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.

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.

CAN-based Control System Design on Minor-caliber Deep Well Rescue Robot

By introducing a small-caliber deep well rescue robot,a hold-hug pattern rescue mechanism was brought forward.In order to reduce the volume,the under-well rescue mechanism is modularizing designed.At the same time,the audio and video systems,the illumination system and the ventilation system are expatiated.The rescuing robot can rescue the falling person in the deep well,it can save much manpower,material resources and time.It’s really an ideal rescue device for the small-caliber fall.

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.

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。

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。

蚕丝基小口径人工血管研究进展

心血管疾病居全球死亡率首位,其中冠状动脉和周边堵塞性血管疾病威胁巨大。为了降低该疾病对人类生命的严重威胁,小口径人工血管移植术(搭桥)是较为普遍的治疗手段,但目前常用的制备方法和材料存在长期通畅率低、易形成血栓和难以在体内促进血管内皮化等问题。桑蚕丝因具备良好的力学性能、生物相容性及可控的生物降解性而被广泛用于小口径人工血管。本文综述了蚕丝基小口径人工血管在动物体内的应用,总结了以蚕丝基为材料制备小口径血管的优势,分析了存在的缺陷和改进方向,以期为蚕丝基小口径人工血管的研究发展提供参考。

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。

大口径锥头弹体高速倾斜入水偏转规律数值模拟

结合某大口径锥头弹体高速倾斜入水试验,采用任意拉格朗日-欧拉(arbitrary Lagrange-Euler,ALE)流固耦合方法对弹体倾斜入水偏转行为进行数值模拟,研究了弹体以500 m/s高速倾斜入水过程中不同受力模式、载荷变化特征以及弹体发生偏转的力学机理,分析了入水角度对弹体偏转规律的影响。结果表明:在俯仰力矩作用下,弹体均发生抬头方向偏转,且偏转速度呈现先增大后减小的趋势,偏转程度在不同入水角度范围内呈现不同的变化趋势。当入水角度小于15°时,弹体会发生“跳弹”现象;当入水角度为30°~60°时,弹体偏转趋势基本一致,均由初始倾斜状态逐渐转动至水平状态、竖直状态并最终以弹头入水反方向的“出水”姿态向水下运动;当入水角度为75°时,弹体转动至水平状态后,并未继续偏转至竖直状态,弹头以朝斜上方的姿态向水下运动;弹体的入水侵深随入水角度的增大而增大,且增大趋势近似满足指数函数关系。

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。

负载铜复合物小口径人工血管材料的构建及其生物功能评价

目的构建负载内源性一氧化氮供体催化剂铜复合物的纳米纤维小口径人工血管材料,评价其生物功能。方法合成催化体内一氧化氮供体释放一氧化氮的铜离子复合物(Cu(Ⅱ)-DTTCT)。用Cu(Ⅱ)-DTTCT和具有良好生物相容性的高分子聚合物——聚己内酯(PCL)为原材料,精确催化剂用量,同轴电纺方式制备小口径人工血管支架材料。对其进行一氧化氮释放量、铜离子复合物包载率以及细胞毒性的测定。采用SD大鼠作为半体外和体内评估载体。应用动静脉分流、植入材料原位移植术、活体超声检测、体式显微镜和扫描电镜观察、HE染色等技术评价其生物功能。结果构建以催化剂Cu(Ⅱ)-DTTCT和PCL为芯,以PCL为壳的具有芯壳结构的小口径人工血管支架材料PCL&Cu(Ⅱ)-DTTCT。PCL&Cu(Ⅱ)-DTTCT在所检测时间没有出现一氧化氮明显突释现象。铜离子复合物包载率为91.60%;PCL&Cu(Ⅱ)-DTTCT纤维薄膜的细胞毒性与对照组(PCL)相比几乎没有明显差异。半体外行动静脉分流实验1 h后,体视显微镜下对照组PCL材料内壁见沉积和血小板黏附现象,实验组PCL&Cu(Ⅱ)-DTTCT材料内壁相对干净光滑,没有明显血栓;扫描电镜下观察,对照组PCL见大量血小板黏附,实验组PCL&Cu(Ⅱ)-DTTCT材料上血小板很少,清晰可见人工血管纤维结构;PCL对照组和PCL&Cu(Ⅱ)-DTTCT实验组在行人工血管原位移植术2周、1个月、3个月、6个月后,用超声检测移入血管均通畅,均无因血管阻塞死亡情况;1个月后活体取材后体视显微镜下实验组PCL&Cu(Ⅱ)-DTTC管壁均匀,内腔干净,没有明显的血栓,对照组由于红细胞的浸润表面出现了一些微血栓;扫描电镜观察可见,两组管腔表面已被完全的覆盖,PCL对照组可见血小板,PCL&Cu(Ⅱ)-DTTCT实验组未见明显血小板影像;通过HE染色来分析血管支架的组织再生情况,对照组和实验组血管支架内腔可以观察到一层再生组织,实验组新生组织的厚度明显高于对照组。实验组有核细胞黏附高于对照组。结论构建的负载内源性一氧化氮供体催化剂铜复合物的纳米纤维小口径人工血管材料PCL&Cu(Ⅱ)-DTTCT,可以促使一氧化氮持续释放,发挥抑制血小板黏附的生理功能,抑制血栓的形成和早期再狭窄的发生,在早期促进组织再生。

近代以来中文语境下的新疆坎儿井文化意象演化研究

新疆坎儿井是我国干旱区传统水利工程的杰出代表,清代开始为汉语史料所明确记载,逐步形成辨识度鲜明的文化意象。清代民国时期,坎儿井作为边疆开发“利器”的巨大效益引发了内地人士的关注,并被知识精英视为古代中原文化影响西域的活化石。1949年之后,以《人民日报》为代表的中央媒体极大提升了新疆坎儿井的知名度,人民史观与民族团结视角灌注期间,虽一度在具体宣传口径方面蕴含张力,最终融合于铸牢中华民族共同体意识的有关话语中,使新疆坎儿井成为各民族共创中华的代表符号之一。民国以来逐步形成的一系列重要修辞策略促进了新疆坎儿井文化意象在中文语境中的公众接受,但其中亦存在欠严谨、缺乏学术支撑等问题,对新疆坎儿井文化意象的提升造成某些明显的负面影响,亟需加以改进。