A novel variable topology design for a multi-flexible ejection mechanism

The airborne missile launch mechanism often subjects to significant deformations induced by the large ejection force during high-speed actuations in missile ejection process,leading to a substantial deviation of separation parameters from designed values that threats safety of the carrier.This study proposes a novel variable topology design for launch mechanism,achieved via a Prsmatic-Revolute-Revolute pair(PR-R)motion formed by the structural gap with a specific direction.It enables launch mechanism variability during missile ejection process and optimizes the ejection force given by the front and back ejection arms,and greatly optimizes the separation parameters during missile ejection.The kinetics simulation analysis is conducted under working conditions of the original ejection mechanism and the novel mechanism with variable topology design,respectively.The results show that the novel variable topology design is more befitting for the launch process in terms of system safety and controllability,effectively improving the separation posture,restraining the flexible effect of the mechanism,and fulfilling the effectiveness of the design value of multi-rigid body.

TWO-STEP MECHANISM IN HETEROGENEOUS CATALYSIS AND DYNAMIC ANALYSIS

Recent development of the dynamic analysis technique has made it possible to measure separately kinetic parameters of a catalytic reaction as well as to study the effect of catalyst preparation parameters. But its application is still limned to first-order reaction. This work is aimed to demonstrate in some detail that,by comparison of the reaction rate expressions with the two-step mechanism used in catalytic kinetics and dynamic analysis, these methods can be extended to non-first-order reaction, and the kinetic parameters measured by dynamic techniques are interpreted for different reaction mechanisms.

Actuation Mechanism of Two-step Reverse Transformation Behavior in TiNi Alloys Deformed at Parent Phase

The actuation mechanism of TiNi shape memory alloy wires, which were deformed at parent phase followed by a cooling process under constant strain constraint, was investigated. The experimental results show that the two-step reverse martensitic transformation behavior occurs during the heating process, and the temperature range of reverse transformation was obviously widened with the increasing of prestrain. The recovery strain vs temperature curves exhibits an actuation characteristic of linear output recovery strain in a wide temperature range.

Preparation of tungsten-particle-reinforced Zr-based bulk metallic glass composites by two-step spark plasma sintering:microstructure evolution,densification mechanism and mechanical properties

A new two-step spark plasma sintering(TSS)process with low-temperature pre-sintering and high-temperature final sintering has been successfully applied to prepare the tungsten-particle(Wp)-reinforced bulk metallic glass composites(Wp/BMGCs).Compared to normal spark plasma sintering(NS),the densification rate and relative density of Wp/BMGCs can be improved by selecting TSS with appropriate sintering pressure in the low temperature pre-sintering stage.However,the compressive strength and plastic strain of 30%Wp/BMGCs prepared by TSS are both higher than those of the samples prepared by NS.The TSS process can significantly enhance the compressive strength of 30%Wp/BMGCs by 12%and remarkably increase the plastic strain by 50%,while the trend is completely opposite for 50%Wp/BMGCs.Quasi-in situ experiments and finite element simulations reveal that uneven temperature distribution among particles during low-temperature pre-sintering causes local overheating at contact points between particles,accelerating formation of sintering neck between particles and plastic deformation of Wp.When the volume fraction of Wp is low,TSS can improve the interface bonding between particles by increasing the number of sintering necks.This makes the fracture mode of Wp/BMGCs being predominantly transgranular fracture.However,as the volume fraction of Wp increases,the adverse effects of Wp plastic deformation are becoming more and more prominent.The aggregated Wp tends to form a solid"cage structure"that hinders the bonding between particles at the interface;correspondingly,the fracture behavior of Wp/BMGCs is mainly dominated by intergranular fracture.Additionally,reducing the sintering pressure during the low-temperature pre-sintering stage of TSS has been shown to effectively decrease plastic deformation in Wp,resulting in a higher degree of densification and better mechanical properties.

Cerium oxide inclusion nucleation mechanism based on classical nucleation theory and two-step nucleation

It is challenging to assess the mechanism responsible for the nucleation of inclusions in metals at high temperatures.The present work therefore systematically investigates the nucleation of cerium oxide inclusions according to classical nucleation theory and a two-step nucleation mechanism.The nucleation rates and nucleation radii of these inclusions are obtained,and the results demonstrate a considerable difference between theoretical and experimental values.On the basis of a two-step nucleation mechanism,(CeO_(2))_(n) and(Ce_(2)O_(3))_(n)(n=1-6)clusters were constructed and the thermodynamic properties of both these clusters and of cerium oxide nanoparticles were analyzed.In addition,the entropies and heat capacity changes of cerium oxides were determined using first principles calculations and are found to be consistent with literature data.The present data indicate that the cerium oxide inclusion nucleation pathway can be summarized as[Ce]+[O]→(CeO_(2))n/(Ce_(2)O_(3))_(n)→(Ce_(2)O_(3))_(n)→(Ce_(2)O_(3))_(2)→core(Ce_(2)O_(3)crystal)-shell((Ce_(2)O_(3))_(2) cluster)nanoparticles→(Ce_(2)O_(3))bulk.

Preparing low-oxygen Ti-6Al-4V alloy powder through direct reduction of oxides and its synergistic reaction mechanism

Ti-6Al-4V alloy powder was prepared through a two-step reduction of a mixture of TiO_(2),V_(2)O_(5) and Al_(2)O_(3) in this study.The oxide mixture was first reduced by Mg in MgCl_(2) at 750℃ in argon,where oxygen was reduced to 2.47 wt%from 40.02 wt%.The oxygen content in the final powder was eventually reduced to an extremely low level(0.055 wt%)using calcium at 900℃ in argon,and the final powder had the composition of 90.12 wt%Ti,5.57 wt%Al,and 3.87 wt%V,which meets the standard specification of Ti-6Al-4V(ASTM F1108-09).Between the two reductions,a heat treatment step was designed to help controlling the specific surface area and particle size.The effect of the heat treatment temperature on the morphology,and composition uniformity of the powder was investigated in detail.Heat treatment above 1300℃ attributed to a dense powder with a controlled specific surface area.Thermodynamic modeling and experimental results indicated that onlyα-Ti enriched with Al andβ-Ti enriched with V exist in the final powder,and other possible phases including Al-Mg and Al-V were excluded.This study also offers a triple-step thermochemical process for producing high-purity Ti-based alloy powder.

心脏收缩力调节器用于心力衰竭的机制和临床研究

心脏收缩力调节器(CCM)作为救治慢性射血分数降低的心力衰竭(HFrEF)的新型植入性电子治疗装置,因可增强心室肌收缩力、改善患者症状体征和心功能指标甚至远期预后,已迅速成为心血管领域倍受关注的热点。本文综述了CCM治疗HFrEF的机制和临床研究,并根据其机制和信号传递算法对其在射血分数保留的心力衰竭(HFpEF)、心脏再同步化治疗(CRT)反应不佳、合并心房颤动的HFrEF患者中的疗效进一步分析和展望,以期推动CCM可以满足更多、不同临床情况的心力衰竭患者的需求。

窄腔内倒扣产品多次顺序抽芯注塑模设计

针对塑件正面窄腔内5个倒扣、背面2个窄腔内环形倒扣、四周侧17个倒扣,背面7个倒扣的结构难点,创新提出了隧道楔紧块、滑块运动方向与侧型芯垂直的吊挂侧型芯式抽芯方法,实现窄腔内倒扣抽芯。设计了4类抽芯机构,通过4次顺序抽芯成功实现窄腔内复杂倒扣产品的脱模。第一次抽芯解决正面窄腔内5个倒扣抽芯难题,由顺序定距分型机构控制抽芯顺序;第二次抽芯解决四周侧17个倒扣抽芯难题;第三次抽芯解决背面7个倒扣抽芯难题;第四次抽芯解决背面2个窄腔内环形倒扣抽芯难题,创新设计了弹簧式快速二次推出机构控制抽芯顺序。经试模验证,该模具结构合理、工作可靠。

顶出式水稻有序抛秧机取秧系统的设计与试验

针对现有水稻抛秧机存在移栽效率低、漏秧、塑料钵苗盘回收难问题,设计了一种硬盘育苗顶出式有序水稻抛秧机取秧系统,由送盘机构、顶出机构及回盘机构等机构组成。为此,构建了取秧系统的三维模型,对顶出机构的端面凸轮进行设计分析,得到凸轮的最大顶出速度;利用Ansys软件对端面凸轮进行强度分析和疲劳寿命分析,得到其最大应力、最大位移变形、最大疲劳寿命和安全系数,各项参数均符合使用要求。试验结果表明:在样机前进速度v=1.5km/h、栽植频率为1300株/min的工况下,水稻抛秧机取秧系统的株距合格率为98%,空穴率为3.2%,秧盘损伤率为0%,满足秧苗移栽作业要求。

烦躁不安排乳反射研究进展

介绍烦躁不安排乳反射的概念、评估工具、发生机制及影响因素等,从改变生活方式、加强社会支持、适当药物治疗和专科心理干预4个方面综述干预措施,以期为医护人员正确识别烦躁不安排乳反射,开展相关研究及干预实践提供参考。

射血分数保留型心力衰竭的病理机制及治疗

射血分数保留型心力衰竭(HFpEF)影响着全球一半左右的心力衰竭患者,其患病率随着人口老龄化呈逐年上升趋势,且具有较高的死亡率。然而,HFp EF的病理机制非常复杂,目前尚缺乏有效的治疗手段。结合近年来相关研究进展,文章阐述并讨论了HFp EF病理机制及现有治疗方法,以期为提高HFp EF患者的生活质量和改善患者的预后提供新思路。

地外天体软着陆过程羽流扬尘特性研究现状及展望

地外天体软着陆过程中,反推发动机羽流作用于天体表面风化层诱发的侵蚀扬尘是影响软着陆安全的最主要因素。首先对羽流扬尘现象的物理过程、侵蚀机制研究现状进行梳理总结,总结出侵蚀机制主要包括粘性剪切侵蚀、扩散气体喷发、承载力破坏和扩散驱动流动4种;其次,对部分探月和探火任务的在轨侵蚀结果、仿真模型和经验公式的研究现状进行研究分析,得出月球表面和火星表面因背景压力和风化层物质特性差异会产生不同的侵蚀机制,而在相同条件下的侵蚀机制也会随发动机个数和总推力的变化而变化,有必要对物理机理和扬尘特性进行进一步细化研究;最后,结合未来地外天体软着陆任务需求,提出了羽流扬尘原位测量、仿真预测模型和羽流扬尘消除3种用于未来探测任务羽流扬尘预测和防护的关键技术,以期对未来软着陆任务顺利执行起到一定的保障作用。

射血分数保留的心力衰竭常见合并症的病理机制及治疗策略

射血分数保留的心力衰竭(HFpEF)的病理生理机制尚未明确,目前认为与肾素-血管紧张素-醛固酮系统、晚期糖基化终末产物及其受体、冠状动脉微血管炎症等介导的细胞自噬、氧化应激、炎症反应及心脏能量代谢障碍等相关。高血压、糖尿病、冠心病、心房颤动等均可通过各种信号途径导致左心室心肌僵硬度增加、舒张期充盈受损等病理改变,最终导致HFpEF的发生。目前研究显示能够改善HFpEF预后的药物主要为钠-葡萄糖共转运蛋白2抑制剂,而射血分数降低的心力衰竭的治疗手段也并不适用于HFpEF,故通过对HFpEF合并症进行早期预防及治疗,以控制HFpEF的发生发展显得尤为重要。现从HFpEF常见合并症的病理机制及治疗等方面进行归纳,以期为HFpEF的临床治疗提供借鉴和指导。

基于网络药理学探讨平阳益心饮治疗射血分数保留型心力衰竭的作用机制

目的基于网络药理学方法预测平阳益心饮治疗射血分数保留型心力衰竭(HFpEF)的潜在作用靶点与通路。方法依托HERB数据库和SwissTarget Prediction数据平台预测平阳益心饮成分靶点,通过OMIM、PhamGKB及GeneCards数据库获得HFpEF靶点,采用Venny 2.1.0对药物与疾病的靶点进行交集选取,采用Cytoscape构建“成分-疾病靶点”网络,进行蛋白互作网络(PPI),并通过网络拓扑分析得到平阳益心饮治疗HFpEF的核心靶点,并将核心靶点通过Metascape数据库进行基因本体论(GO)和京都基因与基因组百科全书(KEGG)分析。结果通过网络药理学的方法,得到平阳益心饮治疗HFpEF的潜在靶点有524个,它们主要参与细胞对氮化合物的反应、系统进程调节、循环系统过程和磷酸化的正调控等生物过程;参与调控癌症相关通路、cGMP-PKG信号通路、cAMP信号通路、脂质与动脉粥样硬化等235条通路。结论平阳益心饮可通过多成分、多靶点、多途径参与细胞凋亡、细胞增殖等,从而达成治疗HFpEF的目的。

含内外螺纹管接头注射模设计

针对管接头同时有内外螺纹的结构,设计了1模2腔的模具,成型塑件的外螺纹及外圆柱面设计了斜导柱+弹簧+滑块的脱模机构,为了实现塑件内螺纹结构的自动脱模,设计了液压缸+齿轮齿条+齿轮传动+螺纹螺母的脱膜机构,在开模前通过液压缸活塞杆驱动该机构运动,使内螺纹型芯一边旋转一边上升完成脱模。经实际生产验证:模具动作稳定可靠,成型的塑件质量符合要求。

射血分数保留型心力衰竭的病理生理及治疗药物进展

射血分数保留型心力衰竭在心力衰竭中占40%~71%,是一种涉及心、肾、肺、血管系统和脂肪组织等的多系统疾病,严重影响患者的生活水平。近年来,随着医疗研究水平不断提升,射血分数保留型心力衰竭临床治疗取得一定的效果,但患者仍然存在预后不良情况,复发率升高而生活质量下降。文章通过对射血分数保留型心力衰竭近年国内外相关研究报道进行综述,发现其病理生理机制主要与高血压、冠脉疾病和冠脉微血管功能障碍、左心功能不全、右心室功能障碍和肺动脉疾病、激素系统异常、肥胖、系统性炎症和代谢异常相关,通常使用利尿剂、RAAS抑制剂、SGLT2is、MRA和他汀类药物进行治疗,不同分型的动物模型的构建也为射血分数保留型心力衰竭临床诊治提供一些有价值参考。

冰箱抽屉注射模设计

对冰箱抽屉结构进行分析,根据其表面质量要求设计了1副带滑块和斜推组件的两板热流道注射模,模具由1个热流道管组成的浇注系统进浇,针对冰箱抽屉的局部特征,分别采用斜滑块、斜导柱+滑块、斜推组件等结构进行成型及脱模。为了防止成型塑件出现推杆痕,采用推件板推出塑件,推件板采用三面环形结构。模具经实际生产验证:结构合理,成型的塑件达到了精度要求。

“滑块式”二次顶出机构在压铸模具中的合理应用

压铸生产中经常遇到一些深腔、薄壁类的外壳或者对外观有特殊要求的铸件,在铸件的内凹面不能排布或者不允许存在顶杆印痕。针对此类零件,通常会设计带有二次顶出机构的压铸模具来保证零件生产。笔者列举实例介绍一种新型的滑块式二次顶出机构,该机构可解决这种内凹面无法放置顶杆的深腔薄壁的压铸件的脱模问题,且使模具整体结构简单,安全可靠,同时可以满足完全自动化、批量化的生产压铸模具需求。

Effects of the two-step ageing treatment on the microstructure and properties of 7B04 alloy pre-stretched thick plates

The effects of the two-step ageing parameters （temperature and time） on the mechanical properties and electrical conductivity of 7B04 （A1-Zn-Mg-Cu） pre-stretched thick plates were studied. The results reveal that the initial T1 ageing contributes a major increase of the tensile strength, and the 0.2% proof stress value reaches 482 MPa after ageing for 7 h at 115℃. Behavioral differences in the tensile properties of the alloy after the two-step ageing treatment were less with the first-step ageing at 115~C for different time periods （7, 14, and 21 h）. The effects of the second ageing parameters on the properties and microstructure of the 7B04 alloy were remarkable. TEM analysis of the samples aged at Temper I （7 h at 115℃ ＋ 12 h at 160℃） and Temper II （7 h at 115℃ ＋ 16 h at 165℃） indicates that two kinds of phases, i.e. 11＇ and 11 phases, precipitate from the matrix and efficiently improve the tensile strength of the alloy, and the grain boundary precipitates are coarse and discrete. There are obvious precipitate free zones （PFZs） along the grain boundary in the microstructure of the alloy after the two-step ageing treatment.

Effect of Cu content on microstructures and mechanical properties of ADI treated by twostep austempering process

The effect of Cu content on the microstructures and mechanical properties (yield strength, ultimate tensile strength, impact energy, fracture toughness) of austempering ductile iron (ADI) treated by two-step austempering process were investigated. High Cu content in nodular cast irons leads to a significant volume fraction of retained austenite in the iron after austempering treatment, but the carbon content of austenite decreases with the increasing of Cu content. Moreover, austenitic stability reaches its maximum when the Cu content is 1.4% and then drops rapidly with further increase of Cu. The ultimate tensile strength and yield strength of the ADI firstly increases and then decreases with increasing the Cu content. The elongation keeps constant at 6.5% as the Cu content increases from 0.2% to 1.4%, and then increases rapidly to 10.0% with further increase Cu content to 2.0%. Impact toughness is enhanced with Cu increasing at first, and reaches a maximum 122.9 J at 1.4% Cu, then decreases with the further increase of Cu. The fracture toughness of ADI shows a constant increase with the increase of Cu content. The influencing mechanism of Cu on austempered ductile iron (ADI) can be classified into two aspects. On the one hand, Cu dissolves into the matrix and functions as solid solution strengthening. On the other hand, Cu reduces solubility of C in austenite and contributes more stable retained austenite.