Science

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Now showing 1 - 10 of 35
  • (1996) Leung, S; Stevens, Gaye; Bandyopadhyay, Srikanta; Sorrell, Charles
    Conference Paper

  • (1998) Wool, R; Kusefoglu, S; Khot, S; Zhao, R; Palmese, Gaetano; Boyd, Andrew; Fisher, Keith; Bandyopadhyay, Srikanta; Williams, J; Wang, Chaoyuan
    Conference Paper

  • (2000) Zhang, Guangqing; Cheng, Chun-Chung; Du, X; Zhao, Yong
    Journal Article
    Bi1.7Pb0.3Sr2Ca2Cu3O10+y was used as an example of Cuprates for our study. The subtle thermal transitions and the jumps of the parameters appear in the sample at about 300 and 700oC, respectively. The unit cell of the sample is composed of two structural blocks: perovskite and rock salt. The size of every block along c direction is about a nanometer. What should be made clear is whether the two thermal and structural changes take place in the whole cell or from different blocks. The bond lengths in the unit cell are analyzed carefully before and after two thermal and structural changes based on the results of X-ray diffraction. Careful analysis of the bond length in the samples demonstrates that the two jumps of the parameters are correlated with the two blocks. After the jump at about 300oC, the bond lengths in the rock salt block change more significant than in the perovskite block. After the jump at about 700oC, the bond lengths in the perovskite block change more significant than in the rock salt block. The change of the bond lengths clearly shows that the different thermal transitions and the jumps of the parameters take place in different blocks.

  • (2000) Zhang, Guangqing; Cheng, Chun-Chung; Zhao, Yong
    Journal Article
    Based on a block model, separating the unit cell of YBa2Cu3O7-[delta] into perovskite and rock salt blocks, the combinative energy between the two blocks in the YBa2Cu3O7-[delta] with the different [delta] value, from 0.07 to 0.62, was calculated. A close relationship between the superconducting transition temperature and the combinative energy in YBa2Cu3O7-[delta] is established, and the change of the combinative energy is closely related to the transformation from orthorhombic I to II. The results also give a clue to reconsider the role of the orthorhombic I and II in YBa2Cu3O7-[delta]. The calculation of the holes in different planes supplies abundant information about the charge distribution in YBa2Cu3O7-[delta], which may possibly connect the electronic phase diagram and the fluctuations of the stripe phase. The results show that the interaction between the two blocks is of great importance for high Tc superconductivity.

  • (1999) Zhao, Yong; Cheng, Chun-Chung; Zhang, Hua
    Journal Article
    The influence of the flux flow on a.c. loss and magnetic penetration process in superconductors has been investigated. Asymptotic solutions of magnetic and electric fields and a.c. loss are presented in the form of a power series of [Lambda], the normalized frequency of the external a.c. magnetic field. The results show that the flux flow retards the response of inner magnetic field to the external one, which results in a deviation from the critical state model and a non-hysteretic loss. In the cases of H0>Hp, the deviation from the critical state is in the order of the second power of [Lambda]. The induced electric field and the macro-penetration depth are decreased by the slowdown of the flux movement, giving a negative contribution to the a.c. loss. However, the negative contribution is compensated by the increase of the current density, leading to a net increase of the a.c. loss. As a result, the a.c. loss exhibits a positive dependence on the frequency and the amplitude of the external magnetic field.

  • (1999) Zhang, Hua; Zhao, Yong; Cheng, Chun-Chung
    Journal Article
    Low-temperature thermal expansion and its correlation with oxygen nonstoichiometry have been studied for Bi1.7Pb0.3Sr2Ca2Cu3O10+y samples. An anomalously big jump of the thermal expansion in the c direction of Bi1.7Pb0.3Sr2Ca2Cu3O10+y has been observed at a temperature slightly above the superconductivity transition temperature. The corresponding temperature and the magnitude of the jump are found to be correlated with the oxygen nonstoichiometry, carrier concentration and superconductivity. The results reveal that the anomalously big jump of the thermal expansion is an electron-assisted lattice softening transition. Its correlation with the superconductivity suggests that phonon-electron interaction still plays a certain role in the superconductivity in high-Tc cuprates.

  • (1995) Dimitrakopoulos, Telis; Alexander, Peter; Hibbert, D. Brynn; Cherkson, L; Morgan, Judith
    Journal Article

  • (2006) Schubert, Emery; Wolfe, Joseph
    Journal Article
    Two models that predict perceived timbrai brightness in terms of the centroid of the frequency spectrum were investigated. One model simply uses the centroid of the frequency spectrum, the other divides this same value by the fundamental frequency: the latter scales the centroid of the frequency spectrum with the fundamental frequency. Different single tone and pitch combinations, presented sequentially, were compared. Participants were not asked to ignore pitch differences and intervals of greater than an octave were compared. The results indicate that brightness is much better correlated with frequency spectrum centroid (r = 0.513, p less than or equal 0.01) than with the ratio of the centroid of the frequency spectrum to the fundamental frequency (r = 0.030. p = 0.441).

  • (2003) Wolfe, Joseph; Schubert, Emery; Butchatsky, Kristen; Solar, Stela
    Conference Paper
    live performance

  • (1997) Rogers, Keith; Gross, Miraca
    Other Resource
    Audio-taped interview