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.     

Corrosion behavior of cold-rolled and post heat-treated 316L stainless steel in 0.9wt%NaCl solution

The effect of cold rolling and post-rolling heat treatment on the microstructural and electrochemical properties of the 316L stainless steel was investigated.Two-pass and four-pass cold-rolled stainless steel specimens were heat-treated by annealing at 900℃followed by quenching in water.During the cold rolling,the microstructure of the as-received specimen transformed from austenite to strain-inducedα′-martensite due to significant plastic deformation that also resulted in significant grain elongation(i.e.,~33%and 223%increases in the grain elongation after two and four rolling passes,respectively).The hardness of the heat-treated as-received specimen decreased from HV 190 to 146 due to the recovery and recrystallization of the austenite grain structure.The cyclic polarization scans of the as-rolled and heat-treated specimens were obtained in 0.9wt%NaCl solution.The pitting potential of the four-pass rolled specimen was significantly increased from 322.3 to 930.5 mV after post-rolling heat treatment.The beneficial effect of the heat treatment process was evident from~10-times-lower corrosion current density and two-orders-of-magnitude-lower passive current density of the heat-treated specimens compared with those of the as-rolled specimens.Similarly,appreciably lower corrosion rate(3.302×10^?4mm/a)and higher pitting resistance(1115.5 mV)were exhibited by the postrolled heat-treated specimens compared with the as-rolled 316L stainless steel specimens.     

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.     

哲学是否应当拥有保质期?（英文）

在"哲学是否应当拥有保质期?"这篇论文中,我考察了宗教标志、科学条目与技术条目如何展示其"保质期"或获得使用与成为公认现实的时限的方式。我有所限定地认为,相同的现象出现于或应当出现于哲学之中。我考察了诸多过时的哲学概念,接下来,我转向了来自现代早期哲学的诸多顽强而又过时的概念,其中最显著的是笛卡尔主义,它持续存在于大量当代哲学之中。     

新疆旅游关注度的时空差异及其影响因素

基于百度指数平台,获取了2011年、2013年及2015年我国大陆31个省、直辖市和自治区的新疆旅游搜索指数.运用季节集中指数、周内分布偏度指数、空间自相关方法对新疆旅游关注度的时空差异进行了分析并引入GWR模型探究其影响因素.结果表明:(1)新疆旅游关注度总体呈现增长态势,且各年关注度表现出明显的季节性特征,节假日、周存在"前兆效应";(2)全国各省、直辖市和自治区的新疆旅游关注度具有显著的空间自相关性,大多数地区呈现出持续的"低—低"集聚现象;(3)GWR模型优于OLS模型,从全域视角看,人口规模、经济发展水平、教育发展水平及互联网发展水平对新疆旅游关注度的影响均呈现不同程度的正向作用;从局域视角看,各影响因素作用整体上与OLS模型结果一致,但各影响因素的敏感度在空间上表现出西部地区高于东部地区的态势.     

托木尔峰自然保护区喀拉玉尔滚河流域土壤盐分特征分析

文章以托木尔峰国家级自然保护区喀拉玉尔滚河上游河谷为研究区域,应用经典统计分析方法对该河谷土壤盐分空间特征进行分析。结果表明:(1)研究区土壤的全盐、Cl-、SO2-4、Mg2+及K++Na+含量的变异系数CV≥100%,属于强变异性;p H值、HCO-3及Ca2+含量的变异系数CV100%,属于中等变异性;(2)土壤盐渍化类型以硫酸盐及偏硫酸盐渍土为主,土壤盐渍化程度以极轻或轻度为主;(3)土壤p H值呈弱碱性,整体空间变化微小,研究区较低海拔的土壤中全盐和K++Na+含量远超过其它盐分离子,且二者含量变化趋势近似一致;随着海拔高度的增加,土壤中各盐分离子含量微小,趋于稳定;(4)主成分分析结果表明,全盐、SO2-4、HCO-3及K++Na+是研究区土壤盐渍化状况的特征因子。     

浅谈如何做好机动车尾气污染的治理工作

机动车尾气是造成大气污染的主要原因,同时机动车尾气对人类健康也产生了严重的危害。为此,本文在详细分析乌鲁木齐机动车尾气污染现状与治理现状后,提出几点做好机动车尾气污染的治理工作的策略,希望可以达到降低机动车尾气污染的目的,使人们处于健康、安全的环境之中。     

朝鲜半岛核问题的解决前景仍很模糊

正今天的朝鲜得到了很多国家的特别关注,既有俄罗斯、中国、韩国、日本这样的邻国,也有美国这样总试图扮演世界霸权和规则制订者角色的国家。然而对朝鲜到底正在发生什么事情,这些国家无一有着准确的认知。这首先因为朝鲜是个封闭国家,人们很难得到关于它的一手信息。其次因为朝鲜发布的官方信息往往晦涩难懂,甚至让专业研究者都不明就里。不过有一点是明确的,那就是朝鲜不希望对大国惟命是从,而是期望在东亚和世界上独立自主。     

霍金遗作:《大问题简答》

正这本书将成为霍金的宣言。它乐观、富有远见,认为科学和对科学的理解对人类未来至关重要。出版商通常迫切希望他们的新书得到评论,一旦标题推出,他们就会用不请自来的出版样本去轰炸报纸、网站和杂志,以获得更多的报道。看看《物理世界》的档案柜:里面满是我们不想要的书,都是由渴望得到宣传的出版商寄来的。然而,对史蒂芬·霍金的最新一本、也是最后一本著作来说,却发生了一些非常不同的事情。《大问题简答》今日发布,为了先一睹为快,《物理世界》     

星系的生命和呼吸

<正>科学家追踪气体随时间和空间的变化,探寻恒星群出生及死亡的方式。天文学家对宇宙的大部分了解来自他们能够看到的东西,因此,他们的理论总是偏爱明亮的恒星和星系。然而,宇宙中的大部分常规物质都是以昏暗的气体形式存在的。称作星系际介质的气体充满星系间的空间;而环星系介质的气体则环绕在星系附近。这两个区域的气体管控星系诞生、成长和死亡,也详细记录了整个宇宙的