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1.
采用EHT近似下的紧束缚能带结构计算方法,计算了YBa_2Cu_3O_(7-δ)和YBa_2Cu_3O_6的能带结构。结果表明,穿越超导休YBa_2Cu_3O_(7-δ)费米面的是三条来自Cu-O面和Cu-O链的能带,半导体YBa_2Cu_3O_6没有来自Cu-O链的能带.  相似文献   

2.
用固相反应法制备,并通过不同条件的热处理得到了一组不同氧含量的Nd0.9Ca0.1Ba2Cu3O7-δ样品。用XRD确定了预烧粉末的结构特征,发现其为(Nd,Ca,Ba)CuO3钙钛矿结构,较之典型立方钙钛矿(SrTiO3)出现新的113峰,且晶胞参数相应增大了一倍。随着氧含量的增大,Nd0.9Ca0.1Ba2Cu3O7-δ的结构发生从四方到正交相变,并讨论了其结构与超导电性的关系。  相似文献   

3.
对La1+zBa2-zCu3Oy相的形成,固溶度和La对Ba的替代进行了系统研究,以期获得制备具有更高Tc的超导体的最佳条件。表明La1+zBa2-zCu3Oy在空气中固溶度为0.20-0.70,N2中为0。在空气中合成La1+zBa2-zCu3Oy时,La能替代Ba,但Ba并不能替代La,空气和O2有利于La对Ba的替代,但当在N2中合成La1+zBa2-zCu3Oy时,La对Ba的替代受到抑制  相似文献   

4.
采用EHT近似下的紧束缚能带结构方法,从能带结构、态密度和电荷分布等方面研究了Tl_2Ba_2CuO_6,Tl_2Ba_2CaCu_2O_8和Tl_2Ba_2Ca_2Cu_3O_(10)超导体系的电子结构.从2-2-0-1,2-2-1-2到2-2-2-3相,费米能级附近的态密度及穿过费米面的能带数目相应增加.解释了随着单胞中Cu-O面数目的增加,超导转变温度升高的原因.  相似文献   

5.
本文研究了不同配比电子型Nd-Ce-CU-O和空穴型Y-Ba-Cu-O系列样品的CO氧化活性、晶体结构、程序升温氧脱附和导电性的特征.结果表明:超导体YBa2Cu1.5O7-x和半导体Ce2CuOx具有良好CO氧化转化率.后者在120℃时,CO达到完全转化.XRD证明它为2CeO2和CuO混合晶相.由于导电和催化反应机制完全不同,活性高低和样品导电性能间没有发现直接关联.讨论了含Ce、Cu样品的活性中心,认为CeO2为吸附氧和供氧中心,而Cun+为CO活化和氧化反应中心,而前者可能为控制步骤.两者紧密协同,使Cu2+的氧化还原循环更容易进行.  相似文献   

6.
高Tc超导体的室温飞秒时间分辨谱研究   总被引:1,自引:0,他引:1  
本文研究了室温下YBa_2Cu_3O_(7-x)(x=0.1,0.4,0.8)和PrBa_2Cu_3O_(6.9)外延膜的飞秒瞬态反射谱。结果表明,瞬态反射信号△R(t)的符号和弛豫时间与载流子浓度密切相关,对超导的YBa_2Cu_3O_(6.9),样品进行不同程度的去氧处理或者用Rr替代Y后,△R(t)的符号由正变负,弛豫时间由小于100fs增加到大于1ps,说明在高Tc氧化物超导体中,载流子浓度的减少使载流子-声子耦合强度降低。  相似文献   

7.
分别以BaCl2和CuCl2为配方试剂之一,制备得到掺Cl的超导体YBa2Cu3OxCly(y=0.2,0.4)。通过对比观测发现,掺Cl的YBCO超导体样品其Tc下降,超导转变温区变宽,晶胞参数发生变化,Cl进入123相晶格,文中还讨论了掺Cl对超导电性的影响。  相似文献   

8.
研究分别用粗粉及细粉工艺制备的先驱物( 液相组份先驱物粉末(BaCuO2 + CuO) ,异相SnO2) 对高温超导体YBa2Cu3O7- δ(Y123) 液相粉末熔融生长(LPMG) 织构工艺及微结构的影响, 结果表明: 在LPMG工艺熔化前的Y123 成相温区及熔融温区适当保持一段时间,可使样品的密度及结构度得到改善; 在部分样品的晶畴内可以观察到几十到几百纳米量级的微粒, 同时有大量的微粒存在于晶界中  相似文献   

9.
研究了YBa2Cu3O7-y超导体系随Bi掺杂浓度变化的特性。并通过X射线衍射数据,分析了其晶体结构的变化,认定Bi^3+的掺杂使样品中形成一正交非超导相。  相似文献   

10.
Y1—xNdxBa2Cu3O7—δ微结构及临界电流密度   总被引:1,自引:1,他引:0  
研究Nd替代Y后对YBa2Cu3O7-δ(Y123)超导织构体的临界电流密度及微结构的影响,采用溶胶-凝胶工艺制备名义组份为Y1-xNdxBa2Cu3O7-δ的先驱物,用熔融织构生长(MTG)工艺生长织构样品.结果表明,组份的熔点[θm(x)]随着x的增加而提高,并随着Δθ=θmax-θm(x)(θmax是MTG工艺过程的最高保持温度)的提高,织构体中CuO的含量增加,晶界之间及织构畴之间的弱连接的性质更加明显.由于晶粒内部及织构畴的磁通钉扎力得到一定程度的提高,临界电流密度JC随x的变化有1个最大值.  相似文献   

11.
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.  相似文献   

12.
The Williston Basin is a significant petroleum province, containing oil production zones that include the Middle Cambrian to Lower Ordovician, Upper Ordovician, Middle Devonian, Upper Devonian and Mississippian and within the Jurassic and Cretaceous. The oils of the Williston Basin exhibit a wide range of geochemical characteristics defined as "oil families", although the geochemical signature of the Cambrian Deadwood Formation and Lower Ordovician Winnipeg reservoired oils does not match any "oil family". Despite their close stratigraphic proximity, it is evident that the oils of the Lower Palaeozoic within the Williston Basin are distinct. This suggests the presence of a new "oil family" within the Williston Basin. Diagnostic geochemical signatures occur in the gasoline range chromatograms, within saturate fraction gas chromatograms and biomarker fingerprints. However, some of the established criteria and cross-plots that are currently used to segregate oils into distinct genetic families within the basin do not always meet with success, particularly when applied to the Lower Palaeozoic oils of the Deadwood and Winnipeg Formation.  相似文献   

13.
王慧 《科技信息》2008,(10):240-240
Wuthering Heights, Emily Bronte's only novel, was published in December of 1847 under the pseudonym Ellis Bell. The book did not gain immediate success, but it is now thought one of the finest novels in the English language. Catherine is the key character of this masterpiece, because everybody and everything center on her though she had a short life. We can understand this masterpiece better if we know Catherine well.  相似文献   

14.
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.  相似文献   

15.
何延凌 《科技信息》2008,(4):258-258
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.  相似文献   

16.
Location based services is promising due to its novel working style and contents.A software platform is proposed to provide application programs of typical location based services and support new applications developing efficiently. The analysis shows that this scheme is easy implemented, low cost and adapt to all kinds of mobile nework system.  相似文献   

17.
以AC-13级配为基础,将橡胶颗粒代替部分集料掺入混合料中,以低温弯曲试验为评价方法对不同橡胶颗粒掺量下沥青混合料的低温抗裂性进行研究,并引入应变能密度值对混合料的低温抗裂性进行综合评价.试验结果表明:橡胶颗粒沥青混合料试件的破坏微应变均超过2 300,满足冬寒区的技术指标;无论是否掺加橡胶颗粒,随着温度的下降,沥青混合料破坏时的最大弯拉强度增大,弯拉应变降低,劲度模量增大;弯曲应变能密度在胶粒掺量为1%左右时具有较大的弯曲应变能密度值,此时橡胶颗粒沥青混合料具有较好的低温抗裂性.  相似文献   

18.
AcomputergeneratorforrandomlylayeredstructuresYUJia shun1,2,HEZhen hua2(1.TheInstituteofGeologicalandNuclearSciences,NewZealand;2.StateKeyLaboratoryofOilandGasReservoirGeologyandExploitation,ChengduUniversityofTechnology,China)Abstract:Analgorithmisintrod…  相似文献   

19.
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。  相似文献   

20.
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.  相似文献   

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