed on the concrete images and simultaneously yield the label images that distinguish crack from non-crack regions. The data set contains 1 344 of such image pairs and includes a large variety of crack structures. The data set may be used for training machine learning models and for objectively testing crack segmentation methods
Indication of critical scaling in time during the relaxation of an open quantum system
Get PDFNear continuous phase transitions, universal power-law scaling, characterized by critical exponents, emerges. This behavior reflects the singular responses of physical systems to continuous control parameters like temperature or external fields. Universal scaling extends to non-equilibrium dynamics in isolated quantum systems after a quench, where time takes the role of the control parameter. Our research unveils critical scaling in time also during the relaxation dynamics of an open quantum system. Here we experimentally realize such a system by the spin of individual Cesium atoms dissipatively coupled through spin-exchange processes to a bath of ultracold Rubidium atoms. Through a finite-size scaling analysis of the entropy dynamics via numerical simulations, we identify a critical point in time in the thermodynamic limit. This critical point is accompanied by the divergence of a characteristic length, which is described by critical exponents that turn out to be unaffected by system specifics
Canonical and non-canonical integrin-based adhesions dynamically interconvert
Get PDFAdhesions are critical for anchoring cells in their environment, as signaling platforms and for cell migration. In line with these diverse functions different types of cell-matrix adhesions have been described. Best-studied are the canonical integrin-based focal adhesions. In addition, non-canonical integrin adhesions lacking focal adhesion proteins have been discovered. These include reticular adhesions also known as clathrin plaques or flat clathrin lattices, that are enriched in clathrin and other endocytic proteins, as well as extensive adhesion networks and retraction fibers. How these different adhesion types that share a common integrin backbone are related and whether they can interconvert is unknown. Here, we identify the protein stonin1 as a marker for non-canonical αVβ5 integrin-based adhesions and demonstrate by live cell imaging that canonical and non-canonical adhesions can reciprocally interconvert by the selective exchange of components on a stable αVβ5 integrin scaffold. Hence, non-canonical adhesions can serve as points of origin for the generation of canonical focal adhesions
Revealing hidden spin polarization in centrosymmetric van der Waals materials on ultrafast timescales
Get PDFOne of the key challenges for spintronic and quantum technologies is to achieve active control of the spin angular momentum of electrons in nanoscale materials on ultrafast, femtosecond timescales. While conventional ferromagnetic materials and materials supporting spin texture suffer both from conceptional limitations in miniaturization and inefficiency of optical and electronic manipulation, non-magnetic centrosymmetric layered materials with hidden spin polarization may offer an alternative pathway to manipulate the spin degree of freedom by external stimuli. Here we demonstrate an approach for generating transient spin polarization on a femtosecond timescale in the otherwise spin-unpolarized band structure of the centrosymmetric 2H-stacked group VI transition metal dichalcogenide WSe2. Using ultrafast optical excitation of a fullerene layer grown on top of WSe2, we trigger an ultrafast interlayer electron transfer from the fullerene layer into the WSe2 crystal. The resulting transient charging of the C60/WSe2 interface leads to a substantial interfacial electric field that by means of spin-layer-valley locking ultimately creates ultrafast spin polarization without the need of an external magnetic field. Our findings open a novel pathway for true optical engineering of spin functionalities such as the sub-picosecond generation and manipulation of ultrafast spin currents in 2D heterostructures
Decoding the genetic program of micronucleus formation: linking chromosomal instability to human disease
Get PDFA recent study by Adams and colleagues published in Nature unveiled more than one hundred genes that are involved in micronucleus formation,1 which is a biomarker for genomic instability and associated with aging, cancer, and other disorders.2 As an outstanding achievement, the authors identified DSCC1 (DNA Replication And Sister Chromatid Cohesion 1) as a critical gene protecting against early developmental defects, genomic instability, reduced proliferative capacity, cohesinopathy-related phenotypes, and tumor development in vivo
Chemical short-range order increases the phonon heat conductivity in a refractory high-entropy alloy
Get PDFWe study the effects of the chemical short-range order (SRO) on the thermal conductivity of the refractory high-entropy alloy HfNbTaTiZr using atomistic simulation. Samples with different degrees of chemical SRO are prepared by a Monte Carlo scheme. With increasing SRO, a tendency of forming HfTi and TiZr clusters is found. The phonon density of states is determined from the velocity auto-correlation function and chemical SRO modifies the high-frequency part of the phonon density of states. Lattice heat conductivity is calculated by non-equilibrium molecular dynamics simulations. The heat conductivity of the random alloy is lower than that of the segregated binary alloys. Phonon scattering by SRO precipitates might be expected to reduce scattering times and, therefore, decrease thermal conductivity. We find that, in contrast, due to the increase of the conductivity alongside SRO cluster percolation pathways, SRO increases the lattice heat conductivity by around 12 %. This is expected to be a general result, extending to other HEAs