Effect of yttria addition on the stability of porous chromium oxide ceramics in supercritical water

Porous chromium oxide (Cr₂O₃) ceramics were prepared by oxidizing highly porous chromium carbides that were obtained by a reactive sintering method, and were evaluated at temperatures ranging from 375 °C to 625 °C in supercritical water (SCW) environments with a fixed pressure of 25–30 MPa. Reactive element yttrium was introduced to the porous oxide ceramic by adding various amounts of yttria of 5, 10 and 20 wt.%, respectively, prior to reactive sintering. The exposure in SCW shows that the porous chromium oxide is quite stable in SCW at 375 °C. However, the stability decreased with increasing temperature. It is well known that chromium oxide can be oxidized to soluble chromium (VI) species in SCW when oxygen is present. Adding yttria increases the stability of chromium oxide in SCW environments. However, adding yttria higher than 5 wt.% increased the weight loss of porous chromium oxide samples because of the direct dissociation of Y₂O₃ in SCW.     

Interpreting results from field deployments of semipermeable membrane devices

Three canisters of semipermeable membrane devices (SPMDs), each containing five SPMDs, were deployed at three different locations on a transect across a small river removed from the impact of near-field point sources. Following a 62-day deployment, the masses of various polynuclear aromatic hydrocarbons (PAH) sequestered by each SPMD in each canister were determined. The compound-specific mean residues (ng/SPMD) obtained for the PAHs with pK(ow) values >4.4 showed statistically significant (alpha = 0.10) differences between the three deployment locations (canisters) ranging from approximately 10 to 160 ng/SPMD, corresponding to relative percent differences (RPDs) ranging from 10% to 54%. There were no statistically significant differences between the same three locations for the single PAH with a pK(ow) <4.4. A detailed discussion of how different (uncontrollable) environmental variables may have impacted the experimental results is provided to illustrate the uncertainties associated with interpreting the results from SPMD field deployments and highlight the need for some means of correcting for these impacts. The results from this work also illustrate the need to account for spatial variability in water column concentrations (i.e., sample heterogeneity) as part of any interpretation.     

战略规划:大都市地区有效治理的方向盘 --大伦敦战略规划的演变与最新发展

20世纪的标志性特征之一是世界城市人口的增长.其中,1900年仅有5至6个城市区域拥有百万人口,而1990年这个数字达到286,最近的增长主要集中在亚洲、南美和非洲的经济快速增长地区(Gilbert et al, 1996).这些城市的增长为如何实现最有效的治理带来很多的问题,不仅仅是管理已有的城市人口,更在于如何调控未来的发展压力.本文试图介绍欧洲的百万城市之一--伦敦在20世纪中后期规划与发展演化的脉络,并分析其为保持作为欧洲的一个真正的全球性城市的地位,如何在21世纪初回应所遇到的挑战.     

Optimization of alkylresorcinols extraction from triticale bran using response surface methodology

Optimization conditions for alkylresorcinols (ARs) extraction from triticale bran were determined using response surface methodology. A central composite design was used to determine the effects of extraction temperature (degrees Celsius) and solid-to-solvent ratio (weight per volume) on yield of saturated, unsaturated and total ARs. Extraction of ARs was affected significantly (p value????0.05) by temperature and solid-to-solvent ratio on the yield of saturated, unsaturated and total ARs. The highest quantity of total ARs from triticale bran was extracted at 24?°C between 16 and 24?h at a solid-to-solvent ratio (weight per volume) of 1:40 and ranged from 278 to 308?mg/100?g, while saturated and unsaturated ARs were 163 to 225?mg/100?g and 22 to 29?mg/100?g, respectively. The ARs identified by high-performance liquid chromatography included: C15:0, C17:0, C19:0, C21:0, C23:0 and C25:0. Also some unsaturated analogues (12.4% to 14.0%) were found including C17:1, C19:1, C21:1 and C23:1. Analysis of variance (p value?=?0.05) indicated that the response surface methodology (RSM) developed for saturated, unsaturated and total ARs were adequate and explained most of the variability (85% to 89%) with high coefficient of multiple determination (R ²?=?0.89). The main effect of the response variable was quadratic rather than a linear function. Our results showed that RSM is a tool that is useful to optimise experimental conditions for the extraction of ARs.     

物理气相沉积(PVD)制备氧化铝涂层

1 引言 由于氧化铝薄膜具有令人关注的优异性能,如高温稳定性、化学稳定性、低的热导率和电导率等,目前利用化学气相沉积(CVD)涂覆氧化铝薄膜作为耐磨涂层材料已广泛应用于硬质合金切削刀片.它在其它领域没有得到广泛应用的主要原因是这类涂层的工业规模制备需利用高温CVD进行处理.虽然CVD处理方法有许多优点,但其最大的缺点是在处理过程中需要高温(1000℃).