基于BOOSt结构下不连续导电模式的PFC电路

采用现代高频功率变换技术的有源功率因数校正（Power Factor Corrector,PFC)技术是解决高频开关变换器谐波污染的有效手段。与传统的PFC电路相比，有源PFC电路的输入电流接近正弦波且与输与电压同相位，能有效抑制电流波形畸变和谐波，因此避免了对同一电网设施的干扰。在PFC电路中，Boost变换器是研究和应用得最多的一种变换器。本文着重分析了Boost电路在不连续导电模式状态下，PFC电路的临界条件，对实际电路结构的设计有很好的指导意义。     

淤泥质土状亚粘土的一些特征

珠江三角洲软土地区存在一种灰色亚粘土，其工程性能与淤泥、淤泥质土相似，但两者的物理力学性质却有明显的不同，这是一种在规范土名定义上处于过渡或边缘状态的粘性土，不是严格定义上的淤泥质土，也不是正常沉积的一般粘性土，土的强度和工程性质与淤泥质土类似，应该近沿海地区淤泥和淤泥质土对待，不应看成一般粘性土。     

磁场对泡沫钻井液电导率的影响研究

磁处理技术是利用磁场对非铁磁性流体作用．使被作用物的性质产生某些期望的变化，从而改善生产效果和使用效益。磁处理对常规钻井液流变性能的影响研究结果表明，磁化能明显改善钻井液性能。通过研究磁化后泡沫钻井液的性质．测定与控制钻井液的电导率，以便从电测曲线上取得更好的地层特性评价。泡沫钻井液的电导率与密度基本呈线性关系，电导率随密度的升高而变大；磁处理后泡沫钻井液的性质发生明显改变．泡沫钻井液的电导率有不同程度的下降，在磁场强度为100mT、蜂数为2的磁场条件下泡沫钻井液的电导率变化率降低最大，电导率平均下降16％左右。     

Precision equipment for symmetrical bending— Part 1. The loading system

The design and performance of precision bending equipment for testing straight beams with constant rectangular section under a pure bending moment is described. Part 1 deals with the loading arrangements and Part 2 with the rig for measuring beam deflection. The methods for recording deflection of strain gauges applied on the beam have been described elsewhere.^1–4
The reactions to the deadweight gravity loads are taken via ball bearings. The total bending moment inaccuracy, i.e. the sum of estimated systematic errors and random errors, the latter expressed as the 2Ga confidence interval about the mean (2G_cim), is about ± 25 x. 10^-4%, for 23 tests with a steel beam with 15 mm × 75 mm cross sectional dimensions, loaded to 1-1.5 mm/m strain.
The measuring rig stands on the beam via hardened and polished spherical segment feet and uses a capacitive transducer system with less than 5nm resolution. Various application tasks are described. The total inaccuracy of the measured deflection, i.e. apart from bending moment inaccuracy, is about ± 35 times 10^4% for about 10 reproduced, not repeated, tests with the same steel beam. The deflection for such a beam is of the order of 2 to 4 mm.     

兰州重离子加速器大型真空室

已建成的兰州重离子加速器的真空室是一个大型整体结构的超高真空容器,直径约10m,高4.5m,重65000kg,内表面积211m~2,容积100m~3,工作真空度为5×10~(-5)Pa。采用有限单元法在计算机上用SAP-5C程序对真空室受力分析进行了计算。真空室结构材料选用瑞典Uddeholm钢厂生产的316 L 超低碳不锈钢。承制此大型容器的是航天工业部风华机器厂。由于结构庞大,首先将真空室分成八大块和几小块在工厂制造,然后运至现场焊制成一整体容器并进行机械加工。所有密封焊缝均用着色渗透液,X-射线探伤和氦质谱探漏仪进行检查和探漏。     

Feasibility study of absolute activity measurement with metallic magnetic microcalorimeters

We report on a feasibility study on precise determination of mass-specific activity of low-energy emitting radioisotopes. Conventional methods of activity measurement suffer from source self-absorption and a strong decrease in detection efficiency for low-energy electrons and photons. We propose a new method based on metallic magnetic microcalorimeters with the source embedded in the detector target in a 4π geometry. First results with a ⁵⁵Fe source show that electrons and photons are detected with a detection efficiency close to unity and with little loss of energy for electrons. The aim of this study is to provide standards of activity with very low uncertainties in the framework of radiation metrology.     

冲击噪声背景下的近场源二维参数估计方法

本文针对背景噪声为冲击噪声的情况,提出了一种新的近场源二维参数估计方法.本方法利用协变异(或协变异系数)构造矩阵,并通过求根的方法估计近场源的方向角和距离参数.该算法可以抑制冲击噪声对估计性能的影响,同时具有无需谱峰搜索的优点.仿真实验证明了该算法的有效性.     

过氧化甲乙酮合成研究

论述了过氧化甲乙酮的合成方法，用阳离子交换树脂催化剂代替传统的无机酸催化剂。考察了离子交换树脂用量、反应温度对反应产率、活性氧含量的影响及溶剂对产品稳定性的影响。