practical type checking of functions defined on context-free languages

A type checking method for the functional language LFC is presented. A distinct feature of LFC is that it uses Context-Free (CF) languages as data types to represent compound data structures. This makes LFC a dynamically typed language. To improve efficiency, a practical type checking method is presented, which consists of both static and dynamic type checking. Although the inclusion relation of CF.languages is not decidable,a special subset of the relation is decidable, i.e., the sentential form relation, which can be statically checked.Moreover, most of the expressions in actual LFC programs appear to satisfy this relation according to the statistic data of experiments. So, despite that the static type checking is not complete, it undertakes most of the type checking task. Consequently the run-time efficiency is effectively improved. Another feature of the type checking is that it converts the expressions with implicit structures to structured representation. Structure reconstruction technique is presented.

带复杂数据结构的模型检测工具

模型检测是近二十几年来最成功的自动验证技术之一,而模型检测工具的开发是将模型检测和实际相结合的关键.为了有效地对涉及到复杂数据类型的并发传值系统进行模型检测,总结了以扩展的带赋值符号迁移图和模态图分别作为并发系统和逻辑公式的语义模型来实现模型检测工具的工作,特别是将复杂数据结构引入传值进程定义语言和带赋值符号迁移图.同时结合实际例子说明模型检测工具的有效性.

图像图形文字混合处理系统PANDA的设计与实现

本文描述了图像、图形、文字混合处理系统PANDA的设计与实现技术。详细讨论了PANDA系统的数据结构组织方法,其中包括多文件、多窗口处理的结构设计以及动态的数据结构设计,同时给出了PANDA系统在其实现过程中所使用的一些关键处理技术。

Numerical analysis and comparison of three metal-oxide-type super-resolution near field structures

Based on the Fresnel-Kirchkoff diffraction theory, we build up a Gaussian diffraction model of metal-oxide-type super-resolution near field structure (super-RENS), which can describe far field optical properties. The spectral contrast induced by refractive index and the structural changes in AgOx, PtOx and PdOx thin films, which are the key functional layers in super-RENS, are studied by using this model. Comparison results indicate that the spectral contrast intensively on laser-induced distribution and change of the refractive index in the metal-oxide films. The readout mechanism of the metal-oxide-type super-RENS optical disc is further clarified. This Gaussian diffraction model can be used as a simple and effective method for choosing proper active materials in super-RENS.

Quantitative relationship between chromatographic retentions and molecular structures of polychlorinated dibenzo-p-dioxins (PCDDs)

A new approach to study the quantitative relationships between chromatographic retentions and molecular structures of polychlorinated dibenzo-p-dioxins (PCDDs) is described. The retention equations of PCDDs log k' = A + B/T in gas chromatography (GC) are used to evaluate the properties of the regression coefficients A and B, which have been widely accepted as highly reliable chromatographic retentions. The quantitative relationships between the A, B values and the molecular structures are found. The molecular descriptors given for the first time in this article are very effective. As a result, the regression equations are derived with correlation coefficients greater than 0.9995. The A, B values of PCDDs with no standards available have been predicted according to these relationships. They are very useful in chromatographic identification. The retention times of all PCDDs can be conveniently predicted at any temperature program. Compared with the data obtained from the relevant experiments, the results of prediction are very accurate. (C) 2000 Elsevier Science Ltd. All rights reserved.

Cathodoluminescence study of GaN-based film structures

GaN films grown on sapphire substrate with an emphasis on epitaxial lateral overgrown (ELOG) layers with an array of rhombic shaped mask area as well as InGaN/GaN MQW laser diode layer structures were investigated by cathodoluminescence (CL) spectroscopy and CL imaging at room and low temperatures. The microscopic imaging with a high-spatial resolution clearly reveals the distribution of threading dislocations and point defects in ELOG GaN films. The secondary electron and CL data measured on cleaved faces of laser diodes are analyzed in consideration with luminescence mechanisms in semiconductor heterostructures and around the p - n junction, providing important information on the defects and carrier dynamics in laser diode devices.

Electronic structures and mechanical properties of uranium monocarbide from first-principles LDA plus U and GGA plus U calculations

The electronic structure, elastic constants, Poisson's ratio, and phonon dispersion curves of UC have been systematically investigated from the first-principles calculations by the projector-augmented-wave (PAW) method. In order to describe precisely the strong on-site Coulomb repulsion among the localized U 5f electrons, we adopt the local density approximation (LDA) + U and generalized gradient approximation (GGA) + U formalisms for the exchange correlation term. We systematically study how the electronic properties and elastic constants of UC are affected by the different choice of U as well as the exchange-correlation potential. We show that by choosing an appropriate Hubbard U parameter within the GGA + U approach, most of our calculated results are in good agreement with the experimental data. Therefore. the results obtained by the GGA + U with effective Hubbard parameter U chosen around 3 eV for UC are considered to be reasonable. (C) 2009 Elsevier B.V. All rights reserved.

Interface-related in-plane optical anisotropy in GaAs/AlxGa1-xAs single-quantum-well structures studied by reflectance difference spectroscopy

The in-plane optical anisotropies of a series of GaAs/AlxGa1-xAs single-quantum-well structures have been observed at room temperature by reflectance difference spectroscopy. The measured degree of polarization of the excitonic transitions is inversely proportional to the well width. Numerical calculations based on the envelope function approximation incorporating the effect of C-2v-interface symmetry have been performed to analyze the origin of the optical anisotropy. Good agreement with the experimental data is obtained when the optical anisotropy is attributed to anisotropic-interface structures. The fitted interface potential parameters are consistent with predicted values.

Conduction band offset and electron effective mass in GaInNAs/GaAs quantum-well structures with low nitrogen concentration

We have investigated the optical transitions in Ga1-yInyNxAs1-x/GaAs single and multiple quantum wells using photovoltaic measurements at room temperature. From a theoretical fit to the experimental data, the conduction band offset Q(c), electron effective mass m(e)*, and band gap energy E-g were estimated. It was found that the Q(c) is dependent on the indium concentration, but independent on the nitrogen concentration over the range x=(0-1)%. The m(e)* of GaInNAs is much greater than that of InGaAs with the same concentration of indium, and increases as the nitrogen concentration increases up to 1%. Our experimental results for the m(e)* and E-g of GaInNAs are quantitatively explained by the two-band model based on the strong interaction of the conduction band minimum with the localized N states. (C) 2001 American Institute of Physics.

Electronic structures of GaAs/AlAs lateral superlattices

The electronic energy subbands and minigaps in lateral superlattices (LSLs) have been calculated by the plane-wave expansion method. The effect of the lateral modulation on the critical well width at which an indirect-direct (X-Gamma) optical transition occurs in the LSLs is investigated. Our theoretical results are in agreement with the available experimental data. Totally at variance with the previous variation calculational results, the minigaps between the first two subbands in LSLs, as functions of the modulation period, exhibit a maximum value at a specific length and disappear on decreasing the modulation period further. The modulations of several types of lateral potential are also evaluated; the indication is that the out-of-phase modulation on either side of the wells is the strongest while the in-phase modulation is the weakest. Our calculations also show that the effect of the difference between the effective masses of the electrons in the different materials on the subband structures is significant.

THEORETICAL CALCULATION FOR SHUBNIKOV-DEHAAS OSCILLATIONS IN DEEP MESA STRUCTURES

We have used the rectangular confinement potential to describe Shubnikov-deHaas oscillations produced by one-dimensional electrons confined in deep mesa structures. The edge distortion of the confinement potential caused by electrostatic image forces is taken into account. The model contains no fitting parameters and relates well with experimental data. The comparison with earlier reported parabolic model is presented,

High-spin isomeric structures in exotic odd-odd nuclei: Exploration of the proton drip line and beyond

We investigate the role of two-quasiparticle isomeric states along the proton drip line, using configuration-constrained potential-energy-surface calculations. In contrast to even-even nuclei, odd-odd nuclei can have coexisting low-lying two-quasiparticle states. The low excitation energy and high angular momentum can lead to long-lived isomers. Also, because of the hindrance by spin selection, the probabilities of beta and proton decays from high-spin isomers can be reduced significantly. The present calculations reproduce reasonably well the available data for observed isomers in such nuclei. Unobserved high-spin isomers are predicted, which could be useful for future experimental studies of exotic nuclei at and beyond the proton drip line.

Syntheses, crystal structures, visible and near-IR luminescent properties of ternary lanthanide (Dy3+, Tm3+) complexes containing 4,4,4-trifluoro-1-phenyl-1,3-butanedione and 1,10-phenanthroline

The ligands 4,4,4-trifluoro-1-phenyl-1.3-butanedione (Hbfa) and 1,10-phenanthroline (phen) were used to prepare ternary lanthanide (Ln) complexes [Dy(bfa)(3)phen and Tm(bfa)(3)phen]. Crystal data: Dy(bfa)(3)phen C(42)H(26)FqN(2)O(6)Dy, triclinic, P (1) over bar, a= 9.9450(6) angstrom, b = 14.0944(9) angstrom, c = 14.6043(9) angstrom, alpha = 82.104(1)degrees, beta = 87.006(1)degrees, gamma = 76.490(1)degrees, V = 1971.1(2)angstrom(3), Z = 2; Tm(bfa)(3)phen C42H26F9N2O6Tm, triclinic, P (1) over bar, a = 9.898(5)angstrom, b = 13.918(5)angstrom, c = 14.753(5)angstrom, a = 83.517(5)degrees, alpha = 86.899(5)degrees, gamma = 76.818(5)degrees, V = 1965.3(14)angstrom(3), Z = 2. The coordination number of the central Ln(3+) (Ln = Dy, Tm) ion is eight, with six oxygen atoms from three Hbfa ligands and two nitrogen atoms from the phen ligand.

Electronic structures and chemical bonding in diatomic ScX to ZnX (X = S, Se, Te)

Bond distances, vibrational frequencies, electron affinities, ionization potentials, dissociation energies, and dipole moments of the title molecules in neutral, positively, and negatively charged ions were studied using density functional method. Ground electronic state was assigned for each molecule. The bonding patterns were analyzed and compared with both the available data and across the series. It was found that, besides ionic component, covalent bonds are formed between the metal s, d orbitals, and the p orbital of S, Se, and Te. For neutral and cationic molecules, the covalent character increases from ScX to CrX and from FeX to CuX with an exception of decrease at MnX and ZnX, while for anionic molecules, the trend is not obvious. For both neutral and charged molecules, the sulfides have the shortest bond distance and largest vibrational frequency, while tellurides have the largest bond distance and smallest vibrational frequency. For neutral and anionic molecules, the dissociation energy of sulfides is the largest, that of tellurides is the smallest, while this only remains true for cationic molecules from ScX+ to FeX+.