Design Scheme of New Type Shell Raising and Feeding System of Medium-large Caliber Naval Gun

The medium -large caliber naval gun is still playing an important role in modern war. The development of highly automatic Shell Raising and Feeding System (SRFS) in the world has been briefly outlined. Several typical SRFS of medium-large caliber naval guns have been analyzed. A re-design of the system is introduced, in which systematic design method has been used to demonstrate its feasibility. The design goal of the system is to realize rapid shell feeding, with application to many types of shells, quick change of shell types , accurate and reliable feeding operation, simple mechanical structure and easy realization of shell withdrawing.

Ballistic limit velocity of small caliber projectiles against SS400 steel plates:Live fire experiments and empirical models

This study presents the ballistic limit velocity of small caliber projectiles against SS400 steel plate derived from live-fire ballistic experiments. Four different small caliber projectiles were tested against SS400 steel plates of 9 mm, 10 mm, and 12 mm thicknesses. The ballistic limit velocity was calculated using two standard methods, MIL-STD-662F and NIJ-STD-0101.06, and additionally using a support vector machine algorithm. The results show a linear relationship between the plate thickness and ballistic limit velocity. Further, the relative penetration performance among five different small caliber projectiles was analyzed using the Penetration Performance Ratio(PPR) introduced in this study, which suggests the potential of PPR to predict the ballistic limit velocity of other untested materials and/or different projectiles.

Numerical Simulation and Experimental Research on Microstructural Evolution During Compact Hot Extrusion of Heavy Caliber Thick-Wall Pipe

Compact hot extrusion(CHE) process of heavy caliber thick-wall pipe is a new material-saving production process. In order to reveal the optimum hot extrusion parameters in CHE process, the e ects of the extrusion parameters on the microstructural evolution are investigated systematically. The metadynamic recrystallization(MDRX) kinetic models and grain size models of as-cast P91 steel are established for the first time according to the hot compression tests performed on the Gleeble-3500 thermal-simulation machine. Then a thermal-mechanical and micro-macro coupled hot extrusion finite element(FE) model is established and further developed in DEFORM software. The results indicated that the grain size of the extruded pipe increases with the increasing of initial temperature and extrusion speed, decreases when extrusion ratio increases. Moreover, the grain size is more sensitive to the initial temperature and the extrusion ratio. The optimum hot extrusion parameters are including that, the initial extrusion temperature of 1250 °C, the extrusion ratio of 9 and the extrusion speed of 50 mm/s. Furthermore, in order to verify the simulation precisions, hot extrusion experiment verification on the heavy caliber thick-wall pipe is carried out on the 500 MN vertical hot extrusion equipment. The load–displacement curve of the extrusion process and the grain sizes of the middle part extruded pipe are in good accuracy with the simulation results, which confirms that the hot extrusion FE models of as-cast P91 steel could estimate the hot extrusion behaviors. The proposed hot extrusion FE model can be used to guide the industrial production research of CHE process.

Retinal vessels caliber changes after strabismus surgery：results of 6mo follow-up

AIM：To evaluate the effect of strabismus surgery on retinal vessels calibers with digital color fundus photographs.METHODS：Two hundred consecutive strabismus patients underwent surgery,and 118 patients（female/male,55/63） who finished 6-month follow-up were finally included in this study.Optic disc-centered digital color fundus photographs of both eyes of all patients were taken prior to surgery and 6mo post surgery.The retinal vascular caliber of 116 operated eyes were measured using the computer program IVAN.The operated eyes were divided into 3 groups according to the surgical methods,recession of one muscle,one muscle recession and one muscle folding,one muscle resection and one muscle recession.The effect of number of altered muscles on retinal vessels was analyzed using statistic software SPSS 16.0.RESULTS：The mean age was 12.4±8.6y.Averaged central retinal artery equivalent（CRAE） of all patients was 120.31 ±23.02 μm preoperatively,and 122.87 ±15.93 μm six months after surgery.Averaged central retinal vein equivalent（CRVE） was 171.11 ±31.73 μm preoperatively and175.02±21.00 μm postoperatively.There was no significant difference of averaged CRAE（P=0.22） or CRVE（P=0.19）before and after operation.Averaged arteriole to venule ratio（AVR） was 0.71 ±0.07 before surgery and 0.70±0.07 after surgery.Comparison of preoperative and postoperative retinal vessels calibers among different surgical groups did not show significant differences.Also,there was no advantage of rectus muscle folding to muscle resection.CONCLUSION：Up to 6mo after strabismus surgery,the retinal vascular calibers were not altered.No more than two muscles in one surgery are safe for retinal perfusion.

Microstructure and texture evolution in AZ31 magnesium alloy during caliber rolling at different temperatures

Magnesium alloy AZ31 was caliber rolled at different temperatures viz.523K,573K,623K,673K and 723K imposing a total cumulative reduction of 92%and a cumulative strain of 2.6.The associated microstructure and texture evolution were studied using Electron Back Scattered Diffraction(EBSD)and X-ray macro-texture observations respectively.Grain refinement was observed in all the caliber rolled bars indicating the occurrence of dynamic recrystallization.Asymmetry parameter and texture index were used to study the evolution of texture.Near doubling of the yield strength at room temperature was observed by caliber rolling at a temperature of 573K.The improvement in mechanical properties was explained on the basis of the fine grain microstructures and suitable development of crystallographic texture.Based on the present study,warm caliber rolling can be used as a good production method for obtaining long bars of high strength magnesium alloy AZ31.

Effects of caliber rolling on microstructure and room temperature tensile properties of Mge3Ale1Zn alloy

Mge3Ale1Zn(AZ31)alloy was caliber rolled isothermally in the temperature range of 250e450
C to develop fine grains of 3.6e12.5 mm.The stressestrain curves obtained from tensile tests at room temperature were found to vary with the temperature employed in caliber rolling.Maximum tensile strength of 290 MPa and ductility of 13.5%were obtained upon caliber rolling at 300
C as compared to 188 MPa and 15.2%,respectively,in the mill-rolled condition.The variations in tensile properties are explained by the concomitant grain size,texture and twins obtained as a function of caliber rolling temperature.

Tailoring strength-ductility balance of caliber-rolled AZ31 Mg alloy through subsequent annealing

Recently,multi-pass caliber rolling has been shown to be effective for Mg alloys.This study investigated the effect of subsequent annealing on the mechanical properties of a caliber-rolled AZ31 Mg alloy to modulate the strength-ductility relationship.This annealing gave rise to different trends in mechanical properties depending on the temperature regime.Low-temperature annealing(T≤473 K)exhibited a typical trade-off relationship,where an increase in annealing temperature resulted in increased ductility but decreased strength and hardness.Such a heat treatment did not degrade the high strength-ductility balance of the caliber-rolled alloy,suggesting that the mechanical properties could be tailored for different potential applications.In contrast,high-temperature annealing(T>473 K)caused a simultaneous deterioration in strength,hardness,and ductility with increasing annealing temperature.These differences are discussed in terms of the varying microstructural features under the different investigated annealing regimes.

Improved tensile properties of AZ31 Mg alloy subjected to various caliber-rolling strains

A multi-pass caliber rolling has attracted attentions as an alternative to severe plastic deformation processes.The present study enhanced strength and ductility of AZ31 Mg alloy simultaneously through the application of caliber rolling.The improving trends in tensile properties were interpreted with various caliber-rolling strains.The oval/circular-shaped calibers imposed a high plastic strain at the center of crosssection,leading to effective grain refinement to submicron scale.This work also confirmed the texture randomizing effect of caliber rolling.Such microstructural evolutions gave rise to the fabrication of high-strength material.Moreover,the caliber-rolled AZ31 Mg alloys exhibited an improvement in ductility as compared to the as-received sheet-rolled material.This was discussed in terms of activation of non-basal slip systems and suppression of mechanical twinning.This study successfully proved the possibility of caliber rolling to produce a bulk Mg rod with enhanced tensile properties.

Diagnostic utility of small-caliber and conventional endoscopes for gastric cancer and analysis of endoscopic false-negative gastric cancers

AIM: To analyze the diagnostic utility of a small-caliber endoscope(SC-E) and clinicopathological features of false-negative gastric cancers(FN-GCs). METHODS: A total of 21638 esophagogastroduodenoscopy(EGD) gastric cancer(GC) screening examinations were analyzed. Secondary endoscopic examinations(n = 3352) were excluded because most secondary examinations tended to be included in the conventional endoscopy(C-E) group. Detection rates of GCs and FN-GCs were compared between SC-E and C-E groups. FN-GC was defined as GC performed with EGD within the past 3 years without GC detection. Macroscopic types, histopathological characteristics and locations of FN-GCs were compared with firstly foundgastric cancers(FF-GCs) in detail. RESULTS: SC-E cases(n = 6657) and C-E cases(n = 11644), a total of 18301 cases, were analyzed. GCs were detected in 16(0.24%) SC-E cases and 40 C-E(0.34%) cases(P = 0.23) and there were 4 FN-GCs(0.06%) in SC-E and 13(0.11%) in C-E(P = 0.27), with no significant difference. FN-GCs/GCs ratio between SC-E and C-E groups was not significantly different(P = 0.75). The comparison of endoscopic macroscopic types of FN-GCs tended to be a less advanced type(P = 0.02). Histopathologically, 70.6% of FN-GCs were differentiated and 29.4% undifferentiated type. On the other hand, 43.0% of FF-GCs were differentiated and 53.8% undifferentiated type, so FN-GCs tended to be more differentiated type(P = 0.048). CONCLUSION: The diagnostic utility of SC-E for the detection of GCs and FN-GCs was not inferior to that of C-E. Careful observation for superficially depressed type lesions in the upper lesser curvature region is needed to decrease FN-GCs.

Research on the floating performance of a novel large caliber machine gun based on the floating principle with complicated boundary conditions

In this paper,a novel large caliber machine gun was taken as the research object to analyze the floating technique based on the principle of fixed-point constraint and secondary counter-recoil.A rigid-flexible coupling multi-body dynamic model of the large caliber machine gun with muzzle brake based on floating principle was established,in which the influence of soil and human body was taken into account.The dynamic simulation was conducted and then the results were compared with the corresponding experimental data The dynamic characteristics of the machine gun with or without floating technique were analyzed to indicate the influence of floating technique upon the performance of the gun.Furthermore,the rigid-flexible coupling dynamic models with five different firing angles was constructed to study the influence caused by the angles.The results indicated that the floating mechanism could reduce the recoil effectively and improve the operational performance of this novel large caliber machine gun.

IN VIVO EFFECT OF HEPARIN PRETREATMENT OF SMALL-CALIBER DECELLULARIZED XENOGRAFT

Objective To develop a new vascular xenograft and to compare the in vivo behavior of thrombogenicity and intimal hyperplasia in the heparin-treated and the non-heparin-treated decellularized xenografts.Methods Canine common carotid arteries were decellularized by enzymatic and detergent extraction procedures.Then a part of decellularized vascular grafts were covalently linked with heparin.Xenografts with(n=24)and without(n=24)heparin treatment were implanted in rabbits' left and right carotid artery respectively as bypass grafts.Graft patency were checked by Duplex ultrasonography at 3 and 6 months after implantation.Twelve rabbits were euthanized randomly at 3 and 6 months respectively and bilateral grafts were explanted.Histological examination and immunohistochemical staining were performed to observe the vascular remodeling.The efficiency of heparin release was demonstrated with toluidine blue staining.HE staining and micrograph analysis system were used for valuating the intima hyperplasia(IH)of bilateral grafts.Results During implantation,thrombosis rate was 4% in the heparin-treated xenografts and 25% in the non-heparin-treated xenografts after 3 weeks(P<0.05).After 6 months,it was 8% versus 58% respectively(P<0.01).Both xenografts of two groups harvested at the end of 3 or 6 months showed a satisfactory cellular reconstruction of either smooth muscle cells or endothelial cells.Intimal hyperplasia in the heparin-treated vascular was less than in the non-heparin treated xenografts.In addition,intimal hyperplasia was liable to appear close to the proximal and distal anastomotic stoma.Toluidine blue staining demonstrated that heparin was slowly released during 6 months.Conclusion This study provides a new strategy to develop a small-caliber vascular xenograft through enzymatic-detergent extraction and heparin treatment.Heparin treatment of the decellularized xenograft is helpful for improving bypass graft patency and reducing intimal hyperplasia.If there was no thrombus,bilateral bypass grafts will undergo a vessel remodeling procedure.Canine common carotid artery treated by detergent and enzymatic extraction and heparin treatment may be used as a new small-caliber vascular xenograft.

Effect of swirling flow on platelet concentration distribution in small-caliber artificial grafts and end-to-end anastomoses

Platelet concentration near the blood vessel wall is one of the major factors in the adhesion of platelets to the wall.In our previous studies,it was found that swirling flows could suppress platelet adhesion in small-caliber artificial grafts and end-to-end anastomoses.In order to better understand the beneficial effect of the swirling flow,we numerically analyzed the near-wall concentration distribution of platelets in a straight tube and a sudden tubular expansion tube under both swirling flow and normal flow conditions.The numerical models were created based on our previous experimental studies.The simulation results revealed that when compared with the normal flow,the swirling flow could significantly reduce the near-wall concentration of platelets in both the straight tube and the expansion tube.The present numerical study therefore indicates that the reduction in platelet adhesion under swirling flow conditions in small-caliber arterial grafts,or in end-to-end anastomoses as observed in our previous experimental study,was possibly through a mechanism of platelet transport,in which the swirling flow reduced the near-wall concentration of platelets.

基于身管应变的小口径火炮弹丸速度测试方法

针对传统火炮弹丸速度测试方法中存在难以获取整条速度曲线、易受环境影响、体积庞大、成本较高、操作复杂等问题,提出了一种基于身管应变的小口径火炮弹丸速度测试方法。基于30 mm口径火炮设计了应变测试仪,实现身管外壁应变测试。根据厚壁圆筒理论计算得出火炮膛压曲线,通过弹底压力解算模型得出弹底压力曲线,与弹载存储测试方法得到的弹底压力曲线进行对比。结合弹丸运动方程得出弹丸速度曲线,采用四阶龙格库塔算法建立弹丸速度仿真模型,将应变测试、弹载存储测试得到的弹丸速度曲线与仿真曲线进行对比。结果表明:应变测试、弹载存储测试与仿真弹丸速度曲线趋势基本吻合,最大速度误差分别为1.1%和0.5%,验证了应变测试方法的可行性,为小口径火炮弹丸测速开辟了新途径。

小口径弹载遥测系统天线设计

天线是弹载遥测系统的核心器件。针对小口径弹载遥测系统的特殊需求,开展弹载天线设计。采用圆极化模式消除炮弹飞行过程中自旋对遥测信号的影响;通过扩展天线的波束宽度适应炮弹的曲线弹道;为满足小口径炮弹对天线小尺寸的需求,通过采用高介电常数介质基板并对辐射单元开槽实现天线小型化;天线和弹载遥测系统板卡之间采用插针相连以实现天线的抗过载要求。对所设计的天线进行试制加工,并测得其阻抗带宽为24 MHz,沿轴线±80°内的轴比均小于3 dB,且其顶点处增益为2.18 dBi。测试结果表明此天线的性能够满足实际使用需求。

面向数字经济的宽口径区块链教材建设研究

区块链相关专业人才不足,成为我国驱动数字经济发展的严重桎梏。当务之急是迅速开发能够满足新兴专业人才培养需求的教材和课程。除了传统的计算机类专业广泛开设区块链系列课程外,目前大量的工学、理学和经管类专业对区块链课程都有迫切需求。针对这种需要和区块链教材现状,以“着眼新工科工程教育要求、面向数字经济”为出发点,以面向电子电气等相关专业的应用为目标,兼顾一般理工科、管理与金融等专业需求,介绍了通用性和侧重性兼顾的宽口径区块链教材建设。首先,介绍了建设面向数字经济特色教材的时代背景,然后,从教材现状、教材建设思路和教材建设实践几个方面阐述了区块链教材建设过程和一些心得体会,以期为区块链教材建设提供一定借鉴和参考。

38 mm型CO_(2)致裂器内部参数对致裂器做功能力影响

为快速获得液态CO_(2)致裂器内部参数对致裂器做功能力的影响特征,优化提高液态CO_(2)致裂器做功能力,提高煤层瓦斯抽采效率,设计液态CO_(2)致裂器做功能力快速评估试验装置。使用煤矿用38 mm型致裂器进行4水平3因素的9组正交试验,分析液态CO_(2)致裂器发热管内部装药量、主管内液态CO_(2)填充量、泄能片厚度以及泄能头释放口径对于致裂器做功能力的影响主次顺序;进一步对其中最重要的影响因素进行固定变量试验,分析最重要影响因素对液态CO_(2)致裂器做功能力的影响特征。结果表明:对于煤矿用38 mm型CO_(2)致裂器,泄能片厚度对于液态CO_(2)致裂器做功能力的影响最大,发热管内部装药量次之,主管内液态CO_(2)填充量及泄能头释放口径影响最弱;液态CO_(2)致裂器做功能力随着泄能片的厚度增加而增加,但当泄能片厚度增加到一定程度时,液态CO_(2)致裂器做功能力增幅不够明显,达到一定厚度泄能片不会破裂,当38 mm型致裂器内部参数设置为CO_(2)质量0.33 kg、释放口径18 mm、装药量60 g、泄能片厚度2.0 mm时致裂器做功能力对应三硝基甲苯(TNT)当量为0.202 kg,相对当前工地使用参数做功能力提升21.9%。

小口径定距空爆弹末端防空拦截实时模拟及开舱距离研究

针对现有小口径定距空爆弹末端防空拦截及开舱距离模拟中,无法体现开舱后子弹云团与目标的动态交会过程,并忽略了定距空爆引信实际启动规律,导致毁伤效能评估不准确的问题,开展小口径定距空爆弹末端防空拦截实时模拟及开舱距离进行研究。通过建立多束定向预制破片战斗部、弹目交会及以巡航导弹为拦截目标的等效目标数值模型,搭建小口径定距空爆弹末端防空拦截实时模拟平台。基于实时模拟平台,引入武器系统误差与定距空爆引信实测启动规律,分析炮弹在不同射击距离下开舱距离与毁伤效能的关系,并对小口径定距空爆弹引信技术发展方向进行展望。研究结果表明,引信实际启动规律使得最优毁伤效能随射击距离的增加而减少的幅度增大,在射击远距离目标时,0~20 m的开舱距离内都存在着较高的完全脱靶率。

小口径人工血管的研究现状及展望

近年来,由于心血管疾病发生率逐渐上升,临床上对再生血管的需求日益增加。目前,大口径人工血管(直径>6 mm)已成功应用于临床,小口径人工血管(直径<6 mm)由于血栓形成、内膜增生、炎症反应和顺应性差导致血流动力学改变等原因,使其移植后远期通畅率低,距离临床应用尚有一段距离。其中,快速内皮化、抑制血栓形成及与自体血管相匹配的顺应性仍是解决问题的关键。本文简述制备小口径人工血管常用材料及技术的特点,重点讨论提高人工血管生物相容性和顺应性的策略,并对未来的研究工作进行展望。

盐雾环境对典型步枪自动机运动影响

盐雾环境对自动步枪战术技术性能和作战效能有着重要影响,但目前对盐雾环境对自动机运动特性和故障的影响机理尚不明确。以某小口径自动步枪为试验对象,设计并进行盐雾全寿命试验,在每次盐雾后通过高速摄影非接触测量自动机运动、高精度天平测量枪机框质量、簧力测试仪测量复进簧参数;对枪机框及导轨表面形貌特征进行拍照,统计全寿命过程中故障情况,获得自动机运动典型故障类型。研究结果表明:随着盐雾时间增长,枪机框质量逐渐增加;复进簧自由长度及预压力逐渐减小,工作压力先减小、后趋于平缓;自动机后坐到位速度先减小、后增大;复进开始及复进到位速度逐渐减小,且二者具有相同变化趋势。盐雾使自动机后座到位速度减小,自动机运动故障次数增多,盐雾环境引起的多参数变化对自动机故障频次影响明显。在试验研究的基础上,构建枪机框质量、复进簧参数、特征点速度随时间变化定量关系公式,为推断盐雾环境自动机运动件参数变化状况和分析其对故障的影响提供参考依据。

基于卡式结构的大口径连续变焦光学系统设计

变焦系统可实现对大视场目标的搜索,但是大视场的轴外像差会对卡式结构的轴外成像产生严重影响,为了能同时实现大视场、长焦距连续变焦的目标,在卡式结构像方增加了一个矫正透镜,设计了一种工作场为0°~1.5°、焦距变化范围为800 mm~1600 mm的红外连续变焦系统。系统由卡塞格林望远镜结构和三组元机械补偿变焦结构组成,工作波长为1064 nm的激光,最大口径为300 mm,各个焦距下最大畸变小于0.5%。在17 lp/mm处各个焦距下的MTF均大于0.5,且接近衍射极限,弥散光斑尺寸很小,均在艾里斑内,成像质量良好,各视场下的像差均得到校正,各项指标都满足设计要求。