Interaction of a surface acoustic wave with a two-dimensional electron gas

When a surface acoustic wave propagates on the surface of a GaAs semiconductor, coupling between electrons in the two-dimensional electron gas beneath the interface and the elastic host crystal through piezoelectric interaction will attenuate the SAW. The coupling coefficient is calculated for the SAW propagating along an arbitrary direction. It is found that the coupling strength is largely dependent on the propagating direction. When the SAW propagates along the [011] direction, the coupling becomes quite weak.Comment: 3 figure

Accurate Reconstruction of Molecular Phylogenies for Proteins Using Codon and Amino Acid Unified Sequence Alignments (CAUSA)

Based on molecular clock hypothesis, and neutral theory of molecular evolution, molecular phylogenies have been widely used for inferring evolutionary history of organisms and individual genes. Traditionally, alignments and phylogeny trees of proteins and their coding DNA sequences are constructed separately, thus often different conclusions were drawn. Here we present a new strategy for sequence alignment and phylogenetic tree reconstruction, codon and amino acid unified sequence alignment (CAUSA), which aligns DNA and protein sequences and draw phylogenetic trees in a unified manner. We demonstrated that CAUSA improves both the accuracy of multiple sequence alignments and phylogenetic trees by solving a variety of molecular evolutionary problems in virus, bacteria and mammals. Our results support the hypothesis that the molecular clock for proteins has two pointers existing separately in DNA and protein sequences. It is more accurate to read the molecular clock by combination (additive) of these two pointers, since the ticking rates of them are sometimes consistent, sometimes different. CAUSA software were released as Open Source under GNU/GPL license, and are downloadable free of charge from the website www.dnapluspro.com

Simulation of random field samples directly from sparse measurements using Bayesian compressive sampling and Karhunen-Loève expansion

Geotechnical materials (e.g., soils and rocks) are natural materials, and they are affected by many spatially varying factors during the geological process, such as properties of their parent materials, weathering and erosion processes, transportation agents, and sedimentation conditions. Geotechnical data therefore exhibit spatial variability, and to some extent, are unique in every site. In recent years, random field has been increasingly used to model spatial variability of geotechnical data. In conventional frequentist approach, measurement data at a specific site are used to estimate random field parameters, such as mean and standard deviation, as well as parameters (e.g., correlation length) of a pre-determined parametric form of correlation function (e.g., an exponential correlation function). Estimation of these random field parameters, particularly the correlation length, and selection of the suitable parametric form of correlation function generally require extensive measurements from a specific site, which are generally not available in geotechnical engineering practice. This paper presents a random field generator that is able to simulate random field samples directly from sparse measurements, bypassing the difficulty in the estimation of correlation function and its parameters. The proposed generator is based on Bayesian compressive sensing/sampling and Karhunen–Loève expansion. The proposed method is illustrated and validated using simulated geotechnical data. It is also compared with the conventional random field models. The results show that the proposed generator can rationally simulate the geotechnical spatial variability at a specific site from sparse measurements.The work described in this paper was supported by grants from the Research Grants Council of the Hong Kong Special Administrative Region, China (Project No. 9042331 (CityU 11225216) and Project No. 9042516 (CityU 11213117)). The financial support is gratefully acknowledged

Three lanthanide complexes with mixed salicylate and 1,10-phenanthroline: syntheses, crystal structures, and luminescent/magnetic properties

Three new lanthanide complexes incorporating salicylate (HSA or SA) and 1,10-phenanthroline (phen), Ln(3)(HSA)(5)(SA)(2)(phen)(3) [Ln=Ho (1) and Er (2)], and Sm-2(HSA)(2)(SA)(2)(phen)(3) (3), have been synthesized. X-ray structural analysis reveals that 1 and 2 are isostructural with a trinuclear pattern, and 3 exhibits a binuclear structure. Comparison of the structural differences between 1/2 and 3 suggests that the identity of metal plays an important role in construction of such complexes. The magnetic properties of 1 are discussed. Moreover, 2 and 3 are both photoluminescent materials, and their emission properties are closely related to their corresponding Ln(III) centers