Effect of Co substitution on the structural,dielectric and optical properties of KBiFe2O5

Cobalt (Co)-modified brownmillerite KBiFe2O5 (KBFO; [KBiFe2(1?x)Co2xO5 (x = 0, 0.05)]) polycrystalline is synthesized following the solid-state reaction route. Rietveld refinement of X-ray diffraction data confirmed the phase purity of KBFO and KBiFe1.9Co0.1O5 (KBFCO). The optical bandgap energy (Eg) of KBFO decreased from 1.59 to 1.51 eV because of Co substitution. The decrease in bandgap can be attributed to the tilting of the Fe–O tetrahedral structure of KBFCO. The observed room-temperature Raman peaks of KBFCO shifted by 3 cm?1 toward a lower wavenumber than that of KBFO. The shift in Raman active modes can be attributed to the change in the bond angles and bond lengths of the Fe–O tetrahedral structure and modification in response to oxygen deficiency in KBFO because of Co doping. Compared with that of KBFO, the frequency-dependent dielectric constant and dielectric loss of KBFCO decrease at room temperature, which is a con-sequence of the reduction in oxygen migration and modification in response to vibrational modes present in the sample.     

Dielectric relaxation and conduction mechanism in Aurivillius ceramic Bi5Ti3FeO15

For this study, we synthesized Aurivillius Bi5Ti3FeO15 ceramic using the generic solid-state reaction route and then performed room-temperature X-ray diffraction to confirm that the compound had a single phase with no impurities. The surface morphology of the prepared sample was observed to contain microstructural grains approximately 0.2–2 μm in size. The dielectric properties of the sample were determ-ined as a function of frequency in a range of approximately 100 Hz to 1 MHz at various temperatures (303 K ≤ T ≤ 773 K). Nyquist plots of the impedance data were found to exhibit a semi-circular arc in the high-temperature region, which is explained by the equivalent electrical circuit (R1C1)(R2QC2), where R1 and R2 represent the resistances associated with the grains and grain boundaries, respectively, C1 and C2 are the re-spective capacitances, and Q is the constant phase element (CPE), which accounts for non-Debye type of behavior. Our results indicate that both the resistance and capacitance of the grain boundaries are more prominent than those of the grains. The alternating current (ac) conductiv-ity data were analyzed based on the Jonscher universal power law, which indicated that the conduction process is dominated by the hopping mechanism. The calculated activation energies of the relaxation and conduction processes were very similar (0.32 to 0.53 eV), from which we conclude that the same type of charge carriers are involved in both processes.     

Microbes,mathematics, and models

Microbial model systems have a long history of fruitful use in fields that include evolution and ecology. In order to develop further insight into modelling practice, we examine how the competitive exclusion and coexistence of competing species have been modelled mathematically and materially over the course of a long research history. In particular, we investigate how microbial models of these dynamics interact with mathematical or computational models of the same phenomena. Our cases illuminate the ways in which microbial systems and equations work as models, and what happens when they generate inconsistent findings about shared targets. We reveal an iterative strategy of comparative modelling in different media, and suggest reasons why microbial models have a special degree of epistemic tractability in multimodel inquiry.     

ICP-MS法测定钼矿石中伴生锂、镓和稀土元素

通过比较氢氟酸-硝酸高压罐密闭消解法、 氢氟酸-硝酸-高氯酸-盐酸低压密闭消解法和氢氟酸-硝酸-高氯酸-盐酸敞口消解法对钼矿样品的分解效果， 选用低压密闭消解法制备样品， 用电感耦合等离子体质谱（ICP-MS)法测定伴生稀有元素Li，Ga和15种稀土元素的质量比. 通过对干扰元素的分析， 选择合适同位素， 并确定¹⁵¹Eu，¹⁵⁷Gd，¹⁵⁹Tb质谱干扰的校正系数. 结果表明，  20 μg/L的铑（Rh）标准溶液作为内标可有效抑制溶液中的基体效应和信号动态漂移， 方法检出限为0.001~0.113 μg/g， 相对标准偏差（RSD， n=7）为0.30%~3.92%.  经标准物质和实际样品验证， 该方法可靠， 适合钼矿中伴生Li，Ga和稀土元素的测定.     

Designing Uniform Computer Sequential Experiments with Mixture Levels Using Lee Discrepancy

Computer experiments are constructed to simulate the behavior of complex physical systems. Uniform designs have good performance in computer experiments from several aspects. In practical use, the experimenter needs to choose a small size uniform design at the beginning of an experiment due to a limit of time, budget, resources, and so on, and later conduct a follow up experiment to obtain precious information about the system, that is, a sequential experiment. The Lee distance has been widely used in coding theory and its corresponding discrepancy is an important measure for constructing uniform designs. This paper proves that all the follow up designs of a uniform design are uniform and at least two of them can be used as optimal follow up experimental designs. Thus, it is not necessary that the union of any two uniform designs yields a uniform sequential design. Therefore, this article presents a theoretical justification for choosing the best follow up design of a uniform design to construct a uniform sequential design that involves a mixture of ω≥ 1 factors with β_k ≥ 2, 1 ≤ k ≤ωlevels. For illustration of the usage of the proposed results, a closer look is given at using these results for the most extensively used six particular cases, three symmetric and three asymmetric designs, which are often met in practice.     

东北梅花鹿肠道纤维素降解微生物的分离筛选

食草动物依赖胃肠道微生物分解利用天然木质纤维素物质。为获得高效纤维素降解菌，本文将东北梅花鹿粪便样品，经过研磨，重悬于羧甲基纤维素钠（CMC-Na）作为唯一碳源的富集培养基中，进行富集培养和筛选，用革兰氏碘液染色显示纤维素水解圈，通过纤维素水解圈直径（D）和菌落直径（d）比值，初步判断纤维素降解菌降解纤维素能力．筛选出106株纤维素降解微生物，包括72株细菌、22株真菌和12株放线菌．细菌16S rDNA和真菌ITS序列测序结果显示，这些纤维素降解菌主要集中分布于变形菌门（Proteobacteria）、厚壁菌门（Firmicutes）、放线菌门（Actinobacteria）和子囊菌门（Ascomycota）．本文提供了一种快速有效的反刍动物肠道纤维素降解微生物的筛选方法，为东北梅花鹿肠道微生物高通量测序结果提供实验数据支持．