Parametrized reduced order modeling for cracked solids

A parametrized reduced order modeling methodology for cracked two dimensional solids is presented, where the parameters correspond to geometric properties of the crack, such as location and size. The method follows the offline‐online paradigm, where in the offline, training phase, solutions are obtained for a set of parameter values, corresponding to specific crack configurations and a basis for a lower dimensional solution space is created. Then in the online phase, this basis is used to obtain solutions for configurations that do not lie in the training set. The use of the same basis for different crack geometries is rendered possible by defining a reference configuration and employing mesh morphing to map the reference to different target configurations. To enable the application to complex geometries, a mesh morphing technique is introduced, based on inverse distance weighting, which increases computational efficiency and allows for special treatment of boundaries. Applications in linear elastic fracture mechanics are considered, with the extended finite element method being used to represent discontinuous and asymptotic fields.ISSN:1097-0207ISSN:0029-598

Unraveling the glucocorticoid receptor pathway in zebrafish

Glucocorticoid receptor (GR) signaling is versatile and plays an essential role in the survival and well-being of organisms. Glucocorticoids are also widely used clinically in order to combat inflammatory medical conditions. In the present thesis we aimed at studying the GR pathway by means of stimulation with synthetic GCs and genetic manipulation. Since the GR is a transcription factor, our main readout for GR function in most of our experimental settings was transcriptome analysis. By gathering whole transcriptome information, we aimed at unraveling the molecular pathways affected by GR signaling in different physiological conditions, thus exploring its functional role. As a model organism we employed the zebrafish, since it allows fine genetic, molecular and cellular experimental approaches and its GR pathway closely resembles that of humans. Our aim was also to further characterize the function of this versatile signaling cascade in zebrafish, in order to establish this animal model as a valid system for detailed as well as high throughput research on GR, enabling us to test hypotheses and complement results obtained from other well-established experimental animal models such as rodents.LEI Universiteit LeidenMoleculaire celbiologi

Vibration-based structural performance assessment via output-only sub-Nyquist/compressive wireless sensor data

This paper assesses two different approaches for efficient output - only Vibration - based Structural Health Monitoring (V - SHM) in large - scale civil engineering structures, promoting the use of dense arrays of low - power wireless sensors. Firstly, a non - uniform deterministic sub - Nyquist multi - coset sampling scheme is considered to acquire ambient stationary structural response signals. This sampling scheme is coupled with a power spectrum blind sampling technique along with the frequency domain decomposition algorithm of operational modal analysis to obtain structural modal properties. This is accomplished without necessitating either signal reconstruction in the time - domain or signal sparsity assumption . Secondly, a spectro-temporal compressive sensing approach is considered applicable to cases where sign al reconstruction in time - domain is desired. The latter approach considers non-uniform in time random sampling at sub - Nyquist average rates informed by prior knowledge of signal sparsity gained through smart on-sensor operations and sensor/server communication. The usefulness and applicability of two approaches is numerically demonstrated by considering field recorded data pertaining to the monitoring of an overpass open to the traffic and of an operating on-shore wind turbine

Low-frequency wide band-gap elastic/acoustic meta-materials using the K-damping concept

The terms "acoustic/elastic meta-materials" describe a class of periodic structures with unit cells exhibiting local resonance. This localized resonant structure has been shown to result in negative effective stiffness and/or mass at frequency ranges close to these local resonances. As a result, these structures present unusual wave propagation properties at wavelengths well below the regime corresponding to band-gap generation based on spatial periodicity, (i.e. "Bragg scattering"). Therefore, acoustic/elastic meta-materials can lead to applications, especially suitable in the low-frequency range. However, low frequency range applications of such meta-materials require very heavy internal moving masses, as well as additional constraints at the amplitudes of the internally oscillating locally resonating structures, which may prohibit their practical implementation. In order to resolve this disadvantage, the K-Damping concept will be analyzed. According to this concept, the acoustic/elastic meta-materials are designed to include negative stiffness elements instead or in addition to the internally resonating added masses. This concept removes the need for the heavy locally added heavy masses, while it simultaneously exploits the negative stiffness damping phenomenon. Application of both Bloch's theory and the classical modal analysis at the one-dimensional mass-in-mass lattice is analyzed and corresponding dispersion relations are derived. The results indicate significant advantages over the conventional mass-in-a mass lattice, such as broader band-gaps and increased damping ratio and reveal significant potential in the proposed solution. Preliminary feasibility analysis for seismic meta-structures and low frequency acoustic isolation-damping confirm the strong potential and applicability of this concept.Comment: Keywords: Acoustic meta-materials, elastic meta-materials, low-frequency vibration absorption, seismic meta-structures, noise absorptio

Reactivity to AQP4 epitopes in relapsing–remitting multiple sclerosis

Autoantibodies against the water channel AQP4, expressed predominately in central nervous system astrocytes, are markers and pathogenic factors in Devic's disease. In this study we examined whether Multiple Sclerosis (MS) patients recognize antigenic epitopes on AQP4 that may define distinct disease subsets. We screened sera from 45 patients with relapsing–remitting MS (RRMS) and 13 patients with primary progressive MS (PMS). 23 Neuromyelitis Optica (NMO) patients previously characterized were used as assay positive/negative controls. Sera from 23 patients with Systemic Lupus Erythematosus, 23 with primary Sjogren syndrome without neurological involvement and from 28 healthy individuals were also used as controls. NMO-positive sera exhibited reactivity against the intracellular epitope AQPaa252-275, confirming previous observations. All RRMS sera tested negative for anti-AQP4 antibodies using a cell-based assay, but surprisingly, 13% of them reacted with the epitope AQPaa252-275. PMS, healthy and disease controls showed no specific reactivity. Whether these antibodies define distinct MS subsets and have a pathogenic potential pointing to convergent pathogenetic mechanism with NMO, or are simply markers of astrocytic damage, remains to be determined

C+L band gain equalization for extended reach WDM-ring PON using hybrid Raman/in line EDFA amplification

“Copyright © [2010] IEEE. Reprinted from ICTON 2010. ISBN 978-1-4244-7798-2. This material is posted here with permission of the IEEE. Internal or personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution must be obtained from the IEEE by writing to [email protected]. By choosing to view this document, you agree to all provisions of the copyright laws protecting it.”In this paper, we investigate by simulation the feasibility of gain enlargement and equalization on extended reach WDM-ring PON by means of hybrid Raman/EDFA amplification. The system under analysis is composed by a bidirectional pump at 1480 nm and 16 channels (8 C band + 8 L band). The simulation describes an 80 km WDM ring with 8 nodes in which 2 channels are added/dropped. The results demonstrate gain equalization with a ripple of 2.54 dB over a bandwidth of 50 nm by using a 1480 nm bidirectional pump with 1 W and spans of EDF with a total length of 22 m

VpROM: a novel variational autoencoder-boosted reduced order model for the treatment of parametric dependencies in nonlinear systems

Reduced Order Models (ROMs) are of considerable importance in many areas of engineering in which computational time presents difficulties. Established approaches employ projection-based reduction, such as Proper Orthogonal Decomposition. The limitation of the linear nature of such operators is typically tackled via a library of local reduction subspaces, which requires the assembly of numerous local ROMs to address parametric dependencies. Our work attempts to define a more generalisable mapping between parametric inputs and reduced bases for the purpose of generative modeling. We propose the use of Variational Autoencoders (VAEs) in place of the typically utilised clustering or interpolation operations, for inferring the fundamental vectors, termed as modes, which approximate the manifold of the model response for any and each parametric input state. The derived ROM still relies on projection bases, built on the basis of full-order model simulations, thus retaining the imprinted physical connotation. However, it additionally exploits a matrix of coefficients that relates each local sample response and dynamics to the global phenomena across the parametric input domain. The VAE scheme is utilised for approximating these coefficients for any input state. This coupling leads to a high-precision low-order representation, which is particularly suited for problems where model dependencies or excitation traits cause the dynamic behavior to span multiple response regimes. Moreover, the probabilistic treatment of the VAE representation allows for uncertainty quantification on the reduction bases, which may then be propagated to the ROM response. The performance of the proposed approach is validated on an open-source simulation benchmark featuring hysteresis and multi-parametric dependencies, and on a large-scale wind turbine tower characterised by nonlinear material behavior and model uncertainty

Metal foam recuperators on micro gas turbines: Multi-objective optimisation of efficiency, power and weight

Small size and high efficiency of micro gas turbines require a higher surface-to-volume ratio of recuperators. Conventional recuperators can achieve a range of 250–3600 m2/m3. Advances in materials and manufacturing, such as metal foams, can increase significantly the exchange surface and improve compactness ranging approximately from 500 to over 10,000 m2/m3, due to their exceptional micro geometry. The main advantage is that the increase of surface area does not impact the cost of the heat exchanger as much as conventional recuperators due to their easy manufacturing. This work addresses the optimisation of the recuperator using multiple objectives satisfying efficiency, power output and weight criteria, offering a holistic approach that takes into account the entire system rather than individual components or channels. A model is developed to represent the performance of a compact heat exchanger in micro gas turbines. The recuperator is an annular heat exchanger with involute profile filled with porous media in a counterflow arrangement on the hot and cold sides. The model allows the evaluation of the effect of the recuperator geometry features on the electrical efficiency, power output and weight savings in a micro gas turbine. Existing models for the global heat transfer coefficient, effective thermal conductivity, surface area and pressure drop of porous media are selected and implemented. The design variables of multi-objective are the pore density, porosity and number of channels, whilst the objectives are the overall electrical efficiency, power output and recuperator weight. The problem is solved using the Non-Dominated Sorting Genetic Algorithm (NSGA-II) to determine an approximation of the Pareto front, whilst the accuracy of the approximation is assessed against the solution obtained by an exhaustive search. The comparison shows that NSGA-II outperforms an exhaustive search by at least 90 % in terms of computational efficiency. These results allow the quantification of the impact of metal foam technology on performance metrics of the recuperator as well as the entire system. This quantitative analysis provides valuable insights into the behaviour of metal foam recuperators in micro gas turbines. An optimal design with 30 % efficiency and 28 kW power output appears in pore densities of approximately 10 and 20 pores per inch (PPI) for the air and gas side respectively, and a porosity of 85 %, which leads to a state-of-the-art recuperator weight of 48 kg. The efficiency improvement over the industry standard is 15 %, with only a 2.5 % reduction in power output

Architected frames for elastic wave attenuation: Experimental validation and local tuning via affine transformation

We experimentally demonstrate the capability of architected plates, with a frame-like cellular structure, to inhibit the propagation of elastic flexural waves. By leveraging the octet topology as a unit cell to design the tested prototypes, a broad and easy-to-tune bandgap is experimentally generated. The experimental outcomes are supported by extensive numerical analyses based on 3D solid elements. Drawing from the underlying dynamic properties of the octet cell, we numerically propose a tailorable design with enhanced filtering capabilities. We transform the geometry of the original unit cell by applying a uniaxial scaling factor that, by breaking the in-plane symmetry of the structure, yields independently tuned struts and consequently multiple tunable bandgaps within the same cell. Our findings expand the spectrum of available numerical analyses on the octet lattice, taking it a significant step closer to its physical implementation. The ability of the octet lattice to control the propagation of flexural vibrations is significant within various applications in the mechanical and civil engineering domains, and we note such frame-like designs could lead to advancements in energy harvesting and vibration protection devices (e.g., lightweight and resonance-tunable absorbers)