铑铁电阻温度计低温性能测试

针对一种商用铑铁电阻温度计进行了低温下的工作性能研究。对传感器进行了常温和液氮温度下的两点校正,校正结果验证了厂商提供的电阻温度拟合关系式。另外,还对该铑铁传感器连续进行了三次热循环实验。实验前,传感器的液氮温度稳定性优于20mK,而在实验后其温度稳定性优于30mK,满足工程应用的要求。所有实验结果表明,该铑铁电阻温度计性能可靠稳定,为其在超导磁体系统中的进一步应用提供了基础。     

冷冻靶制备中辅助加热的理论和数值分析

 为了补偿惯性约束聚变（ICF）冷冻靶冷却过程中非球对称腔体的热流分布,通常在冷却的同时在腔外壁上施加辅助加热。在间接驱动靶中建立了1维热传导理论模型,分析所需辅助热流密度,同时在2维轴对称模型下,利用计算流体力学的FLUENT程序,对辅助加热机制进行了热力学模拟。当把辅助加热设在腔外壁的中平面上下各1.3 mm的范围时,得到了最佳辅助热流密度为635 W/m²,与理论结果基本一致。     

阀门关闭对低温盲支管水击的影响分析

采用SINDA/FLUINT软件建立了具有盲支管的低温加注管路模型,仿真计算得到了不同阀门关闭时间、盲支管长度、阀门关闭顺序、管径下的水击压力变化情况。结果显示,阀门关闭时间越短,造成盲支管内的压力变化越剧烈,形成较大的压力峰值,容易对管路造成损坏;在低温管路处于冷态的情况下,盲支管长度对盲支管内压力峰值影响不大;某一支路阀门关闭使得该阀前压力出现变化,对另一支路压力影响不大,在整个管路形成封闭腔后,阀门关闭造成系统压力急剧变化,影响较大;管径越大,阀门关闭时的水击压力峰值越大。     

1.5T MRI超导磁体低温容器的拉杆设计与校核

1.5T MRI磁体系统冷重约为4吨,为提高该系统稳定性,采用环氧跑道拉杆结构.分析了磁体正常运行时拉杆上承受的重力、冷缩力,运输过程中的动载力,以及拉杆安装过程中施加的预紧力.在分析的基础上,对拉杆的材料、安装角度进行了选取,并结合漏热对横截面积进行了优化.     

Characterization of 3D DNA Assemblies Using Cryogenic Electron Microscopy

DNA nanotechnology utilizes DNA double strands as building units for self-assembly of DNA nanostructures.The specific base-pairing interaction between DNA molecules is the basis of these assemblies.After decades of development,this technology has been able to construct complex and programmable structures.With the increase in delicate nature and complexity of the synthesized nanostructures,a characterization technology that can observe these structures in three dimensions has become necessary,and developing such a technology is considerably challenging.DNA assemblies have been studied using different characterization methods including atomic force microscopy(AFM),scanning electron microscopy(SEM),and transmission electron microscopy(TEM).However,the three-dimensional(3D)DNA assemblies always collapse locally due to the dehydration during the drying process.Cryogenic electron microscopy(cryo-EM)can overcome the challenge by maintaining three-dimensional morphologies of the cryogenic samples and reconstruct the 3D models from cryogenic samples accordingly by collecting thousands of two-dimensional(2D)projection images,which can restore their original morphologies in solution.Here,we have reviewed several typical cases of 3D DNA-assemblies and highlighted the applications of cryo-EM in characterization of these assemblies.By comparing with some other characterization methods,we have shown how cryo-EM promoted the development of structural characterization in the field of DNA nanotechnology.     

Improved resolution and determination of ambient C5−C12 hydrocarbons by GC-coupled refocussing system

Summary A homemade cryogenic system derived from readily available material is described, illustrating its usage as an accessory for adsorption/thermal desorption chromatography. A small Chromsorb-W-HP packing (1 cm) was introduced into a deactivated precolumn as a cryofocussing, preconcentrating unit. This was able to retain the analyte which had been thermally desorpted from a Tenax TA sampling tube at a relatively higher temperature (–80°C–90°C), with the analyte also reinjected on the analytical column in a relatively narrow band. Average overall recoveries for 24 hydrocarbons tested were 97.5%. Cryofocussing enhanced sensitivity and improved resolution. Field studies at a petroleum industry site were carried out and the accessory proved to be useful for complex C₅–C₁₂ hydrocarbon analysis in ambient air.     

拉伸应力下的高温超导带材临界电流特性研究

针对在低温、拉伸应力共同作用下,高温超导带材临界电流测量困难的问题,详细介绍了一种独立改造后的简便拉伸设备,利用四引线法对两种具有代表性的高温超导带材的临界电流进行了测量,并对结果进行了一系列的验证,证明了此设备能较好的完成测量任务。最后,结合带材的物理结构,简要分析了临界电流产生变化的原因。对今后的测量工作和超导磁体的设计与制备有一定的指导意义。     

超导重力仪用液氦恒温器研制

介绍了一套超导重力仪用液氦恒温器,包括技术指标要求、总体结构、关键技术、试验步骤及结果.恒温器液氦消耗量为0.8L/h,真空腔体内部温度稳定度为±5mK,低温下真空腔体真空度优于5×10-4pa,各参数均优于技术指标要求,完全满足超导重力仪工作环境要求.表明该设计方案是合理的,试验流程是正确的.     

低温微量超声雾化声学系统

针对低温微量超声雾化声学系统中的关键部件单波长超声雾化喷嘴进行研究。首先基于等效电路原理和传输矩阵法分别建立了带中心孔换能器和带中心孔复合变幅杆的频率方程,并应用数学分析软件获得了准确的数值解,实现了超声雾化喷嘴的全谐振。然后,对其进行有限元动力学分析和振动特性测试,结果表明二者相对于设计频率25 kHz的偏差率在0.6%以内,且空载超声振幅达13.5μm。之后,应用流体仿真分析软件对砂轮-工件磨削区进行流场特性分析,结果表明低温微量超声雾化声学系统可以解决磨削区涡流现象的产生。最后,通过对该系统使用前后两种润滑方式的磨削结果进行测试发现：低温微量超声雾化润滑不仅切削液使用量少,而且可以避免工件表面出现烧伤和硬度降低。     

Modified semi-rotating cryogenic modulator for comprehensive two-dimensional gas chromatography

A previously constructed semi-rotating cryogenic modulator was modified for comprehensive two-dimensional gas chromatography (GC×GC). The retention time repeatability was improved by replacing the modulator control program unit with a new system. Peak widths obtained with the modified modulator were comparable with those obtained with the previous modulator and other modulator types. The modulator was easy to construct and it can be installed in any commercial GC system. The constructed GC×GC–FID system and data obtained by gas chromatography–mass spectrometry (GC–MS) were used for identification of unknowns in forest aerosol samples. Figure A semi-rotating cryogenic modulator in which modulation is based on two-step cryogenic trapping with continuously flowing carbon dioxide has been developed for comprehensive two-dimensional gas chromatography