Technische Universität Clausthal
  • Clausthal-Zellerfeld, Niedersachsen, Germany
Recent publications
The advancement of high technology manipulation tools to gain unauthorized access to security eminent hardware in mobile devices demands more sophisticated tamper protection solutions. We developed sensory seal envelopes of ultra-thin glass with individual optical spectra used as signature for tamper protection of electronic controls or cryptographic communication units. A miniaturized autonomic read-out system detects and analyzes the state of the seal. The read-out system is located in the protected area under the seal, together with the secret, in order to protect against attacks via electronic interfaces, such as the mimicry of signature data and the deceptive simulation of the seal's integrity. We introduced a single optical waveguide Bragg grating element via femtosecond laser processing into ultra-thin glass slides. This single Bragg grating combines different functions: It is a sensor element which diffracts the light out-of-plane and doing this in a dispersing manner to create a unique spectral signature. This combination allows a miniaturization of the optical analysis of the dispersed light. We demonstrated that a single waveguide Bragg grating element, inscribed into a monolithic ultra-thin glass foil of 10 cm x 10 cm size, is sufficient for the registration of marginal local mechanical forces onto the glass foil, causing vertical deformations of less than 50 µm at any position. In case of manipulation attempts, such as drilling, cutting, and lasing through the glass foil, the seal's monitoring system recognizes the change or complete loss of the individual spectral signature immediately. We present all elements needed for an optical tamper protection system, based on the sensory seal envelopes of ultra-thin glass in a miniaturized setup, thus reflecting the high potential for future commercial solutions.
Open-cell metallic foams in the shape of pelletized catalysts are regarded as potential catalyst substrates for the application in fixed-bed reactors. This work reports an experimental study and a detailed Computational Fluid Dynamics (CFD) model to investigate the heat transfer performance of a fixed-bed reactor made of open-cell metallic foam pellets. The steady-state heat transfer behavior of a hot gas flowing through such a packed bed under wall-cooled conditions was examined. The proposed CFD model is in line with the particle-resolved CFD (PRCFD) approach that accounts explicitly for the random packing structure, so that the transport processes in the interstitial regions are fully resolved. The momentum and energy transports inside the highly porous foam particles are considered by closure equations based on the porous-media model. The Rigid Body Dynamics (RBD) method is adopted to create the packing geometry. The axial temperature and the pressure drop obtained by the CFD simulations show good agreement with experimental data. To evaluate the thermal performance, effective heat transport parameters in a packed bed such as the effective radial thermal conductivity and the apparent wall-fluid heat transfer coefficient are determined, with the aid of a 2D pseudo-homogenous plug-flow reactor model. The correlations for heat transport characteristics as a function of particle Reynolds number for the metallic foam packed bed are also presented.
Isolated Na2O⋅2CaO⋅3SiO2 (NC2S3) single crystals grew at temperatures above glass transition in a melt with a slight soda excess. The enrichment of Na in the continuous solid solution Na4+2zCa4–z[Si6O18] (with 0 ≤ z ≤ 1) upon crystallisation causes a depletion of soda of the growing interfacial diffusion zone. Therefore its viscosity will change. Experimental data and idealized model calculations of the viscosity show the same trend and indicate that the viscosity of the interfacial zone would be up to several orders of magnitude higher than the viscosity of the melt. This increased viscosity at the crystal growth front and the experimentally observed decrease of the crystallisation velocity with crystal size suggest a linear increase of the effective activation enthalpy of the diffusional transport through the diffusion zone with crystal size, which allows to quantitatively model crystal growth data of the NC2S3 glass investigated.
Early Cambrian black shales on the Yangtze Platform host a regionally distributed highly metalliferous sulfide-rich carbonaceous unit which has been the subject of extensive debate. This marker unit, with a few centimeters or tens of centimeters in thickness, displays extreme enrichment in Mo and Ni (wt% range), and in a broad spectrum of other metals such as As, Au, PGE, Re, Cu, Zn, Cd, Ag, Sb, Se, Tl, and Hg, and occurs discontinuously along the western passive margin of the Yangtze Platform. It grades laterally in stratigraphically equivalent meter-thick vanadium-rich shale and tens-of-meter-thick sapropelite (combustible shale). New Cu and Zn isotope data, combined with existing Cd, Cr, Ni, Mo, Hg, and Se isotope and other chemical data, allow to attempt an integrated view on the formation of this intriguing unit of hyper-enriched metalliferous black shale. The authigenic Cu enrichment in the 1000-ppm range has produced no or little Cu isotope fractionation (0.03 ± 0.26 ‰ δ ⁶⁵ Cu) beyond the lithogenic background. Heavy zinc and cadmium isotope enrichment in the sulfidic samples (1.11 ± 0.18 ‰ δ ⁶⁶ Zn, 0.31 ± 0.10 ‰ δ ¹¹⁴ Cd) is controlled by sulfide fractionation and contrasts with V-rich and barren shale (0.60 ± 0.18 ‰ δ ⁶⁶ Zn, 0.00 ± 0.14 ‰ δ ¹¹⁴ Cd). The distinctly negative Ni isotope composition of the metalliferous unit (−0.84 ± 0.05 ‰ δ ⁶⁰ Ni) with Ni in the percent range has been interpreted as due to hydrothermal activity related to the leaching of mafic rocks and their sulfides. Sorption processes (Fe-oxyhydroxides) and redox cycling in the water column and the bottom sediment with microbial activity could be an alternative interpretation. The extreme metal enrichment can be understood as due to a process chain, from high biological productivity in the oxic photic zone to sulfate reduction in the deeper sulfidic water column and upper sediment layer. Key to the metal enrichment seems to be extremely low clastic sedimentation and advanced carbon destruction by anaerobic oxidation. Hydrothermal input of basinal brines along the rifted margin of the Yangtze Platform was likely a part of this scenario.
A transition from fossil to renewable energy requires the development of sustainable electric energy storage systems capable to accommodate an increasing amount of energy, at larger power and for a longer time. Flow batteries are seen as one promising technology to face this challenge. As different innovations in this field of technology are still under development, reproducible, comparable and verifiable life cycle assessment studies are crucial to providing clear evidence on the sustainability of different flow battery systems. Based on a review of 20 relevant life cycle assessment studies for different flow battery systems, published between 1999 and 2021, this contribution explored relevant methodological choices regarding the sequence of phases defined in the ISO 14,040 series: goal and scope definition, inventory analysis, impact assessment and interpretation. Inspired by good practice examples, common gaps and weaknesses were identified and recommendations for comparative life cycle assessment studies were derived. This includes suggestions for an expanded functional unit definition, a provision of more detailed and transparent reporting of LCI data while using input/output tables. Outcomes of this study are also of relevance for the amendment of the Batteries Directive 2006/66/EC, where first drafts are under revision in the European Council, including the introduction of a battery passport, which should encourage battery producers to reduce their carbon footprint and avoid problematic materials.
A zinc-based Metal-Organic Framework (MOF) has been prepared by utilizing adipic acid as an aliphatic ditopic linker via both solvothermal and sonochemical methods. The ultrasound irradiation has reduced the reaction time and has led to smaller particle size. The samples were evaluated for their catalytic efficiency by the electrochemical reduction of CO2, with carbon monoxide and hydrogen being the sole products. At lower potentials (−1.5 V to −1.7 V) the ultrasound sample achieved up to 10% better faradaic efficiency towards CO (FECO). At more negative potentials (−1.8 V to −1.9 V) the FECO of the two samples start to equalize to a maximum of around 58%. The proposed work contributes to circular economy and the results may be useful for further investigation of the opportunities created by the usage of MOFs in the framework of energy recovery and efficiency, waste reduction, responsible consumption of raw materials and natural resources as well as the potential introduction of MOF to Circular Economy and cost-efficient transition to a “green” and sustainable industry.
We present a new method for the determination of self-diffusivities in solids and the corresponding activation energy of diffusion using in-situ Neutron Reflectometry. In contrast to the classical ex-situ approach based on a sequence of isothermal measurements at different temperatures, the in-situ method allows one to work with a single experiment based on ramping the temperature with a constant rate. Our experiment demonstrates the success of the method for the model system of amorphous germanium. The activation energy of 2.2 eV and the absolute values of diffusivities achieved by the new method are in good agreement with the results of the classical approach, while a significantly lower amount of experimental time and samples are necessary. The presented method allows for an all-in-one type of experiment which can provide clearer and quicker results than similar methods using isothermal annealing procedures.
The recovery of oil from a reservoir can be accomplished with various methods, one of the most commonly applied types being waterflooding. A common theory used to describe immiscible displacement is the Buckley–Leverett theory. A brand new type of micromodel, generated and fabricated by using a micro-computer tomography (μCT) image stack of a real sandstone core, was used to conduct immiscible displacement experiments. Critical logging data were recorded, and a high-resolution camera took pictures of the displacement process. In an image processing tool (MATLAB), an algorithm was developed to evaluate the pictures of the experiment and to examine the changes in the saturations of the displacing and the displaced fluid. The main objective of the displacement experiment was to validate the new microchip in two-phase displacement experiments and to assess the feasibility of the image processing algorithm. This was performed by comparing the results of the experimental to the analytical solutions, which were derived from the Buckley–Leverett theory. The comparison of the results showed a good match between the two types of solutions. The applicability of the analytical results to the experimental procedures was observed. Additionally, the usage of the newly fabricated micromodel and its potential to visualize the fluid flow behavior in porous media were assessed.
mRNA-based therapeutics are predicted to have a bright future. Recently, a B2C study was published highlighting the critical bottlenecks of mRNA manufacturing. The study focused on supply bottlenecks of various chemicals as well as shortages of skilled personnel. The assessment of existing messenger ribonucleic acid (mRNA) vaccine processing shows the need for continuous manufacturing processes that are capable of about 80% chemical reduction and more than 70% personnel at factor five more efficient equipment utilization. The key technology to solve these problems is both a higher degree of automation and the maximization of process throughput. In this paper, the application of a quality-by-design process development approach is demonstrated, using process models as digital twins. Their systematic application leads to both robust optimized process parameters, with an increase in productivity of up to 108%, and sophisticated control concepts, preventing batch failures and minimizing the operating workload in terms of personnel and chemicals’ consumption. The approach thereby provides a data-driven decision basis for the industrialization of such processes, which fulfills the regulatory requirements of the approval authorities and paves the way for PAT integration. In the process investigated, it was shown that conventional PID-based controls can regulate fluctuations in the input streams sufficiently well. Model-based control based on digital twins may have potential above all in a further increase in productivity, but is not mandatory to implement for the industrialization of continuous mRNA manufacturing.
The ongoing energy transition requires power grid extensions to connect renewable generators to consumers and to transfer power among distant areas. The process of grid extension requires a large investment of resources and is supposed to make grid operation more robust. Yet, counter-intuitively, increasing the capacity of existing lines or adding new lines may also reduce the overall system performance and even promote blackouts due to Braess’ paradox. Braess’ paradox was theoretically modeled but not yet proven in realistically scaled power grids. Here, we present an experimental setup demonstrating Braess’ paradox in an AC power grid and show how it constrains ongoing large-scale grid extension projects. We present a topological theory that reveals the key mechanism and predicts Braessian grid extensions from the network structure. These results offer a theoretical method to understand and practical guidelines in support of preventing unsuitable infrastructures and the systemic planning of grid extensions.
Background: Embedded feature selection in high-dimensional data with very small sample sizes requires optimized hyperparameters for the model building process. For this hyperparameter optimization, nested cross-validation must be applied to avoid a biased performance estimation. The resulting repeated training with high-dimensional data leads to very long computation times. Moreover, it is likely to observe a high variance in the individual performance evaluation metrics caused by outliers in tiny validation sets. Therefore, early stopping applying standard pruning algorithms to save time risks discarding promising hyperparameter sets. Result: To speed up feature selection for high-dimensional data with tiny sample size, we adapt the use of a state-of-the-art asynchronous successive halving pruner. In addition, we combine it with two complementary pruning strategies based on domain or prior knowledge. One pruning strategy immediately stops computing trials with semantically meaningless results for the selected hyperparameter combinations. The other is a new extrapolating threshold pruning strategy suitable for nested-cross-validation with a high variance of performance evaluation metrics. In repeated experiments, our combined pruning strategy keeps all promising trials. At the same time, the calculation time is substantially reduced compared to using a state-of-the-art asynchronous successive halving pruner alone. Up to 81.3% fewer models were trained achieving the same optimization result. Conclusion: The proposed combined pruning strategy accelerates data analysis or enables deeper searches for hyperparameters within the same computation time. This leads to significant savings in time, money and energy consumption, opening the door to advanced, time-consuming analyses.
The perceived differences between two popular relaxation models [referred to here as the Cole Cole model (CCM) and the Pelton model (PM)], along with their corresponding time constants, has been a source of confusion in recent spectral induced polarization (SIP) literature. These differences complicate comparisons between experimental results recorded by different researchers. A circuit model approach is adopted to better understand the differences between these relaxation models. Either relaxation model can fit SIP datasets equally well, the sole difference corresponds to the measured relaxation time representing the voltage decay for the time domain response to a constant current signal as usually recorded in IP field surveys. The reporting of time constants from a common relaxation model will advance petrophysical investigations of the controls on SIP measurements when exploring databases compiled from previously published datasets.
Chitosan is a biopolymer that, due to its versatile bioactive properties, has applications in several areas, including food, medicine and pharmaceuticals. In the field of tissue engineering, chitosan can be used, for example, as a dressing to treat wounds or dermal damage, such as burns or abrasions. This work deals with the controlled release of tea tree oil from chitosan-based polymeric films and droplets containing gold nanoparticles (AuNP). AuNPs were successfully incorporated into the chitosan matrix using two different approaches. Both solutions were loaded with tea tree oil, and from these solutions, it was possible to obtain drop-cast films and droplets. The controlled release of oil in water was performed both in the films and in the droplets. The addition of AuNP in the controlled release system of melaleuca oil favored a release time of around 25 h. A series of experiments was carried out to investigate the effects of different reaction temperatures and acetic acid concentrations on the formation of AuNPs in the presence of chitosan. For this purpose, images of the AuNP films and droplets were obtained using transmission electron microscopy. In addition, UV-vis spectra were recorded to investigate the release of tea tree oil from the different samples.
These days, additive manufacturing processes have a large representation in current research and in the field of industrial applications [...]
Vaccine supply has a bottleneck in manufacturing capacity due to operation personnel and chemicals needed. Assessment of existing mRNA (messenger ribonucleic acid) vaccine processing show needs for continuous manufacturing processes. This is enabled by strict application of the regulatory demanded quality by design process based on digital twins, process analytical technology, and control automation strategies in order to improve process transfer for manufacturing capacity, reduction out-of-specification batch failures, qualified personnel training and number, optimal utilization of buffers and chemicals as well as speed-up of product release. In this work, process control concepts, which are necessary for achieving autonomous, continuous manufacturing, for mRNA manufacturing are explained and proven to be ready for industrialization. The application of the process control strategies developed in this work enable the previously pointed out benefits. By switching from batch-wise to continuous mRNA production as was shown in previous work, which was the base for this study, a potential cost reduction by a factor 5 (i.e., from EUR 0.380 per dose to EUR 0.085 per dose) is achievable. Mainly, based on reduction of personnel (factor 30) and consumable (factor 7.5) per campaign due to the significant share of raw materials in the manufacturing costs (74–97). Future research focus following this work may be on model-based predictive control to gain further optimization potential of potential batch failure and out of specification (OOS) number reduction.
The demand for clean energy is strongly related with many European and other global legislations and directives [...]
Online shops have become increasingly interactive, using different technologies to create virtual experiences that attempt to simulate a realistic product experience. We explore the impact of high sensory enabling (HSE) virtual product presentation modes using state-of-the-art virtual reality (VR) technology that allows consumers to imitate natural movement and interactions via head-mounted displays (HMD) and dual hand VR controllers. This will compare the HSE virtual product presentation mode with a typical low sensory enabling (LSE) virtual product presentation mode that utilises conventional computer screens, along with mouse and keyboard inputs, on a desktop computer. For the HSE virtual product presentation mode, the results show significantly higher values for the studied variables, including presence, perceived diagnosticity, attitude towards product, and purchase intention. Shopping frequency has a moderating effect on the significant differences of presence between presentation modes. Our research contributes to theory by building on attitude theory, cue summation theory, as well as repetitive learning and memory to explore and explain the effects of HSE virtual product presentation modes on the constructs considered. For managers and industry leaders, this study identifies the importance of using state-of-the-art technology when creating HSE virtual experiences for their products.
Mercury isotopes display both mass-dependent and mass-independent fractionation and allow the tracing of pathways and storage of surface-derived Hg in the lithosphere. While the subduction-related orogenic recycling of Hg from marine reservoirs into hydrothermal systems in continental arc settings has been documented recently, the source of Hg in intracontinental hydrothermal systems remains unclear. We measured Hg isotopes in two intracontinental anorogenic/postorogenic Late Mesozoic hydrothermal gold deposits in the South China craton and the Central Asian orogenic belt of northern China, respectively. The ore and sulfide samples from the studied systems have positive δ202Hg (0.70 ± 0.39‰, 1SD, n = 49) and negative Δ199Hg values (−0.12 ± 0.05‰, 1SD, n = 49). These values are different from their country rocks and regional geological environment (volcanic arc granites, marine sedimentary rocks) which have positive Δ199Hg values, but similar to that of their Precambrian supracrustal basement rocks of largely non-marine continental materials. We conclude that Hg in the intracontinental hydrothermal systems was leached from basement rocks by upper crustal basinal fluid circulation driven by regional heat flow, likely due to lithospheric thinning and upwelling of the asthenosphere in the Late Mesozoic. The intracontinental hydrothermal systems and their continental sources with positive δ202Hg and negative Δ199Hg values are complementary to volcanic-arc and marine sedimentary rocks with opposite δ202Hg - Δ199Hg compositions. The distinct Hg isotopic features of hydrothermal systems in different tectonic settings, in particular the indelible Δ199Hg signature, allow the tracing of large-scale material cycling in the Earth.
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2,132 members
Wolfgang Maus-Friedrichs
  • Department of Energy Research and Physical Technologies
Jelena Fiosina
  • Department of Computer Science
Dieter Mayer
  • Department of Theoretical Physics
Patrick Were
  • Energie-Forschungszentrum Niedersachsen
Matthias Reuter
  • Department of Computer Science
Adolph-Roemer-Straße 2A, 38678, Clausthal-Zellerfeld, Niedersachsen, Germany
Head of institution
Joachim Schachtner
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