Experiments and simulation in structural health monitoring systems using the E/M impedance and cross transfer function methods

As an enabling technology, Structural Health Monitoring (SHM) assesses the state of mechanical structures in real time in order to prevent accidents or disasters during the structures’ operational lifetime. According to basic principles, several methods in SHM techniques can be defined e.g. mechanical, electric, electro-mechanical and electro-magnetic methods. The focus of this work is on the Electro-Mechanical Impedance method (EMI) and Cross Transfer Function method. In this work, the EMI method is further developed for three different fields of application: self-diagnosis of bonded piezoelements, their sensing ability and their use for damage detection in fatigue experiments. Self-diagnosis is used to monitor whether the bonded piezoelectric elements either used as actuators or as sensors can continue to measure or function properly in SHM, which is decided by the change of the EM impedance spectrum. In the investigation of the sensing ability of piezoelectric elements, it is shown how the damage positions and the different frequency ranges of the input signals influence the element measurements using EMI spectrum. This is investigated experimentally in combination with the Spectral Element Method (SEM). In the last part of the work, EMI method is used to monitor the start of the crack in a vibrating aluminium plate in a fatigue experiment. Another focus of this work lies on a better localization of damage using phased array techniques. Such arrays consist of several piezoelectric elements arranged in a certain geometric way. By controlling the phase shift of the input signal between each piezoelectric element and the superposition of all outputs, a wave propagation with a desired direction is obtained, where the direction of propagation is determined by the phase shift. The proposed technique works in the frequency domain and is based on the Cross Transfer Function method which uses the transfer functions between different actuatorsensors permutations of the array. In the frequency domain, the phase shifts are implemented numerically after the experimental determination of the transfer functions using a computer algorithm. This can be seen as a big advantage of the Cross Transfer Function method which makes it more flexible and efficient. The results show that the damage indicators are especially large in those directions where the damage is located.Als eine wichtige Grundlagentechnologie ist es Aufgabe der Strukturüberwachung (engl.: Structural Health Monitoring, SHM) den aktuellen Zustand einer mechanischen Tragstruktur kontinuierlich und on-line festzustellen und dadurch Unfälle oder Katastrophen zu vermeiden, die durch Versagen eines Bauteils während des Betriebs hervorgerufen werden können. Gemäß den grundlegenden physikalischen Prinzipien kann man verschiedene SHM-Techniken unterscheiden, z.B. mechanische, elektrische, elektro-mechanische oder auch elektro-magnetische Verfahren. Der Fokus in dieser Arbeit liegt auf der Elektro-Mechanischen Impedanz (EMI) Methode und der Kreuz-Transferfunktions-Methode (Cross Transfer functions). In der vorliegenden Dissertation wird die EMI-Methode zur Eigendiagnose von piezo-elektrischen Sensorelementen weiterentwickelt. Diese Eigendiagnose ist dazu da, um fetszustellen, ob die applizierten Piezo-Elemente, die Festkörperwellen sowohl als Aktor erzeugen oder auch als Sensor messen können, selbst einwandfrei funktionieren, bevor man eine Schadendiagnose zuverlässig mit ihnen durchführen kann. Diese Selbstdiagnose geschieht mit Hilfe von Veränderungen im Impedanzspektrum. Weiterhin wird untersucht, wie die sensorischen Eigenschaften hinsichtlich Abstand und Richtung eines Schadens vom Sensorort beeinflusst werden und welchen Einfluss der Spektralbereich und die Materialdämpfung dabei haben. Hierzu werden experimentelle Untersuchungen in Verbindung mit der Simulation von Wellenausbreitungsvorgängen mit Hilfe der Spektral-Elemente Method (SEM) durchgeführt und der jeweilige Einfluss auf die Veränderung der Impedanzspektren betrachtet. Schließlich wird die EMI-Methode dazu eingesetzt, um beginnendes Risswachstum in einer schwingenden Aluminiumplatte im Rahmen eines Ermüdungsexperiments festzustellen. Ein weiterer Schwerpunkt der Arbeit stellt die bessere Ortung von Schäden mit Hilfe einer Phased-Array-Technik dar. Dabei wird eine in bestimmter Weise geometrisch angeordnete Gruppe von piezo-elektrischen Elementen verwendet. Die vorgeschlagene Technik beruht auf der Kreuz-Transferfunktions-Methode, wobei jeweils Übertragungsfunktionen für alle möglichen Aktor-Sensorpaare gebildet werden. Durch eine Phasenverschiebung zwischen den Aktoren bzw. Sensoren und einer anschließenden Überlagerung wird eine Welle erzeugt, die sich konzentriert in eine bestimmte Richtung ausbreitet. Die Implementierung im Frequenzbereich erlaubt es, die Phasenverschiebung ohne weitere Experimente im Nachhinein zu variieren. Das macht die Methode flexibel und hardwaretechnisch effizient. Die Ergebnisse zeigen, dass die Schadensindikatoren dann besonders stark in Richtung des Schadens ausschlagen

Technology Review System of Water-Temperature Prediction for Reservoir Construction Project

AbstractIt is the important technical support for technology appraisal to establish technology review system of water-temperature prediction for reservoir construction project. In this study, the technical route, implementation method and process, the required basic data, and key issues were proposed for the water-temperature technology review. The realization of water-temperature technology review can provide technical guarantee for regulating the technical requirements on water temperature prediction in environment impact assessment (EIA) report. Technology review can also prevent arbitrariness in some EIA reports. Moreover technology review could resolve some experts doubts on the prediction result during the process of technology appraisal

Bacteroides vulgatus alleviates dextran sodium sulfate-induced colitis and depression-like behaviour by facilitating gut-brain axis balance

BackgroundPatients with inflammatory bowel disease (IBD) have a higher prevalence of depression. Gut microbiota dysbiosis plays an important role in IBD and depression. However, few studies have explored the characteristic microbiota of patients with IBD and depression (IBDD), or their role in IBDD.MethodsWe performed deep metagenomic sequencing and 16S rDNA quantitative PCR to characterise the gut microbial communities of patients with IBDD and patients with IBD without depression (IBDND). We then assessed the effect of the microbiota on colitis and depression in mouse models of dextran sulfate sodium salt (DSS)-induced colitis and lipopolysaccharide (LPS)-induced depression. Furthermore, liquid chromatography–tandem mass spectrometry was used to analyse the microbiota-derived metabolites involved in gut–brain communication. Evans Blue tracer dye was used to assess blood–brain barrier (BBB) permeability.ResultsOur results showed that the faecal abundance of Bacteroides vulgatus (B. vulgatus) was lower in patients with IBDD than in those with IBDND. In the DSS-induced colitis mouse model, the B. vulgatus group showed a significantly lower disease activity index score, lesser weight loss, and longer colon length than the DSS group. Moreover, B. vulgatus relieved depression-like behaviour in the DSS-induced colitis mouse model and in the LPS-induced depression mouse model. Furthermore, the key metabolite of B. vulgatus was p-hydroxyphenylacetic acid (4-HPAA), which was found to relieve intestinal inflammation and alleviate depression-like behaviours in mouse models. By increasing the expression of the tight junction protein claudin-5 in the vascular endothelium of the BBB, B. vulgatus and 4-HPAA play critical roles in gut–brain communication.ConclusionB. vulgatus and B. vulgatus-derived 4-HPAA ameliorated intestinal inflammation and relieved depressive symptoms through the gut–brain axis. Thus, administration of B. vulgatus or 4-HPAA supplementation is a promising therapeutic strategy for treating IBD, particularly IBDD

An Investigation of the Work Hardening Behavior in Interrupted Cutting Inconel 718 under Cryogenic Conditions

The severe work hardening phenomenon generated in the machining of Inconel 718 is harmful to continue cutting processes, while being good for the component’s service performance. This paper investigates the performance of cryogenic assisted machining used in the cutting processes, which can reduce the waste of fluids. The influence of dry and cryogenic machining conditions with different cutting speeds on the work hardening layer is investigated based on the interrupted cutting of Inconel 718. Cutting temperature distribution obtained from simulations under different conditions is used to discuss the potential mechanism of work hardening. Then, the depth of work hardening and degree of work hardening (DWH) are investigated to analyze the surface deformation behavior, which strengthens the machined surface during metal cutting processes. From the cutting experiments, the depth of the work hardening layer can reach more than 60 μm under the given cutting conditions. In addition, a deeper zone can be obtained by the cooling of liquid nitrogen, which may potentially enhance the wear performance of the component. The results obtained from this work can be utilized to effectively control the work hardening layer beneath the surface, which can be applied to improve the service performance

The Current Distribution of <i>Carex alatauensis</i> in the Qinghai–Tibet Plateau Estimated by MaxEnt

Modeling the current distribution of and predicting suitable habitats for threatened species support the species conservation and restoration planning process. Therefore, the purpose of this study was to model the actual distribution and predict environmentally suitable habitats for Carex alatauensis S.R.Zhang 2015, a locally threatened native grass species on the Qinghai–Tibet Plateau. To realize this objective, based on the geographical samples within the natural distribution of C. alatauensis, the dominant climatic factors in its potential distribution range were analyzed using the maximum entropy (MaxEnt) model. The results showed that the average values of the area under the receiver operating characteristic curve (AUC) of the training data were 0.833 ± 0.044, which indicated that the accuracy of the MaxEnt model was pretty high for modeling potential distribution regions of C. alatauensis. The combined results from the Jackknife test and the presented contribution of environmental variables revealed that the annual precipitation, the growth season precipitation, and the precipitation of the driest month were the key climatic factors that restricted the distribution of C. alatauensis on the Qinghai–Tibet Plateau. It is predicted that the potential distribution area of C. alatauensis on the Qinghai–Tibet Plateau is 1.96 × 106 km2, and the most suitable area is 3.7 × 105 km2, mainly located in the Qilian Mountains, the Himalayas, and the Qingtanggula Mountains

Functionally improved mesenchymal stem cells via nanosecond pulsed electric fields for better treatment of osteoarthritis

Background: Numerous approaches have been utilized to optimize mesenchymal stem cells (MSCs) performance in treating osteoarthritis (OA), however, the constrained diminished activity and chondrogenic differentiation capacity impede their therapeutic efficacy. Previous investigations have successfully shown that pretreatment with nanosecond pulsed electric fields (nsPEFs) significantly enhances the chondrogenic differentiation of MSCs. Therefore, this study aims to explore nsPEFs as a strategy to improve OA therapy by enhancing MSCs' activity and chondrogenic differentiation and also investigate its potential mechanism. Methods: In this study, a million MSCs were carefully suspended within a 0.4-cm gap cuvette and subjected to five pulses of nsPEFs (100 ns at 10 kV/cm, 1 Hz), with a 1-s interval between each pulse. A control group of MSCs was maintained without nsPEFs treatment for comparative analysis. nsPEFs were applied to regulate the MSCs performance and hinder OA progresses. In order to further explore the corresponding mechanism, we examined the changes of MSCs transcriptome after nsPEF pretreatment. Finally, we studied the properties of extracellular vesicles (EVs) secreted by MSCs affected by nsPEF and the therapeutic effect on OA. Results: We found that nsPEFs pretreatment promoted MSCs migration and viability, particularly enhancing their viability temporarily in vivo, which is also confirmed by mRNA sequencing analysis. It also significantly inhibited the development of OA-like chondrocytes in vitro and prevented OA progression in rat models. Additionally, we discovered that nsPEFs pretreatment reprogrammed MSC performance by enhancing EVs production (5.77 ± 0.92 folds), and consequently optimizing their therapeutic potential. Conclusions: In conclusion, nsPEFs pretreatment provides a simple and effective strategy for improving the MSCs performance and the therapeutic effects of MSCs for OA. EVs-nsPEFs may serve as a potent therapeutic material for OA and hold promise for future clinical applications. The translational potential of this article: This study indicates that MSCs pretreated by nsPEFs greatly inhibited the development of OA. nsPEFs pretreatment will be a promising and effective method to optimize the therapeutic effect of MSCs in the future

Highly compressible and anisotropic lamellar ceramic sponges with superior thermal insulation and acoustic absorption performances

Temperature-invariant highly compressible ceramic sponges are attractive for thermal insulators and energy absorbers, but development is limited by complex preparation processes. Here the authors report large-scale fabrication of silica-alumina composite ceramic sponges via blow spinning and calcination