Photonic band structure of ZnO photonic crystal slab laser

We recently reported on the first realization of ultraviolet photonic crystal laser based on zinc oxide [Appl. Phys. Lett. {\bf 85}, 3657 (2004)]. Here we present the details of structural design and its optimization. We develop a computational super-cell technique, that allows a straightforward calculation of the photonic band structure of ZnO photonic crystal slab on sapphire substrate. We find that despite of small index contrast between the substrate and the photonic layer, the low order eigenmodes have predominantly transverse-electric (TE) or transverse-magnetic (TM) polarization. Because emission from ZnO thin film shows strong TE preference, we are able to limit our consideration to TE bands, spectrum of which can possess a complete photonic band gap with an appropriate choice of structure parameters. We demonstrate that the geometry of the system may be optimized so that a sizable band gap is achieved.Comment: 8 pages, 7 figure

Finite dimensional integrable Hamiltonian systems associated with DSI equation by Bargmann constraints

The Davey-Stewartson I equation is a typical integrable equation in 2+1 dimensions. Its Lax system being essentially in 1+1 dimensional form has been found through nonlinearization from 2+1 dimensions to 1+1 dimensions. In the present paper, this essentially 1+1 dimensional Lax system is further nonlinearized into 1+0 dimensional Hamiltonian systems by taking the Bargmann constraints. It is shown that the resulting 1+0 dimensional Hamiltonian systems are completely integrable in Liouville sense by finding a full set of integrals of motion and proving their functional independence.Comment: 10 pages, in LaTeX, to be published in J. Phys. Soc. Jpn. 70 (2001

The brezis-ekeland-nayroles minimization principle with mixed finite element method for elastoplastic dynamic problems

We propose a modification of the Hamiltonian formalism which can be used for dissipative systems, the Brezis-Ekeland-Nayroles principle. The formalism is specialized to the standard plasticity in small strains and dynamics. We apply it to solve the classical problem of a thin tube in plane strain subjected to an internal pressure. The continuum is discretized with mixed finite elements

Ultraviolet photonic crystal laser

We fabricated two dimensional photonic crystal structures in zinc oxide films with focused ion beam etching. Lasing is realized in the near ultraviolet frequency at room temperature under optical pumping. From the measurement of lasing frequency and spatial profile of the lasing modes, as well as the photonic band structure calculation, we conclude that lasing occurs in the strongly localized defect modes near the edges of photonic band gap. These defect modes originate from the structure disorder unintentionally introduced during the fabrication process.Comment: 4 pages, 4 figure

Transport development, intellectual property rights protection and innovation: The case of the Yangtze River Delta Region, China

The links between transport development and economic growth have been widely discussed in the field of transport governance and economics. However, the existing studies have not included an institutional variable when exploring the role of transport development in innovation disparities within a region. In order to fill the research gap, this paper examines whether transport development and the institution of intellectual property rights (IPRs) can assist in understanding disparities between cities in terms of innovation, using the Yangtze River Delta Region (YRDR) as a case study. The impact mechanism is twofold. Firstly, transport development can affect institutions, including IPRs protection, which in turn has an influence on innovation. Secondly, evidence from existing economic literature suggests a link between transport development and innovation through economic agglomeration, production factors and industrial flows. We first employ ordinary least squares (OLS) regression to test the basic associations between transport development and innovation. We then apply two-stage least squares (2SLS) regression analysis to address endogeneity and add a spatial model to examine neighbour effects. The findings show that IPRs protection has a positive effect on patenting and research and development (R&D), while the roles played by transport development stock and density in patenting and R&D are more mixed. Moreover, our findings on neighbour effects show that agglomeration economies exist in the YRDR. These findings have important policy implications regarding urban agglomeration for both the YRDR specifically and China overall

Self-optimization of optical confinement in ultraviolet photonic crystal slab laser

We studied numerically and experimentally the effects of structural disorder on the performance of ultraviolet photonic crystal slab lasers. Optical gain selectively amplifies the high-quality modes of the passive system. For these modes, the in-plane and out-of-plane leakage rates may be automatically balanced in the presence of disorder. The spontaneous optimization of in-plane and out-of-plane confinement of light in a photonic crystal slab may lead to a reduction of the lasing threshold.Comment: 5 pages, 5 figure

Phonon anomaly in BaFe2As2

The detailed optical properties of BaFe2As2 have been determined over a wide frequency range above and below the structural and magnetic transition at T_N = 138 K. A prominent in-plane infrared-active mode is observed at 253 cm^{-1} (31.4 meV) at 295 K. The frequency of this vibration shifts discontinuously at T_N; for T < T_N the frequency of this mode displays almost no temperature dependence, yet it nearly doubles in intensity. This anomalous behavior appears to be a consequence of orbital ordering in the Fe-As layers.Comment: 4 pages, 3 figures and one table (minor revisions

Quantum information approach to the quantum phase transition in the Kitaev honeycomb model

Kitaev honeycomb model with topological phase transition at zero temperature is studied using quantum information method. Based on the exact solution of the ground state, the mutual information between two nearest sites and between two bonds with longest distance are obtained. It is found that the mutual information show some singularities at the critical point where the ground state of the system transits from gapless phase to gapped phase. The finite-size effects and scalar behavior are also studied. The mutual information can serve as good indicators of the topological phase transition, since the mutual information catches some global correlation properties of the system. Meanwhile, this method has other advantages such that the phase transition can be determined easily and the order parameters are not required previously, for the order parameters of some topological phase transitions are hard to know.Comment: 8 pages, 7 figures, published versio