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Deep Geothermal Energy for Lower Saxony (North Germany) – Combined Investigations of Geothermal Reservoir Characteristics
For the economic success of a geothermal project the hydraulic properties and temperature of the geothermal reservoir are crucial. New methodologies in seismics, geoelectrics and reservoir geology are tested within the frame of the collaborative research programme “Geothermal Energy and High-Performance Drilling” (gebo). Within nine geoscientific projects, tools were developed that help in the evaluation and interpretation of acquired data. Special emphasis is placed on the investigation of rock properties, on the development of early reservoir assessment even during drilling, and on the interaction between the drilling devices and the reservoir formation. The propagation of fractures and the transport of fluid and heat within the regional stress field are investigated using different approaches (field studies, seismic monitoring, multi-parameter modelling). Geologic structural models have been created for simulation of the local stress field and hydromechanical processes. Furthermore, a comprehensive dataset of hydrogeochemical environments was collected allowing characterisation and hydrogeochemical modelling of the reservoir.
Pattern transfer of sub-micrometre-scaled structures into solid copper by laser embossing
Laser embossing allows the micron and submicron patterning of metal substrates that is of great interest in a wide range of applications. This replication process enables low-cost patterning of metallic materials by non-thermal, high-speed forming which is driven by laser-induced shock waves. In this study the surface topography characteristics as well as the material structure at laser embossing of sub-micrometre gratings into solid copper is presented. The topography of the laser-embossed copper pattern is analysed with atomic force microscopy (AFM) in comparison to the master surface. The height of the embossed structures and the replicated pattern fidelity increases up to a laser fluence of F ∼ 10 J/cm2. For higher laser fluences the height of the embossed structures saturates at 75% of the master pattern height and the shape is adequate to the master. Structural modifications in the copper mono crystals after the laser embossing process were investigated with transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD). Almost no modifications were detected. The residual stress after laser embossing of 32 MPa (F = 30 J/cm2) has only a limited influence on the surface pattern formation.
Amyloids: From molecular structure to mechanical properties
Many proteins of diverse sequence, structure and function self-assemble into morphologically similar fibrillar aggregates known as amyloids. Amyloids are remarkable polymers in several respects. First of all, amyloids can be formed from proteins with very different amino acid sequences; the common denominator is that the individual proteins constituting the amyloid fold predominantly into a β-sheet structure. Secondly, the formation of the fibril occurs through non-covalent interactions between primarily the β-sheets, causing the monomers to stack into fibrils. The fibrils are remarkably robust, considering that the monomers are bound non-covalently. Finally, a common characteristic of fibrils is their unbranched, straight, fiber-like structure arising from the intertwining of the multiple β-sheet filaments. These remarkably ordered and stable nanofibrils can be useful as building blocks for protein-based functional materials, but they are also implicated in severe neurodegenerative diseases. The overall aim of this article is to highlight recent efforts aimed at obtaining insights into amyloid proteins on different length scales. Starting from molecular information on amyloids, single fibril properties and mechanical properties of networks of fibrils are described. Specifically, we focus on the self-assembly of amyloid protein fibrils composed of peptides and denatured model proteins, as well as the influence of inhibitors of fibril formation. Additionally, we will demonstrate how the application of recently developed vibrational spectroscopic techniques has emerged as a powerful approach to gain spatially resolved information on the structure-function relation of amyloids. While spectroscopy provides information on local molecular conformations and protein secondary structure, information on the single fibril level has been developed by diverse microscopic techniques. The approaches to reveal basic mechanical properties of single fibrils like bending rigidity, shear modulus, ultimate tensile strength and fracture behavior are illustrated. Lastly, mechanics of networks of amyloid fibrils, typically forming viscoelastic gels are outlined, with a focus on (micro-) rheological properties. The resulting fundamental insights are essential for the rational design of novel edible and biodegradable protein-based polymers, but also to devise therapeutic strategies to combat amyloid assembly and accumulation during pathogenic disorders.
Monitoring the chemistry of self-healing by vibrational spectroscopy - Current state and perspectives
Self-healing materials are designed to heal damage caused by, for example, mechanical stress or aging such that the original functionality of the material is at least partially restored. Thus, self-healing materials hold great promise for prolonging the lifetime of machines, particularly those in remote locations, as well as in increasing the reliability and safety associated with functional materials in, for example, aeronautics applications. Recent material science applications of self-healing have led to an increased interest in the field and, consequently, the spectroscopic characterization of a wide range of self-healing materials with respect to their mechanical properties such as stress and strain resistance and elasticity was in the focus. However, the characterization of the chemical mechanisms underlying various self-healing processes locally within the damaged region of materials still presents a major challenge. This requires experimental techniques that work non-destructively in situ and are capable of revealing the chemical composition of a sample with sufficient spatial and temporal resolution without disturbing the healing process. Along these lines, vibrational spectroscopy and, in particular Raman spectroscopy, holds great promise, largely due to the high spatial resolution in the order of several hundreds of nanometers that can be obtained. This article aims to summarize the state of the art and prospective of Raman spectroscopy to contribute significant insights to the research on self-healing materials - in particular focusing on polymer and biopolymer materials.
PS-BBICS: Pulse stretching bulk built-in current sensor for on-chip measurement of single event transients
The bulk built-in current sensor (BBICS) is a cost-effective solution for detection of energetic particle strikes in integrated circuits. With an appropriate number of BBICSs distributed across the chip, the soft error locations can be identified, and the dynamic fault-tolerant mechanisms can be activated locally to correct the soft errors in the affected logic. In this work, we introduce a pulse stretching BBICS (PS-BBICS) constructed by connecting a standard BBICS and a custom-designed pulse stretching cell. The aim of PS-BBICS is to enable the on-chip measurement of the single event transient (SET) pulse width, allowing to detect the linear energy transfer (LET) of incident particles, and thus assess more accurately the radiation conditions. Based on Spectre simulations, we have shown that for the LET from 1 to 100 MeV cm2 mg−1, the SET pulse width detected by PS-BBICS varies by 620–800 ps. The threshold LET of PS-BBICS increases linearly with the number of monitored inverters, and it is around 1.7 MeV cm2 mg−1 for ten monitored inverters. On the other hand, the SET pulse width is independent of the number of monitored inverters for LET > 4 MeV cm2 mg−1. It was shown that supply voltage, temperature and process variations have strong impact on the response of PS-BBICS.
Formation dynamics of ultra-short laser induced micro-dots in the bulk of transparent materials
In this paper, we study the formation dynamics of ultra-short laser-induced micro dots under the surface of transparent materials. Laser-induced micro dots find their application in direct part marking, to address full life cycle traceability. We first demonstrate the possibility of direct laser part marking into the cladding of an optical fiber. Then, we monitor the laser affected zone with the help of a time-resolved phase contrast microscopy setup in a fused silica substrate. We show that the transient energy relaxation processes affect the host material over a region that exceeds the micro dot size by several micrometers.
Progress and challenges in using sustainable carbon anodes in rechargeable metal-ion batteries
Rechargeable lithium-ion batteries (LIBs) are one of the most promising alternatives to effectively bypass fossil fuels. However, long-term energy application of LIBs could be restricted in the future due to the increased production cost of LIB arising from the shortage and inaccessibility of Li in the Earth's crust. Na or K have been considered as substitutes for Li but in spite of their natural abundance, they suffer from low gravimetric/volumetric energy density. An alternative to increase the efficiency of sodium-ion battery (SIBs) and potassium-ion battery (KIBs) is to focus on finding the high‐performing negative electrode, the anode. The large volume changes of alloying and conversion type anodes for KIBs and SIBs make hard carbons to a better option on this regard than usual graphitic carbons, but a key obstacle is the reliance on unsustainable sources. Thus, biomass-derived carbon could offer a promising alternative, and it has indeed been in the focus of much recent work. This review highlights the recent advances in using carbon extracted from various biomass sources in rechargeable Li-, Na-, and K-ion batteries. Maximizing the energy and power densities as well as the lifetime of carbon anodes require an exploration of the right balance between carbon structures, pore morphology, chemical composition and alkali metal-ion storage. Thus, in this review, first, we take stock of key challenges and opportunities to extract carbon from various plants structural components and identify the extracted carbon structure compared to graphite-like structure. Then, we provide an overview on morphological and structural modification of the extracted carbons. Finally, we show how the physicochemical properties, structural alignment and morphological variation of the biomass-derived carbon can affect the storage mechanism and electrochemical performance. The extensive overview of this topic provided here is expected to stimulate further work on environmentally friendly battery design and towards the optimization of the battery performance. Electrode materials in alkali-metal-ion batteries that are based on biomass-derived carbon may allow not only a technical breakthrough, but also an ethically and socially acceptable product.
Processing metallic glasses by selective laser melting
Metallic glasses and their descendants, the so-called bulk metallic glasses (BMGs), can be regarded as frozen liquids with a high resistance to crystallization. The lack of a conventional structure turns them into a material exhibiting near-theoretical strength, low Young's modulus and large elasticity. These unique mechanical properties can be only obtained when the metallic melts are rapidly cooled to bypass the nucleation and growth of crystals. Most of the commonly known and used processing routes, such as casting, melt spinning or gas atomization, have intrinsic limitations regarding the complexity and dimensions of the geometries. Here, it is shown that selective laser melting (SLM), which is usually used to process conventional metallic alloys and polymers, can be applied to implement complex geometries and components from an Fe-base metallic glass. This approach is in principle viable for a large variety of metallic alloys and paves the way for the novel synthesis of materials and the development of parts with advanced functional and structural properties without limitations in size and intricacy.
Ab initio based study of finite-temperature structural, elastic and thermodynamic properties of FeTi
We employ density functional theory (DFT) to calculate pressure dependences of selected thermodynamic, structural and elastic properties as well as electronic structure characteristics of equiatomic B2 FeTi. We predict ground-state single-crystalline Young's modulus and its two-dimensional counterpart, the area modulus, together with homogenized polycrystalline elastic parameters. Regarding the electronic structure of FeTi, we analyze the band structure and electronic density of states. Employing (i) an analytical dynamical matrix parametrized in terms of elastic constants and lattice parameters in combination with (ii) the quasiharmonic approximation we then obtained free energies, the thermal expansion coefficient, heat capacities at constant pressure and volume, as well as isothermal bulk moduli at finite temperatures. Experimental measurements of thermal expansion coefficient complement our theoretical investigation and confirm our theoretical predictions. It is worth mentioning that, as often detected in other intermetallics, some materials properties of FeTi strongly differ from the average of the corresponding values found in elemental Fe and Ti. These findings can have important implications for future materials design of new intermetallic materials.
Toward mixed-element meshing based on restricted Voronoi diagrams
In this paper we propose a method to generate mixed-element meshes (tetrahedra, triangular prisms, square pyramids) for B-Rep models. The vertices, edges, facets, and cells of the final volumetric mesh are determined from the combinatorial analysis of the intersections between the model components and the Voronoi diagram of sites distributed to sample the model. Inside the volumetric regions, Delaunay tetrahedra dual of the Voronoi diagram are built. Where the intersections of the Voronoi cells with the model surfaces have a unique connected component, tetrahedra are modified to fit the input triangulated surfaces. Where these intersections are more complicated, a correspondence between the elements of the Voronoi diagram and the elements of the mixedelement mesh is used to build the final volumetric mesh. The method which was motivated by meshing challenges encountered in geological modeling is demonstrated on several 3D synthetic models of subsurface rock volumes.