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Smart reactors: development of novel process concepts based on the application of stimuli-responsive gels
No full textParametric finite element analysis of naturally corroded steel specimens using 3D surface laser scans
No full textCorrosion is considered a uniform thickness reduction design guideline of the maritime industry. However, additionally, the corroded and irregular morphology of the surface affects the steel's load-bearing capacity and its impact on the strength and elongation behaviour of the steel is not yet fully understood. These effects on the local behaviour of steel structures under tensile loading were investigated with tensile tests on naturally corroded steel specimens and nonlinear finite element simulations including the corroded surface morphology with a uniform surface idealation. The models also include the deformed specimen shape. The developed approach led to highly accurate parametric finite element models predicting the ultimate tensile strength and longitudinal position of fracture. The results show that all included aspects are essential for accurate simulations, while solely the maximum available surface resolution was not as decisive
Protein extration from Bioethanol byproducts for human consumption using liquid hot water pretreatment
No full textThe global demand for protein is increasing due to the strong growth of global population and still expanding markets for protein supplements. Within this context, solid residues from bioethanol production offer an attractive alternative protein source for human nutrition that does not require additional land use. This research targets to investigate and optimize a hydrothermal extraction process for proteins from such solid residues, aiming to maximize protein yield while minimizing protein denaturation. Therefore, initially a compositional analysis of two different types of such residues – one from corn and the other from wheat bioethanol production – is conducted, revealing a protein content of 23 % and 28 %, respectively, based on the dry weight. To separate these proteins, a hydrothermal pre-treatment process using liquid hot water (LHW) is employed to solubilize them in water. To explore the solution space, hydrothermal treatment was conducted at various temperature levels (110 till 190 °C) and treatment times (5 till 70 min) to investigate the influence of these parameters. Wheat stillage exhibited the highest protein extraction yield at 190 °C, whereas corn stillage achieved its peak yield at 150 °C. Overall, the protein concentrations in the hydrolysates ranged between 20 % and 25 %
Echocardiography correlation with seismocardiography-systematic review
No full textA methodological systematic review included literature retrieved from Scopus, PubMed, and IEEE-Explore. 61 studies on seismocardiography (SCG) and echocardiography (ECHO) were found. After screening for aortic and mitral valve timing events, 12 studies were selected. These studies focused on correlating SCG signals with ECHO using M-mode, PW-Doppler, CW-Doppler, and TDI. Variations in sensor placement and subject positioning highlighted the need for standardization. Our review stresses the importance of clear objectives, standardized protocols, and recording disease-specific impacts on heart mechanics for future research
A taxonomy of functional security features and how they can be located
No full textSecurity must be considered in almost every software system. Unfortunately, selecting and implementing security features remains a challenge due to the wide variety of security threats and possible countermeasures. While security standards are intended to help developers, they are usually too abstract and vague to help implementing security features, or they merely help configuring such. A resource that describes security features at an abstraction level that lies between high-level (i.e., rather too general) and low-level (i.e., rather too specific) security standards could facilitate secure systems development. This resource should support the selection of appropriate security features to achieve high-level security goals, allow easy retrieval of relevant low-level details, and provide pointers to suitable ways to realize the security features. To realize security features, developers typically use external security libraries or frameworks, to minimize implementation mistakes. Even when using libraries, developers still make mistakes when writing code to integrate them, often resulting in security vulnerabilities. When security incidents occur or the system needs to be audited or maintained, it is essential to know what security features have been implemented and, more importantly, where they are located. This task, commonly referred to as feature location, is often tedious and error-prone. While dedicated feature location techniques exist, they require significant manual effort or adherence to strict development processes, preventing their use. Therefore, we have to support long-term tracking of implemented security features. We present a study of security features presented in the literature and their coverage in popular security frameworks. We contribute (1) a taxonomy of 68 functional implementation-level security features including a mapping to widely used security standards, (2) an examination of 21 popular security frameworks concerning which of these security features they provide, and (3) a discussion on the representation of security features in source code. Our taxonomy aims to aid developers in selecting appropriate security features and security frameworks, as well as relating them to security standards when they need to choose and implement security features for a software system
Introducing long-range particle interactions into phase-field models of sintering using continuum mechanics principles
No full textThis work presents a novel meso-scale phase-field model of solid-state sintering that couples the continuum thermodynamics and continuum mechanics governing the sintering process. The microstructure evolution is described by a system of equations consisting of one Cahn–Hilliard equation and a set of Allen–Cahn equations to distinguish neighboring particles. These equations are coupled with the balance of momentum of linear elasticity. The latter is defined by applying the Wang sintering forces as distributed body loads to compute advection velocities for the phase-field equations. This introduces long-range interaction mechanisms between particles. Our numerical implementation uses monolithic coupling and implicit time integration. It is based on the hpsint code, an efficient matrix-free finite element solver for phase-field simulations of many-particle sintering processes with advanced grain tracking capabilities and block preconditioning. With a simple academic test setup that analyzes a chain of identical particles we investigate in detail the problems of the original sintering model proposed by Wang around two decades ago and then clearly demonstrate how our new coupled approach resolves them. We then study a series of two- and three-dimensional benchmark problems to demonstrate the advantages of our novel model that clearly exhibits invariance of shrinkage regarding the model size (number of particles in the packing) and renders microstructures whose metrics agree well with estimates based on analytical and experimental studies
Adaptive Fokuslagenkorrektur fasergebundener Laser-Remote-Scanner mit Linsenoptiken für hohe Laserleistungen
No full textLong-term continuous anaerobic co-digestion of residual biomass—model validation and model-based Investigation of different carbon-to-nitrogen ratios
No full textMajor challenges in using lignocellulosic residues as biogas substrates arise from their high diversity and their typically low nitrogen content, which may not provide sufficient nitrogen for the microorganisms. To investigate to what extent such substrates can be used in biogas plants without extensive pre-treatment, this study presents a 300-day continuous co-digestion of lignocellulosic substrates (i.e., sugarcane reed, lemon, and grape leaves) and goat manure while continuously monitoring various process parameters. The results suggest a stable and effective biogas production at a carbon-to-nitrogen ratio (C/N ratio) of 33, with a production of 244 ± 15 mLN gVS−1 d−1 biogas. At a higher C/N ratio of 43, the process remained stable, but hindrance was encountered. Process failure occurred at a C/N ratio of 52, where a rapid decline in biogas production was observed, accompanied by an increase in the volatile fatty acids to total alkalinity ratio (from 7 to 5.4), and an increased CO2-content of the provided biogas (from > 50% to 43%). The compositional analysis of the digestate suggests an insufficient N-supply and a failure of the carbonate and ammonium buffer systems inside the reactor. The experiment also served to validate a previously developed model based on the individual substrates’ degradation kinetics. With a relative root mean square error rRMSE of 8%, the model adequately predicted biogas production within defined limits. However, it could not anticipate process breakdown at high C/N ratios, highlighting a strong limitation.Bundesministerium für Forschung, Technologie und Raumfahrt (BMFTR
Wavelet-based compressed sensing of the system matrix for magnetic particle imaging
No full textMagnetic particle imaging (MPI) is a trending tracer imaging technique relatively newly proposed. In MPI, a time-consuming system matrix (SM) calibration scan is required to reconstruct the spatial distribution of superparamagnetic nanoparticles. Compressed sensing (CS) techniques are widely utilized to reduce the time required for SM calibration, with Discrete Cosine Transform (DCT) being the state-of-the-art sparsifying transform. This paper proposes a wavelet-based CS method for SM reconstruction. To the best of our knowledge, this is the first work to employ wavelets as the sparsifying transform for SM recovery in MPI. To this goal, we employ biorthogonal wavelet transform to sparsify the SM rows. We propose a variant of the iterative shrinkage/thresholding-based algorithm for SM reconstruction with the help of bivariate shrinkage to take advantage of the multiscale nature of wavelets and the dependency between wavelet subband coefficients. The performance of the proposed method is assessed by phantom image reconstructions using the state-of-the-art Kaczmarz algorithm. Experimental results using the DCT and the proposed wavelet-based methods confirm that the proposed method outperforms the state-of-the-art DCT-based compression based on the comparisons of (i) the sparsity levels of several SM frequencies, (ii) the reconstruction error of SM frequencies, where the average error for channels 1 and 2 decreased by approximately 10% when using DWT instead of DCT, and (iii) the visual quality of reconstructed phantom images at different sparsity levels, as no ground truth is available for metric-based comparisons
Fatigue behaviour of 12-month corroded offshore steel joints under accelerated salt spray exposure: an experimental and numerical analysis
No full textThe fatigue strength of steel structures can decrease significantly when corrosion occurs. Pitting corrosion, in particular, can lead to locally high stress concentrations and may interact with existing stress concentrations from weld seams. Particularly in the case of offshore support structures, which are exposed to a corrosive environment and include several welded connections, this issue becomes relevant. Hence, in this study, butt- and fillet-welded joints of structural steel were exposed to accelerated corrosion in a salt spray chamber and then tested for fatigue strength. In order to investigate the long-term behaviour, the specimens were stored for 12 months in a salt spray chamber. Base material specimens were investigated as reference. All specimens were clean blasted and 3D scanned prior to the fatigue tests. It was shown for all specimens that the fatigue strength decreased after 12 months compared to the uncorroded reference tests. However, the fatigue reduction was different for the different geometries. The greatest reduction was observed for the base material from 282 to 122 N/mm², followed by butt-welded joints from 215 to 147 N/mm², and fillet-welded joints from 168 to 144 N/mm². As the fatigue strengths showed only minor difference after 12 months, an equalization effect can be assumed. The results show that a generalized reduction of the fatigue strength, in accordance with the guidelines, is not appropriate and therefore should be revised for a more accurate design of offshore support structures. Finally, numerical analysis based on 3D scans of the specimens was conducted and compared with the test results