制备和表征Fe3O4 /二氧化硅/ Bi2MoO6复合作为磁分离光催化剂
Yanlong Xuemei侯,1日田b,1,张翔b,b Shuliang斗,Lei锅b,b Wenjia王,姚明李娜,
久鹏赵,?
化学工程与技术学院的,哈尔滨工业大学,92号,Xidazhi街,南港地区,哈尔滨,中国
b复合材料中心,哈尔滨工业大学,哈尔滨,中国
摘要
Fe3O4 /二氧化硅/ Bi2MoO6微球制备简单水热法。的扫描电子显微镜(SEM)结果显示,花三维(3 d)Bi2MoO6微球大多以Fe3O4 /二氧化硅磁性纳米颗粒。的紫外可见漫反射光谱显示扩展吸收在可见光范围内与纯
Bi2MoO6相比。我们评估的光催化活动Fe3O4 /二氧化硅/ Bi2MoO6微球的降解可见光照射下罗丹明B(RhB),发现获得的综合表现光催化活性高于纯Bi2MoO6和project。此外,Fe3O4 /二氧化硅/ Bi2MoO6复合展示优秀的稳定性和重用后对其光催化活性有所下降5周期。同时,复合材料可以很容易地通过一个外部磁场分离。捕获的实验结果表明,超氧化物自由基O2和羟基自由基哦发挥重要作用在Fe3O4 /二氧化硅/ Bi2MoO6可见光辐照下系统。的结合花三维(3 d)Bi2MoO6微球和Fe3O4 /二氧化硅磁性团簇提供一个有用的策略设计多功能纳米结构和增强光催化材料活动在水净化的潜在应用。
1。介绍
许多概念收获和储存可再生能源(阳光、风、水)直接或辅助过程正在开发,以减少我们对化石能源的依赖来源。在各种各样的绿色地球和可再生能源项目宽,半导体光催化已收到兴趣,因为它提供了一种简便的方法直接利用能源的自然日光或人工室内照明[1 - 4]。沿着这条线,丰富光催化材料(如金属氧化物、硫化物和氮氧化物)一直在发展有机污染物的降解和分裂的水[5 - 7]。尽管如此,仍有一个问题与困难复苏的光催化剂纳米颗粒混合系统。因此,它是一个关键环节,寻求简单的恢复方法光催化剂纳米光催化的大规模应用流程。
磁性材料的引入是一种有效的方法毫不费力地分离和恢复光催化剂纳米颗粒通过应用一个外部磁场(8、9)。这些磁可分离的催化剂,有新颖的光学显示,磁,与个人singlecomponent或催化性能比较材料[10]。特别是氧化铁是一个最频繁磁性组件用于构建磁可分离的催化剂,由于其超顺磁性超顺磁的材料不受强磁场在色
散相互作用。因此,一些氧化铁基于磁分离催化剂设计,如Fe3O4-TiO2[11],Fe3Fe3 O4-BiOCl[12]
O4-Ag3PO4[13],Fe3 Fe3O4 / SiO2-TiO2[14]Bi2 O4-Bi2O3[15]WO6 /碳/ Fe3O4[16],Fe3O4-BiOI[17]和
Fe3O4-SiO2-Bi2WO6[18]。钼酸铋(Bi2MoO6)作为一个重要的三元铋氧化物复合,因为它已经受到了相当大的关注内在属性,例如介电性质,催化行为和发光[19]。三元三氧化二铋化合物,Bi-M-O(M =莫,W,V,铌或钽)
拥有一个典型的Aurivillius分层钙钛矿的结构组成的八面体(MO4)2表夹在(Bi2O2)2 +层(22 - 24)。这样的分层结构有利于电荷转移,从而会抑制photogenerated运营商的重组。更重要的是,Bi2MoO6显示一个典型的带隙2.60 eV的[25]。这些优秀的结构和光谱性质暗示Bi2MoO6应该是一个很有前途的光催化剂(每股26到29)。毫不奇怪,最近的研究证实,Bi2MoO6 visiblelight——非常好驱动的光催化水分解和活动降解有机污染物(30、31)。尽管有这些优势Bi2MoO6,它仍然是具有挑战性的简单摘要中恢复过来从解决方案。
在此,磁分离Fe3O4 /二氧化硅/ Bi2MoO6复合通过温和的水热方法制备。在获得Fe3O4 /二氧化硅/ Bi2MoO6复合,花三维(3 d)Bi2MoO6装饰着Fe3O4 /二氧化硅磁性微球纳米粒子,从而形成了一个层次结构。的可见光的光催化测试表明,目前的Fe3O4 /二氧化硅/ Bi2MoO6复合具有良好的光催化活性为降低RhB。光催化反应完成后,收集到的组合可以很容易地重用通过应用一个外部磁场。
2。材料和方法
所有化学品都分析品位和使用前未经纯化。去离子水(18 MX cm1)是用于所有实验。
2.1。制备单分散的Fe3O4纳米颗粒
磁Fe3O4纳米颗粒是根据以前的合成只要稍作修改报告[32]。在一个典型的过程,1.3克FeCl36H2O溶解在40毫升乙二醇形成一个明确的解决方案。然后三钠的0.4 g柠檬酸和2.4克剧烈搅拌下加入了乙酸钠。后积极搅拌30分钟,结果均匀分散转移成Teflon-lined不锈钢高压釜容量80毫升,密封,加热在200 C和维护10 h。收集和准备产品磁铁和用乙醇和去离子水清洗几次,然后晒干在60 C真空进一步使用。
2.2。制备Fe3O4 /二氧化硅纳米颗粒
Fe3O4 /二氧化硅纳米粒子的合成是由改性溶胶-凝胶方法通常,0.1 g的准备Fe3O4纳米颗粒治疗
0.1 M盐酸水溶液超声破碎法(50 mL)。治疗后10分钟,磁铁矿粒子分离,用水洗,然后均匀分散在40
毫升乙醇和10毫升去离子的混合物水声波降解法大约10分钟。加在上面的解决方案在连续机械搅拌,然后呢遵循0.1 mL teo一滴一滴地补充道。最后,被允许继续进行反应在室温下6 h。由此产生的产品用乙醇洗净和干在60 C真空
2.3。制备Fe3O4 /二氧化硅/ Bi2MoO6复合
一个温和的水热法的固定Fe3O4 /二氧化硅纳米粒子的表面上Bi2MoO6获得Fe3O4 /二氧化硅/ Bi2MoO6复合。简言之,0.97 g(2中毒)Bi(三)35 h2o和0.03 g Fe3O4 /二氧化硅纳米颗粒加入5毫升的浓硝酸(2米)溶液在室温下,然后混合sonicated 30分钟。老化2 h后,30毫升Na2MoO42H2O(1中毒)
解决办法是补充道。混合物在室温下是sonicated为另一个
30分钟前被转移到一个不锈钢高压聚四氟乙烯衬里80毫升的容量和维持在160 C 12 h。高压后冷却至室温,使用磁铁产品收获,和主题几个周期的磁分离/洗/之前再分散在室温下干燥。纯Bi2MoO6没有Fe3O4 /微球的准备二氧化硅是用于比较。
2.4。表征
粉末x射线衍射(XRD)模式进行准备的产品在Dmax-rA粉末衍射仪铜Ka的辐射源操作电压40千伏和40 mA的操作电流。形态和大小的准备样品的扫描电子的特征
显微镜(SEM,范Helios Nanolab 600我)配备了一个能量色散x射线分析仪(EDX)和透射电子显微镜(TEM,h - 7650,日立)的加速电压100 kV。傅里叶变换红外(ir)光谱范围的收集4000 - 400cm1傅立叶变换红外3 60年,Nicolet在室温下使用KBr颗粒的方法。磁性振动样品在室温下测量
湖Shore7407磁强计(VSM)在15 koe最大的领域。紫外可见吸收光谱研究了紫外可见光谱仪(珀金埃尔默, lambda 950)波长从200到200海里。
2.5。光催化测试
准备样品的光催化活动被退化评估可见光照射下罗丹明B(RhB)。300年wxenon灯截止滤光片是用作可见光源。简单地说,100毫克的光催化剂是悬浮在100毫升RhB解决方案(10 mg L1)不断搅拌。之前在黑暗中照明,暂停了1 h建立吸附-解吸平衡。系统的温度控制在房间温度循环咕咕叫水。在给定的时间间隔,3毫升的混合物被一块磁铁收集和分离。由此产生的浓度上清被检查的吸光度监测使用Lambda 553海里9 50分光光度计。循环反应,催化剂的分离外部磁场,用乙醇和去离子的回收催化剂之前几次水re-dispersed 染料溶液(100毫升,10毫克L1)下一个循环。
3。结果和讨论
3.1。表征的Fe3O4 /二氧化硅/ Bi2MoO6复合
Fe3O4的晶体结构,Fe3O4 /二氧化硅和Fe3O4 /二氧化硅/Bi2MoO6复合以XRD,如图所示图1。纯Fe 3O4纳米粒子(图1)展览衍射特性峰值约为30.1,35.4,43.1,53.4,57.0和62.5匹配与(220)、(311)、(400)、(422)、(511)和(440)水晶飞机的面心立方(fcc)Fe3O4阶段(a = b = c = 8.397)确定JCPDS使用标准的数据19号- 0629(34、35)。没有杂质阶段出现,指示高纯度的Fe3O4纳米颗粒。与一层二氧化硅涂层后,在图1 b没有新的衍射峰观察由于非晶准备阶段的二氧化硅。至于Fe3O4 /二氧化硅/ Bi2MoO6复合,所有的衍射峰很容易索引的斜方晶系的Bi2MoO6(= 5.500 a,b = 16.240 a,c = 5.490,JCPDS号76 - 2388)[36],对无形的绕射Fe3O4的复合,这是因为Fe3O4 /的内容二氧化硅太低了。
图2得了显示的扫描电镜图像的各种合成阶段Fe3O4 /二氧化硅/ Bi2MoO6复合。原始Fe3O4纳米颗粒拥有平均直径约300海里和near-spherical形态。与Fe3O4纳米粒子相比,虽然获得的整体形态Fe3O4 /
二氧化硅纳米颗粒(图2 b)没有显著变化,这些纳米颗粒展览相对光滑的表面。引入Bi2MoO6之后,Fe3O4 /二氧化硅纳米粒子固定在如花三维(3 d)Bi2MoO6微球大小的3 lm,因此层次结构已经形成。事实上,3 d中枯萎Bi2MoO6是由众多的二维结构(2 d)隔行nanosheets。图2 d是EDX元素微量分析的Fe3O4 /二氧化硅/ Bi2MoO6复合,清楚地暗示,铁、硅、Bi、钼和O存在于复合。
Fe3O4 /二氧化硅纳米颗粒的微观结构和Fe3O4 /二氧化硅/利用TEM技术Bi2MoO6综合观察。在图3, Fe3O4纳米颗粒完全封装到二氧化硅层厚度20海里。光圆形状是二氧化硅壳,并与球体形状是Fe3O4黑暗区域核心,清楚地表明Fe3O4 /二氧化硅纳米颗粒核壳结构。然而,这样的核壳结构(小黑色球体在图3 b)成为无形的由于大尺寸Bi2MoO6微球和Fe3O4@SiO2之间的区别纳米颗粒。因此,黑色小球体Fe3O4 /二氧化硅纳米颗粒和Bi2MoO6黑色的大球体
图1。Fe3O4 XRD的模式(一),(b)Fe3O4 /二氧化硅和(c)Fe3O4 /二氧化硅/ Bi2MoO6 复合。
微球所示图3 b。因此,Bi2MoO6微球有来自Fe3O4的磁性纳米粒子,,成为磁分离光催化剂。
为了进一步确认成分,傅里叶变换红外(ir)光谱的Fe3O4 Fe3O4 /二氧化硅和Fe3O4 /二氧化硅/Bi2MoO6组合也被调查。在三个样品,宽阔的峰值在1600年和3400年cm1可以归结拉伸和弯曲振动的吸附水。在图4,乐队在1611年和1396年cm1与羧酸盐有关组。典型的乐队分配给Fe-O伸展可见在cm1 580左右。的新吸收峰Fe3O4 /二氧化硅团簇(图4 b)在473年,796年、950年和1086年cm1被分配到对称和非对称伸缩振动的框架和Si-O-Si振动,这表明Fe3O4封装通过二氧化硅层。至于Fe3O4 /二氧化硅/ Bi2MoO6组合(图。4 c),乐队在840年和798年cm1即可分配不对称和对称拉伸模式MoO6。734的宽带cm1归因于不对称拉伸的MoO6模式。乐队在578年cm1对应的弯曲振动MoO6[37]。一些吸收的Fe3O4 /二氧化硅也仍然存在在Fe3O4 /二氧化硅/ Bi2MoO6复合,显然证明Fe3O4 /二氧化硅团簇表面成功的固定化枯萎Bi2MoO6nanosheets。
在室温下Fe3O4纳米晶体。磁饱和(女士)值的Fe3O4纳米颗粒是78鸸鹋g1[38],而那些
Fe3O4 /二氧化硅纳米颗粒和Fe3O4 /二氧化硅/ Bi2MoO6复合36和5 emu g1,分别。Fe3O4 /磁分离性二氧化硅/ Bi2MoO6复合被放置一块磁铁检查在水中旁边的玻璃瓶。值得注意的是,棕色的粉末很容易磁铁所吸引,因此可以方便地收集。这将提供一个简单和轻松的方式有效地分离从悬架系统通过应用磁性光催化剂外部磁场。
紫外可见漫反射光谱(DRS)的准备样品图6所示。纯Bi2MoO6微球的光谱
展览从紫外线photosbsorption属性地区可见光直到490海里,可以分配到一个带隙2.71 eV[39]。显然, Fe3O4 /二氧化硅/ Bi2MoO6复合显示更密集的吸收在可见光与纯Bi2MoO6微球相比,因为范围Fe3O4的黑体性质的公司。这样的吸收强度的增强,以及超顺磁性,意味着Fe3O4 /二氧化硅/ Bi2MoO6复合是一个很好的候选人大规模光催化的应用技术。
3.2。光催化研究的Fe3O4 /二氧化硅/ Bi2MoO6复合
评估了在水溶液RhB退化
可见光照射。图7显示时间的紫外吸收RhB溶液的吸收光谱的Fe3O4 /二氧化硅/Bi2MoO6复合。可见光区域与辐射的增加迅速降低时间,将近120分钟后消失,这意味着完整的共轭结构的破坏。与此同时,有一个
伴随吸收最大的转变554 nm - 500 nm对应一个分步de-ethylationRhB伴随着颜色的变化,从最初的粉红色淡黄色(39-41)。图7 b代表RhB浓度的变化(C / C0)与照射时间不同的催化剂。空白试验,而光催化剂明显表明self-photolysis RhB非常缓慢的过程。
图2。扫描电镜的图像(一)Fe3O4,(b)Fe3O4 /二氧化硅,(c)Fe3O4 /二氧化硅/ Bi2MoO6复合和(d)EDX的F e3O4 /二氧化硅/ Bi2MoO6复合模式。
图3。TEM图像(a)Fe3O4 /二氧化硅和(b)Fe3O4 /二氧化硅/ Bi2MoO6复合。
图4。傅立叶变换红外光谱(a)Fe3O4的(b)Fe3O4 /二氧化硅和(c)Fe3O4 /二氧化硅/ Bi2MoO6 复合。
图5。Fe3O4的磁化曲线,Fe3O4 /二氧化硅和Fe3O4 /二氧化硅/ Bi2MoO6复合。插入图片显示复合很容易分散在水中(左)通过磁铁(右)和容易分离。
一旦纯Bi2MoO6和Fe3O4 /二氧化硅/ Bi2MoO6复合添加,RhB迅速分解,降解效率达到96%在120分钟,几乎100%。改进后的光催化活性的Fe3O4 /二氧化硅/ Bi2MoO6复合是由于充分利用太阳光线与
Bi2MoO6微球(见图6)。作为比较,常用的光催化剂,二氧化钛(德固赛P25)也使用作为一个参考RhB的退化。
的光催化分解的RhB P25的辐照后是19%120分钟,这可以归结于涂料的效果。
图6。紫外可见DRS的纯Bi2MoO6和Fe3O4 /二氧化硅/ Bi2MoO6复合。
为了定量理解的反应动力学RhB外,我们还采用符合一级模型以适应光催化的数据。ln表达的模型(C0 / Ct)= kt,C0和C中污染物浓度的解决方案时间t0和t分别和k是明显的一阶速率常数(42、43)。作为显示在图7 C、ln(C0 / C)的所有情节与辐照时间(t)几乎是线性的,显示良好的线性依赖关系。Fe3O4 /表观速率常数k二氧化硅/ Bi2MoO6复合,Bi2MoO6微球和所需的计算分别是0.02898、0.02248和0.00176 m in1。也就是说,光催化活性Fe3O4 /二氧化硅/ Bi2MoO6复合是比P25高出约16.5倍,表明吗
Fe3O4 /二氧化硅/ Bi2MoO6组合应该是一个理想的光催化材料来取代TiO2-based材料。
考虑到光降解可能是由于dyesensitized路径选择RhB等有机染料模型污染物,无色的污染物将会是一个更好的选择演示的Fe3O4 /二氧化硅/光催化活动Bi2MoO6复合。因此,除了RhB 4-dichlorophenol
也用作另一个目标,以排除染料敏化。无花果所示。S1,超过70%的2,4 -二氯苯酚分子分解后5 h的可见光
辐照,进一步表明Fe3O4 /二氧化硅/ Bi2MoO6复合拥有一个优秀的可见光的光催化性能。
图7。(a)的吸收光谱与辐照时间RhB Fe3O4 /二氧化硅/ Bi2MoO6。(b)降解率RhB没有催化剂在可见光照射下存在P25、Bi2MoO6 Fe3O4 /二氧化硅/ Bi2MoO6复合。(c)一阶动力学数据的光降解RhB p roject,Bi2MoO6,Fe3O4 /二氧化硅/ Bi2MoO6 复合。(d)的光催化降解循环运行RhB的Fe3O4 /二氧化硅/ Bi2MoO6复合。
此外,我们还调查了稳定和可重用性Fe3O4 /二氧化硅/ Bi2MoO6复合。鉴于超顺磁性复合,当每个光催化反应完成后,光催化剂可以很容易地在外部磁分离字段下的反应。图7 d列出了五个循环测试的结果。重用5周期后,RhB发生轻微的降解率下降,但它仍然是90%。因此,Fe3O4 /二氧化硅/Bi2MoO6组合将是一个广泛使用的光催化剂
的未来。
3.3。硅层的角色Fe3O4 /二氧化硅/ Bi2MoO6复合
据报道,进行带边缘的潜力Bi2MoO6,Fe3O4和二氧化硅0.32,+ 1.23和4.10 eV价带边缘可能这些都是+ 2.39,+ 1.33分别为+ 4.80 eV(27日,44岁,45岁)。显然,只有Bi2MoO6可以由可见光照射产生photogenerated激活电子和洞。考虑更积极的行为乐队和消极的Fe3O4价带,photogenerated电子和空穴转移Bi2MoO6 Fe3O4引入二氧化硅(图S2a)。这种转移将大大加快photogenerated电子和空穴的复合来自极狭窄的带隙(0.1 eV)的Fe3O4,作为一个复合中心。无花果所示。开通,一旦隔离介绍了二氧化硅
层,photogenerated的传输路径携带Bi2MoO6和Fe3O4之间被切断,从而避免了Bi2MoO6的可见光催化活性的丧失。
3.4。可能的Fe3O4 /二氧化硅/ Bi2MoO6光催化机理复合
基于上述分析,我们还讨论了可能的Fe3O4 /二氧化硅/ Bi2MoO6复合光催化机制。自开展带边沿
Bi2MoO6更消极的潜力的氧化还原电势O2 / O2(0.28 eV)[46],photogenerated电子可以减少表面的吸附O2Bi2MoO6形成超氧化物自由基O2,一个强大的氧化剂降解染料分子。价带边缘Bi2MoO6比这更积极的潜力哦/哦(2.27 eV)[46],表明photogenerated洞(h +)能够直接染料分子分解,以及反应
与水和产生羟基自由基哦分解染料分子。换句话说,O2,h +和哦的主要活动物种的光降解RhB对Fe3O4 /二氧化硅/ Bi2MoO6复合。因此,捕获实验也进一步使用确定主要氧化剂的物种。苯醌(BQ0.1毫米),二钠ethylenediaminetetraacetate(EDTA、2毫米),和tertbutyl酒精(稍后通知,2毫米)用作超氧化物自由基食腐动物食腐动物,一个洞和羟基自由基清除剂,分别(图S3)。结果清楚地表明,主要的氧化剂物种O2和哦,而不是h +,这是规定与电子顺磁共振(EPR)结果报告文献[47]。提出了一种假设的机制如下: Bi2MoO6 +hv(可见光)
4。结论
总之,我们成功地开发了一种新型磁通过一个简单的水热可收回Bi2MoO6光催化剂方法。由此产生的Fe3O4 /二氧化硅/ Bi2MoO6复合拥有花三维组成的层次结构(3 d)Bi2MoO6微球和Fe3O4 /二氧化硅磁性纳米颗粒。针对集成Fe3O4 /二氧化硅磁性纳米粒子,可以很容易地分离和收集样品通过应用外部磁场的分散悬浮字段。可见光的光催化测试表明,现在Fe3O4 /二氧化硅/ Bi2MoO6复合的一个很好的光催化活动降解RhB高于个人Bi2MoO6以及纳米二氧化钛。这样的组合光催化剂是一种很有前途的光催化材料去除有害的有机染料废水。然而,表面积现在的Fe3O4 /二氧化硅/ Bi2MoO6综合指数很低(SBET < 10平方米g1)。因此,我们的未来将专注于构建工作结构与大型表面区域,进一步改善光催化活性。
中等分辨率制备分离的 快速色谱技术 W. Clark Still,* Michael K a h n , and Abhijit Mitra Departm(7nt o/ Chemistry, Columbia Uniuersity,1Veu York, Neu; York 10027 ReceiLied January 26, 1978 我们希望找到一种简单的吸附色谱技术用于有机化合物的常规净化。这种技术是适于传统的有机物大规模制备分离，该技术需使用长柱色谱法。尽管这种技术得到的效果非常好，但是其需要消耗大量的时间，并且由于频带拖尾经常出现低复原率。当分离的样本剂量大于1或者2g时，这些问题显得更加突出。近年来，几种制备系统已经进行了改进，能将分离时间减少到1-3h，并允许各成分的分辨率ΔR f≥（使用薄层色谱分析进行分析）。在这些方法中，在我们的实验室中，媒介压力色谱法1和短柱色谱法2是最成功的。最近，我们发现一种可以将分离速度大幅度提升的技术，可用于反应产物的常规提纯，我们将这种技术称为急骤色谱法。虽然这种技术的分辨率只是中等（ΔR f≥），而且构建这个系统花费非常低，并且能在10-15min内分离重量在的样本。4 急骤色谱法是以空气压力驱动的混合介质压力以及短柱色谱法为基础，专门针对快速分离，介质压力以及短柱色谱已经进行了优化。优化实验是在一组标准条件5下进行的，优化实验使用苯甲醇作为样本，放在一个20mm*5in.的硅胶柱60内，使用Tracor 970紫外检测器监测圆柱的输出。分辨率通过持续时间（r）和峰宽（w,w/2）的比率进行测定的（Figure 1），结果如图2-4所示，图2-4分别放映分辨率随着硅胶颗粒大小、洗脱液流速和样本大小的变化。
The smart grid Smart grid is the grid intelligent (electric power), also known as the "grid" 2.0, it is based on the integration, high-speed bidirectional communication network, on the basis of through the use of advanced sensor and measuring technology, advanced equipme nt technology, the advanced control method, and the application of advanced technology of decision support system, realize the power grid reliability, security, economic, efficient, environmental friendly and use the security target, its main features include self-healing, incentives and include user, against attacks, provide meet user requirements of power quality in the 21st century, allow all sorts of different power generation in the form of access, start the electric power market and asset optimizatio n run efficiently. The U.S. department of energy (doe) "the Grid of 2030" : a fully automated power transmission network, able to monitor and control each user and power Grid nodes, guarantee from power plants to end users among all the nodes in the whole process of transmission and distribution of information and energy bi-directional flow. China iot alliance between colleges: smart grid is made up of many parts, can be divided into:intelligent substation, intelligent power distribution network, intelli gent watt-hourmeter,intelligent interactive terminals, intelligent scheduling, smart appliances, intelligent building electricity, smart city power grid, smart power generation system, the new type of energy storage system.Now a part of it to do a simple i ntroduction. European technology BBS: an integration of all users connected to the power grid all the behavior of the power transmission network, to provide sustained and effective economic and security of power. Chinese academy of sciences, institute of electrical: smart grid is including all kinds of power generation equipment, power transmission and distribution network, power equipment and storage equipment, on the basis of the physical power grid will be modern advanced sensor measurement technology, network technology, communication
南京航空航天大学金城学院 毕业设计（论文）外文文献翻译 系部经济系 专业国际经济与贸易 学生姓名陈雅琼学号2011051115 指导教师邓晶职称副教授 2015年5月
Economic policy,tourism trade and productive diversification （Excerpt） Iza Lejárraga,Peter Walkenhorst The broad lesson that can be inferred from the analysis is that promoting tourism linkages with the productive capabilities of a host country is a multi-faceted approach influenced by a variety of country conditions.Among these,fixed or semi-fixed factors of production,such as land,labor,or capital,seem to have a relatively minor influence.Within the domain of natural endowments,only agricultural capital emerged as significant.This is a result that corresponds to expectations,given that foods and beverages are the primary source of demand in the tourism economy.Hence,investments in agricultural technology may foment linkages with the tourism market.It is also worth mentioning that for significant backward linkages to emerge with local agriculture,a larger scale of tourism may be important. According to the regression results,a strong tourism–agriculture nexus will not necessarily develop at a small scale of tourism demand. It appears that variables related to the entrepreneurial capital of the host economy are of notable explanatory significance.The human development index(HDI), which is used to measure a country's general level of development,is significantly and positively associated with tourism linkages.One plausible explanation for this is that international tourists,who often originate in high-income countries,may feel more comfortable and thus be inclined to consume more in a host country that has a life-style to which they can relate easily.Moreover,it is important to remember that the HDI also captures the relative achievements of countries in the level of health and education of the population.Therefore,a higher HDI reflects a healthier and more educated workforce,and thus,the quality of local entrepreneurship.Related to this point,it is important to underscore that the level of participation of women in the host economy also has a significantly positive effect on linkages.In sum, enhancing local entrepreneurial capital may expand the linkages between tourism and other sectors of the host country.
Inventory management Inventory Control On the so-called "inventory control", many people will interpret it as a "storage management", which is actually a big distortion. The traditional narrow view, mainly for warehouse inventory control of materials for inventory, data processing, storage, distribution, etc., through the implementation of anti-corrosion, temperature and humidity control means, to make the custody of the physical inventory to maintain optimum purposes. This is just a form of inventory control, or can be defined as the physical inventory control. How, then, from a broad perspective to understand inventory control? Inventory control should be related to the company's financial and operational objectives, in particular operating cash flow by optimizing the entire demand and supply chain management processes (DSCM), a reasonable set of ERP control strategy, and supported by appropriate information processing tools, tools to achieved in ensuring the timely delivery of the premise, as far as possible to reduce inventory levels, reducing inventory and obsolescence, the risk of devaluation. In this sense, the physical inventory control to achieve financial goals is just a means to control the entire inventory or just a necessary part; from the perspective of organizational functions, physical inventory control, warehouse management is mainly the responsibility of The broad inventory control is the demand and supply chain management, and the whole company's responsibility. Why until now many people's understanding of inventory control, limited physical inventory control? The following two reasons can not be ignored: First, our enterprises do not attach importance to inventory control. Especially those who benefit relatively good business, as long as there is money on the few people to consider the problem of inventory turnover. Inventory control is simply interpreted as warehouse management, unless the time to spend money, it may have been to see the inventory problem, and see the results are often very simple procurement to buy more, or did not do warehouse departments . Second, ERP misleading. Invoicing software is simple audacity to call it ERP, companies on their so-called ERP can reduce the number of inventory, inventory control, seems to rely on their small software can get. Even as SAP, BAAN ERP world, the field of
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New technique of the computer network Abstract The 21 century is an ages of the information economy, being the computer network technique of representative techniques this ages, will be at very fast speed develop soon in continuously creatively, and will go deep into the people's work, life and study. Therefore, control this technique and then seem to be more to deliver the importance. Now I mainly introduce the new technique of a few networks in actuality live of application. keywords Internet Network System Digital Certificates Grid Storage 1. Foreword Internet turns 36, still a work in progress Thirty-six years after computer scientists at UCLA linked two bulky computers using a 15-foot gray cable, testing a new way for exchanging data over networks, what would ultimately become the Internet remains a work in progress. University researchers are experimenting with ways to increase its capacity and speed. Programmers are trying to imbue Web pages with intelligence. And work is underway to re-engineer the network to reduce Spam (junk mail) and security troubles. All the while threats loom: Critics warn that commercial, legal and political pressures could hinder the types of innovations that made the Internet what it is today. Stephen Crocker and Vinton Cerf were among the graduate students who joined UCLA professor Len Klein rock in an engineering lab on Sept. 2, 1969, as bits of meaningless test data flowed silently between the two computers. By January, three other "nodes" joined the fledgling network.
Computer Program 1 Introduction Computer Program, set of instructions that directs a computer to perform someprocessing function or combination of functions. For the instructions to be carried out, a computer must execute a program, that is, the computer reads the program, and then follow the steps encoded in the program in a precise order until completion. A program can be executed many different times, with each execution yielding a potentially different result depending upon the options and data that the user gives the computer. Programs fall into two major classes: application programs and operating systems. An application program is one that carries out somefunction directly for a user, such as word processing or game-playing. An operating system is a program that manages the computer and the various resources and devices connected to it, such as RAM,hard drives, monitors, keyboards, printers, and modems,so that they maybe used by other programs. Examples of operating systems are DOS, Windows 95, OS\2, and UNIX. 2 Program Development Software designers create new programs by using special applications programs, often called utility programs or development programs. A programmer uses another type of program called a text editor to write the new program in a special notation called a programming language. With the text editor, the programmer creates a text file, which is an ordered list of instructions, also called the program source file. The individual instructions that make up the program source file are called source code. At this point, a special applications program translates the source code into machine language, or object code— a format that the operating system
文献翻译 原文 Combining JSP and Servlets The technology of JSP and Servlet is the most important technology which use Java technology to exploit request of server, and it is also the standard which exploit business application .Java developers prefer to use it for a variety of reasons, one of which is already familiar with the Java language for the development of this technology are easy to learn Java to the other is "a preparation, run everywhere" to bring the concept of Web applications, To achieve a "one-prepared everywhere realized." And more importantly, if followed some of the principles of good design, it can be said of separating and content to create high-quality, reusable, easy to maintain and modify the application. For example, if the document in HTML embedded Java code too much (script), will lead the developed application is extremely complex, difficult to read, it is not easy reuse, but also for future maintenance and modification will also cause difficulties. In fact, CSDN the JSP / Servlet forum, can often see some questions, the code is very long, can logic is not very clear, a large number of HTML and Java code mixed together. This is the random development of the defects. Early dynamic pages mainly CGI (Common Gateway Interface, public Gateway Interface) technology, you can use different languages of the CGI programs, such as VB, C / C + + or Delphi, and so on. Though the technology of CGI is developed and powerful, because of difficulties in programming, and low efficiency, modify complex shortcomings, it is gradually being replaced by the trend. Of all the new technology, JSP / Servlet with more efficient and easy to program, more powerful, more secure and has a good portability, they have been many people believe that the future is the most dynamic site of the future development of technology. Similar to CGI, Servlet support request / response model. When a customer submit a request to the server, the server presented the request Servlet, Servlet responsible for handling requests and generate a response, and then gave the server, and then from the server sent to
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英文翻译 A comprehensive overview of substations Along with the economic development and the modern industry developments of quick rising, the design of the power supply system become more and more completely and system. Because the quickly increase electricity of factories, it also increases seriously to the dependable index of the economic condition, power supply in quantity. Therefore they need the higher and more perfect request to the power supply. Whether Design reasonable, not only affect directly the base investment and circulate the expenses with have the metal depletion in colour metal, but also will reflect the dependable in power supply and the safe in many facts. In a word, it is close with the economic performance and the safety of the people. The substation is an importance part of the electric power system, it is consisted of the electric appliances equipments and the Transmission and the Distribution. It obtains the electric power from the electric power system, through its function of transformation and assign, transport and safety. Then transport the power to every place with safe, dependable, and economical. As an important part of power’s transport and control, the transformer substation must change the mode of the traditional design and control, then can adapt to the modern electric power system, the development of modern industry and the of trend of the society life. Electric power industry is one of the foundations of national industry and national economic development to industry, it is a coal, oil, natural gas, hydropower, nuclear power, wind power and other energy conversion into electrical energy of the secondary energy industry, it for the other departments of the national economy fast and stable development of the provision of adequate power, and its level of development is a reflection of the country's economic development an important indicator of the level. As the power in the industry and the importance of the national economy, electricity transmission and distribution of electric energy used in these areas is an indispensable component.。Therefore, power transmission and distribution is critical. Substation is to enable superior power plant power plants or power after adjustments to the lower load of books is an important part of power transmission. Operation of its functions, the capacity of a direct impact on the size of the lower load power, thereby affecting the industrial production and power consumption.Substation system if a link failure, the system will protect the part of action. May result in power outages and so on, to the production and living a great disadvantage. Therefore, the substation in the electric power system for the protection of electricity reliability,
毕业设计说明书 英文文献及中文翻译 学院：专 2011年6月 电子与计算机科学技术软件工程
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