Special Elements of the Lattice of Overcommutative Varieties of Semigroups

The distributive, codistributive, standard, costandard, and neutral elements of the lattice of overcommutative varieties of semigroups are completely described.     

高等数学教学中落实素质教育之浅见

本文主要讨论了数学素质教育的重要性及如何具体在高等数学教学中培养学生的数学素质     

振动轮式微机械陀螺频率配置和气压选择

推导了振动轮式微机械陀螺的输出信号与输入角速度的幅频、相频关系,讨论了在不同的频率配置和品质因数下陀螺的灵敏度、带宽和零位稳定性。陀螺振动频率应设计在2kHz左右,检测轴自然频率比驱动轴高一个陀螺频带宽度。根据实测陀螺振动品质因数与气压的关系曲线,振动轮式微机械陀螺合适的工作气压是100Pa-1000Pa。     

Thermodynamics of Silicon Nitride. Standard molar enthalpy of formation of amorphous Si3N4 at 298.15 K

The standard molar enthalpy of formation Δ_f H _m ⁰=–760±12 kJ for amorphous silicon nitride a-Si₃N₄ has been determined from fluorine combustion calorimetry measurements of the massic energy of the reaction: a-Si₃N₄(s)+6F₂(g)=3SiF₄(g)+2N₂(g). This value combined with Δ_f H _m ⁰= –828.9±3.4 kJ for a-Si₃N₄ indicates that determined for the first time molar enthalpy change for the transition from amorphous to α-crystalline form Δ_trs H _m ⁰=69±13 kJ is very evident, in spite of its large uncertainty range resulting from impurity corrections. This revised version was published online in July 2006 with corrections to the Cover Date.     

Isolation and HPLC Quantitative Determination of 5α-Reductase Inhibitors from Tectona grandis L.f. Leaf Extract

Steroid 5α-reductase plays a crucial role in catalyzing the conversion of testosterone to dihydrotestosterone, which is involved in many androgen-dependent disorders. Leaf-hexane extract from Tectona grandis L.f. has shown promise as a 5α-reductase inhibitor. The objectives of this current study were to isolate and identify 5α-reductase inhibitors from T. grandis leaves and to use them as the bioactive markers for standardization of the extract. Three terpenoid compounds, (+)-eperua-8,13-dien-15-oic acid (1), (+)-eperua-7,13-dien-15-oic acid (2), and lupeol (3), were isolated and evaluated for 5α-reductase inhibitory activity. Compounds 1 and 2 exhibited potent 5α-reductase inhibitory activity, while 3 showed weak inhibitory activity. An HPLC method for the quantitative determination of the two potent inhibitors (1 and 2), applicable for quality control of T. grandis leaf extracts, was also developed. The ethanolic extract showed a significantly higher content of 1 and 2 than found in the hexane extract, suggesting that ethanol is a preferable extraction solvent. This study is the first reported isolation of 5α-reductase inhibitors (1 and 2) from T. grandis leaves. The extraction and quality control methods that are safe and useful for further development of T. grandis leaf extract as an active ingredient for hair loss treatment products are also reported.     

混酸分解-电感耦合等离子体质谱（ICP-MS）法测定地质样品中铌钽锂铍铷钨

地质样品中的铌、钽、锂、铍、铷、钨元素含量相差大,且同一样品中各元素含量差异也较大。如在原矿中的含量只有几十至几百μg/g,而在精矿中的含量则达到了百分之几至百分之几十,高含量样品中的铌钽元素在强酸性溶液中不稳定,极易水解,准确测定这些元素需要多种方法,分析过程繁琐。传统的分析方法过程复杂、难以实现同时测定多种元素。通过考察分解体系酸的用量选择、提取剂的选择、提取剂用量的选择、测定内标元素的选择,建立了混酸分解-电感耦合等离子体质谱法同时测定地质样品中铌、钽、锂、铍、铷、钨元素的测定方法。本文采用氢氟酸-硝酸-盐酸-高氯酸-硫酸分解样品,用3～4滴氢氟酸+ 5 %硫酸+ 5 %过氧化氢萃取体系代替常规有机酸(酒石酸等。)萃取体系。采用ICP -MS同时测定各含量段地质中铌、钽、锂、铍、铷、钨的不同含量。采用该方法测定国家一级标准物质 GBW07155、GBW07153 、GBW07185,结果表明,各元素的检测结果与认定值无显著性误差,精密度RSD（n=6）0.45%～4.05%,准确度?lgC （n=6）在-0.008%～0.009%之间,适用于地质样品中的铌、钽、锂、铍、铷、钨元素的测定。     

价格与质量双重竞争下电商平台渠道模式决策研究

近年来传统电商正加速从经销商转变为连接消费者与供应商的在线市场中间商,电商平台与供应商形成三种渠道结构：经销商模式、混合模式和在线市场模式。本文通过构建Stackelberg博弈模型讨论产品质量与价格双重竞争情境下电商平台与供应商销售合作模式最新选择问题。研究表明,当价格竞争强度适中而佣金比例较大时,混合模式是电商平台最优选择,此时产品质量差异最大;当价格竞争强度较小而佣金比例较大时,在线市场模式则是最优选择;在其他条件下,经销商模式是其最优选择。本文结论对电商平台与供应商合作模式选择、产品质量与定价决策具有参考价值。     

考虑罚金政策的众包物流服务质量网络均衡模型

为优化众包物流服务质量,考虑平台罚金政策,构建了包括发包方、众包平台和接包方在内的三层众包物流服务网络模型,并进行算例分析。结果表明,众包平台实施罚金政策并加大自身服务质量投入成本会促使接包方改善自身的服务质量,众包平台的服务质量和利润随之增大,但一味的增大罚金不但会使得接包方利润下降,众包平台的服务质量和利润也呈稍微下降趋势,因此平台应该选择合适的罚金区间;平台在竞争的同时也要进行一定的合作,因为平台间同步协调改进罚金政策以及质量投入会取得更大的收益和更高的平均服务质量。     

低应变反射波法结合钻芯法检测钻孔灌注桩桩身质量

低应变反射波法具有快速、简便和费用低廉等优点,但同时又存在检测结论不全面、不定量,可靠性低等缺点;而钻芯法具有科学、直观、精确等优点,但它却存在速度慢、实施难、费用高等缺点：如果将两种检测方法巧妙地结合起来进行,既节约检测成本,又能可靠全面地反应钻孔灌注桩桩身质量．     

2006～201O年宁波非公有制经济领域人才需求预测

通过建立GM(1,1)模型,结合宁波市2005年对非公有制经济领域人才资源的抽样调查数据,对2006～2010年期间宁波市非公有制经济领域人才需求量和人才质量进行动态分析和预测.