Evidence for direct observation by Mössbauer spectroscopy of surface tin atoms in platinum–tin particles

The diamond-bearing gravels found along South Africa's West Coast are being beneficiated by means of dense medium separation (DMS) to reclaim the alluvial diamonds. Granular ferrosilicon (Fe–Si) is used as the DMS material and at the end of each operation the Fe–Si is reclaimed from the process stream using a magnetic separator and is then recycled but losses of Fe–Si due to attrition, adhesion to the separation products, density changes and changes to the magnetic properties can occur. The gravel obtained from the mining operation is washed and screened before heavy mineral separation. The concentrate, tailings and Fe–Si samples were investigated by means of SEM and Mössbauer spectroscopy to determine where changes to the Fe–Si, or contamination could occur. The composition of the Fe–Si was determined to be Fe (76.1 at.%), Si (20.3 at.%), Mn (1.5 at.%), Al (1.5 at.%) and Cr (0.6 at.%) resulting in a more or less ordered DO₃ phase with a calculated composition of Fe₃Si for this Fe–Si, consistent with the Mössbauer results where two sextets with hyperfine magnetic fields of 18.6 T and 28.4 T were observed. After DMS, magnetite and ilmenite, the minerals found in the gravel, were still present in the concentrate. In the tailings virtually no magnetite or ilmenite was found and only a doublet, identified as an oxihydroxide, due to the abrasion of the Fe–Si, was found. After magnetic separation, to wash and clean the Fe–Si for re-use, it was found that magnetite and ilmenite were still present in the Fe–Si, which results in a change in density of the Fe–Si, resulting in a higher density and loss of valuable diamonds.     

一个哈密顿系统正则动量的软模振荡

本文进一步研究了以前提出的哈密顿系统,说明非线性振子的实振幅具有的极限圈运动,由于另一类模式耦合扰动,引起振子的线性频率重新激发,而失稳到二维环。据此,分析了有关的实验及理论研究,推断流体力学矩方程之间的耦合,可能在显示Ruelle-Takens途径上起了关键作用,同时猜想向湍流转变的图象是轨迹被吸引在两个二维环上不断调节的运动。     

Leaching of the Anthraquinone Dye Solvent Blue 59 Incorporated into Organically Modified Silica Xerogels

The effects of preparation method and precursor composition on the leaching behavior of the anthraquinone dye Solvent Blue 59 incorporated into silica based xerogels have been studied. Xerogels were prepared under acidic conditions from mixtures of 20 mol% of organically modified silicon alkoxides, R–Si(OR)3, in Si(OR)4 (R = methyl or ethyl, R = methyl, vinyl, phenyl). The dye was added at the beginning of the sol-gel reaction. The reaction was carried out by either hydrolysis under acidic conditions or acidolysis by formic acid. The dye incorporated was leached with refluxing ethanol using a Soxhlet extraction procedure to simulate the long-term stability of the samples prepared. With increasing size of organic substituent (methyl < vinyl < phenyl), the amount of dye leached decreases. Results from nitrogen adsorption experiments show that all samples characterized have about the same average pore diameter, but they differ in total pore volume and BET surface area. With increasing size of the organic residue, the pore volume decreases by an order of magnitude. Therefore, it is concluded that the microstructure of the xerogels prepared determines the retention behavior of dyes incorporated during the sol-gel reaction.     

时变单车路径优化模型及动态规划算法

车辆路径问题由于其广泛的应用领域及经济价值而成为学术研究热点。然而,在已有的研究文献中,车辆的速度时变与服务多任务特性很少被关注。本文讨论了具有这两个特性的单车路径优化问题。建立了以送货完成时间最早为优化目标的时变单车送货路径优化模型。由于很难获得该模型的精确解,本文提出了一种贪婪补货策略压缩原问题解空间,设计动态规划算法给出了车辆行驶时间满足FIFO规则的送货顺序近似最优解。数值算例验证了该算法所得到的解仅是原问题的近似最优解这一结论。算例同时表明优化配送时间随着车辆装载能力的增大而缩短,并在车辆装载能力超过所有客户配送总需求时实现最短配送时间,即,使用较大装载能力车辆能节约更多配送时间。     

绿色合成载银壳聚糖及其等温线、动力学及抑菌性

以吸附绿色合成法制备载银壳聚糖,采用X射线衍射(XRD)、场发射扫描电镜(FESEM)和热重分析研究其微观结构和热稳定性,并研究了壳聚糖对银离子的吸附模型,以此为抗菌材料,通过平板扩散板法评价载银壳聚糖的抗菌效果。实验结果表明:银离子在多糖结构中的引入影响了其原有的晶体结构,提升了其热稳定性。壳聚糖对银离子的吸附等温线与Langmuir和Dubinin-Radushkevich方程相一致,说明了壳聚糖中银离子的吸附过程符合单层吸附和化学吸附,并且根据Langmiur方程计算壳聚糖对银离子的最大吸附量为478.09 mg/g,含银量为32.34%,与Dubinin-Radushkevich计算结果一致。银含量饱和的载银壳聚糖对大肠杆菌(Escherichia coli)和金黄色葡萄球菌(Staphylococcus aureus)具有良好的抗菌性能,其最小抑菌浓度为80 μg/mL。     

Toward cell circuitry: Topological analysis of enzyme reaction networks via reaction route graphs

The first step toward developing complete cell circuitry is to build quantitative networks for enzyme reactions. The conventional King-Altman-Hill (KAH) algorithm for topological analysis of enzyme networks, adapted from electrical networks, is based on “Reaction Graphs” that, unlike electrical circuits, are not quantitative, being straightforward renderings of conventional schematics of reaction mechanisms. Therefore, we propose the use of “Reaction Route (RR) Graphs” instead, as a more suitable graph-theoretical representation for topological analysis of enzyme reaction networks. The RR Graphs are drawn such that they are not only useful for visualizing the various reaction routes or pathways, but unlike Reaction Graphs possess network properties consistent with requisite kinetic, mass balance, and thermodynamic constraints. Therefore, they are better than the conventional Reaction Graphs for topological representation and analysis of enzyme reactions, both via the KAH methodology as well as via numerical matrix inversion. The difference between the two is highlighted based on the example of a single enzyme reaction network for the conversion of 7,8-dihydrofolate and NADPH into 5,6,7,8-tetrahydrofolate and NADP⁺, catalyzed by the enzyme dihydrofolate reductase.     

工程施工中的SRTP问题研究

在大型的建设工程项目中，经常要进行场地平整工作。场地平整过程中需要进行大量的施工材料的调运工作，这引出了一个最短路径调运问题（SRTP），目标是找到一个最短的车辆行走路线，使得整个施工过程的总运输距离最短。该问题属于NP-hard问题，本文采用模拟退火算法求解该问题，最后通过箅例计算，并同贪婪算法的求解结果进行比较，验证了模拟退火算法的高效性。     

A New Route for Synthesis of Entecavir

2-Amino-1,9-dihydro-9-[(1S,3R,4S)-4-hydroxy-3-(hydroxymethyl)-2-methylenecyclopen tyl]-6H-purin-6-one (entecavir, Scheme 1) is a novel carbocyclic 2-deoxyguanosine analog drug which has potent and selective anti hepatitis B virus (HBV) activity1-3. Entecavir is also effective against lamivudine-resistant YMDD mutants4. The US Food and Drug Administration (FDA) approved entecavir as a new preferred drug for the treatment of HBV after lamivudine in March, 2005. Scheme 1 The structure o…     

Optical properties of the complex perovskite ceramic oxide Ba2YZrO6‐d

Nanocrystalline Ba₂YZrO_6‐dhas been successfully synthesized through a single step auto‐ignition combustion route. The samples were analyzed by powder X‐ray diffraction, transmission electron microscopy and Ultraviolet‐Visible spectroscopy. The XRD analysis revealed that the material has an ordered complex cubic perovskite structure. The basic optical properties and optical constants of the as‐prepared nanopowder of Ba₂YZrO_6‐dhave been reported for the first time. The spectral analysis revealed that the material is a wide band gap direct transition semiconductor with band gap of 3.70 eV at room temperature. The poor transmittance in ultraviolet but good transmittance in visible‐near infrared regions make the material potentially important for poultry protection and warming coatings, solar control, antireflection coatings and window layer in solar cells. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Malic acid assisted precursor route to hierarchical structured nickel oxide

A novel malic acid assisted precursor route to prepare NiO materials with novel hierarchical structures has been investigated in this work. The Ni‐based precursors can be synthesized by a malic acid‐assisted hydrothermal route, which have been characterized by powder X‐ray diffraction (XRD), field‐emission scanning electron microscopy (FE‐SEM), thermogravimetric analysis (TGA). NiO materials can be prepared via the thermal treatment of the precursor in ambient atmosphere. The XRD, SEM, Energy dispersive X‐ray spectroscopy (EDS) and UV‐Vis spectroscopy of the NiO materials were also examined. The effects of the reaction conditions, such as the reaction temperature, the quantity of the raw materials on the morphologies of the precursors were discussed, which indicates that it is an effective method to synthesize NiO materials with different hierarchical structures. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)