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41.
H.S RagabA Shehap M.S Abo EllilW.H Osman F.H Abd El-Kader 《Journal of Physics and Chemistry of Solids》2002,63(10):1839-1847
Ternary-phase ceramic system of Li2O Al2O3 4SiO2 doped with CuO, FeO and TiO2 has been prepared and subjected to dc electrical conductivity and thermally stimulated depolarization current (TSDC) measurements as a function of temperature (30-250 °C) and field strength. The electrical conductivity results are explained by assuming both ionic and electronic conduction mechanisms coexist with different contributions over the whole temperature range of experiments. TSDC spectra have been found to be characterized by a broad intense relaxation peak, which can be attributed to an ionic charge polarization. The broad relaxation transitions are apparently a result of the nonuniform nature of this process. Activation energies are calculated for both dc electrical conductivity and TSDC according to Arrhenius equation and initial rise method, respectively. 相似文献
42.
Q. Sun Q. Wang X.G. Gong V. Kumar Y. Kawazoe 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(1):77-81
We report results of the atomic and electronic structures of Al7C cluster using ab initio molecular dynamics with ultrasoft pseudopotentials and generalized gradient approximation. The lowest energy structure is
found to be the one in which carbon atom occupies an interstitial position in Al7 cluster. The electronic structure shows that the recent observation [Chem. Phys. Lett. 316, 31 (2000)] of magic behavior of Al7C- cluster is due to a large highest occupied and lowest unoccupied molecular orbital (HOMO-LUMO) gap which makes Al7C- chemically inert. These results have further led us to the finding of a new neutral magic cluster Al7N which has the same number of valence electrons as in Al7C- and a large HOMO-LUMO gap of 1.99 eV. Further, calculations have been carried out on (Al7N)2 to study interaction between magic clusters.
Received 28 July 2001 相似文献
43.
运用层析法、结晶法从狭苞橐吾全草中分离得到艾里莫芬烷型倍半萜8β-hydroxyeremophil-7(11)-ene-12,8α(4β,6α)-diolide化合物,并通过质谱、核磁共振氢谱和碳谱、氢核-氢核相关谱、异核多量子相干谱和异核多键相干谱进行结构鉴定.其单晶经X射线衍射测试表明,其晶体属正交晶系,空间群为P212121,晶胞参数为: a=6.8519(5),b=10.7191(8),c=18.5942(14)A,V=1365.67(18) A3,Z=4,Dc=1.354 mg/m3.F(000)=592,μ=0.101 mm-1 相似文献
44.
C. Maurel 《Surface science》2006,600(2):442-447
Light emitted in the tunneling junction of a scanning tunneling microscope has been used to establish the electrical characteristics of nanojunctions made of Au islands deposited on flat MoS2 surfaces. It is shown that these characteristics are those of rectifying contacts when the gold islands are isolated and that they evolve toward those of ohmic contacts when the island density increases. It is observed that the rectifying behavior also evolves over time as on infinite metal/semiconductor contacts. Using the STM tip, single gold islands can be manipulated on the MoS2 surface so that their electrical behavior can be changed depending on their position with regard to the other islands. 相似文献
45.
Th. Seyller K.V. Emtsev F. Speck A. Tadich J.D. Riley O. Rader A.M. Shikin 《Surface science》2006,600(18):3906-3911
Photoelectron spectroscopy, low-energy electron diffraction, and scanning probe microscopy were used to investigate the electronic and structural properties of graphite layers grown by solid state graphitization of SiC(0 0 0 1) surfaces. The process leads to well-ordered graphite layers which are rotated against the substrate lattice by 30°. On on-axis 6H-SiC(0 0 0 1) substrates we observe graphitic layers with up to several 100 nm wide terraces. ARUPS spectra of the graphite layers grown on on-axis 6H-SiC(0 0 0 1) surfaces are indicative of a well-developed band structure. For the graphite/n-type 6H-SiC(0 0 0 1) layer system we observe a Schottky barrier height of ?B,n = 0.3 ± 0.1 eV. ARUPS spectra of graphite layers grown on 8° off-axis oriented 4H-SiC(0 0 0 1) show unique replicas which are explained by a carpet-like growth mode combined with a step bunching of the substrate. 相似文献
46.
我国上市公司资本结构影响因素实证分析 总被引:17,自引:0,他引:17
本文选取了可能影响企业资本结构的多个指标变量进行分析 ,利用主成分分析提供的方法将变量综合成彼此互不相关的少数几个主成分。再用主成分 (作为回归自变量 )对企业的 5种资本负债比 (作为回归因变量 )进行多元回归分析 ,得出了影响企业资本结构的主要因素 ,以及这些因素与企业资本结构之间的关系 ,为企业确定资本结构提供参考依据 ,为企业财务决策提供支持。 相似文献
47.
Under idealized conditions, electroconvection in a nematic liquid crystal sets in at a well-defined threshold of the driving ac voltage. Fluctuating convection rolls of a small amplitude below that threshold have been observed recently. The measurement of the amplitude of these fluctuations is described in detail in this paper. It is based on averaging the light intensity signals using the structure function and a quantitative analysis of the light deflection. 相似文献
48.
基于密度泛函理论(DFT),用完全势能线性缀加平面波方法(FPLAPW)计算模拟了MnO2的同质多相变体(金红石型结构、CaCl2型结构、黄铁矿型结构),通过计算,预测了β-MnO2在5 GPa时从金红石型结构转变为CaCl2型结构,在20 GPa时进一步转变为黄铁矿型结构。另外,还总结和比较了几种金红石型结构二氧化物的压致相变特点,得出第Ⅳ主族元素的金红石型结构氧化物有很好的规律性,发生的相变序列基本一致;并随着金属阳离子半径的增大,发生相变的压力值也相应地递减,各氧化物的体积模量值相应地减小。 相似文献
49.
As borders between different entities, lines are an important element of natural images. Indeed, the neurons of the mammalian
visual cortex are tuned to respond best to lines of a given orientation. This preferred orientation varies continuously across
most of the cortex, but also has vortex-like singularities known as pinwheels. In attempting to describe such patterns of
orientation preference, we are led to consider underlying rotation symmetries: Oriented segments in natural images tend to
be collinear; neurons are more likely to be connected if their preferred orientations are aligned to their topographic separation.
These are indications of a reduced symmetry requiring joint rotations of both orientation preference and the underlying topography.
This is verified by direct statistical tests in both natural images and in cortical maps. Using the statistics of natural
scenes we construct filters that are best suited to extracting information from such images, and find qualitative similarities
to mammalian vision.
PACS84.35+i 89.70.+c 87.57.Nk 相似文献
50.
Quenching of the eutectoidal composition of the shape memory alloys (SMA’s) allowed us to display the gradual transition of
the martensitic structure as a function of the composition. Indeed, we have verified that for low Al and Ni percentages, the
martensite structure obtained is β′, while, for high Al and Ni (Al<13.3 mass%) contents, the martensite structure is essentially
of β1′ type. Elsewhere, we have observed that a nickel addition (<4.3 mass%) operates simultaneously on the composition of the
eutectoidal pointand the domain of the different martensitic structures types. During reheating of the quenched structure,
the transformation sequences of the martensite to the parent phase (β1), then the decomposition of the later phase into the
equilibrium phases, and finally, the redissolution of all phases to form the β phase at high temperature, are rather similar.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献