Distribution of Cd and Pb in a wetland ecosystem

Cadmium and lead contents in sediments, dominant species of plants (Phargmites aus-tralis and Scripus mariquter), benthos (Helice tridens tientsinensis, llyoplax deschampsi, and Bul-lacta exarata), and waders (Calidris ruficollis) on the Eastern End of Chongming Island were measured. The results showed that, for cadmium, there are clear stratification in the sediment of reclaimed area and bio-amplification in food chain. However, for lead, a phenomenon was different. The amplification factors (AFs) for cadmium of primary producers, primary consumers, and secondary consumers were 2.59-12.38, 0.09-8.44, and 51.1, respectively. For lead, AFs of primary producers, primary consumers and the top trophic layer were 0.29-2.62, 0.06-5.62, and 7.31, respectively. Each species of macrobenthos showed different strategies to cadmium and lead. Large-sized crabs accumulated more lead, while small-sized crabs and snails accumulated more cadmium. Waders had significantly highest AFs for cadmium and lead in the study. Tha     

基于随机提前期的二级库存系统的优化方法

针对需求和提前期均是随机的情况下,考察了一个简单的二级库存系统,即单个供应商、单个零售商的优化问题,两者均采用s,Q策略进行库存管理,他们的订货数量Qr,Qs都是已知常数,以每计划周期内系统运行期望总费用最小建立了目标函数,寻求系统的决策变量sr,ss,最后给出了求解算法与数值算例.     

石墨炉原子吸收分光光度法测定茶叶中的铅

采用石墨炉原子吸收分光光度法测定了产自福建等地茶叶中的铅含量。方法的线性范围为0—80μg/L，回收率达91．7％-101．5％，相对标准偏差1．47％-3．88％。茶样检测结果表明，铅合格率为92．0％；不同茶类铅含量前3位由高到低依次为绿茶，乌龙茶，红茶；各类茶铅含量平均值为1．069mg／kg。     

氢化物发生原子荧光光谱法测定食品和饲料中的铅

应用ＡＦＳ－２２０１型双道原子荧光光谱仪进行了氢化物发生原子荧光法测定食品和饲料中铅的研究。方法中彩高氢酸做介质，并对各种最佳分析条件进行了探讨和验证。方法的检出限为０．３ｒｇ／Ｌ，线性范围为１．００～５００ｒｇ／Ｌ，回收率为８７％～９８％。用标准物质进行对照，其测定值均在给定的标准值范围之内。该方法操作简单、快速，灵敏度高，精密度和准确度好，线性范围宽，检出限低，所用试剂无毒性，豕仪器性能稳定，     

Tuned Transport Path of Perovskite MAPbI3-based Memristor Structure

In this study, the features of resistive random access memory (RRAM) employing a straightforward Cr/MAPbI₃/FTO three-layer structure have been examined and clarified. The device displays various resistance switching (RS) behavior at various sweep voltages between 0.5 and 5 V. The RS effect has a conversion in the direction of the SET and RESET processes during sweeping for a number of cycles at a specific voltage. The directional change of the RS processes corresponds to the dominant transition between the generation/recombination of iodide ion and vacancy in the MAPbI₃ perovskite layer and the electrochemical metallization of the Cr electrode under the influence of an electric field, which results in the conductive filament (CF) formation/rupture. At each stage, these processes are controlled by specific charge conduction mechanisms, including Ohmic conduction, space-charge-limited conduction (SCLC), and variable-range hopping (VRH). By identifying the biased voltage and the quantity of voltage sweep cycles, one can take a new approach to control or modulate the pathways for effective charge transport. This new approach is made possible by an understanding of the RS characteristics and the corresponding mechanisms causing the variation of RS behavior in the structure.     

Size-controlled synthesis of orderly organized cube-shaped lead sulfide nanocrystals via a solvothermal single-source precursor method

Monodisperse cube-shaped lead sulfide (PbS) nanocrystals were successfully synthesized by virtue of a solvothermal single-source precursor method at mild reaction conditions. These resulted PbS nanocrystals have the average size in a range of 10 nm and a uniform cubic shape, shown by TEM and HRTEM, respectively. Due to their narrow size distribution, orderly self-organized arrays on a large scale can be easily obtained. Experimental results indicate that several factors, such as coordinating ability of the solvent, carbon number of the substitute alkyls (n), reaction temperature, and concentration of the precursor, play key roles in the final size and size distribution of PbS nanocrystals. This finding will enhance our understanding for the formation mechanism of nanostructured materials with special shapes.     

掺杂钴对锆钛酸铅铁电薄膜电性能的影响

采用溶胶-凝胶法在LaNiO3／Si衬底上制备了Pb(Zrx，Ti1-x)O3(PZT)与PbCoy(Zr，Ti1-x)O3(PC—ZT)铁电薄膜，实验发现钴掺杂对PZT的铁电性能产生了很大的影响．不掺杂的PZT铁电薄膜剩余极化强度Pr=14.05uC／cm^2，矫顽场Ec=26．35kV／cm，而钴的掺杂有效地提高了PZT薄膜的剩余极化强度，当掺杂钴达到12%时，Pr=36．26uC／cm^2，矫顽场减小．同时，掺杂钴增强了PZT薄膜的介电性能并且减少了漏电流。     

Coprecipitation of lead and cadmium using copper(II) mercaptobenzothiazole prior to flame atomic absorption spectrometric determination

A coprecipitation method using a combination of 2-mercaptobenzothiazole (MBT) as a chelating reagent and copper as the coprecipitate carrier is described for the determination of trace lead and cadmium by flame atomic absorption spectrometry. The coprecipitation conditions, such as the effect of pH, the amount of carrier element and reagent, standing time, sample volume and matrix effects were examined in detail. It was found that lead and cadmium are coprecipitated quantitatively (≥95%) with Cu(II)-MBT at pH 9 and that the relative standard deviations (n = 7) were ≤1.6%. When using the enrichment factors of 150-fold for lead and cadmium, the detection limits (3s/b) obtained are 1.08 for lead and 0.04 μg L⁻¹ for cadmium. The method was validated with spiked sea water, stream water, well water, and vegetable samples.     

Flow injection micelle-mediated methodology for determination of lead by electrothermal atomic absorption spectrometry

A simple and sensitive flow injection micelle-mediated method was developed for the determination of trace Pb by electrothermal atomic absorption spectrometric (ET-AAS). The formation of the analyte-entrapped surfactant micelles by online merging of the analyte solution with O,O-diethyldithiophosphate solution and Triton X-114 solution sequentially, the adsorption of the resultant analyte-entrapped surfactant micelles onto a microcolumn packed with silica gel. The adsorbed analyte was then eluted with methanol and determined by ET-AAS. With consumption of 6.0 mL sample solution, a detection limit of 0.016 μg L⁻¹, and a concentration factor of 21.6 were obtained at a sample throughput of 20 h⁻¹. The relative standard deviation was 5.1% (c = 2.0 ng mL⁻¹, n = 7). The method has been successfully applied to the analysis of trace Pb in water sample with recoveries ranging from 94.0 to 99.0%. The certified reference material was also analyzed for validation, and the determined value obtained was in good agreement with the certified value.     

The lead amalgam/lead sulfate electrode redesigned and reassessed

To make the (Pb)Hg‖PbSO₄‖SO ₄ ²⁻ electrode really usable and attractive for extensive application to thermodynamic studies, a new, simplified design and a convenient preparative procedure have been introduced, ensuring stable amalgams and reproducible electrode potentials. The electrode so prepared has been exhaustively characterized both thermodynamically and as a SO ₄ ²⁻ -sensing electrode, in different sulfate solutions, including H₂SO₄. The past discrepancies of standard potentials-mainly due to preparation and/or handling problems-are discussed and, for a final resolution of the question, a practical standardization procedure is proposed.