Segregation in the Falicov--Kimball Model

The Falicov–Kimball model is a simple quantum lattice model that describes light and heavy electrons interacting with an on-site repulsion; alternatively, it is a model of itinerant electrons and fixed nuclei. It can be seen as a simplification of the Hubbard model; by neglecting the kinetic (hopping) energy of the spin up particles, one gets the Falicov–Kimball model. We show that away from half-filling, i.e. if the sum of the densities of both kinds of particles differs from 1, the particles segregate at zero temperature and for large enough repulsion. In the language of the Hubbard model, this means creating two regions with a positive and a negative magnetization. Our key mathematical results are lower and upper bounds for the sum of the lowest eigenvalues of the discrete Laplace operator in an arbitrary domain, with Dirichlet boundary conditions. The lower bound consists of a bulk term, independent of the shape of the domain, and of a term proportional to the boundary. Therefore, one lowers the kinetic energy of the itinerant particles by choosing a domain with a small boundary. For the Falicov- Kimball model, this corresponds to having a single “compact” domain that has no heavy particles. Received: 21 June 2001 / Accepted: 4 January 2002     

两种方法制备ITO薄膜的红外特性分析

比较了用电束加热蒸发法和直流磁控溅射法制备的氧化锡铟(ITO)薄膜在红外波段的光学特性实验发现,通过直流磁控溅射在常温下制备的ITO薄膜在红外波段折射率稳定、消光系数小,比电子束加热蒸发制备的膜有较高的透过率在波长1550nm附近的透过率可达86%以上,消光系数约为004,方电阻最低为100Ω/□.     

Two-dimensional Anhydrous Cadmium(II) Phthalate

The in situ hydrolysis of phthalyl-γ-glutaminyl-histidine with Cd(ClO₄)₂·6H₂O in the presence of water and methanol affords a novel two-dimensional cadmium coordination polymer, a new phase, anhydrous cadmium(II) phthalate, ( 1 ). The structure was determined by single crystal X-ray diffraction. Crystal data: P2₁/c, a = 13.8168(14), b = 7.0351(7), c = 8.2054(8) Å, β = 105.540(2)°, V = 768.43(13) ų, Z = 4, R₁ = 0.0380, wR₂ = 0.1111.     

Extensions of Modules over Schur Algebras, Symmetric Groups and Hecke Algebras

We study the relation between the cohomology of general linear and symmetric groups and their respective quantizations, using Schur algebras and standard homological techniques to build appropriate spectral sequences. As our methods fit inside a much more general context within the theory of finite-dimensional algebras, we develop our results first in that general setting, and then specialize to the above situations. From this we obtain new proofs of several known results in modular representation theory of symmetric groups. Moreover, we reduce certain questions about computing extensions for symmetric groups and Hecke algebras to questions about extensions for general linear groups and their quantizations.     

强化物理实验提高教学质量

勿庸置疑，课堂只是学生腾飞的基地，社会才是学生飞翔的天空．如何架设课堂与社会之间的桥梁，使学生从理论走向实践，从空想走向实际，是每位教师必须思考的问题．就物理教学而言，实验是架设课堂和社会的桥梁之一．那就是通过物理实验来实现．     

Fluorous osmium tetraoxide (OsO4): a recoverable and reusable catalyst for dihydroxylation of olefins

A fluorous osmium catalyst was firstly developed. It had been effectively used as recoverable and reusable catalyst in the dihydroxylation of olefins.     

System Identification Models of the Equivalent Permittivity for Rain Medium

The dielectric constant for rain medium is investigated by utilizing the system identification method. The rain rate model and frequency model of permittivity in millimeter waves band for rain medium are presented. The results obtained with models are in very good agreement with references in calculating the attenuation of electromagnetic waves induced by rain, which Shows that the obtained models are valid and practicable. The cross-polar discrimination gotten with rain rate model is in agreement with references.     

Synthesis of 2-pyrone-4-carboxaldehydes from acetylene dicarboxaldehyde monoacetal

Reaction of acetylene dicarboxaldehyde monoacetal with substituted Meldrum’s acid leads good yields in 2-pyranones-4-carboxaldehydes substituted in position 3.     

Evidences of phase separation in moisture‐cured poly(urethane urea)s by means of temperature modulated differential scanning calorimetry

The degree of phase separation in several moisture‐cured poly(urethane urea)s (PUUs) was studied by FTIR spectroscopy, wide angle X‐ray diffraction (WAXD), and temperature‐modulated differential scanning calorimetry (TMDSC). This latter technique was shown to be particularly useful in analysing the degree of phase separation in PUU polymers. Both phase mixing and phase segregation coexisted in the PUUs and the degree of phase separation increased as the urea hard segment (HS) content in the PUU increased. The maximum solubility of urea HSs into the polyol soft segments (SSs) was achieved for 50 wt % urea HS content in diol‐based PUUs, whereas for triol‐based PUUs the highest solubility between HS and SS was reached for lower urea HS amount. Finally, the higher the urea HS content the higher the extent of phase separation in the PUU. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3034–3045, 2007     

Single to 16-Channel Wavelength Conversion at 10 Gb/s Based on Cross-Gain Modulation of ASE Spectrum in SOA

A simple scheme for single to multi-channel wavelength conversion based on cross-gain modulation of amplified spontaneous emission (ASE) spectrum in semiconductor optical amplifier (SOA) is described. Single to 16-channel wavelength conversion at 10 Gb/s is first demonstrated without any additional probe lights, the modulation information carried by input signal could be converted into arbitrary many channels if only the demultiplexer with enough channels is exploited. Output performance and pattern effects are investigated experimentally.