Multi-scale simulation of capillary pores and gel pores in Portland cement paste

The microstructures of Portland cement paste (water to cement ratio is 0.4, curing time is from 1 day to 28 days) are simulated based on the numerical cement hydration model, HUMOSTRUC3D (van Breugel, 1991; Koenders, 1997; Ye, 2003). The nanostructures of inner and outer C-S-H are simulated by the packing of monosized (5 nm) spheres. The pore structures (capillary pores and gel pores) of Portland cement paste are established by upgrading the simulated nanostructures of C-S-H to the simulated microstructures of Portland cement paste. The pore size distribution of Portland cement paste is simulated by using the image segmentation method (Shapiro and Stockman, 2001) to analyse the simulated pore structures of Portland cement paste. The simulation results indicate that the pore size distribution of the simulated capillary pores of Portland cement paste at the age of 1 day to 28 days is in a good agreement with the pore size distribution determined by scanning electron microscopy (SEM). The pore size distribution of the simulated gel pores of Portland cement paste (interlayer gel pores of outer C-S-H and gel pores of inner C-S-H are not included) is validated by the pore size distribution obtained by mercury intrusion porosimetry (MIP). The pores with pore size of 20 nm to 100 nm occupy very small volume fraction in the simulated Portland cement paste at each curing time (0.69% to 1.38%). This is consistent with the experimental results obtained by nuclear magnetic resonance (NMR)

An assembly gap control method based on posture alignment of wing panels in aircraft assembly

The gaps between two mating surfaces should be strictly controlled in precision manufacturing. Oversizing of gaps will decrease the dimensional accuracy and may reduce the fatigue life of a mechanical product. In order to reduce the gaps and keep them within tolerance, the relative posture (orientation and position) of two components should be optimized in the assembly process. This paper presents an optimal posture evaluation model to control the assembly gaps in aircraft wing assembly.Based on the step alignment strategy, i.e. preliminary alignment and refined alignment, the concept of a small posture transformation (SPT) is introduced. In the preliminary alignment, an initial posture is estimated by a set of auxiliary locating points (ALPs), with which the components can be quickly aligned near each other. In the refined alignment, the assembly gaps are calculated and the formulation of the gaps with component posture is derived by the SPT. A comprehensive weighted minimization model with gap tolerance constraints is established for redistributing the gaps in multi-regions. Powell-Hestenes-Rockafellar (PHR) optimization, Singular Value Decomposition (SVD) and KD-tree searching are introduced for the solution of the optimal posture for localization. Using the SPT, the trigonometric posture transformation is linearized, which benefits the iterative solution process. Through the constrained model, overall gaps are minimized and excess gaps are controlled within tolerance. Practical implications – This method has been tested with simulated model data and real product data, the results of which have shown efficient coordination of mating components.This paper proposed an optimal posture evaluation method for minimizing the gaps between mating surfaces through component adjustments. This will promote the assembly automation and variation control in aircraft wing assembly

Linking the SO2 emission of cement plants to the sulfur characteristics of their limestones: A study of 80 NSP cement lines in China

In a properly operated new suspension preheater (NSP) cement line, the SO2 emission is mainly originated from sulfides in the raw meal, and limestone, occupying about 85% wt. of the raw meal, is the dominant sulfur source. However, the sulfur characteristics of limestones and then their influences on the SO2 emission have not been clarified yet. In the present study, 80 NSP cement lines with SO2 emission > 200 mg/Nm3 were recorded, the sulfur content and species as well as pyrite morphology of limestones were analyzed and then correlated to their resulting SO2 emission. The results show that the SO2 emission of stack gas increases linearly with the SO3 content of limestone used, and sulfates lead to a 50% reduction in SO2 emission relative to sulfides. Compared with average SO2 emission, euhedral pyrite leads to a slightly higher SO2 emission, whereas metasomatic pyrite results in a lower SO2 emission, which can be attributed to the effects of accompanying elements (Ti, F, K, and Al etc.) on the desulfurization reaction and clinkerization in the whole NSP cement line. The relationships proposed can be used to predict the SO2 emission based on the sulfur characteristics of limestone and to rationally utilize high-sulfur limestone in cement industry

Co-processing of raw and washed air pollution control residues from energy-from-waste facilities in the cement kiln

Co-processing of industrial wastes as alternative raw materials in cement manufacture is an example of industrial symbiosis for improved material resource efficiency. Since co-processing introduces impurities from wastes, such as air pollution control residue (APCR) from municipal solid waste combustion, into the cement kiln, a better understanding of their environmental impacts and effects on cement manufacturing and quality is needed. Portland cement clinkers containing 5–35% raw or 5–34% washed APCR were prepared, with formation of all typical minerals, but with effects on clinkering reactions, and increased 2CaO·SiO2 and decreased 3CaO·SiO2 and 3CaO·Al2O3. Raw APCR affected the shape of the 2CaO·SiO2 and 3CaO·SiO2 grains, and cement paste from clinker made with 35% APCR exhibited negligible 28d strength. Pastes from the clinkers with lower contents of APCR or washed APCR had strengths that were lower than that of the control at 7d, similar at 28d (∼90 MPa) and higher at 6 m (up to 120 MPa), consistent with their 2CaO·SiO2 and 3CaO·SiO2 contents. Utilization of minerals in APCR thus comes with a trade-off against cement quality. Volatilisation of S, Cl, Pb was reduced by washing, which fully eliminated volatilisation of Zn. Zn was found mainly in the interstitial phases of the clinker, in solid solution in 4CaO·Al2O3·Fe2O3 or 3CaO·Al2O3. Further investigation is required to determine whether Zn and other incorporated elements may be released from the cement paste when these phases react with water. APCR co-processing may reduce CO2 emissions by avoiding CaCO3 decomposition, but this is an uncertain benefit, which may be outweighed by the detrimental effects of APCR alkalis, Cl, S and metals on cement production and quality. Life cycle environmental impacts associated with washing, and dispersal of contaminants in the built environment through construction materials, are additional concerns

A fingerprint based crypto-biometric system for secure communication

To ensure the secure transmission of data, cryptography is treated as the most effective solution. Cryptographic key is an important entity in this procedure. In general, randomly generated cryptographic key (of 256 bits) is difficult to remember. However, such a key needs to be stored in a protected place or transported through a shared communication line which, in fact, poses another threat to security. As an alternative, researchers advocate the generation of cryptographic key using the biometric traits of both sender and receiver during the sessions of communication, thus avoiding key storing and at the same time without compromising the strength in security. Nevertheless, the biometric-based cryptographic key generation possesses few concerns such as privacy of biometrics, sharing of biometric data between both communicating users (i.e., sender and receiver), and generating revocable key from irrevocable biometric. This work addresses the above-mentioned concerns. In this work, a framework for secure communication between two users using fingerprint based crypto-biometric system has been proposed. For this, Diffie-Hellman (DH) algorithm is used to generate public keys from private keys of both sender and receiver which are shared and further used to produce a symmetric cryptographic key at both ends. In this approach, revocable key for symmetric cryptography is generated from irrevocable fingerprint. The biometric data is neither stored nor shared which ensures the security of biometric data, and perfect forward secrecy is achieved using session keys. This work also ensures the long-term security of messages communicated between two users. Based on the experimental evaluation over four datasets of FVC2002 and NIST special database, the proposed framework is privacy-preserving and could be utilized onto real access control systems.Comment: 29 single column pages, 8 figure

Bond-Slip Behavior of Basalt Fiber Reinforced Polymer Bar in Concrete Subjected to Simulated Marine Environment: Effects of BFRP Bar Size, Corrosion Age, and Concrete Strength

Basalt Fiber Reinforced Polymer (BFRP) bars have bright potential application in concrete structures subjected to marine environment due to their superior corrosion resistance. Available literatures mainly focused on the mechanical properties of BFRP concrete structures, while the bond-slip behavior of BFRP bars, which is a key factor influencing the safety and service life of ocean concrete structures, has not been clarified yet. In this paper, effects of BFRP bars size, corrosion age, and concrete strength on the bond-slip behavior of BFRP bars in concrete cured in artificial seawater were investigated, and then an improved Bertero, Popov, and Eligehausen (BPE) model was employed to describe the bond-slip behavior of BFRP bars in concrete. The results indicated that the maximum bond stress and corresponding slip decreased gradually with the increase of corrosion age and size of BFRP bars, and ultimate slip also decreased sharply. The ascending segment of bond-slip curve tends to be more rigid and the descending segment tends to be softer after corrosion. A horizontal end in bond-slip curve indicates that the friction between BFRP bars and concrete decreased sharply

Simultaneous determination of nine phenolic compounds in imitation wild Dendrobium officinale samples using ultrahigh-performance liquid chromatography–tandem mass spectrometry

Dendrobium officinale Kimura et Migo (D. officinale), one of the nine everlasting types of grass, has gained increasing attention owing to its important roles in alternative medicines and drug discovery. Due to its natural resources being in danger of being extinct, imitation wild planting is becoming increasingly common. To assess the product’s quality completely, an efficient ultrahigh performance liquid chromatography-triple quadrupole tandem mass spectrometry (UHPLC-QQQ-MS/MS) method was established to simultaneously quantify nine phenolic compounds in D. officinale samples. The extraction parameters, including solvent, solvent concentration, solid–liquid ratio, and extraction time, were systematically optimized with the single-factor test. The results demonstrated that extraction with a 1:200 solid-to-liquid ratio of 80% methanol for 1.5 h was the most efficient condition for the extraction of flavonoids. Satisfactory retention times and resolution of the nine analytes were acquired on the Thermo Scientific Hypersil GOLD column with multiple reaction monitoring in negative ion scanning mode. The method was validated to demonstrate its selectivity, linearity, precision, accuracy, and robustness. Thus, the verified UHPLC-QQQ-MS/MS method was successfully applied to the quantification of phenolic components present in D. officinale samples. The results indicated that the quantity and composition of phenolic components in D. officinale from various provenances were significantly different. This work provides a theoretical foundation for the cultivation and assessment of wild D. officinale quality

BAF-Net: Bidirectional attention fusion network via CNN and transformers for the pepper leaf segmentation

The segmentation of pepper leaves from pepper images is of great significance for the accurate control of pepper leaf diseases. To address the issue, we propose a bidirectional attention fusion network combing the convolution neural network (CNN) and Swin Transformer, called BAF-Net, to segment the pepper leaf image. Specially, BAF-Net first uses a multi-scale fusion feature (MSFF) branch to extract the long-range dependencies by constructing the cascaded Swin Transformer-based and CNN-based block, which is based on the U-shape architecture. Then, it uses a full-scale feature fusion (FSFF) branch to enhance the boundary information and attain the detailed information. Finally, an adaptive bidirectional attention module is designed to bridge the relation of the MSFF and FSFF features. The results on four pepper leaf datasets demonstrated that our model obtains F1 scores of 96.75%, 91.10%, 97.34% and 94.42%, and IoU of 95.68%, 86.76%, 96.12% and 91.44%, respectively. Compared to the state-of-the-art models, the proposed model achieves better segmentation performance. The code will be available at the website: https://github.com/fangchj2002/BAF-Net

Positioning variation modeling for aircraft panels assembly based on elastic deformation theory

Dimensional variation in aircraft panel assembly is one of the most critical issues that affects the aerodynamic performance of aircraft, due to elastic deformation of parts during the positioning and clamping process. This paper proposes an assembly deformation prediction model and a variation propagation model to predict the assembly variation of aircraft panels, and derives consecutive 3-D deformation expressions which explicitly describe the nonlinear behavior of physical interaction occurring in compliant components assembly. An assembly deformation prediction model is derived from equations of statics of elastic beam to calculate the elastic deformation of panel component resulted from positioning error and clamping force. A variation propagation model is used to describe the relationship between local variations and overall assembly variations. Assembly variations of aircraft panels due to positioning error are obtained by solving differential equations of statics and operating spatial transformations of the coordinate. The calculated results show a good prediction of variation in the experiment. The proposed method provides a better understanding of the panel assembly process and creates an analytical foundation for further work on variation control and tolerance optimization