Generic mathematical programming formulation and solution for computer-aided molecular design

This short communication presents a generic mathematical programming formulation for computer-aided molecular design (CAMD). A given CAMD problem, based on target properties, is formulated as a mixed integer linear/non-linear program (MILP/MINLP). The mathematical programming model presented here, which is formulated as an MILP/MINLP problem, considers first-order and second-order molecular groups for molecular structure representation and property estimation. It is shown that various CAMD problems can be formulated and solved through this model.     

Role of Nd-Ni on structural,spectral and dielectric properties of strontium-barium based nano-sized X-type ferrites

The influence of neodymium and nickel substitution on structural and dielectric parameters was investigated in strontium-barium X-type hexagonal ferrites having composition SrBaCu_2?xNi_xNd_yFe_28?yO₄₆ (x = 0, 0.2, 0.4, 0.6, 0.8, 1 and y = 0, 0.02, 0.04, 0.06, 0.08, 0.1). Sol-gel method was employed for synthesizing these hexagonal ferrites. The XRD plots of all studied materials which were annealed at 1250 °C show single phase characteristics. Lattice parameter ‘c’ increased as a consequence of larger radius of rare earth ion (Nd³⁺) as compared to (Fe³⁺), while lattice parameter ‘a’ showed very small variation. The cell volume was obtained in the range 2508.32–2523.75 (ų). The inclusion of Nd-Ni also affected X-ray density, bulk density and porosity. The FTIR spectroscopy indicated the particular absorption peaks of hexagonal ferrites and it was performed in the range of 500–700 cm^?1. On account of Nd-Ni doping, the dielectric constant, dielectric loss and AC-conductivity showed decreasing trend. The occupancy of Nd³⁺ ions at octahedral site impedes the valence alternation of Fe³⁺; therefore there was decrease in dielectric permittivity. Ac conductivity has been decreased from 9.14 to 6.49 (Ω cm)^?1 at frequency of 2.7 GHz. The Cole-Cole plots of synthesized materials noticeably revealed grain boundary contribution. The appearance of single semi-circle in impedance Cole-Cole graphs confirms the exceptional role of grain boundaries in the conduction process. The considerably lower dielectric parameters of investigated nano X-type ferrites propose their feasibility for high-frequency applications (phase shifters, dielectric resonators, stealth technology etc).     

汽油烃类族组成测试方法对比

介绍了使用荧光指示剂吸附色谱法、多维气相色谱法的测定影响因素和近红外光谱快速法的分析特点以及三种方法在汽油族组成测定中的应用，并就三种方法对同一试样的测定结果进行了对比，找出各种测定方法容易产生误差的原因及分析对策。     

氨氮监测中样品蒸馏预处理对结果的影响分析

氨氮监测采用预蒸馏处理后，比色测定结果明显偏低。在样品预蒸馏处理过程中，硼酸作为吸收液，使显色时溶液pH值偏低，导致显色不充分是其主要影响因素。通过采取增加显色剂加入量的方法，解决了显色pH值偏低的问题，得到满意的测定结果。     

Relationships between urbanization and the oak resource of the Minneapolis/St. Paul Metropolitan area from 1991 to 1998

Urbanization was associated with loss and transformation of the oak forest in the Twin Cities (Minneapolis and St. Paul) metropolitan area (TCMA) over a recent 7-year interval. Between 1991 and 1998, urbanization increased based on several indicators: population density, area of developed land, and area of impervious surface—total impervious area and area within three classes of increasing degree of imperviousness (protected, affected, and degraded). We quantified relationships between changes in urbanization and changes in several parameters describing the oak forest at the scale of ecological subsection. Increased total and affected impervious area were strongly correlated with decreased area of oak forest when changes of the urbanization indicators and oak were expressed as percentages of the subsection area. Relationships were reversed when changes were expressed as percentages of the 1991 values. Increased population density was strongly correlated with increased loss in numbers and increased isolation of oak patches, but weakly correlated with loss of oak forest area. This is the first study to quantify relationships between changes in urbanization and changes in a specific forest cover type. Our results demonstrate complexities of urbanization impacts on a metropolitan forest resource, and highlight the importance of selected variables, spatial and temporal scales, and expressions of change when quantifying these relationships.     

南京老虎山黄土-古土壤剖面不同粒级组分的磁化率及其古气候意义

利用沉降离心法将老虎山黄土-古土壤的酸不溶相分离成<2μm、2～45μm和>45μm三个粒级组分,并分别测定了这些组分和全岩的磁化率。结果表明,无论是全岩,还是三个不同粒级组分,它们的磁化率都可以单独作为长江中下游地区古气候演变的参考指标。其中,<2μm粒级的质量磁化率明显大于全岩和2～45μm、>45μm两粒级,而且其分辨率也明显高于2～45μm和>45μm这两个粒级组分。本实验结果还显示,虽然<2μum的质量磁化率最大,但对全岩质量磁化率的贡献率与2～45μm粒级相当,>45μm粒级的贡献率较低。     

Bifurcation points and bifurcated branches by an asymptotic numerical method and Padé approximants

The aim of this work is to develop a reliable and fast algorithm to compute bifurcation points and bifurcated branches. It is based upon the asymptotic numerical method (ANM) and Padé approximants. The bifurcation point is detected by analysing the poles of Padé approximants or by evaluating, along the computed solution branch, a bifurcation indicator well adapted to ANM. Several examples are presented to assess the effectiveness of the proposed method, that emanate from buckling problems of thin elastic shells. Especially problems involving large rotations are discussed. Copyright © 2004 John Wiley & Sons, Ltd.     

Field observations on the occurrence of new indicators of disinfection efficiency

This paper summarizes studies on the presence of acid-fast and yeast organisms in wastewater and water treatment plants and in surface water. These organisms were found to satisfy three of Bonde's criteria for indicator organisms: presence whenever pathogens are likely to be present; resistance at least equal to that of pathogens; and lack of regrowth in the post-treatment environment. This, plus prior data, indicates that these organisms are at least as acceptable as indicators of disinfection efficiency than the coliform group.     

单小区模型的掉话率分析

掉话率是无线通信网络中最重要的关键性能指标(KPI)之一,本文分析了中国移动在讨论网络性能评估方法时提出的3个不同的掉话率计算公式,通过建立一个单小区的模型,使用一些合理的假设和分析,从理论上确定了一个最为准确的计算公式.     

测量输入光窗台阶指标的指示表的选择

阐述了对近贴聚焦型微通道板像增强管中输入光窗台阶高度和平整度指标进行测量时，所用指示仪表的选择依据，并详细分析了指示表在检定过程中的误差来源，进一步计算出其合成标准不确定度和扩展不确定度，从而选定可用于测试的指标表。