科创中国

In piezoceramic ultrasonic devices,the piezoceramic stacks may fail permanently or function improperly if their working temperatures overstep the Curie temperature of the piezoceramic material.While the end of the horn usually serves near the melting point of the molten metal and is enclosed in an airtight chamber,so that it is difficult to experimentally measure the temperature of the transducer and its variation with time,which bring heavy difficulty to the design of the ultrasonic molten metal treatment system.To find a way out,conjugate heat transfer analysis of an ultrasonic molten metal treatment system is performed with coupled fluid and heat transfer finite element method.In modeling of the system,the RNG model and the SIMPLE algorithm are adopted for turbulence and nonlinear coupling between the momentum equation and the energy equation.Forced air cooling as well as natural air cooling is analyzed to compare the difference of temperature evolution.Numerical results show that,after about 350 s of working time,temperatures in the surface of the ceramic stacks in forced air cooling drop about 7 K compared with that in natural cooling.At 240 s,The molten metal surface emits heat radiation with a maximum rate of about 19 036 W/m2,while the heat insulation disc absorbs heat radiation at a maximum rate of about 7922 W/m2,which indicates the effectiveness of heat insulation of the asbestos pad.Transient heat transfer film coefficient and its distribution,which are difficult to be measured experimentally are also obtained through numerical simulation.At 240 s,the heat transfer film coefficient in the surface of the transducer ranges from–17.86 to 20.17 W/(m2?K).Compared with the trial and error method based on the test,the proposed research provides a more effective way in the design and analysis of the temperature control of the molten metal treatment system.

目的 探讨超声和CT在喉癌患者中甲状软骨受侵时诊断的准确性.方法 对80例正常对照组及87例喉癌可疑患者术前进行甲状软骨超声检查,与CT显示、手术结果进行对照分析.结果 超声对甲状软骨显示良好,本组74例喉癌患者甲状软骨受侵15例.在判断甲状软骨受侵时超声成像灵敏度要优于CT检查(P<0.05).结论 超声能够在喉癌患者中判断甲状软骨是否受侵及受侵情况,可为临床选择治疗方案、制定手术方式提供重要的依据.

The porcelain fracture caused by low metal-ceramic bond strength is a critical issue in porcelain fused to metal(PFM)restorations.Surface roughening methods,such as sand blasting,acid etching and alkaline degreasing for the metal matrix are used to increase bond strength.However,the metal matrix of PFM processed by selective laser melting(SLM)has natural rough surface.To explore the effect of the original roughness on metal-ceramic bond strength,two groups of specimen are fabricated by SLM.One group of specimen surface is polished smooth while another group remains the original rough surface.The dental porcelain is fused to the specimens'surfaces according to the ISO 9693:1999 standard.To gain the bond strength,a three-point bending test is carried out and X ray energy spectrum analysis(EDS),scanning electron microscope(SEM)are used to show fracture mode.The results show that the mean bond strength is 116.5±16 MPa of the group with rough surface(Ra=17.2),and the fracture mode is cohesive.However,when the surface is smooth(Ra=3.8),the mean bond strength is 74.5 MPa 5 MPa and the fracture mode is mixed.The original surface with prominent structures formed by the partly melted powder particles,not only increases surface roughness but also significantly improves the bond strength by forming strong mechanical lock effect.Statistical analysis(Student's t-test)demonstrates a significant difference(p<0.05)of the mean value of bond strength between the two groups.The experiments indicate the natural rough surface can enhance the metal-ceramic bond strength to over four times the minimum value(25 MPa)of the ISO 9693:1999 standard.It is found that the natural rough surface of SLM-made PFM can eliminate the porcelain collapse defect produced by traditional casting method in PFM restorations.

Joining of aluminum to steel has attracted significant attention from the welding research community,automotive and rail transportation industries.Many current welding methods have been developed and applied,however,they can not precisely control the heat input to work-piece,they are high costs,low efficiency and consist lots of complex welding devices,and the generated intermetallic compound layer in weld bead interface is thicker.A novel pulsed double electrode gas metal arc welding(Pulsed DE-GMAW)method is developed.To achieve a stable welding process for joining of aluminum to steel,a mathematical model of coupled arc is established,and a new control scheme that uses the average feedback arc voltage of main loop to adjust the wire feed speed to control coupled arc length is proposed and developed.Then,the impulse control simulation of coupled arc length,wire feed speed and wire extension is conducted to demonstrate the mathematical model and predict the stability of welding process by changing the distance of contact tip to work-piece(CTWD).To prove the proposed PSO based PID control scheme's feasibility,the rapid prototyping experimental system is setup and the bead-on-plate control experiments are conducted to join aluminum to steel.The impulse control simulation shows that the established model can accurately represent the variation of coupled arc length,wire feed speed and the average main arc voltage when the welding process is disturbed,and the developed controller has a faster response and adjustment,only runs about 0.1 s.The captured electric signals show the main arc voltage gradually closes to the supposed arc voltage by adjusting the wire feed speed in 0.8 s.The obtained typical current waveform demonstrates that the main current can be reduced by controlling the bypass current under maintaining a relative large total current.The control experiment proves the accuracy of proposed model and feasibility of new control scheme further.The beautiful and smooth weld beads are also obtained by this method.Pulsed DE-GMAW can thus be considered as an alternative method for low cost,high efficiency joining of aluminum to steel.

Nondestructive techniques for appraising gas metal arc welding(GMAW) faults plays a very important role in on-line quality controllability and prediction of the GMAW process. On-line welding quality controllability and prediction have several disadvantages such as high cost, low efficiency, complication and greatly being affected by the environment. An enhanced, efficient evaluation technique for evaluating welding faults based on Mahalanobis distance(MD) and normal distribution is presented. In addition, a new piece of equipment, designated the weld quality tester(WQT), is developed based on the proposed evaluation technique. MD is superior to other multidimensional distances such as Euclidean distance because the covariance matrix used for calculating MD takes into account correlations in the data and scaling. The values of MD obtained from welding current and arc voltage are assumed to follow a normal distribution. The normal distribution has two parameters: the mean ? and standard deviation of the data. In the proposed evaluation technique used by the WQT, values of MD located in the range from zero to ?+3? are regarded as "good". Two experiments which involve changing the flow of shielding gas and smearing paint on the surface of the substrate are conducted in order to verify the sensitivity of the proposed evaluation technique and the feasibility of using WQT. The experimental results demonstrate the usefulness of the WQT for evaluating welding quality. The proposed technique can be applied to implement the on-line welding quality controllability and prediction, which is of great importance to design some novel equipment for weld quality detection.

熔盐堆是第四代国际核能论坛推荐的6种先进四代堆之一,具有良好的中子经济性、固有安全性、可在线后处理等特点.基于熔盐燃料和冷却剂的流动性,熔盐堆可对堆内产生的放射性气体进行在线移除,周期性地从熔盐泵中除去135Xe和85Kr等中子毒物,以提高燃料循环过程中的中子经济性.目前主要的源项计算软件并不完全适用于熔盐堆在线除气情况下的源项计算,为了解熔盐堆在线处理情况下的源项分布,为熔盐堆辐射防护设计提供参考依据,并验证熔盐堆在线处理情况下源项计算方法的可行性和计算结果的可靠性,采用实际运行过的美国橡树岭国家实验室熔盐实验堆(Molten Salt Reactor Experiment,MSRE)参数,应用自主开发的PostTRITON程序计算了含在线处理情况下的源项,分析了熔盐堆裂变产物产额及氚的产生情况,并应用SCALE5.1软件包中TRITON模块计算了无在线处理情况下的源项,分析了数据偏差的原因,并与橡树岭国家实验室的计算数据进行了比较,计算结果在土8%的范围内符合一致.通过本研究,验证了在线处理下熔盐堆源项计算方法的可行性和结果的可靠性,可为熔盐堆的辐射防护设计提供重要的参考.

各种引起终末期肾病常见的原发性和继发性肾小球疾病均可在肾移植术后复发.常见的复发性原发性肾小球疾病包括IgA肾病、局灶节段性肾小球硬化、特发性膜性肾病和膜增生性肾小球肾炎;常见的复发性继发性肾小球疾病则包括狼疮性肾炎、过敏性紫癜性肾炎、肾淀粉样变性、轻链沉积病、原纤维性/免疫管状肾小球肾炎、混合性冷球蛋白血症性肾病、糖尿病肾病及血管炎肾损害等.由于各移植中心开展移植肾活检的策略不同,因而各移植中心报道的不同病因引起复发性肾小球疾病的发生率也不一致.复发性肾小球疾病患者的病情轻重不一,但无论临床症状还是病理改变一般均轻于自体肾疾病;致使疾病易复发的危险因素各有不同,但一般年轻、自体肾脏疾病重、进展迅速、活体供肾……易致疾病复发;一些疾病经移植前强化治疗可以减少复发;移植后早期确诊疾病复发,且采取积极的治疗措施,能使一些复发性疾病受者临床获益.总之,尽管多种原发性和继发性肾小球疾病在肾移植后均能复发,导致移植肾再次受损,但肾移植仍不失为终末期肾病最有效的疗法之一.

目的探讨子宫输卯管造影术(HSG)在诊治宫腔粘连(IUA)中的价值.方法回顾性分析本院2007年3月~2011年4月经HSG诊断为宫腔粘连的200例患者的临床资料.结果经HSG诊断,宫腔完全性粘连22例(11.0%),中央型粘连34例(17.0%),周围型粘连69例(34.5%),混合性粘连75例(37.5%).经官腔镜检查,HSG与宫腔镜诊断符合率为91.0%,误诊率为9.0%.结论HSG可以确定粘连的部位和范围、程度,且操作简单、方便,患者痛苦较少,是诊断宫腔粘连常规、可靠的检查手段.

日本高度重视水源地保护及水生态修复,在水资源管理体制、法律法规体系建设、水资源开发利用、水源地保护、水生态修复、水污染事故应急处理、水科学研究治理、宣贯教育及公众参与等多个方面取得了先进经验和良好的效果.提出了从日本积极推行的水资源"五保体系",即"社会保水、政策机制保水、科技保水、工程保水、管理保水"中得到借鉴,加强我国在"保水教育、立法保护、污水治理、生态建设、政府主导、全民参与"等方面进行水源地保护及水生态修复工作的建议.

糯扎渡心墙堆石坝最大坝高261.5 m.为强震区建设的超高心墙堆石坝,具有上下游坝坡较陡、地形地质条件复杂,天然土料颗粒级配细、粘粒含量偏高等特点.根据工程特点,从坝料、坝体结构、抗震措施、坝基处理等方面进行了设计,糯扎渡工程特有的设计主要有防渗土料采用人工掺砾石土料、上游坝壳采用含软岩堆石料填筑、坝体顶部采用堆石内加不锈钢钢筋的抗震措施、坝基构造软弱岩带采用高压干磨细水泥固结灌浆等.