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Effect of Plaque Composition on Biomechanical Performance of a Carotid Stent: Computational Study
Get PDFClinical application of bare metal stents is constrained by the occurrence of in-stent restenosis, mainly due to the complex biomechanical environment in the body. Numerical simulation method was used to evaluate the effect of plaque composition on stent performance in a carotid artery. CT angiography (CTA) data were used as a reference, and zero-load state of the carotid artery was used to establish a 3D stenotic artery model. Different plaque compositions, calcified and hypo-cellular were defined in Model 1 and Model 2, respectively. Interactions between the stents and arterial tissues within the stent crimping-expansion process were analyzed to explore the effects of plaque composition on the mechanical parameters of carotid stents. Goodman diagram and fatigue safety factor (FSF) were analyzed to explore the effects of plaque composition on fatigue performance of a carotid stent in the stent service process. In the stent crimping-expansion process, the von Mises stress in the stent and the dog-boning ratio in Model 1 were higher than that in Model 2. The calcified plaque prevented the stent from expanding the stenotic vessel to a pre-set diameter. Thus, the risk of rupture in the calcified plaque was higher than that in the hypo-cellular plaque. Plaque also affected the stress/strain in the vessel wall, which was observed to be lower in Model 1 than in Model 2. This indicated that calcified plaque could decrease the stress-induced injury of arterial tissues. Within the stent service process, the stents used in these two models were predicted to not fail under fatigue rupture as calculated by the Goodman diagram. Additionally, the points closer to the fatigue limit were generally observed at the inner bend of the stent crowns. The FSF of the stent in Model 1 was lower than that in Model 2. The stent operating in the presence of calcified plaques suffered high risk of fractures. Reliability and fatigue performance of the stent were found to be associated with plaque composition. Hence, this study may provide stent designers an approach toward enhancing the mechanical reliability of a stent
A Shaft Pillar Mining Subsidence Calculation Using Both Probability Integral Method and Numerical Simulation
Get PDFIn order to prolong the life cycle of the coal mine, Jinggezhuang (‘JGZ’) coal mine decided to excavate the shaft pillar. The first panel 0091 was designed near the pillar boundary as an experiment in shaft pillar mining. Both probability integral method (PIM) and FLAC3D were used to evaluate the influence on the shaft safety. PIM parameters were obtained from previous surface subsidence station. The rock property is based on the lab mechanical test. A simulated FLAC3D model containing shafts and a panel was built based on stratigraphic information. Surface subsidence results of PIM show that the 0091-panel excavation has no influence on the shafts. The simulated results show that the subsidence of the main shaft and air shaft is small and can be ignored, but it could cause the auxiliary shaft 220 mm horizontal displacement. So, the stress and displacement of the underground part of shaft were analyzed, it shows that the stress changes, subsidence and displacement are mainly located at the top part of the shafts. According to the stress and movement of the simulated shafts, 0091 was decided to be excavated and a surface monitor line was built and measured. In comparison of PIM, FLAC3D, and measured data, the PIM results fit the surface subsidence better. And the FLAC3D results have smaller maximum subsidence and greater influence area than measured. But FLAC3D can provide more details such as displacement, subsidence, stress and strain of both surface and underground. So, for a planned mining excavation, both methods should be used especially for the evaluation of deformation of underground constructions. In the future, with the development of the rock numerical computation technology, the numerical simulation method will be recommended first. The research shows compare of two methods of the coal mine subsidence calculation and provides a solution method for shaft pillar mining
A Distributed LRTCO Algorithm in Large-Scale DVE Multimedia Systems
Get PDFIn the large-scale Distributed Virtual Environment (DVE) multimedia systems, one of key challenges is to distributedly preserve causal order delivery of messages in real time. Most of the existing causal order control approaches with real-time constraints use vector time as causal control information which is closely coupled with system scales. As the scale expands, each message is attached a large amount of control information that introduces too much network transmission overhead to maintain the real-time causal order delivery. In this article, a novel Lightweight Real-Time Causal Order (LRTCO) algorithm is proposed for large-scale DVE multimedia systems. LRTCO predicts and compares the network transmission times of messages so as to select the proper causal control information of which the amount is dynamically adapted to the network latency variations and unconcerned with system scales. The control information in LRTCO is effective to preserve causal order delivery of messages and lightweight to maintain the real-time property of DVE systems. Experimental results demonstrate that LRTCO costs low transmission overhead and communication bandwidth, reduces causal order violations efficiently, and improves the scalability of DVE systems
Reliable Medical Recommendation Based on Privacy-Preserving Collaborative Filtering
Get PDFCollaborative filtering (CF) methods are widely adopted by existing medical recommendation systems, which can help clinicians perform their work by seeking and recommending appropriate medical advice. However, privacy issue arises in this process as sensitive patient private data are collected by the recommendation server. Recently proposed privacy-preserving collaborative filtering methods, using computation-intensive cryptography techniques or data perturbation techniques are not appropriate in medical online service. The aim of this study is to address the privacy issues in the context of neighborhood-based CF methods by proposing a Privacy Preserving Medical Recommendation (PPMR) algorithm, which can protect patients’ treatment information and demographic information during online recommendation process without compromising recommendation accuracy and efficiency. The proposed algorithm includes two privacy preserving operations: Private Neighbor Selection and Neighborhood-based Differential Privacy Recommendation. Private Neighbor Selection is conducted on the basis of the notion of k-anonymity method, meaning that neighbors are privately selected for the target user according to his/her similarities with others. Neighborhood-based Differential Privacy Recommendation and a differential privacy mechanism are introduced in this operation to enhance the performance of recommendation. Our algorithm is evaluated using the real-world hospital EMRs dataset. Experimental results demonstrate that the proposed method achieves stable recommendation accuracy while providing comprehensive privacy for individual patients
Bifurcation-Based Stability Analysis of Electrostatically Actuated Micromirror as a Two Degrees of Freedom System
No full textTorsional micromirror devices have been widely used in micro displays, RF switches, optical communications, and optical coherence tomography systems. In order to study the stability of electrostatically driven torsional micromirror system with double bottom plates and two voltage sources, a dimensionless, two degrees of freedom (2-DoF) dynamic model was constructed. Governed by the dimensionless phase space model equation, the pull-in and bifurcation phenomena were analyzed using the Hamiltonian method and numerical simulation. In particular, the influence of the damping coefficient and the torsion-bending coupling effect on the phase trajectory was investigated. Furthermore, the conditions that can lead to pull-in were numerically determined for saddle-node, pitchfork and Hopf bifurcations in the framework of 2-DoF system. Result showed that the dynamic pull-in voltage as predicted by the proposed 2-DoF system model is considerably lower than that by the one degree of freedom (1-DoF) system model. It was also confirmed that the pull-in voltage varies with the damping coefficient and/or the ratio of the two voltages applied to the bottom plates of the micromirror. The modelling method and stability analysis presented in this paper shall provide valuable insight to the design and control of electrostatically actuated micromirror systems
Heat and Mass Transfer of a non-Newtonian Fluid Flow in an Anisotropic Porous Channel with Chemical Surface Reaction
No full textA numerical study of heat and mass transfer in a non-Newtonian fluid in a parallel-plate channel partly filled with an anisotropic porous medium and subjected to an exothermic chemical reaction on its walls has been conducted. The flow field in the porous region has been modeled by the modified Brinkman-Forchheimer extended Darcy model for power-law fluids and a finite volume method has been used to solve the governing equations. The influence played by a variation of the anisotropic ratio on thermal conductivity, power-law index, Darcy number, and chemical reaction characteristics has been examined. We show that the anisotropy of a porous medium can lead to significant improvements in terms of heat and mass transfer with respect to the isotropic case. The shear-thickening fluids exhibit the highest values of mean Nusselt and Sherwood numbers at large Darcy number. Finally, we show that an increase in the chemical reaction parameters leads to a reduction of the heat and mass transfer rates
Ray-Tracing Based Image Correction of Optical Distortion for PIV Measurements in Packed Beds
Get PDFPacked beds are employed in a wide range of industrial processes, making their optimization an important objective. This requires a thorough understanding of the flow characteristics in the interstices of the bed and the influence of parameters such as packing material, fluid type and flow rate. Next to numerical simulations that have been performed, liquid flows in packed beds have been experimentally investigated by Particle Image Velocimetry (PIV), with optical accessibility obtained using refractive index matching and transparent geometries. For gaseous flows through packed beds, where refractive index matching is not available, there is, in contrast, still a lack of experimental work, because the different optical properties of gas and transparent packing geometries generate optical aberrations. The approximation of gaseous flows with results from dynamically similar, liquid flows provide thereby no reliable alternative because they might be inaccurate and lead to incorrect conclusions about the actual gas flow. The high optical aberrations created by transparent packed beds in PIV experiments can be corrected using ray tracing simulations of a geometric-optical model of the viewing media. The present work proposes a novel image correction technique based on this approach that overcomes the considerable optical distortions caused by arrangements of transparent solid spheres. We analyze the influence of spheres along the camera view in three test cases: the first studies optical distortions of target images, the second PIV computations of a known displacement of a printed particle field, and the third PIV measurements of an air-jet flow. The image correction is qualitatively and quantitatively evaluated by computing errors in target images and in velocity fields. We show that the high optical aberrations that are caused by the spheres can mostly be corrected using ray tracing, allowing for accurate optical measurements in complex geometries, such as packed beds. The approach proposed in this work might be extended to even more challenging geometries in order to solve limitations of existing techniques in the literature
Theoretical Prediction and Experimental Testing of Mechanical Properties for 3D Printed Silk Fibroin-Type II Collagen Scaffolds for Cartilage Regeneration
Get PDFSilk fibroin-typeⅡcollagen scaffold was made by 3D printing technique and freeze-drying method, and its mechanical properties were studied by experiments and theoretical prediction. The results show that the three-dimensional silk fibroin-typeⅡ collagen scaffold has good porosity and water absorption, which is (89.3%+3.26%) and (824.09%+93.05%), respectively. With the given strain value, the stress of scaffold decreases rapidly firstly and then tends to be stable during the stress relaxation. Both initial and instantaneous stresses increase with increase of applied strain value. The creep strains of scaffold with different stress levels show the two stages: the rapidly increasing stage and the second stable stage. It is noted that the scaffold with compressive stress of less than 35 kPa can recover when the compressive stress is removed. However when the compressive stress is higher than 50 kPa, the scaffold is damaged and its structure is destroyed. Not only the compressive property but tensile property of scaffold are dependent on the applied displacement rate or strain rate. Its compressive elastic modulus and tensile modulus increase with increase of strain rate or displacement rate. The nonlinear relaxation model and creep model were constructed respectively and applied to predict the stress relaxation behavior and creep behavior of scaffold. It is found that there are good agreements between the experimental data and predictions, which mean that the built theoretical model can predict the mechanical behavior of scaffold
Joint Time-Frequency Analysis of Seismic Signals: A Critical Review
Get PDFThis paper presents an evaluation of time-frequency methods for the analysis of seismic signals. Background of the present work is to describe, how the frequency content of the signal is changing in time. The theoretical basis of short time Fourier transform, Gabor transform, wavelet transform, S-transform, Wigner distribution, Wigner-Ville distribution, Pseudo Wigner-Ville distribution, Smoothed Pseudo Wigner-Ville distribution, Choi-William distribution, Born-Jordan Distribution and cone shape distribution are presented. The strengths and weaknesses of each technique are verified by applying them to a particular synthetic seismic signal and recorded real time earthquake data
Application of Prunus amygdalus By-products in Eco-friendly Dyeing of Textile Fabrics
Get PDFNatural dyes have become an interesting subject of study because of their better ecological properties in comparison to their synthetic counterparts. This article concerns the dyeing of wool, silk, and polyamide fabrics with natural dyes extracted from almond shells and stems. The developed method of dyeing by these extracts is interesting and very attractive for several reasons: firstly, the extracts used are the black liquor discharged from the industries of delignification, which is a chemical process for removing lignin from agricultural wastes to produce a cellulosic fiber; (ii) these natural dyes are renewable and available in large quantities; (iii) this method is economical; and (iv) lastly, the dyeing performances of the obtained dyed textiles are very promising. The color of each dyed material was investigated in terms of the CIELAB coordinates and their fastness properties measured by washing, rubbing, and light