Venue: Diffusion phenomena of solutions to the Cauchy problem for the dampe wave equationSpeaker: Prof. K. Nishihara (Waseda University, Japan)Time: 15:00-16:00, Mar 15,2013, FridayLocation: Second floor, GongShang Lou, Yuquan Campus, Zhejiang University, Hangzhou, China
Venue: Interplay between superconductivity and magnetism in EuFe2As2Speaker: Prof. Zakir Hossain (IIT Kanpur, India)Time: 16:00-17:00, Mar 11,2013, MondayLocation: Dongsi-242, Zijingang Campus, Zhejiang University, Hangzhou, ChinaAbstract:Superconductivity in iron arsenide compounds is a subject of intense discussion in the scientific community. First iron-arsenide based high temperature superconductor was discovered in F-substituted LaOFeAs with a transition temperature at 26 K. Followed by this four more Fe-based series of compounds were found. Our main interest is in EuFe2As2 which has a very special place in AFe2As2 (A =Ba, Sr, Ca, Eu) series due to the large magnetic moment of Eu2+ (≈7μB) ions in this compound. This compound exhibits Spin density wave (SDW) transition associated with Fe-moments at 190 K and an antiferromagnetic ordering of Eu2+ ions at 19 K. The SDW transition can be suppressed or weakened either by applying hydrostatic pressure or by chemical pressure which induce superconductivity in this system. 50% potassium doping in EuFe2As2 leads to the suppression of SDW transition and gives rise to superconductivity below 33 K. 151Eu Mössbauer spectroscopy provide clear evidence that short range ordering of the Eu moments coexists with the superconducting state below 15 K. Superconducting transition temperature decreases for both under-doped and over-doped samples with maximum Tc for 50% K-doped sample and hence show a dome type T-x phase diagram similar to high Tc cuprates. Ni doping at iron site destroys the spin density wave and antiferromagnetic transition completely giving rise to ferromagnetism below 18 K. We also found evidence of double re-entrance type superconductivity in the EuFe2As2 system. These results will be presented in the perspective of the historical development of the field of superconductivity.
Venue:Nonparametric estimation of probability density functions for irregularly observed spatial dataSpeaker: Dr. Zudi Lu(School of Mathematical Sciences, University of Adelaide, AUSTRALIA )Time: 13:30-15:30, Nov 27,2012, SundayLocation: Second Floor conference room, The Commercial building, Yuquan Campus, Zhejiang University, Hangzhou, ChinaAbstract:Nonparametric estimation of probability density functions, both marginal and joint densities, is a very useful tool in statistics. The kernel method is popular and applicable to dependent data, including time series and spatial data. But at least for the joint density, one has had to assume that data are observed at regular time intervals or on a regular grid in space.Though this is not very restrictive in the time series case, it often is in the spatial case. In fact, to a large degree it has precluded applications of nonparametric methods to spatial data because such data often are irregularly positioned over space. In this paper, we propose nonparametric kernel estimators for both the marginal and in particular the joint probability density functions for non-gridded spatial data. Large sample distributions of the proposed estimators are established under mild conditions, and a new framework of expanding-domain infill asymptotics is suggested to overcome the shortcomings of spatial asymptotics in the existing literature. A practical, reasonable selection of the bandwidths on the basis of cross-validation is also proposed. We demonstrate by both simulations and real data examples of moderate sample size that the proposed methodology is effective and useful in uncovering nonlinear spatial dependence for general, including non-Gaussian, distributions.
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