Members of TU Berlin can publish different kinds of (text) publications on DepositOnce:

  • publications with academic content such as monographs and collected editions, journal articles and book chapters, conference proceedings and conference papers, research reports,
  • publications that must be made public in connection with examination regulations (doctoral theses and post-doctoral theses),
  • theses of TU Berlin students if the thesis has received the grade "very good" and the publication is endorsed by the supervisor or referee.

The following publication types can be selected: Doctoral thesis, Habilitation, Master thesis, Bachelor thesis, Book, Conference Proceedings, Periodical Part, Preprint, Report, Research Paper, Article, Book Part, Conference Object

For further information on requirements and workflows see Checklists and Hints for Publishing.


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Recent Submissions

Now showing 1 - 20 of 15798
  • On the carrier separation, dynamics and optical properties of metal oxide photoelectrodes

    Global warming, resulting from the ongoing combustion of fossil fuels, poses a major challenge to human civilization in the 21st century, so a major transition to renewable energy is urgently needed. Solar energy is the world’s most abundant energy source, but long-term storage remains a challenge. One way to store this energy is through synthetic fuels, such as green hydrogen. Direct solar water spitting, using earth abundant metal oxides (MOs) is considered one way of producing green hydrogen at low cost and in large amounts. However, integrated photoelectrochemical (PEC) systems based on MOs still lack the efficiency and stability that would be required for large-scale, economically viable application. Two of the main obstacles to realizing higher solar-hydrogen efficiencies are appropriate charge separation at the solid/liquid interface as well as sufficient charge transport within the bulk of the absorber layer. At first this work reexamines fundamental aspects of photo-electrochemical energy conversion, specifically, the driving forces that determine charge separation and transport in PEC devices are analyzed in detail. So far, the built-in electrical field at the solid/liquid interface is still considered by many within the PEC research community as both essential and sufficient for charge separation, which is however a misconception. Instead, this work follows a rigorous thermodynamic approach that was originally developed by Peter Würfel to describe the functionality of photovoltaic cells, which is here comprehensively transferred to the concept of a PEC cell. Based on this analysis, a closer look will be taken at how selective contacts have been designed to date, and possible new design approaches for optimized selective contacts will be presented which will allow to further improve PEC device performance in the future. Secondly, bulk transport in established and novel photoabsorber materials is investigated. The charge carrier diffusion length is an important figure of merit to judge if a material is suited as efficient photoabsorber. However, effects such as polaron formation or multiple trapping which lead to time-varying mobilities and lifetimes can complicate the determination of a diffusion length. This challenge is addressed by the development of a new generalized analysis that allows the determination of the diffusion length directly from a photoconductivity transient. The photoconductivity is measured complementary by means of optical pump THz probe spectroscopy (OPTP) and time resolved microwave conductivity (TRMC), which allows to cover a time range from 100 fs to 2 ms. Using this approach the diffusion length of BiVO4, amorphous silicon, a lead halide perovskite and crystalline silicon is found to be 15 nm, 23 nm, 9 µm and 880 µm respectively. Thirdly, limitations of charge transport by localization are investigated in several metal oxide thin films, namely CuFeO2, alpha-Fe2O3, alpha-SnWO4, CuBi2O4 and BaSnO3. The materials are exterminated using by OPTP and TRMC. OPTP probes carrier transport lengths of only a few nanometers and the corresponding short-range mobilities are found to be below 3 cm2V-1s-1. Moreover, even lower mobilities at lower probing frequencies are observed due to partial charge carrier localization on a length scale of 1-6 nm. Such short localization lengths can be rationalized for the case of CuFeO2 by an XRD domain size of ~14 nm and by electrostatic barriers that decay with the Debye length towards the domain center. Based on these results it is concluded that overcoming carrier localization by improving the microstructure should be an objective of future efforts to enhance the charge carrier transport in metal oxides. Fourthly, the optical properties of three metal oxide thin films are investigated. For the case of a polycrystalline BiVO4 strong diffuse scattering of the transmitting light is observed, which is associated with the optical anisotropy of this material. Surface and crystal orientation analysis by means of atomic force microscopy (AFM) and electron back scatter diffraction (EBSD) allow to support this hypothesis.
  • Modal and statistical analysis of the compressible round impinging jet considering turbulent inflow, system geometry and cross-flow effects

    Impinging jets appear both in nature and in various engineering systems, where they are predominately used because they can serve as very efficient cooling devices. However, the physical mechanism governing the heat transfer near the plate is still not fully understood, because it involves time and length scales that are not easily detected by experiments and not fully resolved by LES or RANS simulations. Conversely, the typical Reynolds numbers of relevant impinging-jet configurations are in a range that allows their analysis through direct numerical simulation (DNS) on modern supercomputers. The heat transfer of an impinging jet is strongly affected by a vortex system that originates in the shear layer of the jet upstream of the impingement region. Although some DNS studies exist, there are still open questions concerning how this vortex system is affected by realistic conditions, in which (i) the inflow might be turbulent, (ii) the jet might be subject to cross flow or (iii) the impingement plate might be curved. By using data stemming from previous and original DNS studies, this thesis aims at analyzing and comparing the effects of such conditions on the vortex dynamics of the compressible round impinging jet flow and resulting heat transfer. The influence of the nozzle-to-plate distance is also discussed. Dynamic mode decomposition (DMD) was used to highlight relevant features of the flow, such as vortices and instabilities. For the jet with turbulent inflow, a full statistical analysis was performed, which gives insights on the effects of the turbulent fluctuations on the mean flow and can provide valuable information for the development of turbulence models. Furthermore, the first global linear stability analysis of the round compressible impinging jet at subcritical Reynolds numbers is here presented. The analysis allowed to determine the dependence of the jet natural frequencies on the Reynolds and Mach numbers, as well as the region of the flow most sensitive to external forcing.
  • Citizenship in Iranian culture and its relationship to revival, design and use of urban spaces

    This study, over 6 chapters, aims to identify the infrastructure required to encourage a reciprocal relationship between urban spaces and citizens in Iran. Explained more practically, the research attempts to analyze human experiences, in order to illustrate the apparent conditions, as relevant to each of the respective themes. This descriptive and evaluative research has been done in three parallel phases analyzing: the concept of citizenship; urban spaces; and the interaction of the two. These three phases have been examined using literature reviews, data analysis of existing conditions, a field study and participative questionnaires. The study includes various pictures, maps, tables and diagrams to give the readers the opportunity to fully understand the subject matter; not only through text but also visually. The role of both Citizens and citizenship has been reviewed with regard to the governmental structure of Iran and Isfahan through examination of laws and urban development plans. In relation to urban management in Iran, it was found that different organizations, institutions and ministries, at national, regional and local levels, have involvement in urban affairs. Furthermore, it’s understood that other authoritative and official factors, individuals and institutions can also informally have influence over the preparation, decision-making and execution of urban projects and initiatives. Whilst undertaking a more detailed survey examining urban spaces in Iran, related issues including definitions, space types, related rules and regulations, stakeholders and most importantly, observed activities, have been examined. Incidentally, the recognition of stakeholders within urban laws in Iran, and more specifically in Isfahan, has been analyzed. The research is supported by three case studies in Isfahan, which direct the research away from the more abstract theoretical framework and aim to illustrate the character of the city in a more concrete and precise way. The case studies are investigated utilizing different social, urban and structural criteria to allow acknowledgment of variations between the historic, and contrastingly modern areas of the city. These reviews were concluded with SWOT analyses of each of the case study areas. The analysis demonstrates that the basic infrastructure, allowing interaction between citizens and urban spaces, is partly available, but future advancements of this infrastructure should be more considered, involve amendments to urban plans and laws, be accepted by citizens, and be cognizant of financial issues. A gradual considered approach, rather than shortcuts, is considered as a more secure way to achieve higher performing urban spaces for citizens. In the final chapter some practical solutions, which can be implemented within the social, administrative, spatial and cultural context of Iran have been suggested. The achievability, respective stakeholders, and the potential positive effects of proposed projects have been detailed. The study attempts to find appropriate answers to these two main questions: • What barriers and opportunities are there with regard to increased presence and participation of citizens in urban spaces? • How can a reciprocal relationship between citizens and urban spaces be cultivated and maintained?
  • Dekarbonisierung des Verkehrssektors in Berlin: Bürger:innengutachten zu wissenschaftlich erstellten Szenarien

    Ein Bürgerrat wurde eingerichtet, um Feedback zu Maßnahmen zur Dekarbonisierung des Berliner Verkehrssektors zu erhalten. Das generelle Ziel der Dekarbonisierung fand breite Unterstützung. Auf der Grundlage bereits vorliegender Studien wurden jeweilige Diskussionen für den privaten Personenverkehr, den kommerziellen Personenverkehr, den Güterverkehr und Sonderverkehre geführt. Für alle Segmente mit Ausnahme des privaten Personenverkehrs konnte eine Einigung über die Dekarbonisierungspfade erzielt werden. Für letzteren werden Pull-Maßnahmen allgemein akzeptiert, was mit dem generellen Wunsch einhergeht, nicht nur mit der Umstellung auf nicht-fossile Antriebe einhergeht, sondern auch das Verkehrssystem in Berlin weniger autozentriert zu gestalten. Simulationen zeigen, dass Pull-Maßnahmen allein bei weitem nicht ausreichen werden, um den privaten Personenverkehr zu dekarbonisieren. Wirksamere Push-Maßnahmen, wie höhere Preise oder Verbote fossiler Fahrzeuge, ergaben für dieses Segment keine klaren Mehrheiten.
  • Generative Reasoning Integrated Label Noise Robust Deep Image Representation Learning

    The development of deep learning based image representation learning (IRL) methods has attracted great attention for various image understanding problems. Most of these methods require the availability of a set of high quantity and quality of annotated training images, which can be time-consuming, complex and costly to gather. To reduce labeling costs, crowdsourced data, automatic labeling procedures or citizen science projects can be considered. However, such approaches increase the risk of including label noise in training data. It may result in overfitting on noisy labels when discriminative reasoning is employed as in most of the existing methods. This leads to sub-optimal learning procedures, and thus inaccurate characterization of images. To address this issue, in this paper, we introduce a generative reasoning integrated label noise robust deep representation learning (GRID) approach. The proposed GRID approach aims to model the complementary characteristics of discriminative and generative reasoning for IRL under noisy labels. To this end, we first integrate generative reasoning into discriminative reasoning through a supervised variational autoencoder. This allows the proposed GRID approach to automatically detect training samples with noisy labels. Then, through our label noise robust hybrid representation learning strategy, GRID adjusts the whole learning procedure for IRL of these samples through generative reasoning and that of the other samples through discriminative reasoning. Our approach learns discriminative image representations while preventing interference of noisy labels during training independently from the IRL method being selected. Thus, unlike the existing label noise robust methods, GRID does not depend on the type of annotation, label noise, neural network architecture, loss function or learning task, and thus can be directly utilized for various image understanding problems. Experimental results show the effectiveness of the proposed GR...
  • Milieus und Lebensstile in der postmigrantischen Gesellschaft

    Die Beziehung von markierter Minderheit und unmarkierter Mehrheit bildet bis dato den Schwerpunkt der Migrationsforschung. Für die Analyse spätmoderner, postmigrantischer Gesellschaften, die von Mobilität und lebensstilistischer Diversität geprägt sind, ist diese einseitige Herkunftsfixierung unzureichend. Es gilt daher, Menschen mit Migrationshintergrund in konsequent gesamtgesellschaftlich angelegten Analysen zu berücksichtigen. An die Stelle der Assimilationstheorie soll eine postmigrantisch revidierte Milieuanalyse treten, deren Entwurf in diesem Werk programmatisch skizziert wird.
  • Technik spielend (kennen)lernen

    Jugendliche und Kinder jenseits von Schule und Lerndruck für Technik begeistern: Mit dem Praxisbuch können auch fachfremde Mitarbeiter:innen in der offenen Kinder- und Jugendarbeit Workshops rund um Physik, Technik und Informatik planen und durchführen. Die Workshop-Kurzbeschreibungen stellen Inhalte, Materialien und Methoden vor, die die Beschäftigung mit Elektrotechnik oder Programmieren so selbstverständlich und spannend machen, dass sie Kinder und Jugendliche in ihren Bann ziehen und echtes Interesse an MINT-Themen wecken. Die handlungsorientierten Workshops rund um Physik, Elektrotechnik, Programmieren und 3D-Druck wurden in Berliner Jugendfreizeiteinrichtungen erprobt und entwickelt. Ansätze, Ideen, Inhalte und Umsetzungsfragen der verschiedenen Kurse werden im großen Praxisteil in gut verständlicher Sprache erläutert. In der wissenschaftlich orientierten Einführung stellt die Herausgeberin die Resonanztheorie nach Hartmut Rosa und weitere konzeptionelle Grundlagen der Kurse vor. Die Kapitel können auch einzeln heruntergeladen werden.
  • Numerical simulation of slug flow in horizontal pipes and comparison with slug frequency prediction methods from literature

    In scope of a European project conducted by the Physikalisch-Technische Bundesanstalt, OpenFOAM is utilized to simulate slug flow. Because the slug frequency is an important parameter to predict corrosion, erosion and pressure drop in pipe flow, numerous efforts to predict the slug frequency have been made in the past by various authors. The objective of this thesis is to simulate slug flow with OpenFOAM and compare the slug frequency with prediction methods from literature. Twelve of the most commonly cited slug frequency prediction methods have been analyzed and common trends as well as contradictions among them were summarized. With very few exceptions, three parameters are included in every prediction method: superficial liquid velocity, superficial gas velocity, and diameter. Discrepancies were observed for the influence of material properties on slug frequency. Many methods do not take any influence of fluid properties into account, whereas some methods include a dependency on fluid properties. Outliers were identified and several methods were selected, that agreed well with the common trends. To simulate slug flow, a mesh convergence study was performed to assure a sufficient mesh resolution. The cylindrical mesh was refined in radial and longitudinal direction separately. Furthermore, the impact of simulating a half cylindrical mesh was analyzed. It was shown, that a half cylindrical mesh is sufficient, when the resolution is fine enough. To investigate the influence of different parameters on the simulated slug frequency, a total of 27 simulations were conducted, with the focus on the most common parameters of the prediction methods from literature: diameter and superficial gas and liquid velocity. Flow conditions were chosen with the support of a flow pattern map, to assure slug or plug flow is simulated. Four simulations were set-up to investigate the influence of fluid properties by simulating different liquid viscosities, and one simulation with different liquid and gas density respectively. Results show that the simulated slug frequency lies well within the range of predicted slug frequencies, when flow conditions are similar to the conditions of the mesh study. Small divergences from the flow conditions of the mesh study can cause significant discrepancies between simulation results and predicted values. The mesh study was performed for low superficial gas velocities in the plug flow region. With increasing superficial gas velocity, slugs become aerated and the volume of fluid model might become inaccurate and require higher mesh resolutions. Simulated trends on fluid properties were in agreement with predicted trends.
  • Linear modeling of coherent structures in the self-similar region of a round turbulent jet

    Linear mean-field based modeling methods targeting the prediction of coherent structures in turbulent flows are an important part of turbulence research. The research area comprises the development of linear modeling methods, the physical interpretation based on such analyses, and the application to generic and technically relevant flows to predict the occurring turbulent structures. The present thesis addresses all three of these areas and investigates coherent structures in the far field of a round turbulent jet. Such a flow is characterized by self-similarity and broadband turbulent dynamics. The investigation of these structures is based on experiments and two mean-field based modeling approaches. In the experimental part, time-resolved stereoscopic (2D-3C) PIV measurements in streamwise and cross-stream sections of the flow are conducted, spanning a region of 35 to 95 diameters downstream of the nozzle exit. Empirical coherent structures are identified by means of spectral proper orthogonal decomposition (SPOD). For the investigated azimuthal wavenumbers ranging from m=0 to m=+-5, a dominant SPOD mode is identified in almost the entire frequency range, even for the highest experimentally resolved frequencies that are associated with the inertial subrange. In the modeling part, linear stability analysis (LSA) and resolvent analysis (RA) are carried out in a local parallel framework based on the measured mean velocity profiles. Both types of analyses are based on the identical linear operator that is build via a linearization of the Navier-Stokes equations around the mean field for an incompressible flow. The operator is modified with a simple scale-independent and spatially constant eddy viscosity, that stems from a fit to the Boussinesq approximation. The resulting modes of LSA and RA show strikingly similar trends and are both in very good agreement with the empirical modes. This even applies to modes in the frequency range which is associated with the inertial subrange. The eddy viscosity is found to be a key parameter for the modeling success. The role of eddy viscosity in LSA/RA modeling is currently discussed controversially and is, therefore, part of the investigation. The last part of the thesis deals with the swirling jet far field and aims to investigate effects of the break in symmetry in the mean flow on the far field structures. The self-similar state of the flow is analyzed and LSA modeling results are compared to the empirical modes. The present work aims to determine the potential and limitations of mean-field based linear models predicting the far field dynamics of a round turbulent jet. It is shown that turbulent structures in this flow can be decomposed into dominant SPOD modes and linear modeling methods (LSA and RA) are capable of reproducing modes in a very large range of scales when modifying the linear operator with a simple constant eddy viscosity. The success of the modeling approaches is attributed to several factors, including a predominantly resonant amplification mechanism, and the self-similar state of the flow, in which the introduction of an eddy viscosity provides a suitable framework for describing the dissipative part of the nonlinear energy transfer in the flow.
  • Interaction of atomic hydrogen with GaAs(110) surfaces: adsorption, defect generation, facetation, and cleaning

    The commonly used method of hydrogen cleaning of III-V nanowire side facets is investigated by atomically resolved scanning tunneling microscopy and spectroscopy. For a fundamental approach, the initial stages of hydrogen adsorption on GaAs(110) surfaces are investigated ad room temperature, in order to achieve an understanding of the morphological and electronic changes induced on an atomic level. Two effects are demonstrated to manifest simultaneously, rather than subsequently with hydrogen exposure: A phase separation between fully hydrogen covered areas and hydrogen free areas occurs. The fully hydrogen covered areas are characterized by hydrogen equally bonding to As- and Ga- derived dangling bonds, passivating the surface area. Additionally, upon hydrogen exposure, hydrogen induced point defects are generated in both areas with increasing density. These kinds of newly reported point defects are classified using a defect-molecule model. They are suggested to be at the origin of the observed Fermi level pinning 0:25 eV to 0:30 eV above the valence band edge for n- and p-doped GaAs(110) surfaces. The temperatures used for hydrogen cleaning are observed to be too low without simultaneous hydrogen exposure in order to achieve the changes observed upon hydrogen cleaning. At 400 ± 20 ◦C, no changes or desorption of material can be validated. However, upon simultaneous hydrogen exposure,a layer-by-layer etching of the GaAs(110) surfaces is observed. At n-doped surfaces, the layer-by-layer etching removes islands and forms preferentially Ga terminated step edges with [001] normal vector. Additionally, a large density of Ga vacancies formed on the newly exhibited surfaces is observed. Their charge transfer level is in line with the interpretation that no further Ga adatoms remain at the hydrogen cleaned surfaces, suggesting a preferential bonding of hydrogen atoms to Ga adatoms and subsequent Ga-H desorption. At p-doped surfaces, the layer-by-layer etching not only takes place at step edges, but also at defects such as As vacancies forming laterally growing vacancy clusters (pits) with increasing hydrogen exposure and simultaneous annealing. Therefore, a preferential etching of the twofold coordinated Ga atoms is concluded corroborating the conclusion drawn for n-doped surfaces. Hence, surfaces achieved by hydrogen cleaning do reveal morphological and electronic properties of etched surfaces rather than of cleavage surfaces. These results imply that the morphological and electronic properties of III-V nanowire sidewall facets obtained by hydrogen cleaning are those of etched surfaces rather than the initial growth surfaces.
  • MODUS-COVID Bericht vom 14.09.2023

    In diesem Bericht untersuchen wir das Potenzial von zwei verschiedenen Arten von Mobilitätsdaten für den Einsatz in der Pandemiemodellierung. Wir ergänzen unsere bisher für die Modellierung verwendeten Mobilfunkzellen-basierten “Längsschnitt”-Daten, um GPS-basierte “Querschnitts”-Daten und erklären die Vor- und Nachteile. GPS-basierte Daten zeichnen sich durch eine höhere Genauigkeit bzgl. der Verortung aus, sind jedoch - verglichen mit den Mobilfunkzellendaten - in einer deutlich kleineren Stichprobe verfügbar. Die höhere Genauigkeit ermöglicht es, verschiedene Aktivitätentypen (wie z.B. Schule, Arbeit oder Restaurant), getrennt auszuwerten - dies ist mit den Mobilfunkzellendaten nicht ohne Weiteres möglich. Die Integration von GPS-Daten reduziert den manuellen Aufwand, verstärkt die datengetriebene Natur des Modells und minimiert Modellannahmen. Dieser Bericht präsentiert erste Ergebnisse und Validierungen der GPS-Daten für das erste Pandemiejahr. Die Kombination beider Datenquellen bietet Potenzial, um Verhaltensänderungen während der Pandemie genauer zu erforschen und die Pandemiemodellierung zu verbessern.
  • Profile and Goals of the Collaborative Research Center 1265 “Re-Figuration of Spaces” in its Second Phase

    This working paper provides an overview of the research program and profile of the Collaborative Research Center 1265 (CRC 1265). It outlines some of the central results of its first funding period as well as research objectives and approaches for its second funding period, namely the investigation of new spatial arrangements, conflicts and multiple spatialities. The text is a slightly revised English translation of key parts of the CRC’s proposal for the second phase of its funding by the German Research Foundation (DFG). The CRC 1265 focuses on the investigation of current processes of spatial reordering and societal restructuring as a refiguration of spaces. Central to its investigation is the conceptualization of sociality as an inherently spatial phenomenon. The work of the CRC thereby aims to develop an empirically grounded theory of contemporary social change as a processual, spatial-communicative refiguration. As the CRC 1265 progresses with its investigation in its second funding phase, it aspires to contribute to the field of social science research by offering a comprehensive and empirically grounded perspective on contemporary processes of social change.
  • Environmental enrichment through virtual reality as multisensory stimulation to mitigate the negative effects of prolonged bed rest

    Prolonged bed rest causes a multitude of deleterious physiological changes in the human body that require interventions even during immobilization to prevent or minimize these negative effects. In addition to other interventions such as physical and nutritional therapy, non-physical interventions such as cognitive training, motor imagery, and action observation have demonstrated efficacy in mitigating or improving not only cognitive but also motor outcomes in bedridden patients. Recent technological advances have opened new opportunities to implement such non-physical interventions in semi- or fully-immersive environments to enable the development of bed rest countermeasures. Extended Reality (XR), which covers augmented reality (AR), mixed reality (MR), and virtual reality (VR), can enhance the training process by further engaging the kinesthetic, visual, and auditory senses. XR-based enriched environments offer a promising research avenue to investigate the effects of multisensory stimulation on motor rehabilitation and to counteract dysfunctional brain mechanisms that occur during prolonged bed rest. This review discussed the use of enriched environment applications in bedridden patients as a promising tool to improve patient rehabilitation outcomes and suggested their integration into existing treatment protocols to improve patient care. Finally, the neurobiological mechanisms associated with the positive cognitive and motor effects of an enriched environment are highlighted.
  • Anaerobic Digestion of Olive Mill Wastewater and Process Derivatives—Biomethane Potential, Operation of a Continuous Fixed Bed Digester, and Germination Index

    Olive mill wastewater (OMW) management is an economic and environmental challenge for olive oil-producing countries. The recovery of components with high added value, such as antioxidants, is a highly researched approach that could help refinance performant wastewater treatment systems. Anaerobic (co-)digestion is a suitable process to valorize the energetic and nutritional content of OMW and OMW-derived waste streams from resource recovery processes. Issues of process stability, operation, and yields discourage industrial application. Deepening the understanding of biomethane potential, continuous anaerobic digester operational parameters, and co-substrates is key to large-scale implementation. The biomethane potential of different OMW-derived samples and organic solid market waste as co-substrate was 106–350 NL methane per kg volatile solids (VS). The highest yields were obtained with the co-substrate and depolyphenolized OMW mixed with retentate from an ultrafiltration pretreatment. Over 150 days, an anaerobic fixed-bed 300 L digester was operated with different OMW-derived substrates, including OMW with selectively reduced polyphenol concentrations. Different combinations of organic loading rate and hydraulic retention time were set. The biogas yields ranged from 0.97 to 0.99 L of biogas per g of volatile solids (VS) eliminated, with an average methane content in the produced biogas of 64%. Potential inhibition of the process due to high polyphenol concentrations or over-acidification through volatile fatty acids was avoided in the continuous process through process and substrate manipulation. High concentrations of potassium and low concentrations of nitrogen and phosphate end up in the digestate. Sulfate reduction results in high H2S concentrations in the biogas. The digestate was tested for phytotoxic properties via the germination index. Diluted digestate samples improved germination by up to 50%.
  • Optimal Performance of Mg-SiC Nanocomposite: Unraveling the Influence of Reinforcement Particle Size on Compaction and Densification in Materials Processed via Mechanical Milling and Cold Iso-Static Pressing

    Achieving uniformly distributed reinforcement particles in a dense matrix is crucial for enhancing the mechanical properties of nanocomposites. This study focuses on fabricating Mg-SiC nanocomposites with a high-volume fraction of SiC particles (10 vol.%) using cold isostatic pressing (CIP). The objective is to obtain a fully dense material with a uniform dispersion of nanoparticles. The SiC particle size impact on the compressibility and density distribution of milled Mg-SiC nanocomposites is studied through the elastoplastic Modified Drucker-Prager Cap (MDPC) model and finite element method (FEM) simulations. The findings demonstrate significant variations in the size and dispersion of SiC particles within the Mg matrix. Specifically, the Mg-SiC nanocomposite with 10% submicron-scale SiC content (M10Sµ) exhibits superior compressibility, higher relative density, increased element volume (EVOL), and more consistent density distribution compared to the composite containing 10% nanoscale SiC (M10Sn) following CIP simulation. Under 700 MPa, M10Sµ shows improvements in both computational and experimental results for volume reduction percentage, 2.31% and 2.81%, respectively, and relative density, 4.14% and 3.73%, respectively, compared to M10Sn. The relative density and volume reduction outcomes are in qualitative alignment with experimental findings, emphasizing the significance of particle size in optimizing nanocomposite characteristics.
  • Laser-Based Manufacturing of Ceramics: A Review

    Ceramics are widely used in microelectronics, semiconductor manufacturing, medical devices, aerospace, and aviation, cutting tools, precision optics, MEMS and NEMS devices, insulating components, and ceramic molds. But the fabrication and machining of the ceramic-based materials by conventional processes are always difficult due to their higher hardness and mechanical properties. Therefore, advanced manufacturing techniques are being preferred for these advanced materials, and out of that, laser-based processes are widely used. The benefits of laser fabrication and machining of ceramics include high precision, reduced thermal damage, non-contact processing, and the ability to work with complex geometries. Laser technology continues to advance, enabling even more intricate and diverse applications for ceramics in a wide range of industries. This paper explains various laser based ceramic processing techniques, such as selective laser sintering and melting, and laser machining techniques, such as laser drilling, etc. Identifying and optimizing the process parameters that influence the output quality of laser processed parts is the key technique to improving the quality, which is also focused on in this paper. It aims to facilitate the researchers by providing knowledge on laser-based manufacturing of ceramics and their composites to establish the field further.
  • Adjustable Elasticity of Anatomically Shaped Lattice Bone Scaffold Built by Electron Beam Melting Ti6Al4V Powder

    This study investigates the elasticity of specific lattice structures made from titanium alloy (Ti6Al4V), namely, anatomically shaped lattice scaffolds (ASLS) aimed for reinforcement of the bone tissue graft that substitute a missing piece of the previously injured bone during its recovery. ASLSs that were used for testing were fabricated using the Electron Beam Melting (EBM) method. The mechanical properties of the ASLS were examined through uniaxial compression tests. Compression testing revealed the complex non-linear behavior of the scaffold structure’s elasticity, with distinct compression stages and deformation dependencies. The ASLS structures exhibited quasi-elastic deformation followed by the rupture of individual struts. Results demonstrate that the ASLSs can be stiffened by applying appropriate compression load and accordingly achieve the target elasticity of the structure for the specific load range. The modulus of elasticity was determined for different compression stages of ASLS, allowing interpolation of the functional relation between the modulus of elasticity and compressive force that is used for stiffening the ASLS. This study enhances the understanding of the mechanical behavior of the specific lattice structures made of Ti6Al4V and provides insights for the development of mechanically optimized anatomically shaped lattice scaffolds.
  • Process Setup and Boundaries of Wire Electron Beam Additive Manufacturing of High-Strength Aluminum Bronze

    In recent years, in addition to the commonly known wire-based processes of Directed Energy Deposition using lasers, a process variant using the electron beam has also developed to industrial market maturity. The process variant offers particular potential for processing highly conductive, reflective or oxidation-prone materials. However, for industrial usage, there is a lack of comprehensive data on performance, limitations and possible applications. The present study bridges the gap using the example of the high-strength aluminum bronze CuAl8Ni6. Multi-stage test welds are used to determine the limitations of the process and to draw conclusions about the suitability of the parameters for additive manufacturing. For this purpose, optimal ranges for energy input, possible welding speeds and the scalability of the process were investigated. Finally, additive test specimens in the form of cylinders and walls are produced, and the hardness profile, microstructure and mechanical properties are investigated. It is found that the material CuAl8Ni6 can be well processed using wire electron beam additive manufacturing. The microstructure is similar to a cast structure, the hardness profile over the height of the specimens is constant, and the tensile strength and elongation at fracture values achieved the specification of the raw material.
  • Selenium, Zinc, and Copper Status of Vegetarians and Vegans in Comparison to Omnivores in the Nutritional Evaluation (NuEva) Study

    Plant-based diets usually contain more nutrient-dense foods such as vegetables, legumes, whole grains, and fruits than a standard Western diet. Yet, the amount and especially the bioavailability of several nutrients, such as trace elements, is supposed to be lower in comparison to diets with consumption of animal-derived foods. Based on this, the Nutritional Evaluation (NuEva) study (172 participants) was initiated to compare the trace element status of omnivores, flexitarians, vegetarians, and vegans. Serum selenium, zinc, and copper concentrations and biomarkers were evaluated at baseline and during a 12-month intervention with energy- and nutrient-optimized menu plans. The implementation of optimized menu plans did not substantially influence the status of trace elements. At baseline, serum selenium biomarkers were lower in vegetarians and vegans compared to omnivores and flexitarians. The zinc intake of vegetarians and vegans was significantly lower compared to omnivores, whereas the Phytate Diet Score was increased. Accordingly, total serum zinc concentrations were reduced in vegans which was, however, only significant in women and was further supported by the analysis of free zinc. Regarding copper status, no differences were observed for total serum copper. Overall, we identified selenium and zinc as critical nutrients especially when maintaining a vegan diet.
  • Long-Distance Electric Truck Traffic: Analysis, Modeling and Designing a Demand-Oriented Charging Network for Germany

    The majority of freight in Germany is carried out by trucks, resulting in emitting approximately 9% of Germany’s carbon dioxide equivalent emissions. In particular, long-distance truck journeys contribute significantly to these emissions. This paper aims to explore the conditions and impacts of introducing E-Trucks in Germany by utilizing a microscopic traffic simulation approach. Therefore, five different electrification levels of the long-distance truck traffic are evaluated. The demand-oriented charging network dimensioning aims for a realistic and implementable design and is based on an average charging power of 720 kW. Additionaly, it considers the necessary infrastructure requirements at service and rest areas next to the motorway. The results of this research provide valuable insights in terms of usage, requirements and demand. For an electrification level of 1%, 177 chargers at 173 charging sites must be implemented, while 1296 chargers and 457 charging sites must be built for an electrification level of 20%. The increase in the electrification level leads to more efficient occupancy of the charging facilities; i.e., an increase from 1% to 5% improves the average occupation time ratio per charger by approximately 130%. Of the total energy consumed, 65% is recharged en-route at public chargers. Between Monday and Thursday, each 1% electrification level increase requires 2.68 GW h more energy for the public recharging network.