Chemical Impurities and Physical Properties of Polar Ice

The Greenland Ice Sheet and the Antarctic Ice Sheet are the largest reservoirs of freshwater on our planet. They consist of ice which formed over thousands of years out of the precipitation and due to natural densification of snow. As such, polar ice represents a unique archive of the past climate. The large ice masses flow under their own weight causing a transport of ice from the inlands towards the oceans. Numerical flow models are used to simulate the ice dynamics, i. a., in order to project future contributions of the ice sheets to the rising sea level. The viscoplastic deformation of ice on the micro-scale involves similar mechanisms as the deformation of other poly-crystalline materials. The shear of individual crystals is accompanied by recrystallization and the development of characteristic microstructures. Thus, structural-geological concepts and methods can be applied to natural ice samples in order to study their deformation state and active physical processes. Chemical impurities are deposited in snow and ice during the precipitation and reflect the aerosol composition of the atmosphere. As such they play an important role for the reconstructions of the climate of the past. Despite their extremely low concentrations, impurities influence many physical properties of ice, in particular also the deformation rate. The concentrations of the different impurities vary with depth and these variations are correlated with heterogeneities in the flow-velocity profile. This results in the development of localized shear zones in ice. A better understanding of the mechanisms is necessary in order to implement the effect of impurities into the flow models. The presented thesis addresses the relationship between the chemical impurities and the physical properties of polar ice. A central challenge of the project is to understand in which form impurities integrate in ice and where they are located in the bulk, respectively how they interact with it during deformation and recrystallization. A combination of methods for the microstructural analysis was applied to natural ice material from ice cores. The distribution and composition of impurities was analyzed using a confocal cryo-Raman microscope. Within the scope of this thesis, new routines for the acquisition and data processing were developed. The results reveal a complex interplay between impurities, crystal structure and localized deformation in ice. On the one hand, high impurity concentrations cause higher strain rates occurring together with small grain sizes. On the other hand, the deforming ice matrix affects the distribution of impurities and possibly also their chemical composition. The portion of dissociated components in ice could be estimated only qualitatively and through the comparison to the chemical analysis of the meltwater. However, the Raman-spectroscopy data clearly suggest that microscopic inclusions of second phase are present in solid ice in significantly higher concentrations, compared to liquid water. Mixing and chemical reactions of impurities is promoted through the deforming ice matrix. Our image of “ice as a frozen archive” could be replaced by “ice as an effective reactor”, depending on the spatial scales and time spans referred to. The resulting implication for the chrono-stratigraphic integrity of ice-core records may still be positive, because the reaction products often posses lower diffusion rates. A universal mechanism for the impurity effect on ice deformation could not be identified. The localized deformation seems to be in fact an intrinsic property of ice produced by the mechanical anisotropy and triggered by the varying impurity concentrations. However, many questions regarding the form and effect of impurities in ice remain open for future investigations.Der Grönländische und der Antarktische Eisschild sind die größten Süßwasserreservoirs unseres Planeten. Das darin enthaltene Eis bildete sich über Jahrtausende aus dem Niederschlag und durch natürliche Verdichtung von Schnee, und stellt damit ein einzigartiges Klimaarchiv dar. Die großen Eismassen fließen unter ihrem eigenen Gewicht und verfrachten so Eis vom Landesinneren in die Ozeane. Die Eisdynamik wird mithilfe von numerischen Fließmodellen simuliert, u. a. um den zukünftigen Beitrag von Eisschilden zum Meeresspiegelanstieg zu prognostizieren. Die viskoplastische Verformung von Eis auf der Mikroskala involviert ähnliche Mechanismen wie die Deformation anderer polykristalliner Materialen. Die Scherung einzelner Kristalle wird durch Rekristallisation und Bildung bestimmter Mikrostrukturen begleitet. Daher können Konzepte und Vorgehensweisen der Strukturgeologie auf natürliche Eisproben angewandt werden, um ihren Deformationsstatus und die daran beteiligten Prozesse zu studieren. Chemische Spurenstoffe im Schnee und Eis setzen sich mit dem Niederschlag ab und spiegeln die Zusammensetzung der in der Atmosphäre enthaltenen Aerosole wider. Als solche spielen sie eine wichtige Rolle für paläoklimatische Rekonstruktionen. Trotz ihrer extrem niedrigen Konzentrationen beeinflussen Spurenstoffe viele physikalischen Eigenschaften von Eis, insbesondere auch das Deformationsvermögen. Konzentrationschwankungen diverser Spurenstoffkomponenten mit der Tiefe korrelieren mit Heterogenitäten im Fließgeschwindigkeitsprofil und scheinen die Bildung von lokalisierten Scherzonen zu begünstigen. Ein besseres Verständnis dieser Zusammenhänge und der dahinterstehenden Mechanismen ist notwendig um den Effekt von Spurenstoffen realistisch in Fließmodelle implementieren zu können. Die vorgelegte Arbeit befasst sich mit dem Zusammenhang zwischen chemischen Spurenstoffen und physikalischen Eigenschaften von polarem Eis. Eine zentrale Herausforderung ist es zu verstehen, in welcher Form und wo Spurenstoffe in der Eismatrix integriert sind, bzw. wie sie mit ihr während der Deformation und Rekristallisation interagieren. Natürliches Eismaterial aus Eiskernbohrungen wurde mittels einer Kombination verschiedener Methoden zur Mikrostrukturanalyse untersucht. Die Verteilungen und Zusammensetzungen von Spurenstoffen wurden mittels eines konfokalen Kryo-Raman-Mikroskops analysiert. Im Rahmen dieser Arbeit wurden neue Routinen zur Messung und Datenerfassung entwickelt. Die Ergebnisse zeigen ein komplexes Zusammenspiel zwischen Spurenstoffen, Kristallstruktur und lokalisierter Deformation von Eis. Einerseits verursachen hohe Spurenstoffkonzentrationen höhere Deformationsraten, die von feinkörniger Kristallstruktur begleitet werden. Andererseits wird die Verteilung und möglicherweise Zusammensetzung der Spurenstoffe durch die Deformation des Eises beeinflusst. Der Anteil dissoziirter Stoffe im Eis konnte nur qualitativ und indirekt durch den Vergleich der Ramananalyise mit den Ergebnissen einer chemischer Analyse von Schmelzwasser geschätzt werden. Die Ramanspektroskopischen Messungen deuten allerdings klar darauf hin, dass mikroskopische Einschlüsse sekundärer Phasen im Eis einen erheblich höheren Anteil bilden, als im flüssigen Wasser. Das Mischen von Spurenstoffen und chemische Reaktionen zwischen ihnen werden durch die Eisdeformation begünstigt. Unser Bild von “Eis als gefrorenes Archiv” könnte durch “Eis als effektiver Reaktor” ersetzt werden, je nachdem welche zeitlichen und räumlichen Spannen gemeint sind. Die darausfolgende Auswirkung auf die chrono-stratigraphische Integrität von Eiskerndaten ist insgesamt jedoch positiv, da die Reaktionsprodukte oft niedrigere Diffusionsraten besitzen. Ein universeller Mechanismus für die Auswirkung von Spurenstoffen auf die Eisdeformation konnte nicht vollständig aufgedekt werden. Vielmehr scheint Deformationslokalisierung als Folge der mechanischen Anisotropie eine intrinsische Eigenschaft von Eis zu sein, die durch die Variation in Spurenstoffkonzentrationen getriggert wird. Viele Fragen hinsichtlich der Form und Wirkung von Spurenstoffen im Eis stehen allerdings noch offen für zukünftige Forschungsprojekte

Stanley Hoffman: Chaos and Violence: What Globalization, Failed States, and Terrorism Mean for U.S. Foreign Policy.

Stanley Hoffman: Chaos and Violence: What Globalization, Failed States, and Terrorism Mean for U.S. Foreign Policy. 1st ed. Lanham, Md.: Rowman & Littlefield Publisher, 2006, 226 stran, ISBN 0-7425-4071-2 (signatura knihovny ÚMV 53 326)

Document Structure in Long Document Transformers

Long documents often exhibit structure with hierarchically organized elements of different functions, such as section headers and paragraphs. Despite the omnipresence of document structure, its role in natural language processing (NLP) remains opaque. Do long-document Transformer models acquire an internal representation of document structure during pre-training? How can structural information be communicated to a model after pre-training, and how does it influence downstream performance? To answer these questions, we develop a novel suite of probing tasks to assess structure-awareness of long-document Transformers, propose general-purpose structure infusion methods, and evaluate the effects of structure infusion on QASPER and Evidence Inference, two challenging long-document NLP tasks. Results on LED and LongT5 suggest that they acquire implicit understanding of document structure during pre-training, which can be further enhanced by structure infusion, leading to improved end-task performance. To foster research on the role of document structure in NLP modeling, we make our data and code publicly available.Comment: Accepted at EACL 2024. Code and data: http://github.com/UKPLab/eacl2024-doc-structur

Modal Resonant Frequencies and Radiation Quality Factors of Microstrip Antennas

The chosen rectangular and fractal microstrip patch antennas above an infinite ground plane are analyzed by the theory of characteristic modes. The resonant frequencies and radiation Q are evaluated. A novel method by Vandenbosch for rigorous evaluation of the radiation Q is employed for modal currents on a Rao-Wilton-Glisson (RWG) mesh. It is found that the resonant frequency of a rectangular patch antenna with a dominant mode presents quite complicated behaviour including having a minimum at a specific height. Similarly, as predicted from the simple wire model, the radiation Q exhibits a minimum too. It is observed that the presence of out-of-phase currents flowing along the patch antenna leads to a significant increase of the Q factor

Impact of Particle and Equipment Properties on Residence Time Distribution of Pharmaceutical Excipients in Rotary Tablet Presses

Paddle feeders are devices commonly used in rotary tablet presses to facilitate constant and efficient die filling. Adversely, the shear stress applied by the rotating paddles is known to affect the bulk properties of the processed powder dependent on the residence time. This study focuses on the residence time distribution (RTD) of two commonly applied excipients (microcrystalline cellulose, MCC; dicalcium phosphate, DCP), which exhibit different flow properties inside rotary tablet presses. To realistically depict the powder flow inside rotary tablet presses, custom-made tracer powder was developed. The applied method was proven to be appropriate as the tracer and bulk powder showed comparable properties. The RTDs of both materials were examined in two differently scaled rotary tablet presses and the influence of process parameters was determined. To analyze RTDs independent of the mass flow, the normalized variance was used to quantify intermixing. Substantial differences between both materials and tablet presses were found. Broader RTDs were measured for the poorer flowing MCC as well as for the production scale press. The obtained results can be used to improve the general understanding of powder flow inside rotary tablet presses and amplify scale-up and continuous production process development

Micro-inclusions in the EGRIP ice core identified with Raman-spectroscopy

Soluble and insoluble impurities play a crucial role regarding the deformability and thus the flow of polar ice. To better understand this interplay from a mechanistic point of view it is especially important to investigate the location and chemical composition of micro-inclusions (Stoll et al., 2021), which are among the most abundant impurities in polar ice. New results from a systematic analysis of micro-inclusions in Holocene ice from the East Greenland Ice Core Project (EGRIP), which has been drilled near the onset of the Northeast Greenland Ice Stream (NEGIS), offer unique insights into the dynamics of fast flowing ice over different scales, ranging from kilometres to micrometres. Investigating the small-scale properties of eleven samples from Holocene ice, i.e. the upper 1340 m of the EGRIP ice core, we mapped the locations of several thousand micro-inclusions inside the ice. The use of cryo-Raman spectroscopy allowed us to obtain a representative overview of the mineralogy of these inclusions in the ice without the risk of contamination. We identified a variety of Raman spectra, mainly from sulphates (dominated by gypsum) and terrestrial dust, such as quartz, mica and feldspar. The observed mineralogy changes with depth and EGRIP Holocene ice can be categorised in two different depth regimes, i.e. the upper (100-900 m) and lower (900-1340 m) regimes, depending on their mineralogy. Furthermore, micro- inclusions show certain spatial patterns, such as clustering or layering, which are partly related to their mineralogy. We thus conclude that Greenlandic Holocene ice has a broader, and more variable, mineralogy than previously reported and that chemical reactions might take place within the ice sheet, possibly altering the paleo-climate record. Our approach further demonstrates the added value of systematic, combined high-resolution impurity and microstructural studies, and the importance of considering different spatial scales and is thus another step towards a more holistic understanding of impurities in ice

A Review of the Microstructural Location of Impurities in Polar Ice and Their Impacts on Deformation

Insoluble and soluble impurities, enclosed in polar ice sheets, have a major impact on the deformation behaviour of the ice. Macro- and Micro-scale deformation observed in ice sheets and ice cores has been retraced to chemical loads in the ice, even though the absolute concentration is negligible. And therefore the exact location of the impurities matters: Allocating impurities to specific locations inside the ice microstructure inherently determines the physical explanation of the observed interaction between chemical load and the deformational behaviour. Both, soluble and non-soluble impurities were located in grain boundaries, triple junctions or in the grain interior, using different methods, samples and theoretical approaches. While each of the observations is adding to the growing understanding of the effect of impurities in polar ice, the growing number of ambiguous results calls for a dedicated and holistic approach in assessing the findings. Thus, we here aim to give a state of the art overview of the development in microstructural impurity research over the last 20 years. We evaluate the used methods, discuss proposed deformation mechanisms and identify two main reasons for the observed ambiguity: 1) limitations and biases of measurement techniques and 2) the physical state of the analysed impurity. To overcome these obstacles we suggest possible approaches, such as the continuous analysis of impurities in deep ice cores with complementary methods, the implementation of these analyses into established in-situ ice core processing routines, a more holistic analysis of the microstructural location of impurities, and an enhanced knowledge-transfer via an open access data base

Using a composite flow law to model deformation in the NEEM deep ice core, Greenland — Part 2: The role of grain size and premelting on ice deformation at high homologous temperature

The ice microstructure in the lower part of the North Greenland Eemian Ice Drilling (NEEM) ice core consists of relatively fine-grained ice with a single maximum crystallographic preferred orientation (CPO) alternated by much coarser-grained ice with a partial (great circle) girdle or multi-maxima CPO. In this study, the grain-size-sensitive (GSS) composite flow law of Goldsby and Kohlstedt (2001) was used to study the effects of grain size and premelting (liquid-like layer along the grain boundaries) on strain rate in the lower part of the NEEM ice core. The results show that the strain rates predicted in the fine-grained layers are about an order of magnitude higher than in the much coarser-grained layers. The dominant deformation mechanisms, based on the flow relation of Goldsby and Kohlstedt (2001), between the layers is also different, with basal slip rate limited by grain boundary sliding (GBS-limited creep) being the dominant deformation mechanism in the finer-grained layers, while GBS-limited creep and dislocation creep (basal slip rate limited by non-basal slip) contribute both roughly equally to bulk strain in the coarse-grained layers. Due to the large difference in microstructure between finer-grained ice and the coarse-grained ice at premelting temperatures (T>262 K), it is expected that the fine-grained layers deform at high strain rates, while the coarse-grained layers are relatively stagnant. The difference in microstructure, and consequently in viscosity, between impurity-rich and low-impurity ice can have important consequences for ice dynamics close to the bedrock

Microstructure, micro-inclusions, and mineralogy along the EGRIP (East Greenland Ice Core Project) ice core – Part 2: Implications for palaeo-mineralogy

Impurities in polar ice do not only allow the re- construction of past atmospheric aerosol concentrations but also influence the physical properties of the ice. However, the localisation of impurities inside the microstructure is still un- der debate and little is known about the mineralogy of solid inclusions. In particular, the general mineralogical diversity throughout an ice core and the specific distribution inside the microstructure is poorly investigated; the impact of the mineralogy on the localisation of inclusions and other pro- cesses is thus hardly known. We use dust particle concen- tration, optical microscopy, and cryo-Raman spectroscopy to systematically locate and analyse the mineralogy of micro- inclusions in situ inside 11 solid ice samples from the up- per 1340 m of the East Greenland Ice Core Project ice core. Micro-inclusions are more variable in mineralogy than pre- viously observed and are mainly composed of mineral dust (quartz, mica, and feldspar) and sulfates (mainly gypsum). Inclusions of the same composition tend to cluster, but clus- tering frequency and mineralogy changes with depth. A va- riety of sulfates dominate the upper 900 m, while gypsum is the only sulfate in deeper samples, which however contain more mineral dust, nitrates, and dolomite. The analysed part of the core can thus be divided into two depth regimes of different mineralogy, and to a lesser degree of spatial distri- bution, which could originate from different chemical reac- tions in the ice or large-scale changes in ice cover in north- east Greenland during the mid-Holocene. The complexity of impurity mineralogy on the metre scale and centimetre scale in polar ice is still underestimated, and new methodological approaches are necessary to establish a comprehensive un- derstanding of the role of impurities. Our results show that applying new methods to the mineralogy in ice cores and recognising its complexity, as well as the importance for lo- calisation studies, open new avenues for understanding the role of impurities in ice cores

Macrophage Polarization is Deregulated in Haemophilia

Macrophages make important contributions to inflammation and wound healing. We show here that macrophage polarization is deregulated in haemophilia in response to macrophage colony-stimulating factor (M-CSF) and partially in response to granulocyte-macrophage colony-stimulating factor (GM-CSF). As a result, haemophilia macrophages exhibit a specific impairment of M-CSF-mediated functions involved in wound healing such as clot invasion and phagocytosis. Haemophilia monocytes express reduced amounts of the receptors for M-CSF and GM-CSF, which correlates with a failure to express tumour necrosis factor α (TNFα) and CD163 in M-CSF-treated haemophilia macrophages and reduced expression of TNFα and CD206 after treatment with GM-CSF. Protein expression in response to M-CSF was regained with respect to CD163 and CD206 after embedding haemophilia monocytes in clotted plasma suggesting that a functioning coagulation system has positive effects on macrophage M2 polarization. Mimicking the functional deficits of haemophilia macrophages in normal macrophages was possible by adding leptin, which we found to be elevated in the blood of haemophilia patients, to a monocyte cell line. The increase of leptin occurred in conjunction with C-reactive protein in a body mass index-controlled cohort suggesting that haemophilia patients harbour chronic low-grade inflammation. Together, our data indicate that impaired clotting in haemophilia patients leads to increased inflammation and a deregulation in macrophage differentiation, which may explain the commonly observed deficits in wound healing and tissue regeneration