Electron concentration dependence of exciton localization and freeze-out at local potential fluctuations in InN films

InN films with electron concentration ranging from n similar to 10(17) to 10(20) cm(-3) grown by metal-organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE) were investigated by variable-temperature photoluminescence and absorption measurements. The energy positions of absorption edge as well as photoluminescence peak of these InN samples with electron concentration above 10(18) cm(-3) show a distinct S-shape temperature dependence. With a model of potential fluctuations caused by electron-impurity interactions, the behavior can be quantitatively explained in terms of exciton freeze-out in local potential minima at sufficiently low temperatures, followed by thermal redistribution of the localized excitons when the band gap shrinks with increasing temperature. The exciton localization energy sigma (loc) is found to follow the n (5/12) power relation, which testifies to the observed strong localization effects in InN with high electron concentrations.

Large depth-of-view portable three-dimensional laser scanner and its segmental calibration for robot vision

A portable 3D laser scanning system has been designed and built for robot vision. By tilting the charge coupled device (CCD) plane of portable 3D scanning system according to the Scheimpflug condition, the depth-of-view is successfully extended from less than 40 to 100 mm. Based on the tilted camera model, the traditional two-step camera calibration method is modified by introducing the angle factor. Meanwhile, a novel segmental calibration approach, i.e., dividing the whole work range into two parts and calibrating, respectively, with corresponding system parameters, is proposed to effectively improve the measurement accuracy of the large depth-of-view 3D laser scanner. In the process of 3D reconstruction, different calibration parameters are used to transform the 2D coordinates into 3D coordinates according to the different positions of the image in the CCD plane, and the measurement accuracy of 60 mu m is obtained experimentally. Finally, the experiment of scanning a lamina by the large depth-of-view portable 3D laser scanner used by an industrial robot IRB 4400 is also employed to demonstrate the effectiveness and high measurement accuracy of our scanning system. (C) 2007 Elsevier Ltd. All rights reserved.

WANNIER-STARK LOCALIZATION IN INGAAS/GAAS SUPERLATTICES AND ITS APPLICATION TO ELECTROOPTICAL DEVICES

We have observed Wannier-Stark localization in strained In0.2Ga0.8As/GaAs superlattices by low- and room-temperature photocurrent spectra measurements. The experimental results are well in agreement with the theoretical predictions. A large field-induced modulation response of the absorption edge of the superlattices at room temperature suggests the possibilities of the application to the design of various kinds of electro-optical devices operating at a wavelength of 0.98 mum, based on Wannier-Stark localization effects.

WANNIER LOCALIZATION IN GAAS/GAALAS SUPERLATTICES UNDER ELECTRIC-FIELD

We have studied the Wannier-Stark effect in GaAs/GaAlAs short-period superlattices under applied electric field perpendicular to the layers by room- and low-temperature photocurrent measurements. The changes in the transition intensities with biasing are well fitted to a theoretical calculation based on the finite Kronig-Penney model on which the potential of an applied electric field is superposed. With increasing electric field, the 0h peak grows to a maximum while the -1h and +1h peaks monotonousely decrease. By a comparison of the spectra measured at different temperatures, the two peaks in the room temperature photocurrent spectra at relatively low electric field (1.0 X 10(4) V/cm) are identified to be caused by the Wannier localization effect instead of saddle-point excitons.

Exciton Localization and Delocalization in GaNAs/GaAs Quantum Wells

We have studied exciton localization and delocalization effect in GaNAs/GaAs quantum wells (QWs) grown by molecular beam epitaxy (MBE) using photoluminescence (PL) and timeresolved PL measurements. Studied results suggest that, at low temperature and under a conventional CW excitation, measured PL spectra were dominated by localized exciton (LE) emission caused by potential fluctuations in GaNAs layer. However, under short pulse laser excitation, it is different. An extra high-energy PL peak comes out from GaNAs/GaAs QWs and dominates the PL spectra under high excitation and/or at high temperature. By investigation, we have attributed the new PL peak to the recombination of delocalized excitons in QWs. This recombination process competes with the localized exciton emission, which, we believe, constitutes the "S-shaped" temperature-dependent emission shift often reported in ternary nitrides of InGaN and AlGaN in the literature.

Study on the localization of the electric dipole sources

The research of dipole source localization has great significance in both clinical research and applications. For example, the EEG recording from the scalp is widely used for the localization of sources of electrical activity in the brain. This paper presents a closed formula that describes the electric field of dipoles at arbitrary position, which is a linear transformer called the transfer matrix. The expression of transfer matrix and its many useful characteristics are given, which can be used for the analysis of the electrical fields of dipoles. This paper also presents the closed formula for determining the location and magnitude of single dipole or multi-dipoles according to its electrical field distribution. A calculation result for a single dipole shows that the dipole will be located at the midpoint of a line segment if there are equivalent fields at its two ends.

Localization of Na+-K+ ATPases in Quasi-Native Cell Membranes

Na+-K+ ATPases have been observed and located by in situ AFM and single molecule recognition technique, topography and recognition imaging (TREC) that is a unique technique to specifically identify single protein in complex during AFM imaging. Na+-K+ ATPases were well distributed in the inner leaflet of cell membranes with about 10% aggregations in total recognized proteins. The height of Na+-K+ ATPases measured by AFM is in the range of 12-14 nm, which is very consistent with the cryoelectron microscopy result. The unbinding force between Na+-K+ ATPases in the membrane and anti-ATPases on the AFM tip is about 80 pN with the apparent loading rate at 40 nN/s.

Chromosomal localization and molecular marker development of the lipopolysaccharide and beta-1,3-glucan binding protein gene in the Zhikong scallop Chlamys farreri (Jones et Preston) (Pectinoida, Pectinidae)

Zhikong scallop Chlamys farreri(Jones et Preston) is an economically important species in China. Understanding its immune system would be of great help in controlling diseases. In the present study, an important immunity-related gene, the Lipopolysaccharide and Beta-1,3-glucan Binding Protein (LGBP) gene, was located on C. farreri chromosomes by mapping several lgbp-containing BAC clones through fluorescence in situ hybridization (FISH). Through the localization of various BAC clones, it was shown that only one locus of this gene existed in the genome of C. farreri, and that this was located on the long arm of a pair of homologous chromosomes. Molecular markers, consisting of eight single nucleotide polymorphism (SNPs) markers and one insertion-deletion (indel), were developed from the LGBP gene. Indel marker testing in an F1 family revealed slightly distorted segregation (p = 0.0472). These markers can be used to map the LGBP gene to the linkage map and assign the linkage group to the corresponding chromosome. Segregation distortion of the indel marker indicated genes with deleterious alleles might exist in the surrounding region of the LGBP gene.