高于90K的钇钡铜氧系化合物的超导电性

1973年以来,对高温超导电性的研究几乎停顿不前.Bednorz和Mulle在La—Ba—Cu—O系中高于30K超导电性的发现迅速改变了这种局面。以后的发展近乎日新月异。赵忠贤等首先报道了在Y—Ba—Cu—O体系中发现高于液氮温度(77K)的超导电性并公布了材料组分。接着C.W.Chu等在Y—Ba—Cu—O多相氧化物超导体中得到了高于90K的的超导电性。最近,更多的研究组在单相YBa_2Cu_3O_(9~-y)氧化物超导体中发现了高于90K超导电性。我们在研制单相YBa_2Cu_2O_(9~-y)超导材料过程中发现,制备条件对超导性质的影响很大。我们选用分析纯钇钡铜的氧化物或碳酸盐。阳离子配比为Y∶B∶Cu=1∶2∶3。在玛瑙研钵里充分研磨以后,在管式炉内900—1100℃通氧烧结12—24小时。冷却速率对超导性质的影响是显著的。缓慢(超过6小时)冷却到室温可得到零电阻温度高于90K的超导电性,如图1所示。快速冷却的零电阻温度低于77K,如图2所     

白光LED用Na_3SrB_5O_(10):Dy~(3+)的合成及发光性能研究

采用高温固相法合成Na_3SrB_5O_(10):Dy~(3+)(n=0. 5,0. 8,1. 0,1. 5,2. 0)系列荧光粉,利用X射线衍射仪、荧光光谱仪对材料的结构和发光性能进行了测试和分析. XRD测试结果表明掺Dy~(3+)量不应超过2%.荧光光谱图显示,在588 nm监测波长下的最佳激发波长为345 nm,在345 nm波长激发下有490 nm(B)和589 nm(Y)两个主要特征峰,其中589 nm处的特征峰最强.随着Dy~(3+)浓度的增大,发射峰Y和B的强度比值Y/B有微小变化,荧光粉表现出较好的发光稳定性.从发射光谱可知当掺Dy~(3+)量达到2. 0%时发生浓度猝灭,表明最佳掺杂浓度为1. 5%.计算出该基质中Dy~(3+)的临界传递距离为3. 05 nm.激发波长取345 nm时,Na_3SrB_5O_(10):Dy~(3+):n%Dy~(3+)(0. 5～2. 0)系列荧光的色温范围为3 200 K～3 500 K,发光为暖白光.     

Gd在Ba_2RCu_3O(7+δ)(R=Y,HO)高温超导体表面上引起的化学反应

本文利用X射线光电子谱(XPS)对Gd原子在Ba_2RCu_3O_(7+8)(R=Y, Ho)高温超导体表面上引起的化学反应进行了研究.实验发现,在该超导样品表面上蒸镀的Gd原子被氧化,超导体中对超导特性起重要作的Cu-O链遭到破坏,其中一部分处于Cu~(2+)态的Cu元素被还原,超导体内其它各元素也不同程度地受到了影响.当样品表面上Gd覆盖度达到22A(R=Y)和30A(R=Ho)时,界面上的化学反应不再继续     

YBa_2Cu_3O_(9-x)在烧结过程中的四方→正交转变与超导电性

利用高温X射线原位测定法直接测定配比为YBa_2Cu_3O_(9-x)的物料在升温、保温和降温的烧结过程中超导相结构的形成,四方→正交转变及其对烧结产物超导性能的影响.实验表明在升温到880℃时首先形成过渡的立方结构相,然后发展为层状四方钙钛矿结构.随着高温保持时间的延长,四方结构向正交结构转变.在降温至600℃附近,还发生第二次四考→正交转变.上述二次四方正交转变均对超导性能产生影响     

Y—Al—Si—O—C氧碳玻璃的研制

以SiO_2,Al_2O_3,Y_2O_3,α-SiC粉体为原料,采用粉末烧结法,于1550℃～1650℃无压烧结2hr.,研制Y-Al-Si-O-C氧碳玻璃。结果表明:在1650℃×2h.的烧结条件下,在元素质量百分比为(wt％)Y(15.75)-Al(5.29)-Si(28.82)-O(49.14)-C(1.00)和Y(15.75)-Al(5.29)-Si(29.60)-O(47.36)-C(2.00)的两个成份点可获得氧碳玻璃。     

醇-水溶液加热法制备稀土Ce掺杂纳米ZrO_2(3Y)及其特性研究

采用醇水溶液加热法制备了掺杂3?2O3的纳米ZrO2(3Y)粉体,并制得了相应的敏感元件,研究了掺杂对纳米ZrO2(3Y)结构和敏感特性的影响.结果表明,掺入3%的Ce2O3明显改善了样品的结晶程度并使其晶相结构在一定的温度范围内保持稳定,同时也减缓了样品由四方相结构向单斜相结构转变的速度,极大地改善了元件氧灵敏度的线性化程度.     

在钇钡铜超导氧化物中以锶代钡的实验研究

自从YBaCuO系统高温超导体被发现以来,人们在该系统的基础上作了广泛的研究,其中包括化学掺杂和离子代换.去年6月在美国Berkeley举行的“超导奇异机理的国际讨论会”上,Tarascon等人指出:对于YBa_(2-x)Sr_xCu_3O_(7-y)系统,Sr的最大溶解度为x=1.4,因为Sr和Ba是同族元素,离子半径比Ba小,随着Sr含量的增加,正交超导相晶格常数a,b和c单调减小,T_(?)随之从93K(x=0)单调地减少到8OK(x=1.4).后来,C.Y.范等人曾宣布研制成一种以Sr代Ba的超导陶瓷,呈现超导转变温度达45℃.显然他们给出的以Sr代Ba的实验结果是不一致的.     

影响BiSr_1Ca_1Cu_2O_x及Y_1Ba_2Cu_sO_(7-x)超导相形成的几个重要因素

目前,已有大量不同的所谓高温超导体,其可分为两类。第一类是以La_(2-x)Sr_xCuO_(4-x)为代表,T_c=30～40K,晶体是K_2NiF_4结构;第二类是以YBa_2Cu_3O_(7-x)为代表,T_c=90K左右,晶体是缺氧钙钛矿结构,即所谓“123”结构。新高温超导体都是混合含氧化物,显示出陶瓷的机械和物理性能。新材料性能的关键在于化学键合在一起的铜(Cu)和氧(O)原子构成的原子平面,铜-氧化学键合的特殊性质使得材料在某些方向能很好地传导电流,这与大多数陶瓷为绝缘体形成对照。目前,人们在BiSrCaCuO系中以微量Pb取代部分Sr已可获得160K的高临界温度。作者利用化学纯原料成功地研制出零电阻温度达125K的Bi_1Ca_1Cu_2O_x系超导体和T_c在90K以上的Y_1Ba_2Cu_3O_(7-x)高温超导陶瓷。在研制过程中发现Y_1Ba_2Cu_3O_(7-x)超导相的形成过程中,氧环境及退火降温速度对其形成起十分重要的作用,而原料中的微量杂质对其形成不起关键作用;BiSrCaCuO系对微量杂质不敏感,而对退火温度要求甚高。     

Y—Ba—Cu—O体系超导相结构的研究

Y-Ba-Cu-O超导相结构己用单晶四园X射线衍射方法测定。晶体属正交晶系。Pmmm空间群,晶格参数是a=3.855(2),b=3.857(2),c=11.653(3)。超导相的实验式为YBa_2Cu_2.84O_6.85.     

锑掺杂钒磷封接玻璃的析晶稳定性研究

以80V_2O_5-20P_2O_5-xSb_2O_3(x=0,1,3,5mol%)系统玻璃为研究对象,对其进行红外吸收光谱、拉曼光谱、X射线光电子能谱和固体静态核磁共振测试,研究玻璃的网络结构,分析钒磷玻璃中掺杂锑后析晶稳定性提高的机理.结果表明:钒磷系封接玻璃中加入少量的Sb_2O_3后,玻璃网络结构中桥氧比例增加,非桥氧比例下降;同时V~(4+)/V~(5+)增加,这两点原因导致形成V_2O_5晶相所需的V=O键大幅断裂,抑制了该晶相的生成.Sb_2O_3的引入,破坏了网络平衡态的结构,使(VO_3)_n单链逐渐转化为(V_2O_8)n锯齿状链,玻璃结构更加紧密,难以析晶,析晶稳定性提高.     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

Features of Women's language

Language is a means of verbal communication. People use language to communicate with each other. In the society, no two speakers are exactly alike in the way of speaking. Some differences are due to age, gender, statue and personality. Above all, gender is one of the obvious reasons. The writer of this paper tries to describe the features of women＇s language from these perspectives： pronunciation, intonation, diction, subjects, grammar and discourse. From the discussion of the features of women＇s language, more attention should be paid to language use in social context. What＇s more, the linguistic phenomena in a speaking community can be understood more thoroughly.     

Characterization of Ordovician carbonate reservoirs, southeastern Saskatchewan, Canada

The discovery of the prolific Ordovician Red River reservoirs in 1995 in southeastern Saskatchewan was the catalyst for extensive exploration activity which resulted in the discovery of more than 15 new Red River pools. The best yields of Red River production to date have been from dolomite reservoirs. Understanding the processes of dolomitization is, therefore, crucial for the prediction of the connectivity, spatial distribution and heterogeneity of dolomite reservoirs.The Red River reservoirs in the Midale area consist of 3～4 thin dolomitized zones, with a total thickness of about 20 m, which occur at the top of the Yeoman Formation. Two types of replacement dolomite were recognized in the Red River reservoir: dolomitized burrow infills and dolomitized host matrix. The spatial distribution of dolomite suggests that burrowing organisms played an important role in facilitating the fluid flow in the backfilled sediments. This resulted in penecontemporaneous dolomitization of burrow infills by normal seawater. The dolomite in the host matrix is interpreted as having occurred at shallow burial by evaporitic seawater during precipitation of Lake Almar anhydrite that immediately overlies the Yeoman Formation. However, the low δ18O values of dolomited burrow infills (-5.9‰～ -7.8‰, PDB) and matrix dolomites (-6.6‰～ -8.1‰, avg. -7.4‰ PDB) compared to the estimated values for the late Ordovician marine dolomite could be attributed to modification and alteration of dolomite at higher temperatures during deeper burial, which could also be responsible for its 87Sr/86Sr ratios (0.7084～0.7088) that are higher than suggested for the late Ordovician seawaters (0.7078～0.7080). The trace amounts of saddle dolomite cement in the Red River carbonates are probably related to "cannibalization" of earlier replacement dolomite during the chemical compaction.     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

A computer generator for randomly layered structures

AcomputergeneratorforrandomlylayeredstructuresYUJia shun1,2,HEZhen hua2(1.TheInstituteofGeologicalandNuclearSciences,NewZealand;2.StateKeyLaboratoryofOilandGasReservoirGeologyandExploitation,ChengduUniversityofTechnology,China)Abstract:Analgorithmisintrod…     

An Index mechanism for multi-scale view in spatial databases

There are numerous geometric objects stored in the spatial databases. An importance function in a spatial database is that users can browse the geometric objects as a map efficiently. Thus the spatial database should display the geometric objects users concern about swiftly onto the display window. This process includes two operations:retrieve data from database and then draw them onto screen. Accordingly, to improve the efficiency, we should try to reduce time of both retrieving object and displaying them. The former can be achieved with the aid of spatial index such as R-tree, the latter require to simplify the objects. Simplification means that objects are shown with sufficient but not with unnecessary detail which depend on the scale of browse. So the major problem is how to retrieve data at different detail level efficiently. This paper introduces the implementation of a multi-scale index in the spatial database SISP (Spatial Information Shared Platform) which is generalized from R-tree. The difference between the generalization and the R-tree lies on two facets: One is that every node and geometric object in the generalization is assigned with a importance value which denote the importance of them, and every vertex in the objects are assigned with a importance value,too. The importance value can be use to decide which data should be retrieve from disk in a query. The other difference is that geometric objects in the generalization are divided into one or more sub-blocks, and vertexes are total ordered by their importance value. With the help of the generalized R-tree, one can easily retrieve data at different detail levels.Some experiments are performed on real-life data to evaluate the performance of solutions that separately use normal spatial index and multi-scale spatial index. The results show that the solution using multi-scale index in SISP is satisfying.     

Jane Eyre——A Feminist In The 19th Century

In the 19th century the society was controlled by men, and women were just appendants of them, they had not any rights and freedom. But Jane was an exception, she showed some characteristics of early feminist. Jane showed her characteristics of feminism in three aspects: rebellion, equality, and independence. These characteristics were helpful to her success, and feminism is the only way out for women of that time.     

Achieving Unusual States of Matter Under High Pressure

正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-     

Exchange-Correlation and Electronic Excitation Energies from Pairing Matrix Fluctuations

We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-