Tech Science Press
Not a member yet
3972 research outputs found
Sort by
Time Series Analysis for Vibration-Based Structural Health Monitoring: A Review
Get PDFStructural health monitoring (SHM) is a vast, interdisciplinary research field whose literature spans several decades with focusing on condition assessment of different types of structures including aerospace, mechanical and civil structures. The need for quantitative global damage detection methods that can be applied to complex structures has led to vibration-based inspection. Statistical time series methods for SHM form an important and rapidly evolving category within the broader vibration-based methods. In the literature on the structural damage detection, many time series-based methods have been proposed. When a considered time series model approximates the vibration response of a structure and model coefficients or residual error are obtained, any deviations in these coefficients or residual error can be inferred as an indication of a change or damage in the structure. Depending on the technique employed, various damage sensitive features have been proposed to capture the deviations. This paper reviews the application of time series analysis for SHM. The different types of time series analysis are described, and the basic principles are explained in detail. Then, the literature is reviewed based on how a damage sensitive feature is formed. In addition, some investigations that have attempted to modify and/or combine time series analysis with other approaches for better damage identification are presented
Application of Amine-Functionalized Cellulose Foam for CO2 Capture and Storage in the Brewing Industry
Get PDFDue to a lack of technology, smaller breweries simply dump excess CO2 into the atmosphere, fueling the greenhouse effect and global warming. State-of-the-art CO2 capture technologies using nanofibrillated cellulose are expensive and require laborious freeze-drying. Consequently, there is a high demand for affordable alternatives in order to reduce the environmental impact in this industry sector. This work describes a novel route for a quick and cost-efficient synthesis of amine-functionalized cellulose pellets by a surfactant-assisted steam explosion process. Typical values with this method were porosity of 92% and density of 67 g/cm³. Investigations on polyethylenimine (PEI) content and distribution revealed a maximum PEI concentration of 20 wt% with decreasing concentration to the core of a pellet. Sufficient stability against brewery exhaust gas was determined and CO2 release at ~ 120 °C could be confirmed. Capacity tests under simulated working conditions with a novel laboratory reactor yielded a CO2 capacity of 1.0 mmol/g or 67 mol/m³, which is comparable to values known from the literature for other cellulose-based adsorbents
Candelilla Wax as Natural Slow-Release Matrix for Fertilizers Encapsulated by Spray Chilling
Get PDFEfforts to improve crop yields with efficient use of fertilizers are needed to guarantee global food security. Enhanced slow-release fertilizer systems (SRFs) encapsulated in biodegradable matrices are being developed to address this global concern. From a wide range of strategies for SRFs development, we explored a nature-inspired solution based on the plant cuticle model and its function as a membrane for water and nutrient transport control. Here, Candelilla wax, extracted from Candelilla wild plants (Euphorbia antisyphilitica), is studied as a renewable slow-release matrix for fertilizers encapsulated by a modified spray chilling process. From this process, microencapsulates containing 40 wt% of phosphorus fertilizer are obtained with distinctive sizes and chemical characteristics, presenting a slow-release behavior. Considering the abovementioned features, novel insights into fertilizer release mechanisms based on plant cuticle models are discussed
Impact of Natural Oil-Based Recycled Polyols on Properties of Cast Polyurethanes
No full textIn this study, castor oil, rapeseed oil and medium chain triglycerides of coconut oil, were transesterified by means of 2-ethyl-2-hydroxymethyl-1,3-propanediol (trimethylolpropane) and consequently used to convert polycarbonate waste from end-of-life vehicles into liquid polyols. The prepared recycled polyols, composed uniquely of renewable and recycled components, had a hydroxyl number of ca. 250 mg KOH·g−1. They were successfully applied as 100% replacement of a virgin polyol for preparation of solid crosslinked polyurethanes (PU) by solvent-free casting. The produced rigid cast PU exhibited the main transition temperature ranging from 44°C to 53°C, the hardness value from 46 to 61 Shore D and the beneficial low water absorption (0.4-0.5 wt.%). The PU network structure was highly influenced by the presence of aromatic structures of polycarbonate-units and fatty acid compositions. A suitable selection of natural oil thus enabled to adjust thermo-mechanical properties and promote excellent optical transparency of the produced PU
Semi-Interpenetrating Novolac-Epoxy Thermoset Polymer Networks Derived from Plant Biomass
No full textBio-based phenol-formaldehyde polymer (BioNovolac) was developed by reacting molar excess of bio-oil/phenol with formaldehyde in acidic medium. Glycidyl 3,5-diglycidoxybenzoate (GDGB), was prepared by direct glycidylation of α-resorcylic acid (RA), a naturally occurring phenolic monomer. GDGB was crosslinked in the presence of BioNovolac by anionic polymerization. Fourier transform infrared spectroscopy (FTIR) confirmed the formation of semi-interpenetrating polymer networks. The glass transition temperature and moduli of bio-based crosslinked systems were observed to increase with increasing GDGB content. Active chain density and mass retention measured by dynamic mechanical analysis (DMA) and Soxhlet extraction, respectively, indicated a high crosslink density of the cured networks. Scanning electron microscopy (SEM) images depicted the homogeneity of the bulk phase. The preparation of bio-based epoxy-novolac thermoset network resulted in reduced consumption of petroleum-based chemicals
Joint Bearing Mechanism of Coal Pillar and Backfilling Body in Roadway Backfilling Mining Technology
Get PDFIn the traditional mining technology, the coal resources trapped beneath surface buildings, railways, and water bodies cannot be mined massively, thereby causing the lower coal recovery and dynamic disasters. In order to solve the aforementioned problems, the roadway backfilling mining technology is developed and the joint bearing mechanism of coal pillar and backfilling body is presented in this paper. The mechanical model of bearing system of coal pillar and backfilling body is established, by analyzing the basic characteristics of overlying strata deformation in roadway backfilling mining technology. According to the Ritz method in energy variation principle, the elastic solution expression of coal pillar deformation is deduced in roadway backfilling mining technology. Based on elastic-viscoelastic correspondence principle, combining with the burgers rheological constitutive model and Laplace transform theory, the viscoelastic solution expression of coal pillar deformation is obtained in roadway backfilling mining technology. By analyzing the compressive mechanical property of backfilling body, the time formula required for coal pillar and backfilling body to play the joint bearing function in roadway backfilling mining technology is obtained. The example analysis indicates that the time is 140 days. The results can be treated as an important basis for theoretical research and process design in roadway backfilling mining technology
Modelling the Roles of Cewebrity Trust and Platform Trust in Consumers’ Propensity of Live-Streaming: An Extended TAM Method
Get PDFLive streaming is a booming industry in China, involving an increasing number of Internet users. Previous studies show that trust is a cornerstone to develop e-commerce. Trust in the streaming industry is different from that of other e-commerce areas. There are two major dimensions of trust in the live streaming context: platform trust and cewebrity trust, which are both important for customers to adopt and reuse a specific live streaming service. We collected questionnaire data from 520 participates who have used live streaming services in China. We model the collected data and identified factors that can influence users’ propensity by an extended technology acceptance model (TAM) method. According to our analysis, both cewebrity trust and platform trust will greatly influence users’ intention to reuse a certain platform. Moreover, results also indicate that cewebrity trust is far more important than platform trust. These findings can lead to several management strategies to improve the adherence of users to streaming platforms
Coverless Steganography for Digital Images Based on a Generative Model
Get PDFIn this paper, we propose a novel coverless image steganographic scheme based on a generative model. In our scheme, the secret image is first fed to the generative model database, to generate a meaning-normal and independent image different from the secret image. The generated image is then transmitted to the receiver and fed to the generative model database to generate another image visually the same as the secret image. Thus, we only need to transmit the meaning-normal image which is not related to the secret image, and we can achieve the same effect as the transmission of the secret image. This is the first time to propose the coverless image information steganographic scheme based on generative model, compared with the traditional image steganography. The transmitted image is not embedded with any information of the secret image in this method, therefore, can effectively resist steganalysis tools. Experimental results show that our scheme has high capacity, security and reliability
Method of Time Series Similarity Measurement Based on Dynamic Time Warping
Get PDFWith the rapid development of mobile communication all over the world, the similarity of mobile phone communication data has received widely attention due to its advantage for the construction of smart cities. Mobile phone communication data can be regarded as a type of time series and dynamic time warping (DTW) and derivative dynamic time warping (DDTW) are usually used to analyze the similarity of these data. However, many traditional methods only calculate the distance between time series while neglecting the shape characteristics of time series. In this paper, a novel hybrid method based on the combination of dynamic time warping and derivative dynamic time warping is proposed. The new method considers not only the distance between time series, but also the shape characteristics of time series. We demonstrated that our method can outperform DTW and DDTW through extensive experiments with respect to cophenetic correlation
A Method for Improving CNN-Based Image Recognition Using DCGAN
Get PDFImage recognition has always been a hot research topic in the scientific community and industry. The emergence of convolutional neural networks(CNN) has made this technology turned into research focus on the field of computer vision, especially in image recognition. But it makes the recognition result largely dependent on the number and quality of training samples. Recently, DCGAN has become a frontier method for generating images, sounds, and videos. In this paper, DCGAN is used to generate sample that is difficult to collect and proposed an efficient design method of generating model. We combine DCGAN with CNN for the second time. Use DCGAN to generate samples and training in image recognition model, which based by CNN. This method can enhance the classification model and effectively improve the accuracy of image recognition. In the experiment, we used the radar profile as dataset for 4 categories and achieved satisfactory classification performance. This paper applies image recognition technology to the meteorological field