Continuous flow and flow injection stripping voltammetric determination of silver(I), mercury(II), and bismuth(III) at a bulk modified graphite tube electrode

The epoxy-impregnated graphite tube electrode bulk modified with 2-mercaptobenzoxazole, employed in a wall-jet configuration, was found to be useful for the continuous flow and flow injection stripping voltammetric determinations of Ag^I, Hg^II and Bi^III. For continuous flow, detection limits for Ag^I, Hg^II and Bi^III were 1.8 × 10⁻¹⁰ M, 1.9 × 10⁻⁹ M and 9.5 × 10⁻⁹ M, respectively (10 min accumulation, S/N = 3). Precisions for 5.00 × 10⁻⁹ M Ag^I, 1.00 × 10⁻⁸ M Hg^II and 1.00 × 10⁻⁷ M Bi^III were 10.5%, 5.77 % and 7.90% (relative standard deviations, n = 6), respectively. In the case of flow injection stripping, with a 500 μL injection loop, detection limits of 0.59 ng, 2.0 ng and 120 ng were obtained for Ag^I, Hg^II and Bi^III, respectively (S/N = 3). Selected metal ions, inorganic and organic substances were investigated for interferences. The electrode was tested with a certified sample and then applied to the determinations of the metal ions in a urine and a sea-water sample.     

Differential pulse voltammetric determination of trace Te(IV) at a poly(3,3′-diaminobenzidine) film modified gold electrode in flow systems

Electropolymerization of 3,3′-diaminobenzidine on a gold surface gave an adherent, stable film of poly(3,3′-diaminobenzidine) (PDAB). This polymer film retained the complexational functionalities of its monomer, demonstrating preconcentration abilities for several ions, including Se(IV) and Te(IV). In particular, in this work, continuous flow and flow injection methods were developed for the sensitive and selective determination of Te(IV). The optimized method for the continuous flow mode had a detection limit of 5.6×10⁻⁹ mol l⁻¹ for 10 min preconcentration. Typical relative standard deviations for six consecutive determinations were 1.82 and 2.56% for Te(IV) concentrations of 1.0×10⁻⁶ and 5.0×10⁻⁸ mol l⁻¹, respectively (10 min preconcentration). The method was applied to the determination of Te(IV) in real samples.     

On the Dimension of Posets with Cover Graphs of Treewidth 2

In 1977, Trotter and Moore proved that a poset has dimension at most 3 whenever its cover graph is a forest, or equivalently, has treewidth at most 1. On the other hand, a well-known construction of Kelly shows that there are posets of arbitrarily large dimension whose cover graphs have treewidth 3. In this paper we focus on the boundary case of treewidth 2. It was recently shown that the dimension is bounded if the cover graph is outerplanar (Felsner, Trotter, and Wiechert) or if it has pathwidth 2 (Biró, Keller, and Young). This can be interpreted as evidence that the dimension should be bounded more generally when the cover graph has treewidth 2. We show that it is indeed the case: Every such poset has dimension at most 1276.     

Laboratory Studies of Depressurization with a High Concentration of Surfactant in Low-Permeability Reservoirs

To solve the problem of high pressure of water injection in low permeability reservoirs, a high concentration of surfactant system was developed in this article. With the solubilization of oil in aqueous surfactant solution as a criterion, a formula was screened from anionic and nonionic-anionic surfactants, and the optimal depressurized system was obtained as follows, 13.3% surfactant HEX +2.23% n-propanol +4.47% n-butanol, the solubilization capability being up to 0.66 g/g. This system had good salt tolerance, and it exhibited water external microemulsion in the range of of 1 to 200 g/L NaCl. Core flooding results show that this high concentration of surfactant system formed water external microemulsion with the residual oil in the core, reducing the displacement pressure over 35%. Meanwhile, the effects of concentration and injection volume on depressurization were also investigated. It is indicated that a good depressurization effect was achieved after injecting 1 pore volume of the system with the salt concentration of 100 g/L.     

2,3,7,8,12,13‐Hexaaryltruxenes: An ortho‐Substituted Multiarm Design and Microwave‐Accelerated Synthesis toward Starburst Macromolecular Materials with Well‐Defined π Delocalization

We present herein a novel design and the efficient synthesis towards a “homogeneous” starburst fluorene system based on the novel 2,3,7,8,12,13‐hexaaryltruxene scaffold. Controlled microwave heating provides a facile and powerful approach for each step in the synthesis of these bulky materials with large steric hindrance, suggesting an avenue to access structurally well‐defined complex organic semiconductors (OSCs) rapidly and conveniently with high yield and purity. The resulting materials exhibited good thermal stability and an excellent glassy structure as revealed by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) as well as wide‐angle X‐ray diffraction (WAXD) studies. Moreover, compared with their corresponding three‐arm‐substituted counterparts T1 – T4 , the introduction of the ortho substituents around the truxene core in Tr1 – Tr4 results in significant blueshifts (of 7–24 nm) of the absorption maxima λ_max and higher energy optical gaps (E_g). Comparative studies with corresponding linear, rod‐shaped oligofluorene counterparts (OFX) have revealed that the longest para‐conjugated segment in the TrX (X=1–4) structures plays the dominant role in determining their electronic properties. UV/Vis data and cyclic voltammetry (CV) investigations have indicated that there is little electronic interaction between the arms, even for the shortest armed oligomer Tr1 . A clear linear relationship of both 1/λ_max and E_g with the inverse of (n+1) for these branched systems was found. Our findings highlight a novel molecular design comprising an ortho‐substituted, multiarmed architecture that would allow the introduction of isotropic physical and/or mechanical properties, while at the same time maintaining most of the important electronic properties of the rod‐shaped constituents of a fully conjugated system.     

On the numerical radius of Lipschitz operators in Banach spaces

We study the numerical radius of Lipschitz operators on Banach spaces via the Lipschitz numerical index, which is an analogue of the numerical index in Banach space theory. We give a characterization of the numerical radius and obtain a necessary and sufficient condition for Banach spaces to have Lipschitz numerical index 1. As an application, we show that real lush spaces and C  -rich subspaces have Lipschitz numerical index 1. Moreover, using the Gâteaux differentiability of Lipschitz operators, we characterize the Lipschitz numerical index of separable Banach spaces with the RNP. Finally, we prove that the Lipschitz numerical index has the stability properties for the _c0$c_0$-, _l1$l_1$-, and _l∞$l_{\infty }$-sums of spaces and vector-valued function spaces. From this, we show that the C(K)$C(K)$ spaces, _L1(μ)$L_1(\mu )$-spaces and _L∞(ν)$L_{\infty }(\nu )$-spaces have Lipschitz numerical index 1.     

Hepatoprotective action of Radix Paeoniae Rubra aqueous extract against CCl4-induced hepatic damage

In the present study the capacity of Radix Paeoniae Rubra aqueous extract (RPRAE) as an antioxidant to protect against carbon tetrachloride (CCl(4))-induced oxidative stress and hepatotoxicity in Wistar rats was investigated. Six groups of rats were used. Radix Paeoniae Rubra aqueous extract (100 or 200 or 300 mg/kg of bw) or bifendate (100 mg/kg of bw) were given daily by gavage to the animals on 28 consecutive days to elucidate the protective effects against CCl(4)-induced hepatotoxicity. The 20% CCl(4)/olive oil was gavage of gastric tube twice a week (on the third and seventh days of each week). The animals of normal control group were given only vehicle. The animals of CCl(4)-treated group were administered with CCl(4) twice a week (on the third and seventh days of each week) and with vehicle on rest of the days. The test materials were found effective as hepatoprotective agents, as evidenced by plasma and liver biochemical parameters. Therefore, the results of this study show that Radix Paeoniae Rubra aqueous extract can protect the liver against CCl(4)-induced oxidative damage in rats, and the hepatoprotective effects might be correlated with its antioxidant and free radical scavenger effects.     

高强混凝土单轴压缩声发射频率特征试验研究

为研究高强混凝土破裂前声发射信号的频率特征,对C60、C70、C80高强混凝土试件进行单轴压缩下的高、低频双通道声发射试验,得到破裂过程的力学参数和声发射参数,探求高强混凝土不同加载阶段声发射信号频率的分布特征。研究表明,三种高强混凝土在峰值应力前,高、低频通道声发射信号均集中在特定的频段内;临近峰值应力时,高、低频通道的声发射信号频率向低频段移动,同时优势频段内的频率趋于分散,这可作为预测高强混凝土破坏的前兆信息。     

压缩载荷下孔隙结构变化的CT实验研究

为了研究孔隙对岩石力学性能的影响,利用自制的孔隙物理模型,通过 单轴压缩和CT扫描实验研究了受载条件下孔隙率对岩石孔隙结构的演化及其对外部物理力 学性能的影响,得到了不同加载阶段和不同CT观察尺度下孔隙模型的裂纹扩展规律以及孔隙 和固体介质的损伤变化情况. 实验结果表明：孔隙模型在受载条件下裂纹主要发生在峰值荷 载之后,主裂纹大都集中在孔隙密集的地方且伴随许多细小裂纹的产生;峰值载荷前出现了 少数微裂纹,微裂纹的产生与演化主要发生在孔隙周边.     

论结构主义学习观与化学教学改革

结构主义理论越来越受到教育界的关注,这种理论带给新一轮基础教育课程改革许多值得深思的理念。本文在结构主义理论的基础上,从新知识观的视角出发,着重论述了结构主义学习观在当前基础教育课程改革中的作用以及化学教学在以结构主义学习观为理论指导下教师观念的转变。