Patterns and levels of PCDD/F in a Chinese graphite electrode sludge

The graphite electrode sludge was sampled from a huge chloralkali plant in central China. The total level of PCDD/F was found as high as 378.85 mu g/kg sludge (dry weight). The patterns of PCDD/F in each homologue indicated the predominance of tetra- to octa-chlorinated PCDFs, Furthermore, the toxic 2,3,7,8-substituted PCDFs constituted over 80% of the total PCDFs in the sludge and the corresponding PCDDs were only at 15 mu g/kg level. The calculated value of the international toxic equivalence (I-TEQ) in sludge was 21.65 mu g/kg sludge (dry weight). This typical "dioxin chloralkali pattern" was apparently identified in the sediments near the effluent outlet of the chloralkali plant.

On the formation of well-aligned ZnO nanowall networks by catalyst-free thermal evaporation method

Two-dimensional ZnO nanowall networks were grown on ZnO-coated silicon by thermal evaporation at low temperature without catalysts or additives. All of the results from scanning electronic spectroscope, X-ray diffraction and Raman scattering confirmed that the ZnO nanowalls were vertically aligned and c-axis oriented. The room-temperature photoluminescence spectra showed a dominated UV peak at 378 nm, and a much suppressed orange emission centered at similar to 590 nm. This demonstrates fairly good crystal quality and optical properties of the product. A possible three-step, zinc vapor-controlled process was proposed to explain the growth of well-aligned ZnO nanowall networks. The pre-coated ZnO template layer plays a key role during the synthesis process, which guides the growth direction of the synthesized products. (C) 2007 Elsevier B.V. All rights reserved.

Stimulated luminescence and photo-gated hole burning in BaFCl0.8Br0.2 : Sm2+,Sm3+ phosphors

The photo- and thermo-stimulated luminescence (PSL and TSL) of BaFCl0.8Br0.2:Sm2+,Sm3+ phosphors were investigated. It is found that the stimulated luminescence intensity of Sm2+ is almost equal to that of Sm3+ even if the content of Sm2+ is much lower than that of Sm3+. Only the stimulated luminescence of Sm2+ is observed in the sample in which the content of Sm2+ is much higher than Sm3+, demonstrating that the PSL or TSL efficiency of Sm2+ is much higher than that of Sm3+. This is attributed to the effective overlap of the e-h emission with the absorption of Sm2+ centers which may make the energy transfer from the electron-hole pairs to Sm2+ effectively. In BaFCl0.8Br0.2:Sm2+,Sm3+ the stimulated luminescence is considered to be occurred via the recombination of photoreleased electrons with the [Sm2+ + h] or [Sm3+ + h] complex and the energy transfer from the electron-hole pairs to the luminescence centers (Sm2+ and Sm3+) is concerned to be the major step to determine the stimulated luminescence efficiency. The X-ray-induced stimulated luminescence is compared and connected to the photon gated hole burning. The net result of the two processes is quite similar and may be comparable. It is suggested from the observations of stimulated luminescence that electron migration between Sm2+ and Sm3+ is not the major process, color centers may play an important role in hole burning. The information from stimulated luminescence is helpful for the understanding of the hole burning mechanism. (C) 1999 Elsevier Science Ltd. All rights reserved.

Linear and nonlinear intersubband optical properties in a step quantum well with an applied electric field

Within the framework of the effective-mass envelope-function theory, the field-dependent intersubband optical properties of a Al0.4Ga0.6As/Al0.2Ga0.8As/GaAs step quantum well are investigated theoretically based on the periodic boundary condition. A very large Stark shift occurs when the lowest subband electron remains confined to the small well while the higher subband electron confined to the big well. The optical nonlinearity in a step well due to resonant intersubband transition (ISBT) is analyzed using a density-matrix approach. The second-harmonic generation coefficient chi(2 omega)((2)) and nonlinear optical rectification chi(0)((2)) have also been investigated theoretically. The results show that the ISBT in a step well can generate very large second order optical nonlinearities, chi(0)((2)) and chi(2 omega)((2)) can be tuned by the electric field over a wide range.

Experimental study on flow characters of CH3CCl2F hydrate slurry

The flow behaviors of CH3CCl2F hydrate slurry with volume concentration of 10-70% were studied in a new built flow loop with a diameter of 42.0 mm and length of 30.0 m. Morphologies of the fluids from slurrylike hydrates to slushlike hydrates with increasing of hydrate volume concentration in pipeline were observed. Pressure drops in pipeline also were studied and an exceptional pressure transition zone with hydrate volume concentration between 30% and 40% was found for the first time, which can be used as a notation to judge if the pipeline runs safely or not. Fanning friction factors of the hydrate slurries with all hydrate contents tend to constants between 0.38 and 0.5, which depend on the volume concentration in slurries, when the velocity reaches 1.5 m/s. A simple relation to estimate the pressure drop of hydrate slurry in pipeline was presented and verified. Experimental results were compared to the estimated results, which showed a good agreement. 

黄土高原沟壑区王东沟流域土地利用/覆被变化过程初探

黄土高原沟壑区王东沟流域从1986年至2006年的土地利用/覆被发生了较大变化,土地利用动态指数分别为:耕地3.21%,园地-36.11%,林地-4.05%,牧草地4.24%,居民点及独立工矿用地-0.62%,交通运输用地-12.27%,未利用地1.85%;变化趋势是:耕地逐年向园地流转,园地变化烈度较大,其他各类用地变化不太显著。引起这一变化的主要因素是自然、社会、经济、技术以及政策因素。结合这一变化,针对黄土高原沟壑区的实际情况,在黄土高原沟壑区土地利用经营与管理方面,应重视土地产出效益与粮食安全的关系,在保障区域粮食安全的基础上实现效益最大化。

台面尺寸对垂直腔面发射激光器电学特性的影响

采用求泊松方程、电流密度方程、载流子扩散方程以及有源层结压降方程自洽解的方法，计算了不同台面大小的台面结构垂直腔面发射激光器内部的电势分布和有源层中的注入电流密度、载流子浓度及结压降分布。结果表明，台面尺寸对垂直腔面发射激光器内部的电势分布和有源层中的注入电流密度、载流子浓度及结压降分布有重要影响。在一定的外加电压下，随着台面尺寸减小，有源层中心处的注入电流密度、载流子浓度和结压降急剧减小，垂直腔面发射激光器性能恶化。

不同干扰条件对辽东山区次生林植物多样性的影响

次生林作为中国森林资源的主体，在其形成和演替过程中，时刻受到自然和人为干扰的影响。明确干扰对次生林，特别是对其植物多样性的影响规律和原因，以及多样性对干扰的响应，对人类利用干扰的正面影响为生产实践服务和保护自然生态系统具有重要意义。本文以辽东山区次生林为研究对象，通过野外调查和数据分析，对不同干扰条件下的次生林植物多样性进行了比较研究，以期为该地区次生林的保护和经营提供参考。 主要结论：1）2004~2005年两个生长季共采集和鉴定植物378种，分别隶属于78科、215属；2）该地区次生林具有较高的物种多样性，各次生林类型Shannon-Weiner多样性指数在3.20~3.60之间；3）依据林分距离居民区和一、二级道路的远近将人为干扰划分为三个水平，即低度干扰、中度干扰和高度干扰，基本呈现了受中等水平干扰的林分具有较高的物种多样性和均匀度，且该地区的人为干扰主要对林分的灌木层和草本层产生影响；4）依据林分郁闭度与受害乔木株数百分比将雪/风灾害干扰划分为三个水平，受各水平雪/风灾害干扰的桦木林在近3年后已基本恢复，多样性水平差异不大，植物多样性随干扰强度的增加呈现平缓的增加趋势；5）该地区人为干扰和自然干扰主要的差异表现在发生方式、发生频度、影响对象、发生面积和空间分布等方面，对林分不同层次物种多样性的影响也有所差异。