• Deutsch
Login

Open Access

  • Home
  • Search
  • Browse
  • Publish
  • FAQ
Schließen
  • Institutes

Naturwissenschaftliche Fakultät

  • Naturwissenschaftliche Fakultät -ohne weitere Spezifikation- (1116) subscribe to RSS feed
  • Department Biologie (58) subscribe to RSS feed
  • Department Chemie und Pharmazie (105) subscribe to RSS feed
  • Department Geographie und Geowissenschaften (43) subscribe to RSS feed
  • Department Mathematik (39) subscribe to RSS feed
  • Department Physik (134) subscribe to RSS feed

Refine

Author

  • Guldi, Dirk M. (42)
  • Hirsch, Andreas (27)
  • Backert, Steffen (23)
  • Heinemann, Frank W. (19)
  • Bräuning, Achim (18)
  • Clark, Timothy (18)
  • Buettner, Andrea (17)
  • Leuchs, Gerd (16)
  • Sonnewald, Uwe (16)
  • Tegtmeyer, Nicole (16)
+ more

Year of publication

  • 2021 (5)
  • 2020 (221)
  • 2019 (131)
  • 2018 (110)
  • 2017 (132)
  • 2016 (177)
  • 2015 (177)
  • 2014 (198)
  • 2013 (57)
  • 2012 (4)
+ more

Document Type

  • Article (755)
  • Doctoral Thesis (460)
  • Master's Thesis (2)
  • Bachelor Thesis (1)
  • Part of a Book (1)
  • Review (1)

Language

  • English (1085)
  • German (135)

Has Fulltext

  • yes (1220)

Keywords

  • - (431)
  • Optics, quantum optics and lasers (14)
  • Helicobacter pylori (13)
  • Quantum information and quantum mechanics (10)
  • Biochemical simulations (9)
  • Crystal structure (9)
  • Arabidopsis (8)
  • Arabidopsis thaliana (8)
  • Computational physics (8)
  • Instrumentation and measurement (8)
+ more

Institute

  • Naturwissenschaftliche Fakultät (1220)
  • Medizinische Fakultät (17)
  • Technische Fakultät (3)
  • Humangenetisches Institut (1)
  • Medizinische Fakultät -ohne weitere Spezifikation- (1)
  • Medizinische Klinik 5 - Hämatologie und Internistische Onkologie (1)
  • Neurologische Klinik (1)

1220 search hits

  • 1 to 20
  • 10
  • 20
  • 50
  • 100

Sort by

  • Year
  • Year
  • Title
  • Title
  • Author
  • Author
Stable isotope variations in tree rings as indicators of environmental change and paleohydroclimate variability in north Iran (2021)
Foroozan, Zeynab
Summary Precise knowledge about the long-term hydroclimatic variability is essential to analyze the impact of natural and anthropogenically induced climate change, especially in the world's arid to semi-arid regions. Iran is located in one of the world's most water-scarce and dry areas in Southwestern Asia. Hence, the country is highly subjected to water scarcity, water-related natural hazards such as drought and flash flood, and thus prone to their consequences on the ecosystem and human society. Besides, the growing population and the thirst for socio-economic development, in turn, increase the region's vulnerability to climate change. However, the current solutions to the aggravating water crisis are inadequate and inefficient without a clear picture of regional water availability in the future. In this context, a major defect is the lack of hydroclimate (precipitation) data of the past and present. A neglected area in this regard is the high potential of natural climate archives for extending our knowledge about past and present variations in hydroclimate. This research was thus initiated to explore the potential of a natural climate proxy for paleoclimate reconstructions to improve our understanding of long-term regional climate variability in Iran. Accordingly, we evaluated the potential of stable isotopes in tree-ring cellulose to serve as paleoclimate indicators. We determined the climate signal recorded in δ13C and δ18O variations in tree-ring cellulose. Besides, this study tested the ecological responses of two tree species belonging to different plant functional types, an evergreen conifer (Juniperus polycarpos) and a broadleaved deciduous oak (Quercus macranthera), growing under distinct climate conditions to their environments, to increased CO2, and recent climate change by analyzing trends of intrinsic water-use efficiency (iWUE). In this thesis, we evaluated species-specific responses to drought of those tree species to provide baseline data for possible forest management efforts alleviating the impacts of expected climate change. The observed increasing trends in iWUE indicated reduced stomatal conductance in both study species in response to the changing climate and elevated atmospheric CO2. The mean correlations among individual δ13C series in each site and between the site δ13C chronologies provide strong evidence of a robust common climate signal in isotope series. The proxy-climate analysis revealed that the interplay between the combined influence of climate and local site conditions and species behavior determines δ13C variations in both species. The results showed that drought stress, which is controlled by precipitation, is the dominant climatic control on the δ13C fluctuations in both oak and juniper trees. In general, juniper responded more sensitive to moisture stress and is thus a more suitable proxy for paleohydroclimatic studies in northern Iran. Furthermore, δ18O-climate analysis indicated a strong effect of moisture availability on δ18O of tree-ring cellulose in juniper. Accordingly, the first set of analyses and data comparison indicated a high potential of δ18O variations in juniper tree-ring cellulose for paleohydroclimatic investigations in northern Iran. In the next step, this thesis assessed various pooling techniques for combining cross-dated tree-rings from different tree individuals before isotopic analysis. The evaluations indicated that an alternative approach to individual-tree isotope measurements, combined with high time and cost efficiency, is inter-tree pooling. Accordingly, the results confirmed that a pooled δ18O chronology can be used for paleoclimate reconstructions in northern Iran without compromising high-frequency climate signals. Subsequently, we were able to develop a well-replicated 501-year spanning tree-ring δ18O chronology, representing the first stable isotope archive with annual resolution for paleohydroclimatic investigations in Iran. The statistical characteristics of the tree-ring δ18O chronology, such as the expressed population signal (EPS), confirmed that the isotope chronology contained a robust climate signal. The regional δ18O chronology showed a significant negative correlation with precipitation and vapor pressure deficit, and a positive correlation with temperature during the growing season. Therefore, it was concluded that the proxy record reflects site moisture conditions controlled mainly by precipitation and is thus useful for the reconstruction of past hydroclimate conditions, like long-term precipitation variations. Consequently, we succeeded in reconstructing hydroclimatic variability for the northern semi-arid region of Iran over the period 1515-2015 using the juniper δ18O chronology. The reconstructed precipitation series captured the magnitude of inter-annual and long-term variability in precipitation and the intensity, duration, and frequency of dry/wet events. During the past 500 years, pronounced phases with wetter (18th century) and drier (16th century) conditions than today are apparent. The reconstructed spring precipitation record gradually declined from the beginning of the 19th century and culminated in a drier period in the early 20th century. It is also evident that since the 18th century, the overall frequency of years with dry events has increased significantly. The study suggests the strong influence of regional atmospheric factors such as the nearby Caspian Sea, the local topography, the high elevation, and the influence of the westerlies on precipitation variations at the study site. This thesis managed to obtain conclusive evidence for the high potential of stable isotope dendroclimatology to investigate long-term hydroclimate variability in a semi-arid region of Iran. The findings of this study could support decision-makers in sustainable water resource management and climate change adaptation plans. An additional important implication of this research is the contribution to complement the sparse network of available instrumental climate stations and available proxy records, and the projection of future changes in the region's climate.
Past and recent climate variability and glacier fluctuations across the Southern Patagonian Andes - A multi‐parameter approach using tree‐ring parameters and remote sensing (2021)
Meier, Wolfgang
During recent decades, high mountain ecosystems across the globe are highly affected by unequivocal rising temperatures and variability in precipitation. The rapid rate of increasing global surface temperatures since the late 19th century and in particular during the recent decades is unprecedented compared to the long-term climate, triggering substantial changes in the hydro-, bio- and cryosphere. The complex topography of high mountain areas comprises ecosystems that are scarcely investigated due to their high elevation and remoteness. The temperate glaciers of southernmost South America (Patagonia) are considered being highly sensitive to recent climatic changes. Compared to global scale, the glaciers of the Southern Andes are experiencing one of the most dramatic decreases in ice thickness and glacier area during the last 50 years. Contrasting the high number of glaciers across the Patagonian Andes, a relatively small number of studies have been conducted to investigate spatio-temporal glacier variability. This concerns in particular the lack of information on Late Holocene glacier history predating the “satellite era”. During the Holocene, several phases of Holocene glacier resurgence (Neoglaciations) took place, while the most recent one is commonly referred to as the Little Ice Age (LIA). The LIA maximum glacier extent marks an important tipping point from a climate regime that favours advancing of glaciers to a subsequent retreating system. During this transient “steady-state” phase, well-defined glacier-morphological deposits are formed, that can be mapped and dated by biological proxies. The regional knowledge about the reciprocal dependence of climate, topography and glacier systems during past and present climates is still scarce, highlighting a need for high-resolution (annual) palaeoclimatic proxies. This thesis therefore focuses to gain insight into past and present climate and glacier variations across the Southern Andes, by applying multi-proxy and multi-parameter approaches. In broad terms, the thesis can be categorized into two main thematic approaches: i) a remote sensing section to derive spatiotemporal consistent information on glacier variability and ii) palaeoclimatic investigations to assess information on climate variability and responsible driving forcings. Based on remote sensing the former extent of more than 2,600 individual LIA glaciers of the Southern Andes (including the Northern- and Southern Patagonian Icefields and Tierra del Fuego) were digitized and compared to recently derived glacier outlines. To test the transferability of this methodological approach for a differing glaciological setting, an additional study located in the high-mountain areas of the central-Nepalese Himalaya was carried out. Both study sites, although from different climatic settings, demonstrate an extensive loss in glacierized area since the LIA, locally exceeding more than 50% of the initial area. Conspicuously, the glacier loss rates are not evenly distributed, highlighting strong regional contrasts mostly between windward and leeward side of the respective orogen. Glaciers that are located on the downwind mountain slope, exhibit the highest relative area reduction, in particular glaciers featuring a small initial LIA area, decreased frequently up to 80% or have disappeared completely. This heterogenic glacier pattern is further emphasised by a study focusing on recent elevation changes of the major icefields in Southern Patagonia. The obtained results display, that the large outlet glaciers of the Southern Patagonian Icefield are not solely driven by climatic variations. Primarily individual glaciers depend on dynamical glacier adjustments and varying hypsometric curves. The LIA terminal moraines of a glacier located at Tierra del Fuego in southern South America were dated using dendroglaciological methods. Based on the maximum ages of trees growing on moraines and additionally analysed subfossil trunks incorporated in moraine deposits it was possible to exactly date the maximum LIA position and major Neoglacial advances during the last 2,300 years. These datings were consolidated with pre-existing datasets from the Patagonian Andes to further emphasise common and contrasting historical variations in the region. To disentangle the effects of changing climate on forest ecosystems in Southern Patagonia and to densify the high-resolution proxy network, several new tree-ring width chronologies from the windward (humid) and from the downwind (less humid) side of the Andes were established. Since the climate imprints on tree-ring width result in rather limited common characteristics, suggesting local climatic forcing or varying site conditions, stable oxygen isotope variations in tree-ring cellulose δ18O_TRC ) were additionally analysed at a windward and leeward sampling site in southernmost Patagonia, respectively. To date, these two time series represent the southernmost δ18O_TRC chronologies derived from tree ring cellulose in South America. Both chronologies share a positive response to variations in temperature (also reflected in surface net solar radiation, evaporation and sea level pressure) and a strong negative response to moisture variations (precipitation, relative humidity) during the vegetation season. Since the δ18O_TRC chronologies indicate a strong relation to the leading mode of climate variability in the Southern Hemisphere (Antarctic Oscillation, AAO) it was possible to reconstruct the AAO variability for the last 150 years. Accordingly, a new proxy for providing information of temperature- and precipitation fluctuations and the overlying large-scale circulation patterns was established for southern Patagonia.
Dominance of in situ produced particulate organic carbon in a subtropical reservoir inferred from carbon stable isotopes (2020)
de Castro Bueno, Carolina ; Frascareli, Daniele ; Gontijo, Erik S. J. ; van Geldern, Robert ; Rosa, André H. ; Friese, Kurt ; Barth, Johannes A. C.
Sources of particulate organic carbon (POC) play important roles in aqueous carbon cycling because internal production can provide labile material that can easily be turned into CO2. On the other hand, more recalcitrant external POC inputs can cause increased loads to sedimentary organic matter that may ultimately cause CH4 release. In order to differentiate sources, stable isotopes offer a useful tool. We present a study on the Itupararanga Reservoir (Brazil) where origins of POC were explored by comparing its isotope ratios (δ13CPOC) to those of dissolved inorganic carbon (δ13CDIC). The δ13CPOC averaged around − 25.1‰ in near-surface waters, which indicates higher primary production inferred from a fractionation model that takes into account carbon transfer with a combined evaluation of δ13CPOC, δ13CDIC and aqueous CO2. However, δ13CPOC values for water depths from 3 to 15 m decreased to − 35.6‰ and indicated different carbon sources. Accordingly, the δ13CDIC values of the reservoir averaged around + 0.6‰ in the top 3 m of the water column. This indicates CO2 degassing and photosynthesis. Below this depth, DIC isotope values of as low as − 10.1‰ showed stronger influences of respiration. A fractionation model with both isotope parameters revealed that 24% of the POC in the reservoir originated from detritus outside the reservoir and 76% of it was produced internally by aqueous CO2 fixation.
The EU Food Label ‘Protected Geographical Indication’: Economic Implications and Their Spatial Dimension (2020)
Chilla, Tobias ; Fink, Benedikt ; Balling, Richard ; Reitmeier, Simon ; Schober, Karola
This study analyses the economic effects of the EU policy on the protection of origin. The focus is on three types of food products with Protected Geographical Indication (PGI), whose reference areas are located in the Free State of Bavaria: Beer (Bayerisches Bier PGI), asparagus (Franken-Spargel PGI, Schrobenhausener Spargel PGI), and carp (Aischgründer Karpfen PGI, Oberpfälzer Karpfen PGI). The study is based on secondary statistical analysis and a series of expert interviews. The results show positive effects on sales mainly for beer on international markets, and positive effects on price mainly for carp on the local and regional levels. All in all, we see that protection of origin stabilizes and supports the economic trajectory of its product. This study also shows that its economic effects vary widely: Firstly, price and sales effects are not automatic and differ in intensity; and secondly, the spatial dimensions of the economic effects exhibit different patterns. The primarily price-related effects at the local–regional level for carp (and to some extent for asparagus) are categorized as local effects (type A). The sales effect at the global level for beer is categorized as type B (export effect). Finally, this study postulates further potential forms of ‘price and sales geographies’.
A near 90-year record of the evolution of El Morado Glacier and its proglacial lake, Central Chilean Andes (2020)
Farías-Barahona, David ; Wilson, Ryan ; Bravo, Claudio ; Vivero, Sebastián ; Caro, Alexis ; Shaw, Thomas E. ; Casassa, Gino ; Ayala, Álvaro ; Mejías, Alonso ; Harrison, Stephan ; Glasser, Neil F. ; McPhee, James ; Wündrich, Olaf ; Braun, Matthias H.
Using an ensemble of close- and long-range remote sensing, lake bathymetry and regional meteorological data, we present a detailed assessment of the geometric changes of El Morado Glacier in the Central Andes of Chile and its adjacent proglacial lake between 1932 and 2019. Overall, the results revealed a period of marked glacier down wasting, with a mean geodetic glacier mass balance of −0.39 ± 0.15 m w.e.a−1 observed for the entire glacier between 1955 and 2015 with an area loss of 40% between 1955 and 2019. We estimate an ice elevation change of −1.00 ± 0.17 m a−1 for the glacier tongue between 1932 and 2019. The increase in the ice thinning rates and area loss during the last decade is coincident with the severe drought in this region (2010–present), which our minimal surface mass-balance model is able to reproduce. As a result of the glacier changes observed, the proglacial lake increased in area substantially between 1955 and 2019, with bathymetry data suggesting a water volume of 3.6 million m3 in 2017. This study highlights the need for further monitoring of glacierised areas in the Central Andes. Such efforts would facilitate a better understanding of the downstream impacts of glacier downwasting.
Arsenian Pyrite and Cinnabar from Active Submarine Nearshore Vents, Paleochori Bay, Milos Island, Greece (2021)
Voudouris, Panagiotis ; Kati, Marianna ; Magganas, Andreas ; Keith, Manuel ; Valsami-Jones, Eugenia ; Haase, Karsten ; Klemd, Reiner ; Nestmeyer, Mark
Active, shallow-water (2–10 m below sea level) and low temperature (up to 115 °C) hydrothermal venting at Paleochori Bay, nearshore Milos Island, Greece, discharges CO2 and H2S rich vapors (e.g., low-Cl fluid) and high-salinity liquids, which leads to a diverse assemblage of sulfide and alteration phases in an area of approximately 1 km2. Volcaniclastic detritus recovered from the seafloor is cemented by hydrothermal pyrite and marcasite, while semi-massive to massive pyrite-marcasite constitute mounds and chimney-like edifices. Paragenetic relationships indicate deposition of two distinct mineralogical assemblages related to the venting of high-Cl and low-Cl fluids, respectively: (1) colloform As- and Hg-bearing pyrite (Py I), associated with marcasite, calcite, and apatite, as well as (2) porous and/or massive As-rich pyrite (Py II), associated with barite, alunite/jarosite, and late-stage hydrous ferric oxides. Mercury, in the form of cinnabar, occurs within the As-rich pyrite (Py I) layers, usually forming distinct cinnabar-enriched micro-layers. Arsenic in colloform pyrite I shows a negative correlation with S indicating that As1− dominates in the pyrite structure suggesting formation from a relatively reducing As-rich fluid at conditions similar to low-sulfidation epithermal systems. On the contrary, As3+ dominates in the structure of porous to massive pyrite II suggesting deposition from a sulfate-dominated fluid with lower pH and higher fO2. Bulk sulfide data of pyrite-bearing hydrothermal precipitates also show elevated As (up to 2587 ppm) together with various epithermal-type elements, such as Sb (up to 274 ppm), Tl (up to 513 ppm), and Hg (up to 34 ppm) suggesting an epithermal nature for the hydrothermal activity at Paleochori Bay. Textural relationships indicate a contemporaneous deposition of As and Hg, which is suggested to be the result of venting from both high-salinity, liquid-dominated, as well as CO2- and H2S-rich vapor-dominated fluids that formed during fluid boiling. The CO2- and H2S-rich vapor that physically separated during fluid boiling from the high-salinity liquid led to calcite formation upon condensation in seawater together with the precipitation of As- and Hg-bearing pyrite I. This also led to the formation of sulfuric acid, thereby causing leaching and dissolution of primary iron-rich minerals in the volcaniclastic sediments, finally resulting in pyrite II precipitation in association with alunite/jarosite. The Paleochori vents contain the first documented occurrence of cinnabar on the seafloor in the Mediterranean area and provide an important link between offshore hydrothermal activity and the onshore mercury and arsenic mineralizing system on Milos Island. The results of this study therefore demonstrate that metal and metalloid precipitation in shallow-water continental arc environments is controlled by epithermal processes known from their subaerial analogues.
Uniqueness Criteria for the Fock Quantization of Dirac Fields and Applications in Hybrid Loop Quantum Cosmology (2020)
Cortez, Jerónimo ; Navascués, Beatriz Elizaga ; Mena Marugán, Guillermo A. ; Prado, Santiago ; Velhinho, José M.
In generic curved spacetimes, the unavailability of a natural choice of vacuum state introduces a serious ambiguity in the Fock quantization of fields. In this review, we study the case of fermions described by a Dirac field in non-stationary spacetimes, and present recent results obtained by us and our collaborators about well-motivated criteria capable to ensure the uniqueness in the selection of a vacuum up to unitary transformations, at least in certain situations of interest in cosmology. These criteria are based on two reasonable requirements. First, the invariance of the vacuum under the symmetries of the Dirac equations in the considered spacetime. These symmetries include the spatial isometries. Second, the unitary implementability of the Heisenberg dynamics of the annihilation and creation operators when the curved spacetime is treated as a fixed background. This last requirement not only permits the uniqueness of the Fock quantization but, remarkably, it also allows us to determine an essentially unique splitting between the phase space variables assigned to the background and the fermionic annihilation and creation variables. We first consider Dirac fields in 2 + 1 dimensions and then discuss the more relevant case of 3 + 1 dimensions, particularizing the analysis to cosmological spacetimes with spatial sections of spherical or toroidal topology. We use this analysis to investigate the combined, hybrid quantization of the Dirac field and a flat homogeneous and isotropic background cosmology when the latter is treated as a quantum entity, and the former as a perturbation. Specifically, we focus our study on a background quantization along the lines of loop quantum cosmology. Among the Fock quantizations for the fermionic perturbations admissible according to our criteria, we discuss the possibility of further restricting the choice of a vacuum by the requisite of a finite fermionic backreaction and, moreover, by the diagonalization of the fermionic contribution to the total Hamiltonian in the asymptotic limit of large wave numbers of the Dirac modes. Finally, we argue in support of the uniqueness of the vacuum state selected by the extension of this diagonalization condition beyond the commented asymptotic region, in particular proving that it picks out the standard Poincaré and Bunch–Davies vacua for fixed flat and de Sitter background spacetimes, respectively.
Investigation of nanostructured lithium-ion battery materials (2021)
Zhuo, Ying
The lithium-ion battery represents one of the most feasible ways for energy storage, which can be utilized in portable devices and electric vehicles. With the intensively growing demand of lithium-ion battery with larger capacity, materials to improve the battery performance are investigated. Of the two electrodes, the positive electrode limits the capacity of the battery because of its low specific capacity, while the negative electrode restricts the lifetime of the battery besides the capacity. Due to high volume variation, poor electron transport, capacity fading and low coulombic efficiency, the negative electrode has seen much more limited advances than its positive counterpart. In this work, we mainly focused on studying anode materials for lithium-ion battery. Alloy-type anode materials (elemental Si and Sn) feature high specific capacity and are promising candidates to substitute graphite in the future. However, anodes, which are made of these materials, suffer from the fracture and pulverization due to their inherently large volume changes upon charge and discharge (> 300%), and this impedes their commercialization. Herein, attempts have been made to tune the morphology of the anode materials so that they can survive from the large volume change. SnO2 nanotube arrays based on anodic aluminum oxide (AAO) matrix are systematically studied as the anode material first. Different from the traditional way to prepare the electrodes by making slurry, SnO2 nanotube arrays are generated by atomic layer deposition (ALD). Moreover, due to the good conductivity of SnO2, this anode material is tested for charge and discharge without any additives, such as polyvinylidene fluoride or carbon black, which serve as standard binder and conductive material in LIBs. Finally, a SnO2 nanotube sample (30 μm length, 10 nm wall thickness and around 350 nm inner diameter) shows its capability to survive the huge volume variation during charge and discharge. Besides, owing to its nanotube structure, it offers a short and straight pathway for the electrolyte to diffuse towards the electrode easily, which results in the anode perfectly recovering from its initial capacity loss upon charge and discharge at large current rate. Elemental Si is then investigated in a manner to the SnO2 nanostructure since Si owns the highest theoretical specific capacity (~ 4200 mAh g–1). Amorphous Si nanotube arrays are gained by reducing amorphous SiO2 nanotube arrays, which are built on AAO matrix by ALD. Unlike crystalline Si, amorphous Si does not present a significant capacity loss, which is caused by the transition from crystalline to disordered (amorphous) state. Therefore, Si nanotubes reveal relatively stable capacity. The interface of the electrode is studied as well.
Towards a Situated Spatial Epidemiology of Violence: A Placially-Informed Geospatial Analysis of Homicide in Alagoas, Brazil (2020)
Walker, Blake Byron ; Moura de Souza, Cléssio ; Pedroso, Enrique ; Lai, Ryan S. ; Hunter, Paige ; Tam, Jessy ; Cave, Isaac ; Swanlund, David ; Barbosa, Kevan Guilherme Nóbrega
This paper presents an empirically grounded call for a more nuanced engagement and situatedness with placial characteristics within a spatial epidemiology frame. By using qualitative data collected through interviews and observation to parameterise standard and spatial regression models, and through a critical interpretation of their results, we present initial inroads for a situated spatial epidemiology and an analytical framework for health/medical geographers to iteratively engage with data, modelling, and the context of both the subject and process of analysis. In this study, we explore the socioeconomic factors that influence homicide rates in the Brazilian state of Alagoas from a critical public health perspective. Informed by field observation and interviews with 24 youths in low-income neighbourhoods and prisons in Alagoas, we derive and critically reflect on three regression models to predict municipal homicide rates from 2016–2020. The model results indicate significant effects for the male population, persons without elementary school completion, households with reported income, divorced persons, households without piped water, and persons working outside their home municipality. These results are situated in the broader socioeconomic context, trajectories, and cycles of inequality in the study area and underscore the need for integrative and contextually engaged mixed method study design in spatial epidemiology.
Laser-Induced Deposition of Plasmonic Ag and Pt Nanoparticles, and Periodic Arrays (2021)
Mamonova, Daria V. ; Vasileva, Anna A. ; Petrov, Yuri V. ; Danilov, Denis V. ; Kolesnikov, Ilya E. ; Kalinichev, Alexey A. ; Bachmann, Julien ; Manshina, Alina A.
Surfaces functionalized with metal nanoparticles (NPs) are of great interest due to their wide potential applications in sensing, biomedicine, nanophotonics, etc. However, the precisely controllable decoration with plasmonic nanoparticles requires sophisticated techniques that are often multistep and complex. Here, we present a laser-induced deposition (LID) approach allowing for single-step surface decoration with NPs of controllable composition, morphology, and spatial distribution. The formation of Ag, Pt, and mixed Ag-Pt nanoparticles on a substrate surface was successfully demonstrated as a result of the LID process from commercially available precursors. The deposited nanoparticles were characterized with SEM, TEM, EDX, X-ray diffraction, and UV-VIS absorption spectroscopy, which confirmed the formation of crystalline nanoparticles of Pt (3–5 nm) and Ag (ca. 100 nm) with plasmonic properties. The advantageous features of the LID process allow us to demonstrate the spatially selective deposition of plasmonic NPs in a laser interference pattern, and thereby, the formation of periodic arrays of Ag NPs forming diffraction grating
Revisiting extreme precipitation amounts over southern South America and implications for the Patagonian Icefields (2020)
Sauter, Tobias
Patagonia is thought to be one of the wettest regions on Earth, although available regional precipitation estimates vary considerably. This uncertainty complicates understanding and quantifying the observed environmental changes, such as glacier recession, biodiversity decline in fjord ecosystems and enhanced net primary production. The Patagonian Icefields, for example, are one of the largest contributors to sea-level rise outside the polar regions, and robust hydroclimatic projections are needed to understand and quantify current and future mass changes. The reported projections of precipitation from numerical modelling studies tend to overestimate those from in situ determinations, and the plausibility of these numbers has never been carefully scrutinized, despite the significance of this topic to our understanding of observed environmental changes. Here I use simple physical arguments and a linear model to test the plausibility of the current precipitation estimates and its impact on the Patagonian Icefields. The results show that environmental conditions required to sustain a mean precipitation amount exceeding 6.09±0.64 m yr−1 are untenable according to the regional moisture flux. The revised precipitation values imply a significant reduction in the surface mass balance of the Patagonian Icefields compared to previously reported values. This yields a new perspective on the response of Patagonia's glaciers to climate change and their sea-level contribution and might also help reduce uncertainties in the change of other precipitation-driven environmental phenomena.
Drivers of beta diversity in modern and ancient reef-associated soft-bottom environments (2020)
Roden​, Vanessa Julie ; Zuschin, Martin ; Nützel, Alexander ; Hausmann, Imelda M. ; Kiessling, Wolfgang
Beta diversity, the compositional variation among communities, is often associated with environmental gradients. Other drivers of beta diversity include stochastic processes, priority effects, predation, or competitive exclusion. Temporal turnover may also explain differences in faunal composition between fossil assemblages. To assess the drivers of beta diversity in reef-associated soft-bottom environments, we investigate community patterns in a Middle to Late Triassic reef basin assemblage from the Cassian Formation in the Dolomites, Northern Italy, and compare results with a Recent reef basin assemblage from the Northern Bay of Safaga, Red Sea, Egypt. We evaluate beta diversity with regard to age, water depth, and spatial distance, and compare the results with a null model to evaluate the stochasticity of these differences. Using pairwise proportional dissimilarity, we find very high beta diversity for the Cassian Formation (0.91 ± 0.02) and slightly lower beta diversity for the Bay of Safaga (0.89 ± 0.04). Null models show that stochasticity only plays a minor role in determining faunal differences. Spatial distance is also irrelevant. Contrary to expectations, there is no tendency of beta diversity to decrease with water depth. Although water depth has frequently been found to be a key factor in determining beta diversity, we find that it is not the major driver in these reef-associated soft-bottom environments. We postulate that priority effects and the biotic structuring of the sediment may be key determinants of beta diversity.
Tritium as a hydrological tracer in Mediterranean precipitation events (2020)
Juhlke, Tobias R. ; Sültenfuß, Jürgen ; Trachte, Katja ; Huneau, Frédéric ; Garel, Emilie ; Santoni, Sébastien ; Barth, Johannes A. C. ; van Geldern, Robert
Climate models are in need of improved constraints for water vapor transport in the atmosphere, and tritium can serve as a powerful tracer in the hydrological cycle. Although the general principles of tritium distribution and transfer processes within and between the various hydrological compartments are known, variation on short timescales and aspects of altitude dependence are still under debate. To address questions regarding tritium sources, sinks, and transfer processes, the sampling of individual precipitation events in Corte on the island of Corsica in the Mediterranean Sea was performed between April 2017 and April 2018. Tritium concentrations of 46 event samples were compared to their moisture origin and corresponding air mass history. Air mass back-trajectories were generated from the novel high-resolution ERA5 dataset from the ECMWF (European Centre for Medium-Range Weather Forecasts). Geographical source regions with similar tritium concentrations were predefined using generally known tritium distribution patterns, such as the “continental effect”, and from data records derived at long-term measurement stations of tritium in precipitation across the working area. Our model-derived source region tritium concentrations agreed well with annual mean station values. Moisture that originated from continental Europe and the Atlantic Ocean was most distinct regarding tritium concentrations with values up to 8.8 TU (tritium units) and near 0 TU, respectively. The seasonality of tritium values ranged from 1.6 TU in January to 10.1 TU in May, and they exhibited well-known elevated concentrations in spring and early summer due to increased stratosphere–troposphere exchange. However, this pattern was interrupted by extreme events. The average altitude of trajectories was correlated with the tritium concentrations in precipitation, especially in spring and early summer and if outlier values of extreme tritium concentrations were excluded. However, in combination with the trajectory information, these outlier values proved to be valuable for improving the comprehension of tritium movement in the atmosphere. Our work shows how event-based tritium research can advance the understanding of its distribution in the atmosphere.
Münchens sozial-ökologische Stadtentwicklung zwischen Anspruch und Wirklichkeit : Kommentar zu Lisa Vollmer und Boris Michel „Wohnen in der Klimakrise. Die Wohnungsfrage als ökologische Frage“ (2020)
Geiselhart, Klaus
In zwei städtebaulichen Entwicklungsprojekten der Stadt München wird eine Verbindung von ökologischem und sozialem Bauen umgesetzt. Dieser Beitrag stellt diese Projekte kritisch vor und fragt nach deren Bedeutung für die Münchner Stadtentwicklung sowie nach möglichen Implikationen für die kritische Stadtforschung.
Poor Doors in Erlangen : Umweltbezogene Mikrosegregation unter Bedingungen der Reurbanisierung (2020)
Geiselhart, Klaus ; Eisemann, Carolin ; Feick, Fabian ; Kammerbauer, Stefan
In der sich im Zuge der Reurbanisierung verschärfenden Konkurrenz um städtische Ressourcen gestalten sich Prozesse der Segregation zunehmend kleinräumiger. Eine Fallstudie in Erlangen zeigt, wie bei den Planungen eines Quartiers im Röthelheimpark und der Rathenausiedlung bevorzugte Wohnlagen geschaffen werden, nicht zuletzt durch die Einrichtung benachteiligter Wohnlagen. Es entstehen Phänomene einer Mikrosegregation auf Quartiersebene, die über die gängigen Methoden statistischer Messung kaum noch empirisch zu erfassen sind. Die besondere Brisanz erhält das Thema durch die Tatsache, dass hierbei gesundheitliche Risiken ungleich verteilt werden, denn Umweltbelastungen werden gezielt den ärmeren Bewohner_innengruppen zugemutet, während Umweltressourcen den Wohlhabenden zugutekommen.
Detailed quantification of glacier elevation and mass changes in South Georgia (2020)
Farías-Barahona, David ; Sommer, Christian ; Sauter, Tobias ; Bannister, Daniel ; Seehaus, Thorsten C. ; Malz, Philipp ; Casassa, Gino ; Mayewski, Paul A. ; Turton, Jenny V. ; Braun, Matthias H.
Most glaciers in South America and on the Antarctic Peninsula are retreating and thinning. They are considered strong contributors to global sea level rise. However, there is a lack of glacier mass balance studies in other areas of the Southern Hemisphere, such as the surrounding Antarctic Islands. Here, we present a detailed quantification of the 21st century glacier elevation and mass changes for the entire South Georgia Island using bi-static synthetic aperture radar interferometry between 2000 and 2013. The results suggest a significant mass loss since the beginning of the present century. We calculate an average glacier mass balance of −1.04 ± 0.09 m w.e.a−1 and a mass loss rate of 2.28 ± 0.19 Gt a−1 (2000–2013), contributing 0.006 ± 0.001 mm a−1 to sea-level rise. Additionally, we calculate a subaqueous mass loss of 0.77 ± 0.04 Gt a−1 (2003–2016), with an area change at the marine and lake-terminating glacier fronts of −6.58 ± 0.33 km2 a−1, corresponding to ~4% of the total glacier area. Overall, we observe negative mass balance rates in South Georgia, with the highest thinning and retreat rates at the large outlet glaciers located at the north-east coast. Although the spaceborne remote sensing dataset analysed in this research is a key contribution to better understanding of the glacier changes in South Georgia, more detailed field measurements, glacier dynamics studies or further long-term analysis with high-resolution regional climate models are required to precisely identify the forcing factors.
Equilibrium Orientation and Adsorption of an Ellipsoidal Janus Particle at a Fluid−Fluid Interface (2020)
Günther, Florian ; Xie, Qingguang ; Harting, Jens
We investigate the equilibrium orientation and adsorption process of a single, ellipsoidal Janus particle at a fluid–fluid interface. The particle surface comprises equally sized parts that are hydrophobic or hydrophilic. We present free energy models to predict the equilibrium orientation and compare the theoretical predictions with lattice Boltzmann simulations. We find that the deformation of the fluid interface strongly influences the equilibrium orientation of the Janus ellipsoid. The adsorption process of the Janus ellipsoid can lead to different final orientations determined by the interplay of particle aspect ratio and particle wettablity contrast.
Canonical Quantum Gravity, Constructive QFT, and Renormalisation (2020)
Thiemann, Thomas
The canonical approach to quantum gravity has been put on a firm mathematical foundation in the recent decades. Even the quantum dynamics can be rigorously defined, however, due to the tremendously non-polynomial character of the gravitational interaction, the corresponding Wheeler–DeWitt operator-valued distribution suffers from quantisation ambiguities that need to be fixed. In a very recent series of works, we have employed methods from the constructive quantum field theory in order to address those ambiguities. Constructive QFT trades quantum fields for random variables and measures, thereby phrasing the theory in the language of quantum statistical physics. The connection to the canonical formulation is made via Osterwalder–Schrader reconstruction. It is well known in quantum statistics that the corresponding ambiguities in measures can be fixed using renormalisation. The associated renormalisation flow can thus be used to define a canonical renormalisation programme. The purpose of this article was to review and further develop these ideas and to put them into context with closely related earlier and parallel programmes.
Is Social Contact With the Resident Population a Prerequisite of Well-Being and Place Attachment? The Case of Refugees in Rural Regions of Germany (2020)
Glorius, Birgit ; Kordel, Stefan ; Weidinger, Tobias ; Bürer, Miriam ; Schneider, Hanne ; Spenger, David
Due to dispersal policies applied in many European countries, such as Germany, rural regions are important arrival regions for asylum seekers and refugees. For German policy makers, who have faced a large number of immigrants since 2015, it is crucial that asylum seekers and refugees stay in those rural regions and benefit the development of those areas. This paper addresses the quality and quantity of social contact between refugees and resident populations as a prerequisite for integration and long-term migration-development effects from a social geographical perspective. Drawing from survey data and qualitative interviews, we examine expectations, perceptions and experiences of everyday encounters and social relationships in neighborhoods in small rural towns and villages from the perspective of both local residents and refugees. Our results support arguments from research literature for faster social inclusion in rural areas due to greater nearness, but also obstacles toward the integration of foreigners due to a higher homogeneity of rural neighborhoods and only few experiences of positive everyday contact with foreigners among rural residents. The interviewed refugees display a high level of reflexivity regarding their new neighborhood and how they might be seen by rural residents. Their experiences encompass various forms of social relationships, while social bridges are crucial, ranging from serendipitous encounters and functional interactions to connections based on mutual interest around family issues or cultural aspects. Openness and tolerance from at least some parts of the local population can help immigrants to feel at home, and support staying aspirations, while simultaneously evoking wider social change. A peculiarity of rural areas is the intersectionality with further challenges related to structural changes, encompassing, for instance, socio-demographic and economic restructuring. However, social interactions and opportunities for encounters are only one factor in the development of long-term settlement. More in-depth research is needed to consider the interrelations of both structural contexts and complex and changing needs for personal development in the future, also from an intergenerational perspective.
Toward a Corrected Knife-Edge-Based Reconstruction of Tightly Focused Higher Order Beams (2020)
Orlov, Sergej ; Huber, Christian ; Marchenko, Pavel ; Banzer, Peter ; Leuchs, Gerd
The knife-edge method is an established technique for profiling of even tightly focused light beams. However, the straightforward implementation of this method fails if the materials and geometry of the knife-edges are not chosen carefully or, in particular, if knife-edges are used that are made of pure materials. Artifacts are introduced in these cases in the shape and position of the reconstructed beam profile due to the interaction of the light beam under study with the knife. Hence, corrections to the standard knife-edge evaluation method are required. Here we investigate the knife-edge method for highly focused radially and azimuthally polarized beams and their linearly polarized constituents. We introduce relative shifts for those constituents and report on the consistency with the case of a linearly polarized fundamental Gaussian beam. An adapted knife-edge reconstruction technique is presented and proof-of-concept tests are shown, demonstrating the reconstruction of beam profiles.
  • 1 to 20

DINI-Zertifikat 2013     DINI-Zertifikat 2016     Members of COAR OPUS4 Logo

  • Contact
  • Imprint
  • Sitelinks