Tech Science Press
Not a member yet
3972 research outputs found
Sort by
A “Three-index” Seismic Performance Evaluation Method Based on Sino-US Seismic Code
Get PDFThe Code for Seismic Design of Buildings (GB50011-2010) in 2016 and the method of seismic performance-based design for high-rise buildings in the Guide for Performance-based Design of High-Rise Buildings (TBI2017) are compared. In view of the characteristics and limitations of the seismic performance index set by the Sino-US seismic code, a “three-index” performance index system and evaluation process considering the displacement angle of the structural interlayer, the plastic damage degree of components and the plastic strain of material is put forward; combining the example of time-history analysis of a out-of-code high-rise building under the rare earthquakes is verified. The results show that the method of seismic performance evaluation by using deformation control index in Sino-US seismic code is relatively simple; however, both are lacking in the setting of specific components and the whole structure level respectively. The "three-index" system can comprehensively and quantitatively evaluate the seismic performance of out-of-code high-rise buildings
Preparation and Characterization of Eco-friendly Carboxymethyl Cellulose Antimicrobial Nanocomposite Hydrogels
Get PDFCarboxymethyl cellulose hydrogels were developed through crosslinking process using eco-friendly crosslinkers such as maleic, succinic, and citric acids. Carboxymethyl cellulose was prepared from the cellulosic fraction of olive industry residues. A series of hydrogels with varying crosslinker acid concentrations, reaction times, and reaction temperatures was produced to study the swelling capacities and gel fraction of the obtained hydrogels. Additional study pertains to the preparation of antimicrobial nanocomposite hydrogels through in-situ incorporation of the silver nanoparticles during the crosslinking reaction. Silver nanoparticles were prepared by reduction of AgNO3with leaves of Ricinus communis. The particle size of prepared silver nanoparticles was detected by transmission electron microscopy (TEM). Chemical structure and morphological characterizations of the prepared hydrogels were performed using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). Finally, the antimicrobial activity of the loaded silver hydrogels against Gram negative (G -ve), Gram positive (G +ve), and Candida albicans yeast was demonstrated
Anisotropic Visco-Elastoplastic Modeling of Quasi-Unidirectional Flax Fiber Reinforced Epoxy Behavior: An Investigation on Low-Velocity Impact Response
Get PDFBased on experimental test results, flax fiber reinforced polymer composites are characterized by nonlinear visco-elastoplastic behavior. The aim of this work is to model the quasi-unidirectional flax fiber reinforced composite behavior through a three dimensional formulation with orthotropic elasticity and orthotropic plasticity using Hill criterion. The isotropic hardening and Johnson Cook parameters are identified from unidirectional tensile tests at different strain rates. The adjustment of Hill’s yield criterion is developed based on yield stresses obtained in tensile tests at different directions. The numerical integration of the constitutive equations is implemented in a user-defined material, UMAT subroutines for the commercial finite element code ABAQUS. Once model parameters are identified using tensile tests, the model needs to be validated by confronting it with other experimental results. That is why experimental and numerical three-point bending tests are carried out in order to validate the proposed model with tests that have not served for the identification. Finally, a numerical parametric study on low velocity impact of a flax/epoxy composite circular plate is investigated
Enzymatic Synthesis of Polycaprolactone: Effect of Immobilization Mechanism of CALB on Polycaprolactone Synthesis
No full textSurface-modified rice husk ash was used as an inorganic support material for immobilization of Candida antarctica lipase B. (3-aminopropyl) trimethoxysilane was used for surface modification. Immobilization of CALB was performed via both physical adsorption and cross-linking. PCL synthesis was carried out by using these immobilized enzymes, free enzyme and Novozyme 435®. Molecular weight distribution of polymer samples was obtained by gel permeation chromatography (GPC) and chain structures of the polymer samples were observed by hydrogen nuclear magnetic resonance (1H-NMR). The highest monomer conversion is generally obtained by using cross-linked enzyme, around 90%. PDI values for all polymer samples were approximately 1.5 which can be considered as acceptable. In general cross-linked enzymes were better than physically adsorbed enzymes in terms of average molecular weights. It can be concluded that PCL can be synthesized with these immobilized enzymes with high molecular weight and low PDI values
Loose Gangues Backfill Body’s Acoustic Emissions Rules During Compaction Test: Based on Solid Backfill Mining
Get PDFIn fully mechanized solid backfilling mining (FMSBM), the loose gangues backfill body (LGBB) that filled into the goaf becomes the main body of bearing the overburden load. The deformation resistance of LGBB is critical for controlling overburden movement and surface subsidence. During the process of load bearing, LGBB will experience grain crushing, which has a significant effect on its deformation resistance. Gangues block will be accompanied with obvious acoustic emissions (AE) features in process of slipping, flipping and damaging. Under confined compression test, monitoring the AE parameters of LGBB can reveal the impact mechanism of grain crushing on LGBB deformation. The study is of great significance for obtaining an in-depth understanding of the mechanical properties of LGBB, and providing guidance to the engineering practice of FMSBM. In order to study the rules of acoustic emissions (AE) of graded Loose gangues backfill body (LGBB) in confined compression test, this article introduces the AE systems to conventional confined compression test to monitor AE signals resulted from the friction and fragmentation among LGBB. The test results show that in the process of LGBB compaction, AE parameters are highly correlated with the strain-stress curve. AE events of balanced-sized graded gangues are more inactive than other two graded samples in different compression stages, AE events of large-particle-dominated graded gangues are most active. In the spatial distribution, AE events are the most active on the edges and the middle part of test samples and the phenomenon of grain crushing is the most obvious in these positions
A Computer-Aided Tuning Method for Microwave Filters by Combing T-S Fuzzy Neural Networks and Improved Space Mapping
Get PDFA computer-aided tuning method that combines T-S fuzzy neural network (T-S FNN) and offers improved space mapping (SM) is presented in this study. This method consists of three main aspects. First, the coupling matrix is effectively extracted under the influence of phase shift and cavity loss after the initial tuning. Second, the surrogate model is realized by using a T-S FNN based on subspace clustering. Third, the mapping relationship between the actual and the surrogate models is established by the improved space mapping algorithm, and the optimal position of the tuning screws are found by updating the input and output parameters of the surrogate model. Finally, the effectiveness of different methods is verified by an experiment with a nine order cross coupled filter. Experimental results show that, compared to a back propagation neural network method based on electromagnetic simulation and an SM method based on a least squares support vector machine, the proposed method has obvious advantages in terms of tuning accuracy and tuning time
Kautz Function Based Continuous-Time Model Predictive Controller for Load Frequency Control in a Multi-Area Power System
Get PDFA continuous-time Model Predictive Controller was proposed using Kautz function in order to improve the performance of Load Frequency Control (LFC). A dynamic model of an interconnected power system was used for Model Predictive Controller (MPC) design. MPC predicts the future trajectory of the dynamic model by calculating the optimal closed loop feedback gain matrix. In this paper, the optimal closed loop feedback gain matrix was calculated using Kautz function. Being an Orthonormal Basis Function (OBF), Kautz function has an advantage of solving complex pole-based nonlinear system. Genetic Algorithm (GA) was applied to optimally tune the Kautz function-based MPC. A constraint based on phase plane analysis was implemented with the cost function in order to improve the robustness of the Kautz function-based MPC. The proposed method was simulated with three area interconnected power system and the efficiency of the proposed method was measured and exhibited by comparing with conventional Proportional and Integral (PI) controller and Linear Quadratic Regulation (LQR)
The Stability of Anionic States of Thymine-Glycine Dimers with Excess Electron
Get PDFIt has been demonstrated that low energy electrons (LEEs) can induce serious DNA damages including bases loss and even single and double strand breaks. Experiments also showed that LEE induced DNA damages will be reduced with the presence of amino acids. For understanding of the protection of amino acids to DNA, the stability of 6 kinds of thymine and glycine (T-g) dimers with planar configurations with an excess electron were studied with density functional theory (DFT) method. The results show that, when the excess electron is vertically attached, all the dimers become more active with higher energy. After re-optimization, 4 kinds (66.7%) of T-g dimers become more stable than the corresponding neutral states. For the most stable anionic dimer noted as [34-A]-, the excess electron is localized on the thymine, while one proton transfers from glycine to thymine. The proton transformation decreases the activities and prevents further reactions of the excess electron. For other three dimers, there is no chemical topology change. The glycine attracts the excess electron with hydrogen-bonding to the thymine
A Numerical Study of the Transitions of Laminar Natural Flows in a Square Cavity
Get PDFThis paper deals with the numerical study of heat and mass transfer occurring in a cavity filled with a low Prandtl number liquid. The model includes the momentum, energy and mass balance equations. These equations are discretized by a finite volume technique and solved in the framework of a custom SIMPLER method developed in FORTRAN. The effect of the problem characteristic parameters, namely the Lewis and Prandtl numbers, on the instability of the flow and related solute distribution is studied for positive and negative thermal and solutal buoyancy forces ratio. Nusselt and Sherwood numbers are derived for values of the Prandtl number ranging between 10-2 and 101 with the Lewis number spanning the interval 1-104. The results show unicellular and multi-cellular flows featured by solute and kinematic boundary layers with thickness depending on the Prandtl number
Turbulent Flow Produced by Twin Slot Jets Impinging a Wall
Get PDFThe dynamics of two fully developed turbulent jets, perpendicular to a heated flat plate and related heat transfer mechanism are analysed numerically. This problem is relevant to several thermal engineering applications. The governing equations are solved by a finite volume method with a second order RSM model combined with wall functions used for turbulent modelling. The possibility to improve heat transfer is assessed taking into account the characteristic parameters for the jet-wall interaction. In particular, a parametric study is conducted by varying the jet Reynolds number (Re) and the nozzle to plate distance (D). The distance between the two jets (H) is set to 20 times the nozzle thicknesses (w). The results show the presence of a complex scarf vortex formed around each impinging jet, and a fountain-up wash flow resulting from the interaction of the jet with the wall. Though an increase in the Reynolds number has a weak effect on the overall flow structure, it produces a systematic rise of Nusselt number. The maximum heat transfer is reached at the stagnation points (dynamics similar to those already known for a single jet). The influence of the non-dimensional parameter (D/w) on the Nusselt number, however, is significant. The maximum local heat exchange between the wall and the flow occurs when the wall is located at the end of the potential core (D=6 w). The average Nusselt number is correlated with the Reynolds number, for two ranges of impinging distances (wall located before and after the potential core end)