Progressive censoring methodology: an appraisal

Properties of progressively censored order statistics and inferential procedures based on progressively censored samples have recently attracted considerable attention in the literature. In this paper, I provide an overview of various developments that have taken place in this direction and also suggest some potential problems of interest for further research. This invited paper is discussed in the comments available at: , , , , , , , , , .     

Influence of inorganic anions on electrochemical behaviour of pyrite

This work gives an investigation of pyrite behaviour during anodic oxidation in solutions of four inorganic acids: sulphuric, hydrochloric, phosphoric and perichloric acid. In wider range of concentrations, the influence of acids on following parameters was investigated: rate of establishment and corrosion potential value, Tafel's slope, corrosion current and electrodic reaction order. Based on potentiodynamic and chronoamperometric investigations, it was found out that pyrite oxidation is developed in three regions conditionally named active, passive and transpassive region. It was also found out that pyrite is intensively dissolved at potentials higher than 0.75 V versus SCE and that oxidation rate of pyrite is the highest in hydrochloric acid solutions (≥1 M HCl). By comparison of obtained results, it was concluded that there are no distinctive differences in pyrite behaviour during anodic oxidation in solutions of investigated acids.     

大都市边缘区空间结构演变中的多元利益主体格局——以广州市大石街为例

大都市边缘区在由农业用地向城市用地转变的过程中,受到大都市的拉力与自身发展诉求的推力,形成了地方政府(镇政府)、开发商、村委会和村民等多个利益主体,由于各利益主体在空间开发中追求自身利益的最大化,导致城市建设无序、高层次公共服务设施缺失及忽略公共空间等问题.随着未来社会经济环境的变化、制度改革的深化和城市空间演变方式的转变,各利益主体的角色也将发生变化,逐渐演变为由地方政府(市政府)、开发商、市民组成的新多元利益主体.     

MIEX对水中溴离子的去除效能及其影响因素

利用烧杯试验研究了一种新型磁性离子交换树脂(MIEX)对水中溴离子的去除效能,并考察了水中常见阴离子及有机物对其去除效果的影响.试验结果表明,MIEX可以有效去除纯水中的溴离子,投加量为10 mL/L和20 mL/L时其对溴离子去除率均在90％以上,且达到交换平衡时间分别为5 min和3 min.水中常见的其它带负电物质会在一定程度上影响溴离子的去除效果,在常见的含量条件下10 mL/L的MIEX对溴离子的去除率一般在50％以上.阴离子含量以及MIEX的选择性是影响其对溴离子去除效果的主要因素.有机物的存在使MIEX对溴离子的去除率明显下降,去除率在70％左右.MIEX对有机物、阴离子的去除过程存在差异:10 mL/L的MIEX去除阴离子的反应平衡时间在5 min左右,而去除有机物的平衡时间则较长,其对2种表征有机物含量的指标(UV254、DOC)的去除稳定时间均在20 min以上.     

Solvation of protons and the strength of superacids

Analysis of literature indicates that the strength of superacids is mainly determined by unusual chemical properties of weakly solvated protons while the extent of dissociation of superacids is rather low and is less important. A higher chemical activity of protons in very concentrated acids and in such water-free superacids as liquid HF or 100% H₂SO₄ results from a weaker solvation of these species with the molecules of superacids which are less basic than water. In contrast, solvation by superacids of the negatively charged anions is stronger than in water solutions. These conclusions are illustrated by the ab initio quantum chemical calculations performed for self-dissociation of anhydrous liquid hydrofluoric acid. This revised version was published online in August 2006 with corrections to the Cover Date.     

Leaching optimization and dissolution behavior of alkaline anions in bauxite residue

Bauxite residue is a highly alkaline waste containing soluble alkaline anions, which can cause environmental concerns. The optimal leaching conditions, distribution of alkaline anions, types of pivotal alkaline anions and their dissolution behaviors were investigated based on the combination of single factors-orthogonal experiments and leaching stage experiment. Using a two-stage leaching, 86% of the soluble alkaline anions $\left({\text{CO}}_3^{2?},{\text{HCO}}_3^{?},\text{Al}{\left(\text{OH}\right)}_4^{?},{\text{OH}}^{?}\right)$ were leached with a L/S ratio of 2 mL/g, at 30 °C, over 23 h. During the first stage of leaching, approximately 88% of alkaline anions were leached from the dissolution of free alkali (NaOH, carbonate, bicarbonate, NaAl(OH)₄) with the rest originating from the dissolution of alkaline minerals (calcite, cancrinite and hydrogarnet). Supernatant alkalinity was 69.78 mmol/L with ${\text{CO}}_3^{2?}$ accounting for 75%. Furthermore, carbonate leaching was controlled by solid film diffusion using the Stumm Model with an apparent activation energy of 10.24 kJ/mol.     

Factors affecting the anodic behaviour of zinc electrode in borate solutions

The anodic behaviour of Zn electrode in 1 × 10⁻² M Na₂B₄O₇ solutions in the absence and presence of various concentrations of Na₂SO₄, Na₂S₂O₃ or Na₂S as aggressive agent was studied by galvanostatic polarization technique. In the absence of sulphur-containing anions in solution, the polarization curves are characterized by one distinct arrest corresponding to Zn(OH)₂ and/or ZnO, after which the potential increases linearly with time due to the formation of barrier oxide film before reaching the oxygen evolution reaction. The duration time of the arrest decreases with increasing current density while the rate of oxide film formation increases. On the other hand, the duration time of the arrest increases with the number of anodic cyclization while the rate of oxide film formation decreases. Additions of low concentration of the aggressive anions have no effect on the passive film formed on the metal surface. The potential starts to oscillate within the oxygen evolution region with increases in the concentration of these aggressive anions. Further increases in the concentration of these aggressive anions are associated with impaired Zn passivity that might indicate pitting attack. The aggressiveness of the sulphur species decreases in the order: . The effect of raising pH of the solution on the anodic behaviour of Zn electrode in the presence of anions was also investigated. It was found that the raising the pH of the solution affecting on the rate of oxide film formation and the breakdown potential value.     

Sorption behaviors of aromatic anions on loess soil modified with cationic surfactant

Modification of soils with hydrophobic cationic surfactants is an effective approach for enhancing the sorptive capabilities of soil in the vadose zone for the purpose of retaining organic contaminants prior to cleanup. The objective of this study was to examine the sorptive behavior of the cationic surfactant-modified loess soil for aromatic anions in the aqueous phase in an attempt to define the sorptive mechanisms. Some dominant factors governing the sorption, such as ionic strength and divalent heavy metal cation, were investigated. The sorption isotherms of 2,4-dinitrophenol (DNP) and benzoic acid (BA) in the modified soil samples were obtained using the batch equilibration method. Under the laboratory conditions, the modified loess soil utilized in this study was prepared by replacing the cations of loess soil with a cationic surfactant—hexadecyltrimethylammonium (HDTMA) bromide. The acidic aromatic compounds, DNP and BA existing as aromatic anions in the natural mixture of loess soil and aqueous phase, were selected as indicator compounds to measured the sorption behaviors of aromatic anions on the HDTMA-modified loess soil. The results confirmed that the sorptive capabilities of aromatic anions in loess soil were greatly enhanced by modification with HDTMA. The increase of ionic strength and the addition of divalent heavy metal cation Zn²⁺ significantly increased the sorption of aromatic anions on the HDTMA-modified loess soil. In binary solute systems, the sorbed amounts either of DNP or BA on the HDTMA-modified loess soil were reduced if two compounds existed simultaneously in the soil. This results indicated that competitive adsorption between the two aromatic anions occurred in soil matrix.     

BX_4~-(X=H,F,Cl,Br,I)的相对论赝势从头算研究(Ⅲ)

本文应用相对论赝势ab initio的方法,系统地研究了三卤化硼与卤素负离子反应生成的四卤化硼负离子的几何结构,并预测了BX_4~-(X=cl,Br,I)的键长。计算了该系列的稳定化能,得出稳定性顺序为BH_4~->>BF_4~->>BCl_4~->BBr_4~->BI_4~-。分析其电子结构得出,该系列分子的成键主要通过硼和卤素的σ轨道作用。