Erosion of efficiency in non-uniform linear chromatography

In linear chromatography (i.e. chromatography performed in the absence of sample overloading), when the plate height of a column is roughly uniform along its length, variations in the velocities of solutes are the only possible causes of erosion of efficiency. The sources of these variations (variations in capacity ratio and in the density of the mobile phase, etc.) play no direct role in the erosion of efficiency except through their effect on solute velocities. In other words, what eventually causes the erosion of efficiency is merely variation in the time required for solutes to traverse equally small segments of a column. Significant erosion can only arise from abrupt and deep deceleration of solutes in one or several relatively small segments of a column. If erosion of efficiency caused by pressure gradients in linear SFC is to be large, the depth and the sharpness of the deceleration of a solute must go beyond that hitherto confirmed experimentally. Many relevant examples are analyzed graphically.     

溶剂热法制备纳米氧化镍及其表征

以乙酰丙酮镍、油酸、油胺为原料，十八烯为溶剂，聚乙烯吡咯烷酮为表面活性剂，采用溶剂热法，在不同反应条件制备了纳米级氧化镍材料.通过X射线衍射（X-ray diffraction，XRD）、透射电子显微镜（Transmission electron microscope，TEM）、紫外-可见光吸收光谱（Ultraviolet-visible spectroscopy，UV-Vis）光谱分析以及塔菲尔（Tafel）测试考察了反应物比例、保温时间、表面活性剂（PVP）、油胺的量对产物微结构、粒径、形貌、光学以及电化学活性性能的影响.实验结果表明：在反应物n[Ni（acac）₂]∶n（OA）=1∶2、添加剂PVP质量分数为1.66%、油胺物质的量为30 mmol、200℃下保温8 h时，可获得粒径约为30～40 nm纯相氧化镍，具有最佳电化学活性，交换电流密度为J₀=1.23×10^-2 mA·cm^-2.     

Friedel-crafts acylation of 2-methoxynaphthalene over h-beta catalysts: effect of Si/Al ratio

The acylation of 2-methoxynaphthalene with acetic anhydride was carried out over zeolite beta catalysts having various Si/Al ratios. It was found that the reaction performance is strongly dependent on the Si/Al ratio of the catalyst. The catalytic reaction features were elucidated in terms of the acidic properties of the catalysts. This revised version was published online in June 2006 with corrections to the Cover Date.     

震区中小跨径桥梁墩柱配筋率取值范围

为研究配筋率对钢筋混凝土桥梁延性抗震性能的影响,并在不同设防烈度对主筋配筋率的合理取值进行细分。以钢筋混凝土桥梁为研究对象,通过拟静力模型试验与有限元数值分析的方法,研究竖向钢筋(主筋)配筋率对桥墩延性的影响,提出典型桥墩的多级性能水平量化指标;并探究在氯离子侵蚀的恶劣环境下,不同配筋率对桥梁抗震性能所带来的影响,从而对氯离子侵蚀环境下的震区中小跨径桥梁墩柱配筋率取值范围提供参考建议。结果表明：考虑氯离子侵蚀作用下的恢复力模型能够较好地反映刚度的退化特性,墩柱的最佳配筋率取值范围为1.11%～2.72%;当加速度为0.3g(g为重力加速度)时,仅从配筋率的角度已无法满足墩柱的损伤指标,建议采用减隔震体系进行抗震设计,如采用延性体系时配筋率不得小于2.64%。研究结果可为中小跨径连续桥梁抗震设计提供参考。     

城镇企业职工基本养老金调整方案测算研究

我国尚未针对城镇企业职工基本养老金的调整比例出台公式化的操作规则,给养老金调整政策的出台带来了压力。为此,本研究依据养老金调整目标和人口老龄化形势,设定养老金调整参数;借鉴国际经验,基于2005~2021年全国数据设计并测算3种基本养老金调整方案,从人口结构与经济发展角度衡量各方案;进而基于最优方案对我国2022~2050年间的养老金调整比例和养老金负担水平进行测算,根据测算结果,提出探索建立科学、合理的基本养老金调整机制的政策建议。     

基于掺铕钨酸盐荧光强度比的非接触温度传感

为了突破传统测温技术应用的局限性,利用NaY （WO₄）₂：Eu³⁺玻璃陶瓷（glass ceramics,GC）实现了具有非接触、实时响应、自校准等优势的双模荧光强度比（luminescence intensity ratio,LIR）测温。采用高温熔融淬灭法制备出含NaY （WO₄）₂：Eu³⁺纳米晶的透明GC样品,并进行系列光谱测量和热敏性能分析。结果表明,样品中Eu³⁺的激发态能级⁵D₁和⁵D₀和基态能级⁷F₂和⁷F₀为两对独立的热耦合能级,可分别基于这两对热耦合能级实现性能优异的双模LIR温度传感。该双模LIR测温技术数据可靠、测温范围广、灵敏度高,再结合GC材料优势,是可用于光纤温度传感器的核心技术材料。     

Critical exponents,hyperscaling, and universal amplitude ratios for two- and three-dimensional self-avoiding walks

We make a high-precision Monte Carlo study of two- and three-dimensional self-avoiding walks (SAWs) of length up to 80,000 steps, using the pivot algorithm and the Karp-Luby algorithm. We study the critical exponentsv and 2 ₄ – as well as several universal amplitude ratios; in particular, we make an extremely sensitive test of the hyperscaling relationdv = 2 ₄ –. In two dimensions, we confirm the predicted exponentv=3/4 and the hyperscaling relation; we estimate the universal ratios <R _g ² >/<R _e ² >=0.14026±0.00007, <R _m ² >/<R _e ² >=0.43961±0.00034, and ^*=0.66296±0.00043 (68% confidence limits). In three dimensions, we estimatev=0.5877±0.0006 with a correctionto-scaling exponent ₁=0.56±0.03 (subjective 68% confidence limits). This value forv agrees excellently with the field-theoretic renormalization-group prediction, but there is some discrepancy for ₁. Earlier Monte Carlo estimates ofv, which were 0.592, are now seen to be biased by corrections to scaling. We estimate the universal ratios <R _g ² >/<R _e ² >=0.1599±0.0002 and ^*=0.2471±0.0003; since ^*>0, hyperscaling holds. The approach to ^* is from above, contrary to the prediction of the two-parameter renormalization-group theory. We critically reexamine this theory, and explain where the error lies. In an appendix, we prove rigorously (modulo some standard scaling assumptions) the hyperscaling relationdv = 2 ₄ – for two-dimensional SAWs.     

The distribution of the likelihood ratio for mixtures of densities from the one-parameter exponential family

We here consider testing the hypothesis ofhomogeneity against the alternative of a two-component mixture of densities. The paper focuses on the asymptotic null distribution of 2 log _n , where _n is the likelihood ratio statistic. The main result, obtained by simulation, is that its limiting distribution appears pivotal (in the sense of constant percentiles over the unknown parameter), but model specific (differs if the model is changed from Poisson to normal, say), and is not at all well approximated by the conventional ₍₂₎ ² -distribution obtained by counting parameters. In Section 3, the binomial with sample size parameter 2 is considered. Via a simple geometric characterization the case for which the likelihood ratio is 1 can easily be identified and the corresponding probability is found. Closed form expressions for the likelihood ratio _n are possible and the asymptotic distribution of 2 log _n is shown to be the mixture giving equal weights to the one point distribution with all its mass equal to zero and the ²-distribution with 1 degree of freedom. A similar result is reached in Section 4 for the Poisson with a small parameter value (0.1), although the geometric characterization is different. In Section 5 we consider the Poisson case in full generality. There is still a positive asymptotic probability that the likelihood ratio is 1. The upper precentiles of the null distribution of 2 log _n are found by simulation for various populations and shown to be nearly independent of the population parameter, and approximately equal to the (1–2)100 percentiles of ₍₁₎ ² . In Sections 6 and 7, we close with a study of two continuous densities, theexponential and thenormal with known variance. In these models the asymptotic distribution of 2 log _n is pivotal. Selected (1–) 100 percentiles are presented and shown to differ between the two models.     

砂土中螺旋桩在斜拉荷载作用下的承载性能

为研究斜拉荷载倾斜角度和叶片埋深对螺旋桩极限承载力的影响,基于ABAQUS软件构建了砂土中螺旋桩的有限元模型,通过螺旋桩水平承载机理砂箱试验与竖向拉拔试验数据,对模型的准确性和可行性进行验证。设置4组不同叶片埋深的螺旋桩模型,分别施加不同角度的斜拉荷载,探讨了砂土地基中螺旋桩的承载性能与斜拉角度、叶片埋深的相关性。结果表明:砂土中螺旋桩的极限承载力随着斜拉角度的增大不断减小;当斜拉角度小于30°时,螺旋桩极限承载力与斜拉角度的关系曲线近似呈线性;螺旋桩极限承载力存在一个临界埋深比,当埋深比大于等于4时,承载力不随埋深比的增大而变化。推导了深埋状态下螺旋桩受斜拉荷载作用的极限承载力公式,经验证该公式能较好反映螺旋桩极限承载力随斜拉角度增大而逐渐下降的规律。