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Transport and reactions of light elements in pegmatitic systems under thermal disequilibrium – implications for magmatic/hydrothermal ore processes
No full textRare-element pegmatites are valuable resources for critical raw materials like Li and B. The role of a free fluid phase in their formation and in particular its impact on the enrichment of these elements is still elusive. We have conducted an extensive experimental diffusion study to investigate transport and enrichment processes of Li and B in pegmatitic systems. Li and B were selected as elements with contrasting structural roles and diffusivities in silicate melts, which nevertheless are commonly enriched simultaneously in rare-element pegmatites. Glasses were synthesized resembling a flux-rich boundary layer that is generally acknowledged to play a critical role during pegmatite formation. Diffusion couple experiments were performed by opposing nominally Li- and B-free glasses to their high-Li and -B counterparts in order to investigate their chemical diffusion in a pegmatite-forming melt. Self-diffusion experiments were performed for B using a glass with the same chemical composition, but enriched in 11B, to determine the mobility of B under the absence of chemical potential gradients. Moreover, a novel experimental setup was developed to investigate the elemental and isotopic transport of Li and B during the interaction between a coexisting melt and a fluid phase. Experiments were performed at 100 MPa with Ar as the pressure medium. A temperature range of 650–1250 °C was covered using either a rapid-heat and rapid-quench cold-seal pressure vessel, or an internally heated pressure vessel.
In diffusion couple experiments, Li diffusion profiles formed rapidly by an interdiffusive exchange with Na in an otherwise immobile matrix. The B flux was balanced by an opposing flux of all other elements and the binary diffusion approach was applied for simplification. The activation energy for Li interdiffusion (99 ± 7 kJ mol-1) is smaller than for the chemical diffusion of B (200 ± 17 kJ mol-1) in dry melts. The addition of 3.1–3.9 wt % H2O to the melts substantially decreases the activation energy of B diffusion to 138 ± 8 kJ mol-1 and B diffusion correlates with the Eyring diffusivity in dry and hydrous experiments. Both Li and B isotopes fractionate kinetically during diffusion, but for Li is the effect is considerably larger (β = 0.20) compared to B (β = 0.032).
The melt–fluid experiments have shown that Li and B can be transported from a source melt into a sink melt via a fluid phase, without the two melts being in direct contact. The enrichment of Li and B in the sink depends most notably on the experimental duration, but also on the fluid composition and the composition of the porous filling material between the two melts. Exposing the experimental charges to a temperature gradient likely enhances fluid convection and subsequently the amount of transported Li and B in the sink melt. There is no evidence for kinetic isotope fractionation during transport in the fluid. On the contrary, δ7Li is higher in the sink compared to the source melt indicating fractionation due to different bond strengths in the melt and the fluid. For B, no such effects were observed within the analytical uncertainty. We present evidence that especially for Li, the transport is significantly faster in a melt than in a fluid phase and that any relevant transport in a fluid phase occurs via physical processes (e.g. convection)
Uncertainty quantification for inelastic materials and structures: Time-separated stochastic mechanics
Get PDFUncertainty quantification is crucial for the design of resource-efficient and reliable structures. Uncertainties of the material properties arise naturally in the production process and have significant effect on the structural behavior.
In this work, a novel method for the uncertainty quantification of inelastic materials and structures is presented. The method is based on a separation of random but time-independent from deterministic but time-dependent behavior.
As a result, only a low number of deterministic time-dependent basis functions are calculated. This allows uncertainty quantification at greatly reduced costs
Evaluation of an In+ Coulomb crystal clock with relative uncertainties in the low 10−18 range
Get PDFClocks have been among the most accurate man-made devices for centuries. Atomic clocks, which have been defining time by means of a microwave transition in the 133Cs atom since 1967, represent a major step in this development. A redefinition of the SI unit of time based on optical atomic clocks is currently under discussion. This forthcoming redefinition requires, among other criteria, the repeated demonstration of the consistency of different optical frequency standards in the low 10−18 range. In this work, the first evaluation of the systematic shifts and their uncertainties in a 115In+–172Yb+ Coulomb crystal clock is presented. This clock utilizes the 1S0 ↔ 3P0 transition in 115In+. 172Yb+ ions are co-trapped with the 115In+ ions in a segmented Paul trap and used for sympathetic cooling. With a systematic uncertainty of 2.5×10−18 when operating with a 1In+–3Yb+ crystal and 2.6×10−18 when operating with a 2In+–4Yb+ crystal, this clock is one of the most accurate clocks in the world. In addition, the operation of the clock with multiple clock ions is the first of its kind at this level of uncertainty. Measurements with up to four clock ions show a reduction in instability from 1.6×10−15/√
τ for a single indium ion to 9.2(4)×10−16/√τ when operating with four indium ions. By using an additional quench laser, the instability in another series of measurements was reduced from a single-ion instability of 1.5×10−15/√ τ to a four-ion instability of 7.1(15)×10−16/√τ , which is consistent with the expected scaling of 1/√N with the number of clock ions N. In this work, the hyperfine structure of the 3P0 ↔ 1P1 transition used for quenching was also resolved for the first
time and the hyperfine constants were determined to be AHFS = 265.42(75)MHz and BHFS = 291.4(135) MHz. In frequency comparisons with other clocks, the optical frequency ratios 115In+/171Yb+(E3) and 115In+/87Sr were determined. With a relative total uncertainty of 4.2 × 10−18, the former ratio is the most accurate frequency ratio of different species published to date. It is also the first to meet one of the requirements defined on the roadmap for redefining the SI unit of the second: Measurements of frequency ratios with relative total measurement uncertainties below 5 × 10−18. The determination of the absolute frequency results in an uncertainty of 1.3 × 10−16 for the 1S0 ↔ 3P0 transition in 115In+, which is limited by that of the cesium fountains.
The results obtained summarized:
ν115In+
ν171Yb+(E3)
=1.973 773 591 557 215 788(8)
ν115In+
ν87Sr
=2.952 748 749 874 860 781(27)
ν115In+ =1 267 402 452 901 038.87(16) H
Novel Ultrafast Light Sources Based on Third-Order Parametric Nonlinear Effects
No full textParametric third-order nonlinear effects offer a promising approach for the generation of ultrashort pulses within the ultraviolet (UV) spectral range through the conversion of near infrared laser radiation. Third-harmonic generation (THG) combines three identical photons into a single high-energy photon, thereby enabling direct generation of ultrashort UV pulses without intermediate conversion steps across the visible spectrum. In addition, four-wave mixing (FWM), which involves the combination of three independent photons by summation and subtraction, offers broad tunability while achieving the high photon energies required for UV pulse generation. However, the practical realisation of these processes is often hindered by weak nonlinearities, absorption losses in nonlinear crystals and difficulties in phase matching. This study proposes innovative approaches to exploit third-order nonlinear effects for efficient ultrashort pulse generation, compression and frequency conversion. The first approach is based on THG in dielectric coatings. A study of THG in a single dielectric layer is conducted to reveal the influence of interference effects, Kerr nonlinearity and higher order effects. Based on these findings, multilayer structures are utilised to enhance the THG efficiency by several orders of magnitude in comparison to the single layer. An alternative is the use of gaseous media, which have the advantage of lower absorption and greater control over dispersion and nonlinearity through pressure tuning. In combination with hollow-core fibres, gases offer an extremely versatile platform for high power nonlinear optics. In this work, the generation of tunable UV pulses by dispersive wave generation in Kagome fibres is investigated. Dispersive wave generation using four-wave mixing offers spectral tunability, making it a powerful technique for nonlinear pulse generation. The first experimental demonstration of dispersive waves driven by few-cycle pulses is presented, with numerical simulations showing the potential for sub-femtosecond pulses in the extreme ultraviolet region. Instead of focusing solely on enhancing the efficiency of UV generation via nonlinear processes, an alternative approach involves enhancing the pulse energy in the UV range by increasing the pulse energy of the pump laser systems. Self-phase modulation, a third-order parametric process, can be employed for pulse compression in multipass cells (MPCs). This technique is explored in this work to achieve the compression of pulses in the near infrared spectral range with a duration of several hundred femtoseconds down to the range of a few-cycles while maintaining high transmission efficiency. For this purpose, a two-stage MPC system is designed based on numerical simulations, with the first stage successfully implemented in experiments. The results of this study highlight the potential of third-order nonlinear effects for the development of more efficient and versatile ultrafast optical systems, which offer new opportunities for applications such as spectroscopy and strong-field physics
Physically-based modeling of underwater sound mitigation by a bubble curtain at pile driving
Get PDFOffshore wind energy is an important part of the future energy supply. Typically, piles are driven into the seabed to create the foundations for wind turbines. This process is associated with high levels of underwater noise, threatening the marine environment, including harbour porpoises, which rely on hearing for foraging, communication and orientation. To protect them, regulators have set limits, such as the 160dB re 1\mu Pa^2s sound exposure level at 750m distance from the pile in the German North Sea and Baltic Sea. Various noise abatement systems have been developed in recent years to keep noise levels below the specified limits. The Big Bubble Curtain is the most widely used system, providing reliable noise reduction. However, despite its importance to the offshore wind industry, no physically based models could provide insight into the important mechanisms that cause the noise reduction effect. Furthermore, there have been no measures to predict the resulting insertion loss reliably.
Therefore, a model representing the acoustic properties of the bubble curtain is introduced in this thesis, which is based on three submodels representing the fluid dynamics, the bubble formation process and the bubble acoustics. The fluid dynamics is represented by an integral bubble plume model, which provides the local gas fraction. The bubble formation process is represented by a simplified model of the bubble population dynamics combined with an integral model of the bubble flow, providing the bubble size distribution. The bubble acoustics is based on an established effective medium theory, which assumes that a bubble interacts with the sound wave field as a linear oscillator, strongly attenuating the sound energy close to its resonant frequency. Coupling the three submodels allows the local effective wavenumber field of the bubble curtain to be determined. In a subsequent step, the wavenumber field is integrated into a model of the acoustic scenario, which includes also the pile, the water column and the soil and allows the simulation of the bubble curtain under realistic environmental conditions. The resulting model has been validated with acoustic measurement data sets from different offshore construction sites. Finally, it has been used to study in detail the sound wave transmission through the bubble curtain and the effect of the bubble curtain on the sound wave field behind the bubble curtain. This allows a precise analysis of the effects that contribute to the insertion loss through the bubble curtain.Die Offshore-Windenergie ist eine wichtige Säule der zukünftigen Energieversorgung in Deutschland und Europa. Um die Fundamente für die Windenergieanlagen herzustellen, werden üblicherweise Pfähle in den Meeresboden gerammt. Dabei entstehen hohe Unterwasserschallpegel, die eine Bedrohung für die Meeresumwelt darstellen, wie zum Beispiel für den Schweinswal, der zur Nahrungssuche, Kommunikation und Orientierung auf sein Gehör angewiesen ist. Zum Schutz
der Umwelt hat die zuständige Zulassungsbehörde daher Grenzwerte für die deutsche Nordund Ostsee festgelegt, wie z.B. den 160 dB re 1 µPa2 s Einzelereignispegel in einer Entfernung von 750 m vom Pfahl. In den letzten Jahren wurden verschiedene Schallminderungssysteme entwickelt, um den resultierenden Schall unter den festgelegten Grenzwerten zu halten. Der große Blasenschleier (engl.: "Big Bubble Curtain") ist das am häufigsten eingesetzte System und sorgt für eine zuverlässige Schallminderung. Trotz seiner Bedeutung für die Offshore-Windindustrie gibt es jedoch bisher keine physikalisch basierten Modelle, die Aufschluss über die wichtigsten Mechanismen der Schallminderung geben können, und somit auch keine Maßnahmen, um diese zuverlässig vorherzusagen.
Im Rahmen der hier vorgestellten Arbeit wurde daher ein Modell entwickelt, das die akustischen Eigenschaften des Blasenschleiers abbildet. Dieses setzt sich aus drei Teilmodellen zusammen, die
die Strömungsmechanik, den Blasenbildungsprozess und die Blasenakustik abbilden. Die Strömungsmechanik wird durch ein integrales Modell der Blasenfahne repräsentiert. Damit wird der lokale Gasgehalt bestimmt. Der Blasenbildungsprozess wird durch ein vereinfachtes Modell der Blasenpopulationsdynamik in Kombination mit einem integralen Modell der Blasenströmung abgebildet. Dieses ermöglicht es, die Blasengrößenverteilung im Blasenschleier zu bestimmen. Das Teilmodell der Blasenakustik basiert auf einer etablierten Effektive-Medium-Theorie, bei der im Wesentlichen davon ausgegangen wird, dass eine Blase als lineares schwingungsfähiges System mit dem Schallwellenfeld interagiert und die Schallenergie in der Nähe ihrer Eigenfrequenz stark abschwächt. Durch die Kopplung der drei Teilmodelle kann das lokale akustische Wellenzahlfeld des Blasenschleiers bestimmt werden. Die Integration des Wellenzahlfelds in ein Modell des akustischen Szenarios, das auch den Pfahl, die Wassersäule und den Boden umfasst, ermöglicht es den Blasenschleier unter realistischen Umgebungsbedingungen zu simulieren. Das resultierende Modell wurde mit akustischen Messdatensätzen von unterschiedlichen OffshoreBaustellen validiert. Schließlich wurde es verwendet, um die Schallübertragung im Blasenschleier und die Auswirkungen des Blasenschleiers auf das Schallwellenfeld hinter dem Blasenschleier zu untersuchen. Dies ermöglicht eine genaue Analyse der Effekte, die zur Einfügedämpfung durch den Blasenschleier beitragen
Cross-national perspectives on educational inequalities between second-generation immigrant and ethnic majority students : the influence of educational tracking on three educational outcomes during secondary education in Western countries.
Get PDFWhile previous studies have documented educational disadvantages among second-generation immigrant students in many contexts, these disparities vary depending on the specific education-al outcome and country studied. This dissertation aims to understand how such inequalities are shaped by educational tracking – that is, the practice of grouping students by ability for instruc-tional purposes. The extent to which countries implement tracking is widely recognized as a key institutional feature of education systems that contributes to educational inequality.
Theoretically, the dissertation distinguishes between institutional (macro-level) and organiza-tional (meso-level) characteristics of tracking, as well as the mechanisms operating at the school and classroom levels. Addressing the cross-national variation in how institutional tracking mani-fests (i.e., between and within schools and classes), the thesis analyzes the relationship between the macro-level tracking degree and its meso-level consequences. A key argument advanced in this thesis is that macro-level tracking moderates the extent to which meso-level mechanisms – such as differential learning environments, signaling effects, and structured opportunities – unfold, with more pronounced negative consequences for second-generation immigrant students in countries with a higher degree of tracking.
Empirically, the dissertation advances previous research by accounting for variation in the de-gree of tracking across countries and by explicitly testing meso-level tracking mechanisms as ex-planations for immigrant inequalities in educational achievement, expectations, and their realiza-tion. Drawing on cross-national data from PISA and CILS4EU, the findings show, first, that macro-level tracking moderates meso-level mechanisms in shaping educational expectations and their realization, though this pattern is less evident for achievement. Second, the degree of tracking contributes to inequalities between second-generation immigrant and ethnic majority students in educational achievement and, to some extent, expectations – partially explained by the hypothesized meso-level mechanisms. However, no evidence is found that tracking affects immigrant inequalities in the realization of expectations.
This thesis demonstrates that incorporating meso-level mechanisms into the study of tracking enhances our understanding of how and for which outcomes tracking structures educational ine-qualities, while also providing a framework for their empirical analysis in cross-national research. Through the lens of the life-course perspective and by drawing on a range of micro-level theories of immigrant educational disparities, the thesis further offers new insights into how tracking contributes to cumulative disadvantages for the more vulnerable immigrant students in secondary education
Genetic engineering in the oilseed crop camelina: establishment and application
Get PDFAbstract
Die in vitro-Regeneration und Agrobakterien-vermittelte genetische Transformation sind essentielle Methoden der Pflanzen- und Züchtungsforschung. Die Anwendungsmöglichkeiten moderner biotechnologischer Methoden sind jedoch bei einigen Nutzpflanzen durch noch zu ineffiziente Protokolle limitiert. Davon betroffen ist insbesondere die Nutzung des erheblichen Potenzials der Genom-Editierung. Um diese Einschränkungen bei der zunehmende Bedeutung gewinnenden Ölsaat Leindotter (Camelina, Camelina sativa) zu überwinden, wurden unreife zygotische Embryonen für die in vitro-Regeneration verwendet, da davon auszugehen war, dass Gewebe dieser Ausgangsexplantate im Verlgeich zu herkömmlichen, ausdifferenzierten Pflanzenteilen eine höhere Totipotenz aufweisen. Nachdem die Bildung von Adventivsprossen und deren Weiterentwicklung zu Pflanzen unter Verwendung der experimentellen Akzession Cam139 tatsächlich mit hoher Effizienz erreicht worden war, wurden die dem zugrunde liegenden initialen Entwicklungsprozesse auf zellulärer Ebene anhand von mikroskopischen Präparaten untersucht und dabei ermittelt, dass die regenerativen Strukturen ihren Ursprung in den äußersten Schichten des Hypokotyls haben. Zudem ist es gelungen dieses für dikotyledone Pflanzen weitgehend neuartige Regenerationsprinzip auch für die aktuelle Camelina-Sorte Ligena anzuwenden.
Das neu entwickelte Regenerationsprinzip wurde dazu genutzt, eine Methode der Agrobakterien-vermittelten Transformation für Camelina zu etablieren. Bei diesen experimentellen Arbeiten wurden mehrere Einflussfaktoren variiert, darunter die gezielte mechanische Verwundung, die Dauer der Vor- und Co-Kultur sowie die Konzentration des Selektionsagens Hygromycin. Auch diese Methode erwies sich für aktuelle Sorten anwendbar, wobei Transformationsraten von bis zu 17 % (bezogen auf die Anzahl kultivierter Explantate) erreicht wurden. Schließlich wurde die neu etablierte Transformationsmethode verwendet, um das Gen des Fettsäure-modifizierenden Enzyms FATTY ACID ELONGASE 1 (FAE1) durch genspezifische Mutagenese mittels CRISPR-assoziierter (Cas)9-Endonuklease auszuschalten. Dazu wurde eine protoplastenbasierte Methode der funktionellen Validierung von in silico vorselektierten Cas9-Zielmotiven und den entsprechenden guide (g)RNAs entwickelt. Anhand dieses Tests wurden Mutationen in allen drei vorläufig ausgewählten, FAE1-spezifischen Zielmotiven aller drei homöologen Camelina-Subgenome nachgewiesen. Bei der Tiefensequenzierung Zielregion-spezifischer PCR-Amplicons von genomischer Protoplasten-DNA waren dabei bis zu 15 % der Sequenzier-Reads mutiert. Nach Verwendung des gleichen Konstrukts für die Herstellung stabil transgener Pflanzen wurden Mutationsereignisse ebenfalls in allen drei FAE1-spezifischen Zielmotiven aller drei Homöoallele nachgewiesen. Aufgrund dieser hohen Effizienz wiesen 8 von 9 primär-transgenen Pflanzen Mutationen in allen drei FAE1-Homöoallelen auf. Folglich konnten dreifach-homozygote fae1-Knockout-Mutanten bereits in der ersten Selbstungsgeneration identifiziert werden. Fettsäure-Profilanalysen dieser Knockout-Linien ergaben, dass die ernährungsphysiologisch besonders wertvollen Anteile von Linolsäure (C18:1) und -Linolensäure (C18:2) signifikant erhöht und die zu beeinträchtigter Ölqualität führende Erucasäure (C22:1) auf kaum detektierbare Spuren reduziert war.
Insgesamt gesehen umfasst die vorliegende Arbeit bedeutende Fortschritte von der biotechnologischen Erschließung der Ölsaat Camelina bis hin zum erfolgreichen Einsatz der Genom-Editierung mit dem Ergebnis der Entwicklung von Elite-Linien mit bislang unerreicht hoher Ölqualität als wichtige Grundlage einer gesunden Ernährung.In vitro regeneration and Agrobacterium-mediated genetic transformation are essential methods in plant and breeding research. However, the opportunities for applying modern biotechnological methods to some crops are limited by protocols that are still too inefficient. This particularly affects the utilization of the considerable potential of genome editing. To overcome these limitations in the increasingly important oilseed camelina (Camelina sativa), immature zygotic embryos were used for in vitro regeneration, as it was assumed that tissue from this explant type has a higher totipotency compared to conventionally used, more differentiated plant parts. After the formation of adventitious shoots and their further
development into plants using the experimental accession Cam139 had indeed been achieved with high efficiency, the underlying initial developmental processes were investigated at the cellular level using microscopic preparations, and it was determined that the regenerative structures originate in the outermost layers of the embryonic hypocotyl. In addition, this regeneration principle, which is largely unexplored for dicotyledonous plants, has also been successfully applied to the current camelina variety Ligena. The newly developed regeneration method was then used to establish Agrobacteriummediated transformation for camelina. Several influencing factors were varied in this experimental work, including the targeted mechanical wounding, the duration of the pre- and co-culture and the concentration of the selection agent hygromycin. This method also proved to be applicable to current varieties, with transformation efficiencies of up to 17% (based on
the number of cultivated explants) being achieved. Finally, the newly established transformation method was used to knock out the gene encoding the fatty acid-modifying enzyme FATTY ACID ELONGASE 1 (FAE1) by targeted
mutagenesis using CRISPR-associated (Cas) 9 endonuclease. To this end, a protoplast-based method of functional validation of in silico pre-selected Cas9 target motifs and their cognate guide (g)RNAs was developed. Using this test, mutations were detected in all three preselected FAE1-specific target motifs of all three homeologous camelina subgenomes. In the deep-sequencing of target region-specific PCR amplicons of genomic protoplast DNA, up to 15% of the sequencing reads proved mutated. After using the same construct to produce stably transgenic plants, mutation events were also detected in all three FAE1-specific target motifs of all three homeoalleles. Thanks to this high efficiency, 8 out of 9 primary transgenic
plants carried mutations in all three FAE1 homeoalleles. Consequently, triple-homozygous fae1 knockout mutants could already be identified in the first selfing generation. The fatty acid profiles of these knockout lines showed that the nutritionally particularly valuable proportions of linoleic acid (C18:1) and a-linolenic acid (C18:2) were significantly increased and that erucic acid (C22:1), which leads to impaired oil quality, was reduced to barely detectable traces. Overall, this work comprises significant advances from a basic biotechnological exploration of the oilseed camelina to the successful use of genome editing, resulting in the development of elite lines with unprecedented high oil quality as an important prerequisite for a healthy diet
Soil organic matter quality in an olive orchard differently managed for 21 years: Insights into its distribution through soil aggregates and depth
Get PDFAmong the current global challenges, the research of new practices aimed at mitigating soil impoverishment, exacerbated by the pressing climate changes, is the most urgent. Studying soil organic matter (SOM) ecological dynamics and comparing the conventional intensive farming practices with the emerging alternative sustainable ones can represent a key indicator in soil health investigation, helping to find new guidelines for conservative agrosystems management. In this study, the soil from a Mediterranean olive orchard, with both sustainable (Smng) and conventional (Cmng) land use for 21 years, was investigated for its physicochemical properties, with a particular attention to the soil organic matter from aggregates (SOM-A) and its interaction and distribution at different soil depths. Significantly higher amounts of total carbon (+50.7 %) and nitrogen (+74.9 %), as well as of SOM-A aromatic component (+76.0 %), were detected in the topsoil layer (0–5 cm) of the Smng, compared to the Cmng, a sign that the organic matter from surface deeply seeps slowly. This evidence was highlighted especially in micro-aggregates (< 0.063 mm) of the Smng, compared to the Cmng (C = +59.3 %; N = +86.7 %; SOM-A aromatic component = +87.7 % in the Smng). This trend was also reflected in an increase in the bacterial abundance and in a different accumulation of organic compounds deriving from microbial fermentation processes in Smng soil, as highlighted by the SOM-A qualitative characterization by metabolomics. The soil mineralogical analysis showed that minerals maintained a higher crystallinity in the Smng than in the Cmng, where soil tillage promoted their alteration. Moreover, Fourier-transform infrared (FTIR) spectroscopy analysis highlighted that soil disturbance in the Cmng can affect SOM distribution, creating different spatial distributions in the particle aggregates and soil depths. Distinguishing SOM quantity, quality, and interaction with mineral components can help to understand its degradability and dynamics, both essential for mitigating the effects of climate change and promoting land protection