A simulation study of a dual-plate in-room PET system for dose verification in carbon ion therapy

During carbon ion therapy, lots of positron emitters such as 11C, 15O, 11C are generated in irradiated tissues by nuclear reactions, and can be used to track the carbon beam in the tissue by a positron emission tomography （PET） scanner. In this study, an dual-plate in-room PET scanner has been designed and evaluated based on the GATE simulation platform to monitor patient dose in carbon ion therapy. The dual-plate PET is designed to avoid interference with the carbon beamline and with patient positioning. Its performance was compared with that of four-head and full-ring PET scanners. The dual-plate, four-head and full-ring PET scanners consisted of 30, 60, 60 detector modules, respectively, with a 36 cm distance measurements. Each detector module consisted of a between directly opposite detector modules for dose deposition 24~24 array of 2 mm×2 mm×18 mm LYSO pixels coupled to a Hamamatsu H8500 PMT. To estimate the production yield of positron emitters, a 10 cm×15 cm×15 cm cuboid PMMA phantom was irradiated with 172, 200, 250 MeV/u 12C beams. 3D images of the activity distribution measured by the three types of scanner are produced by an iterative reconstruction algorithm. By comparing the longitudinal profile of positron emitters along the carbon beam path, it is indicated that use of the dual-plate PET scanner is feasible for monitoring the dose distribution in carbon ion therapy.     

HIRFL装置主动式点扫描束流配送系统的Monte Carlo模拟优化

为获得适用于HIRFL 装置主动式点扫描束流配送系统配送的碳离子束,利用Monte Carlo (MC) 工具SHIELD-HIT12A 研究了配送距离和微型脊形过滤器结构周期对治疗室等中心处束斑半高宽(FWHM) 和剂量平坦度的影响。模拟研究发现:束流配送距离越短,束斑FWHM越小,但剂量平坦度越差;微型脊形滤器结构周期是影响剂量平坦度的关键因素,周期越小,剂量平坦度越好。通过模拟研究得出:在HIRFL装置重离子治疗终端将真空窗设置在距等中心距离小于125 cm 时,采用结构周期为2 mm微型脊形过滤器可以满足主动式点扫描照射对束斑FWHM和剂量平坦度的要求。To obtain carbon ion beams suitable for the active spot scanning beam delivery system at the Heavy Ion Research Facility in Lanzhou (HIRFL), the Monte Carlo program SHIELD-HIT12A was used to study the influences of beam delivery distance and structure period of mini ridge filter on full width at the half maximum (FWHM) of beam spot and dose flatness at the isocenter of the treatment room. The present simulation study shows that the shorter was the beam delivery distance, the smaller was the FWHM of beam spot, but the worse was the dose flatness. The structure period of mini ridge filter was a key factor to account for the dose flatness at the isocenter. The smaller was the structure period of mini ridge filter, the better was the dose flatness. Based on the simulation results, we conclude that 2 mm structure period for a mini ridge filter statisfies the requirements on the FWHM of beam spot and dose flatness at the isocenter for the active spot scanning beam delivery system at HIRFL when the distance between the vacuum window and the isocenter is set shorter than 125 cm in the nozzle.     

低阻抗大面积二极管的研制

采用高纯石墨环状阴极和有机玻璃绝缘子,研制了一套低阻抗大面积二极管系统。使用理论计算和数值模拟方法对二极管进行优化设计,在保证绝缘要求的同时,尽量优化二极管轴向长度和内外筒距离以减小二极管的回路电感。实验结果表明,优化后的二极管能在200 kV左右的电压上稳定工作,绝缘结构未发生击穿现象;实验中最高输出电压为213 kV,电流为221 kA,特性阻抗约为1 ,电流密度为8 kA/cm2,脉宽(FWHM)为50 ns。     

FeCl3催化羰基化合物的还原卤代反应

在甲基二氯硅烷作用下, FeCl₃能催化羰基化合物(醛、酮)的还原氯代反应, 得到相应的氯代产物; 在甲基二氯硅烷、PBr₃或NaI作用下, FeCl₃可以催化羰基化合物(醛、酮)的还原溴代或碘代反应, 分别以良好的收率得到相应的溴代烷或碘代烷.     

氨基酸描述子VHSEH用于多肽定量序效建模研究

从20 种天然氨基酸的171个物化性质出发, 按照疏水、立体和电性特征及氢键贡献将其分类后, 分别进行主成分分析, 得到一个新描述子VHSEH(Principal component score vector of hydrophobic, steric, electronic properties and, hydrogen bonds contributions). 对后叶催产素的结构进行了表征, 并以偏最小二乘法及D-优化划分样本建立了PLS定量序效关系模型, 得到复相关系数R2分别为 0.958 和 0.957, Q2分别为0.903和0.845, 约高于VHSE描述子模型值; 对抗菌肽进行了结构表征, 建立了PLS和OSC-PLS模型, 其R2分别为0.84和 0.995, Q2分别为0.546和0.926, 较SZOTT描述子结果好; 对58 个血管紧张素转化酶抑制剂进行QSAM研究, 得到R2, Q2及RMS分别为0.877, 0.838和0.361. 研究结果表明, VHSEH 描述子信息量大, 物化意义明确, 结果更易解释.     

Ag/TiO2光催化还原硝酸氮

利用化学还原法制备不同Ag掺杂量TiO₂纳米催化剂,采用TEM、XRD、XRF和UV-Vis对催化剂进行表征。考察了催化剂在紫外光(254 nm)和可见光照射下还原初始浓度100 mgN·L^-1水相硝酸氮的活性和效果。重点考察了紫外光照射下Ag掺杂量、不同空穴捕获剂(甲酸、甲醇、乙酸、乙醇、草酸、草酸钠等)及甲酸浓度对硝酸氮还原的影响;对硝酸氮转化率和总氮去除率、形成亚硝酸氮、氨氮浓度及氮气选择性的影响。甲酸浓度为0.030 mol·L^-1、Ag掺杂量为1.0wt%时催化剂效果最佳。此时,硝酸氮、总氮的转化率分别为98.43%、78.13%;亚硝酸氮浓度为零,转化的硝酸氮中只有20.76%转化为氨氮,氮气选择性为79.24%。可见光下进行光催化还原反应时,硝酸氮转化率仅37.98%,但氮气的选择性较高。     

甲基咪唑乙酸盐介质中CuBr催化的MMA活性聚合

以甲基咪唑乙酸盐为聚合介质、α-溴代异丁酸乙酯/溴化亚铜为引发体系,研究了甲基丙烯酸甲酯(MMA)的原子转移自由基聚合(ATRP).结果表明:MMA的聚合具有活性自由基聚合的特征.聚合体系中的引发剂和催化剂CuBr比例分别为0.33:1、1:1和1:3时,聚合体系具有活性可控的特征,所得的PMMA分子量分布较窄Mw/Mn＜1.26,体系的引发效率随着引发剂浓度的增加而降低.     

竹胶板-薄壁钢管约束收尘石粉混凝土组合柱轴压性能

提出一种新型的竹胶板-薄壁钢管复合约束收尘石粉混凝土组合柱(BSDCC),对10根BSD-CC试件进行轴压试验,考察试件的破坏特点和形态,调查收尘石粉混凝土的含量率和强度、试件长细比、截面组合与拉杆约束方式、拉杆间距比对试件承载能力和变形的影响规律.结果表明,BSD-CC试件的受压破坏形态主要为试件中部约束拉杆之间竹胶...     

高效液相色谱法测定平胃丸中橙皮苷的含量

提出了高效液相色谱法测定平胃丸中橙皮苷含量的方法。采用Hypersil BDS C18(200mm×4.6mm,5μm)色谱柱;以甲醇-乙酸-水(35+4+61)混合溶液为流动相,流量1mL.min-1,检测波长为283nm,橙皮苷的质量浓度与峰面积在8.08～121.2mg.L-1范围内呈线性关系。方法用于平胃丸中橙皮苷的测定,平均回收率为101.1%,相对标准偏差(n=9)为1.2%。     

非贵金属催化酮的不对称硅氢加成反应的研究进展

手性二级醇作为手性药物、香料等的原料,主要通过不对称加氢来制备.近来通过不对称硅氢加成的方法来制备手性醇的方法,由于其温和的反应条件及相对低廉的催化剂成本而受到广泛关注.介绍了近年来锌、铁、铜、钛等非贵金属催化剂催化潜手性酮的不对称硅氢加成反应的研究进展.