Anti-sintering behavior and combustion process of aluminum nano particles coated with PTFE:A molecular dynamics study

The characteristic of easy sintering of aluminum nanoparticle(ANP)limits its application in solid propellants.Coating ANP with fluoropolymer could effectively improve its combustion performance.To find out how the coating layer inhibits sintering and promotes complete combustion of particles from an atomic view,a comparative study has been done for bare ANP and PTFE coated ANP by using reactive molecular dynamics simulations.The sintering process is quantified by shrinkage ratio and gyration radius.Our results show that,at the same heating rate and combustion temperatures,bare ANPs are sintered together after the temperature exceeds the melting point of aluminum but the decomposition of PTFE coating layer pushes particles away and increases reaction surface area by producing small Al-F clusters.The sintering of ANPs which are heated in PTFE is alleviated compared with particles heated in oxygen,but particles still sinter together due to the lack of intimate contact between PTFE and alumina surface.The effect of temperature on the combustion of PTFE coated ANPs is also studied from 1000 to3500 K.The number density analysis shows the particles will not be sintered at any temperature.Aluminum fluoride prefers diffusing to the external space and the remained particles are mainly composed of Al,C and O.Fast ignition simulations are performed by adopting micro canonical ensemble.With the expansion of aluminum core and the melting of alumina shell,bare ANPs are sintered into a liquid particle directly.For PTFE coated ANPs,the volatilization of gaseous aluminum fluoride products continually endows particles opposite momentum.

Matrix metalloproteinase 9 level as an indicator for restenosis following cervical and intracranial angioplasty and stenting

Cervical and intracranial angioplasty and stenting is an effective and safe method of reducing the risk of ischemic stroke, but it may be affected by in-stent restenosis. The present study in-vestigated serum level of matrix metalloproteinase 9 as a predictor of restenosis after 40 patients underwent cervical and/or intracranial angioplasty and stenting. Results showed that resteno-sis occurred in 30% （3/10） of patients when the serum level of matrix metalloproteinase 9 at 3 days after surgery was 2.5 times higher than preoperative level. No restenosis occurred when the serum level of matrix metalloproteinase 9 at 3 days after surgery was not 2.5 times higher than preoperative level. Restenosis occurred in 12% （2/17） of patients when the serum level of matrix metalloproteinase 9 was higher than preoperative level for more than 30 days after surgery, but only occurred in 4% （1/23） of patients when the serum level of matrix metalloproteinase 9 was higher than preoperative level for less than 30 days after surgery. However, the differences observed were not statistically signiifcant （P 〉 0.05）. Experimental ifndings indicate that when the serum level of matrix metalloproteinase 9 is 2.5 times higher than preoperative level at 3 days after cervi-cal and intracranial angioplasty and stenting, it may serve as a predictor of in-stent restenosis.

Hardware Implementation and Simulations of Joint Coding and Modulation Diversity MIMO-OFDM Scheme

This paper presents an efficient Joint Coding and Modulation Diversity ( JCMD ) scheme. The proposed scheme applied modulation diversity technique to MIMO-OFDM system which can effectively use time, frequency and space diversity combined with channel coding. In fading channel,the proposed scheme not only achieves high spectral efficiency,but also greatly enhances the reliability of wireless transmission. The self- developed hardware prototype system proves that the proposed scheme can be realized and has high reliability. Compared with traditional MIMO-OFDM scheme based on bit-interleaved coded modulation ( BICM) ,software and hardware simulation results show that the proposed scheme with the optimal rotational angle can obtain a significant performance advantage both for precoded and non-precoded system in the condition of non-perfect channel knowledge and non-ideal synchronization.

Lead dislodgement complicated with paroxysmal atrial fibrillation as a rare cause of inappropriate implantable cardioverter defibrillator shock:a case report

Inappropriate shock of implantable cardioverter defibrillator(ICD)is a rare but catastrophic phenomenon.Inappropriate shock is usually caused by oversensing of noise or supraventricular tachycardias(SVTs).However,inappropriate shock can also be triggered by other uncommon mechanisms.Lead dislodgement is also rare in patients with cardiac implantable electronic devices,which can manifest as pacing failure and mis-sensing of other signals.

Axial mechanical experiments of unbonded flexible pipes

Axial structural damping behavior induced by internal friction and viscoelastic properties of polymeric layers may have an inevitable influence on the global analysis of flexible pipes.In order to characterize this phenomenon and axial mechanical responses,a full-scale axial tensile experiment on a complex flexible pipe is conducted at room temperature,in which oscillation forces at different frequencies are applied on the sample.The parameters to be identified are axial strains which are measured by three kinds of instrumentations:linear variable differential transformer,strain gauge and camera united particle-tracking technology.The corresponding plots of axial force versus axial elongation exhibit obvious nonlinear hysteretic relationship.Consequently,the loss factor related to the axial structural damping behavior is found,which increases as the oscillation loading frequency grows.The axial strains from the three measurement systems in the mechanical experiment indicate good agreement,as well as the values of the equivalent axial stiffness.The damping generated by polymeric layers is relatively smaller than that caused by friction forces.Therefore,it can be concluded that friction forces maybe dominate the axial structural damping,especially on the conditions of high frequency.

随机波背景下基于NLSE模型的极端波分析

该文采用非线性薛定谔方程(NLSE)模拟极端波的形成与演化,利用NLSE呼吸子解理论上的频谱特征研究极端波的可预测性。为探究NLSE呼吸子解的频谱预测特性在接近真实海况下是否依旧适用,选取NLSE一阶呼吸子解作为极端波模型,基于JONSWAP谱的随机波作为背景波,将两者线性叠加,构造了具有随机背景波的极端波模型。并通过数值水池模拟叠加波面的演化,结果显示:在随机波成分占比不高时,含有背景波的合成波演化过程中,仍然保持呼吸子形成极端波的主要频谱特征,但随机成分可能会破坏极端波的形成,且频谱预测特征的显现与极端波的形成存在正相关性。