桁架结构的拓扑优化设计

本文提出了一种杆系结构的拓扑优化设计方法。在本方法中,通过求解一个给出位移场的线性规划确定出结构的新的拓扑形式;将m个位移约束与n个应力约束等效为n个独立的应力约束;接着,利用专家系统技术对所得到的具有新拓扑的结构进行机动性分析並提供修改方案。几个数值实例说明了本方法的可行性。     

高考填空题压轴题的解题策略及思考

作为独立题型,填空题大多是计算型(尤其是推理计算型)和概念性质运用型的试题,解答时必须按规则进行切实的计算与合乎逻辑的推演和判断,但填空题要是考点多、解题长度较长、影响结论的因素较多等,那么即使做到了最后一步才出     

S波段低温低噪声放大器的研制

介绍了基于ADS仿真的低噪声放大器的设计与制作方法;重点研究了LNA的直流偏置、稳定性分析、匹配设计、版图制作和调试;提出了源级负反馈和栅极加并联阻抗的方法来实现了电路全频段稳定和低温正常工作。采用ATF-34143制作了中心频率在2.25的低噪声放大器,在77K温度下,该放大器带内输入输出驻波比小于1.2,增益达到23dB,噪声系数为0.24dB。     

用HI-13串列加速器质谱装置测量182Hf的研究

¹⁸²Hf的半衰期为(8.90±0.09)Ma, 是一个接近灭绝的放射性核素. 超新星爆炸是自然界中已知的惟一能产生¹⁸²Hf的途径. 因此¹⁸²Hf是研究近1亿年来在地球附近可能发生的超新星事件的理想核素. 另外, ¹⁸²Hf是核工程中特别感兴趣的一个长寿命放射性核素. 精确测量超痕量的¹⁸²Hf对反应堆的设计和核天体物理学以及其他研究领域都是非常重要的. 用加速器质谱有可能实现对超低含量¹⁸²Hf的测量. 在中国原子能科学研究院的HI-13加速器质谱装置上对¹⁸²Hf的测量方法以及样品的化学去钨方法进行了研究, 分别得到了空白样品以及系列标准样品的¹⁸²Hf和¹⁸³W的能量-飞行时间双维谱. ¹⁸²W对¹⁸²Hf计数的贡献是通过测量¹⁸³W的计数归一扣除的. 目前本工作对¹⁸²Hf的测量灵敏度为4.15±10^－11 (¹⁸²Hf/¹⁸⁰Hf比值).     

Measurements of 79Se with AMS based on extracting molecular negative ions

A new method for measuring selenium-79 with AMS, which is based on extracting molecular negative ions, is described in this paper. According to the experimental results, the extraction ion form SeO₂^－ could depress the interference of Bromine-79 as much as 5 order levels, that is to say, the background of ⁷⁹Br can be deducted to ⁷⁹Br/Se≈10^－10. By the way, the chemical form of sample and preparation flow was also developed. Finally, three ⁷⁹Se AMS calibration standard samples with theoretical ⁷⁹Se/Se ratios of 5.06×10^－7, 6.87×10^－8, 5.40×10^－10 were obtained and the method of ⁷⁹Se measurement was set up, which actualized transmission and detection of ⁷⁹Se. By using our Bragg curve detector, the two isobars ⁷⁹Br and ⁷⁹Se could be partly identified to a certain extent and ⁷⁹Se can be identified from ⁷⁹Br about 1 order level. AMS measurements of the three calibration standard samples above were performed and good linearity was obtained. The sensitivity of the measurement is (5.16±1.80)×10^－11.     

电子衍射教学实验中的几个问题

本文叙述了电子射线射入薄金片时产生的衍射环的分布规律以及衍射线指、标定的方法．     

高考填空题压轴题的解题策略及思考

作为独立题型,填空题大多是计算型（尤其是推理计算型）和概念性质运用型的试题,解答时必须按规则进行切实的计算与合乎逻辑的推演和判断,但填空题要是考点多、解题长度较长、影响结论的因素较多等,那么即使做到了最后一步才出错,在得分上却和一窍不通的考生是没有任何差别的,尽管他们在水平上存在很大差异,这正是它的缺点,客观上影响了考试的信度与效度．然而,     

AMS measurement of In-situ produced cosmogenic 10Be in Loess Quartz in Luochuan

Loess is the most important and the most typical continental classic sediments of Quaternary. So the measurement of In-situ produced cosmogenic ¹⁰Be is expected to be used for the Loess stratigraphic age. But the production rate of In-situ produced cosmogenic ¹⁰Be in Loess quartz is very low. It requires very high sensitivity and accuracy of measurement. This work has measured the concentrations of ¹⁰Be of two layers in Loess section of Luochuan including L8, L9 and the concentrations of ¹⁰Be in (of) blank sample with the HI-13 AMS system at China Insitute of Atomic Energy(CIAE), then calculated the content of ¹⁰Be in loess quartz for each layer. The ratio of ¹⁰Be/⁹Be was found in the range of 10^－13. The background of ¹⁰Be/⁹Be was about 3×10^－14.     

Primary result of ~(236)U measurement with accelerator mass spectrometry at CIAE

The rare isotope 236U has a half-life of 2.342(3)×107 years,and is produced principally by thermal neutron capture on 235U.The isotopic atom ratio of 236U/238U depends on the integral thermal neutron flux received by the material of interest.236U is potentially useful as a fingerprint for indicating the presence of neutron-irradiated uranium usually originating from nuclear activity.By extracting negative molecular ion UO- from the uranium oxide target,simulating the 236U16O- beam transport with 238U16O- an...