Christian Doppler Laboratory for Thermoelectricity

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    38038 research outputs found

    Revealing Ultrafast Population Transfer between Nearly Degenerated Electronic States

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    The response of a molecule to photoexcitation is governed by the coupling of its electronic states. However, if the energetic spacing between the electronically excited states at the Franck–Condon window becomes sufficiently small, it is infeasible to selectively excite and monitor individual states with conventional time-resolved spectroscopy, preventing insight into the energy transfer and relaxation dynamics of the molecule. Here, we demonstrate how the combination of time-resolved spectroscopy and extensive surface hopping dynamics simulations with a global fit approach on individually-excited ensembles overcomes this limitation and resolves the dynamics in the n3p Rydberg states in acetone. Photoelectron transients of the three closely spaced states n3px , n3py , and n3pz are used to validate the theoretical results, which in turn allow retrieving a comprehensive kinetic model describing the mutual interactions of these states for the first time

    Vanadium and its isotope composition of river water and seawater: Analytical improvement and implications for vanadium isotope fractionation

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    Investigation of redox variations in recent and paleo-oceans has been of particular scientific interest to elucidate the rise and variations of the atmospheric oxygen level by analyses of isotopic signatures of redox-sensitive elements like Fe, Mo, and U. Vanadium is another redox-sensitive metal that has become the target of stable isotope research during the last decade. Research of the oceanic V cycle revealed a rather complex interplay of riverine V as a major V source to the oceans on one side with V deposition in sediments and at hydrothermal vents as major sinks on the other. The balance between these major V pools is sensitive to the ocean water oxygen level and chemistry. The current data set of stable V isotope signatures of seawater is still very small, but indicates already subtle variation of the V isotope signatures in the marine environment. However, the V isotopes of marine sediments and particularly the riverine V isotope composition of dissolved and particulate V, i.e. the major source of V in modern marine environments, has not been constrained at all so far. In this study, we present a new method for efficient V separation from seawater that allows multiple analyses of the V isotope composition of a single sample. To separate V from large amounts (volume ≥2 L) of seawater samples, we employ the Bio-Rad® Chelex-100 resin and conventional cation and anion resins to yield a high V recovery of ≥90% from an UV-irradiated sample. Non-irradiated samples were marked by lower V recovery rates of ca. 75%, which was also observed in earlier studies. Further tests however revealed that even such reduced V yields do not incur significant V isotope fractionation within analytical uncertainty. Our δ51VAA value of +0.27‰ ±0.14 (2s.d., n = 3) for the NASS-6 seawater reference solution perfectly matched earlier results. In addition, seawater collected in the Wadden Sea at the German North Sea coast is marked by a δ51VAA signature of around +0.02‰ ±0.19 (2s.d., n = 17), which is slightly lower than those of the great oceans, and may be related to an influx of river water, bioactivity, or a tide-induced V mobilization. To characterize the V isotope composition of the major V source to the oceans, we determined for the first time V isotope signatures of 13 selected rivers (dissolved and particulate fractions of source water, tributary rivers, and the Yangtze River) in the Yangtze River Basin, China. A large variation of dissolved V (ca. 0.07 to 6.0 μg/L) and particulate-bound V (ca. 0.03 to 17 μg/L) was found for the sample suite. The obtained δ51VAA values of the dissolved V pool span a range of −0.76‰ (±0.18; 2s.d.) to −0.10‰ (±0.22, 2s.d.), whereas particulate-bound V extends to lower δ51V signatures between −2.13‰ (±0.30, 2s.d.) and −0.11‰ (±0.11, 2s.d.). Notably, dissolved V from the river sources and small tributaries scatters between ca. −0.4‰ to −0.7‰, and agrees well with the predicted average δ51VAA value of −0.6‰ ±0.3 for continental run-off. For the lower Yangtze River, however, the dissolved δ51VAA signatures increase from the Three-Gorges Dam towards the estuary from −0.76‰ to −0.10‰, suggesting V isotope fractionation due to adsorption to abundant particulate Fe oxides, but may also reflect an input of anthropogenic V. The low δ51VAA of particulate V largely follow this trend, and thus indicate ongoing V isotope fractionation during riverine V transport to the ocean. Our first results of stable V isotope investigation of river waters show that V isotope signatures can indeed carry their host rock signature, but are also sensitive to adsorption-driven fractionation in oxidized environments. The latter strongly depends, as predicted from earlier theoretical calculations, on the presence of particulate Fe-(oxyhydr)oxides and highlights gradual V isotope fractionation during riverine V transport to the ocean

    Regional variations in fluid formation and metal sources in MVT mineralization in the Pennine Orefield, UK: Implications from rare earth element and yttrium distribution, Sr-Nd isotopes and fluid inclusion compositions of hydrothermal vein fluorites

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    The Pennine Orefield is one of the most important ore fields for Pb-Zn-Ba-F mineralization in Great Britain. It is subdivided into the Northern Pennine Orefield (NPO), consisting of the Alston and Askrigg Blocks, and the Southern Pennine Orefield (SPO). The Alston Block is underlain by the early Devonian Weardale Granite and the Askrigg Block by the coeval Wensleydale Granite. The potential relationship between the batholiths and the mineralization is a matter of debate. We here studied the rare earth elements and Y (REY) geochemistry, Sr-Nd isotopes and fluid inclusion (FI) compositions of fluorites from the two structural blocks in the NPO and found that the fluorite mineralization in these blocks differ substantially. The REY in Askrigg fluorites show features that are characteristic for leaching of adjacent Lower Carboniferous limestones. In contrast, Alston fluorites have significantly higher REY concentrations, lack REYSN limestone signatures and show a decoupling of redox-sensitive Eu from its trivalent REY ‘neighbours’. Neodymium isotopes indicate a similar crustal source of REY in both blocks, but higher REY concentrations and lower Y/Ho ratios suggest Lower Carboniferous shales as potential REY source in the Alston Block. The fluids that precipitated the Alston fluorites experienced temperatures > 250 °C prior to mineral formation, as evidenced by Eu geothermometry. Fluorite formation, however, occurred at much lower temperatures, as suggested by homogenization temperatures in FI, that fall within ranges of 105–159 °C in Alston and 99–160 °C in Askrigg fluorites. Mineralization of the Mississippi-Valley Type usually lack association with igneous activity. We show that some of the fluids responsible for the NPO mineralization were influenced by magmatic sources. The REY systematics in Alston fluorites may be linked to an interaction of the Permian-age Whin Sill dolerite with the basement granite, which heated fluids and focussed fluid flow into the overlying sedimentary rocks. In the Askrigg Block, where such a dolerite intrusion was not described, fluorites lack any positive EuSN anomalies, indicating that these fluids had never been subjected to temperatures exceeding 200–250 °C

    General Trajectory Surface Hopping Method for Ultrafast Nonadiabatic Dynamics

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    Nonadiabatic dynamics is a central concept in the study of ultrafast chemical and physical processes, especially light-induced processes. One method to computationally study such processes is provided by the "Surface Hopping including ARbitrary Couplings" (SHARC) approach, which we present here. We focus on a general description of the involved approximations, and the strengths and limitations of the approach. We also discuss the choice of electronic structure method and give an overview over techniques to analyze the trajectories obtained in the simulations

    Performing Black British Memory: Kat François’s Spoken-Word Show Raising Lazarus as Embodied Auto/Biography

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    Since the 1990s, Black British poets have been at the forefront of developing the ‘one-person poetry show’ or spoken-word play, an apt format for negotiating diasporic history and cultural memory in a public arena. The focus of this paper is Kat François’s one-woman show Raising Lazarus (2009/2016), which stages the poet’s own quest for information about her Grenadian relative Lazarus François, a WWI soldier. In a media-specific analysis, this paper explores how François’s text is semantically enriched when translated into a live performance. The authenticity effect typically produced in spoken-word poetry through the unity of author and performer is compounded in Raising Lazarus by textual and paratextual keys that frame François’ show as embodied auto/biography. Merging life-writing, monodrama, and spoken-word poetry, Raising Lazarus reveals the one-person show to be an effective and popular medium for Black British poets to articulate personal experience and negotiate collective identities through performance

    Mobilization and isotope fractionation of chromium during water-rock interaction in presence of siderophores

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    Chromium mobilization and isotope fractionation during water-rock interaction in presence of the biogenic siderophore desferrioxamine B (DFOB) was studied with batch leaching experiments on chromitite and other igneous oxide and silicate rocks. Siderophores are a group of organic ligands synthesized and excreted by bacteria, fungi and plants to enhance the bioavailability of key nutrients like Fe. However, the DFOB siderophore also has a strong affinity for complexation with other metals such as Cr, U and rare earth elements. Here we show that leaching of rocks in the presence of the hydroxamate siderophore DFOB significantly increased the mobilization of Cr from all investigated rocks and caused an enrichment of the heavier 53Cr isotope in leachates from chromitite (δ53Crleach = +0.15 ± 0.087‰ to +2.14 ± 0.042‰) and from altered silicate rock (δ53Crleach = +0.48 ± 0.07‰). In contrast, stable isotope fractionation of Cr was not observed in DFOB leachates of pristine silicate and low-Cr oxide rocks. Leaching in the presence of citric acid significantly enhanced Cr mobility, but did not result in fractionation of Cr isotopes. Chromium isotope fractionation is used in geochemistry as a quantitative proxy for oxidative weathering, because Cr(III) is oxidized to Cr(VI) in presence of MnO2 and the associated Cr isotope fractionation is commonly linked to the presence of oxygen in the atmosphere. Our findings indicate that the presence of specific biogenic ligands with a high affinity for Cr may also cause Cr isotope fractionation. The presence of biomolecules like siderophores during weathering, hydrothermal alteration or during mineral precipitation, therefore, may put constraints on the applicability of certain trace metals and their isotopes as redox proxies in modern and past environments. The results of our study also suggest that siderophores may have a high potential for (bio)remediation of Cr-contaminated sites and detoxification of contaminated natural waters

    Caroline Winkler: Video documentation of selecting a selfie on the phone (2018)

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    Caroline Winkler: Video documentation of selecting a selfie on the phone, created in a course taught by Simon Ganahl at Vorarlberg University of Applied Sciences in 2018

    Review: Theorizing Ethnicity and Nationality in the Chick Lit Genre, edited by Erin Hurt

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    More than two decades ago, chick lit was proclaimed the newest subgenre of romance, considered by some writers and critics so defiant of genre conventions that they would not count it as romance at all. Since then, both the initial “unquestioning adoration of fans” and “the unmitigated disdain of critics” (Ferriss and Young, 1) have receded. Starting in 1996 with Helen Fielding’s Bridget Jones’s Diary and Candace Bushnell’s Sex and the City, chick lit broke with some well-established romance conventions such as the one man-one woman ratio or the unrestricted focus on the quest for great love in preference to portraying professional women who dated several men. The combination of romance tropes with more emancipated, economically independent heroines resonated with readers in a new era and triggered, in the words of New York Times journalist Rachel Donadio (2006), a global “Chick-Lit Pandemic” with similar novels springing up in various places and languages

    Digital Preservation in a High Security Environment - iPRES 2019 Amsterdam

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    For the past five years, Princeton University Library – specifically the University Archives – has striven to create a robust digital preservation program for its born-digital and digitized records. Due to lack of time and available staff, the Library decided that a third party digital preservation service would be the best solution. It could be acquired relatively quickly, and it wouldn’t require asking for funding to hire multiple dedicated staff to build a home-grown digital preservation system. Obtaining buy-in from stakeholders and finding a service that met Princeton’s needs proved to be a challenge, especially due to the sensitivity of student records in the collections, which would require a high level of privacy and encryption key maintenance in addition to standard data integrity and preservation processing tools. Throughout 2018, Princeton worked to partner with a service previously unavailable due to University data sovereignty requirements – Arkivum’s Perpetua – and work began to develop a Princetonspecific solution that met the needs of the University: Most importantly, geographically dispersed cloud storage locations, Princeton-based control over data integrity and authenticity checks, an encryption key management system for student records maintained by the vendor but managed by repository staff, and a reliable and quick exit strategy


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