Diversity Variation of Ground-dwelling Beetle(Insecta:Coleoptera) Communities in Jiaozi Mountain, Yunnan, China

对云南轿子雪山自然保护区地表甲虫物的种组成及生物多样性季节变化进行了连续跟踪调查.调查结果如下:(1)通过对4种典型微环境样地(草地、灌丛、林地以及农田生态系统)连续3次跟踪连续调查,共获得标本2451头,分别隶属于24科.其中步甲科(Carabidae)为优势类群,占总数的62.10%;隐翅虫科(Staphylinidae)其次,占12.77%.可能由于海拔、气温等因素影响,该地区昆虫活动高峰期较短.(2)通过对4种典型微生态环境中地表甲虫的生物多样性的比较,表明不同生境内甲虫的多样性指数存在动态变化,在不同生境片区内甲虫存在迁移活动,甲虫多在灌丛中越冬,并随季节及食物源迁移.

Species identification of Chinese sturgeon using acoustic descriptors and ascertaining their spatial distribution in the spawning ground of Gezhouba Dam

This study has developed an improved subjective approach of classification in conjunction with Step wise DFA analysis to discriminate Chinese sturgeon signals from other targets. The results showed that all together 25 Chinese sturgeon echo-signals were detected in the spawning ground of Gezhouba Dam during the last 3 years, and the identification accuracy reached 90.9%. In Stepwise DFA, 24 out of 67 variables were applied in discrimination and identification. PCA combined with DFA was then used to ensure the significance of the 24 variables and detailed the identification pattern. The results indicated that we can discriminate Chinese sturgeon from other fish species and noise using certain descriptors such as the behaviour variables, echo characteristics and acoustic cross-section characteristics. However, identification of Chinese sturgeon from sediments is more difficult and needs a total of 24 variables. This is due to the limited knowledge about the acoustic-scattering properties of the substrate regions. Based on identified Chinese sturgeon individuals, 18 individuals were distributed in the region between the site of Gezhouba Dam and Miaozui reach, with a surface area of about 3.4 km(2). Seven individuals were distributed in the region between Miaozui and Yanshouba reach, with a surface area of about 13 km(2).

Effects of Organic-Rich Sediment and Below-Ground Sulfide Exposure on Submerged Macrophyte, Hydrilla verticillata

The effects of organic-rich sediment and sulfide exposure on Hydrilla verticillata were investigated. The organic richness of sediment was simulated by adding sucrose into sediments, and sulfide exposure was conducted by adding sodium sulfide to plant roots. The length, biomass and density of shoot reduced in the sucrose-amended sediments, and the largest reduction occurred in the highest 1.0% addition treatment by 84.2%, 56.7% and 92.4%, respectively. However, the 0.1% addition treatment stimulated the growth of root. The effects of below-ground sulfide exposure on the physiological activities of H. verticillata were determined by adding sulfide to the below-ground tissue. Significantly inhibitory effects of sulfide were observed on plant photosynthesis, root carbohydrate and nitrogen synthetic reserves. The net photosynthetic rates, soluble carbohydrate and soluble protein contents in root were reduced by 104%, 71.8% and 49.8%, respectively, in the 0.6 mM sulfide treatment.

Mechanical and chemical bonding properties of ground state BeH2

The crystal structure, mechanical properties and electronic structure of ground state BeH2 are calculated employing the first-principles methods based on the density functional theory. Our calculated structural parameters at equilibrium volume are well consistent with experimental results. Elastic constants, which well obey the mechanical stability criteria, are firstly theoretically acquired. The bulk modulus B, Shear modulus G, Young's modulus E, and Poisson's ratio upsilon are deduced from the elastic constants. The bonding nature in BeH2 is fully interpreted by combining characteristics in band structure, density of states, and charge distribution. The ionicity in the Be-H bond is mainly featured by charge transfer from Be 2s to H 1s atomic orbitals while its covalency is dominated by the hybridization of H 1s and Be 2p states. The Bader analysis of BeH2 and MgH2 are performed to describe the ionic/covalent character quantitatively and we find that about 1.61 (1.6) electrons transfer from each Be (Mg) atom to H atoms.

First-principles study of ground-state properties and high pressure behavior of ThO2

The mechanical properties, electronic structure and phonon dispersion of ground state ThO2 as well as the structure behavior up to 240 GPa are studied using first-principles density-functional theory. Our calculated elastic constants indicate that both the ground-state fluorite structure and high pressure cotunnite structure of ThO2 are mechanically stable. The bulk modulus, shear modulus, and Young's modulus of cotunnite ThO2 are all smaller by approximately 25% compared with those of fluorite ThO2. The Poisson's ratios of both structures are approximately equal to 0.3 and the hardness of fluorite ThO2 is 22.4 GPa. The electronic structure and bonding nature of fluorite ThO2 are fully analyzed, and show that the Th-O bond displays a mixed ionic/covalent character. The phase transition from the fluorite to cotunnite structure is calculated to occur at the pressure of 26.5 GPa, consistent with recent experimental measurement by ldiri et al. [1]. For the cotunnite phase it is further predicted that an isostructural transition takes place in the pressure region of 80-130 GPa.

Tuning of the two electron states in quantum rings through the spin-orbit interaction

The effect of the Coulomb interaction on the energy spectrum and anisotropic distribution of two electron states in a quantum ring in the presence of Rashba spin-orbit interaction (RSOI) and Dresselhaus SOI (DSOI) is investigated in the presence of a perpendicular magnetic field. We find that the interplay between the RSOI and DSOI makes the single quantum ring behaves like a laterally coupled quantum dot and the interdot coupling can be tuned by changing the strengths of the SOIs. The interplay can lead to singlet-triplet state mixing and anticrossing behavior when the singlet and triplet states meet with increasing magnetic field. The two electron ground state displays a bar-bell-like spatial anisotropic distribution in a quantum ring at a specific crystallographic direction, i.e., [110] or [1 (1) over bar0], which can be switched by reversing the direction of the perpendicular electric field. The ground state exhibits a singlet-triplet state transition with increasing magnetic field and strengths of RSOI and DSOI. An anisotropic electron distribution is predicted which can be detected through the measurement of its optical properties.

Carrier capture by threading dislocations in (In,Ga)N/GaN heteroepitaxial layers

Using spatially resolved cathodoluminescence spectroscopy, we investigate the spatial luminescence distribution in a fully strained (In,Ga)N layer, in particular, its correlation with the distribution of threading dislocations (TDs). Regarding the impact of TDs on the luminescence properties, we can clearly distinguish between pure edge-type TDs and TDs with screw component. At the positions of both types of TDs, we establish nonradiative recombination sinks. The radius for carrier capture is at least four times larger for TDs with screw component as for pure edge-type TDs. The large capture radius of the former is due to a spiral-like growth mode resulting in an increase in the In content in the center of the spiral domains in comparison to their periphery.

Raman scattering characterization of Mn composition and strain in Ga1-xMnxSb/GaSb epitaxial layers

Raman scattering (RS) experiments have been performed for simultaneous determination of Mn composition and strain in Ga1-xMnxSb thin films grown on GaSb substrate by liquid phase epitaxy technique. The Raman spectra obtained from various Ga1-xMnxSb samples show only GaSb-like phonon modes whose frequency positions are found to have Mn compositional dependence. With the combination of epilayer strain model, RS and energy dispersive x-ray (EDX) experiments, the compositional dependence of GaSb-like LO phonon frequency is proposed both in strained and unstrained conditions. The proposed relationships are used to evaluate Mn composition and strain from the Ga1-xMnxSb samples. The results obtained from the RS data are found to be in good agreement with those determined independently by the EDX analysis. Furthermore, the frequency positions of MnSb-like phonon modes are suggested by reduced-mass model. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

The influence of Schottky contact metals on the strain of AlGaN barrier layers

Ir and Ni Schottky contacts on strained Al0.25Ga0.75N/GaN heterostructures, and the Ni Schottky contact with different areas on strained Al0.3Ga0.7N/GaN heterostructures have been prepared. Using the measured capacitance-voltage curves and the current-voltage curves obtained from the prepared Schottky contacts, the polarization charge densities of the AlGaN barrier layer for the Schottky contacts were analyzed and calculated by self-consistently solving Schrodinger's and Poisson's equations. It is found that the polarization charge density of the AlGaN barrier layer for the Ir Schottky contact on strained Al0.25Ga0.75N/GaN heterostructures is different from that of the Ni Schottky contact, and the polarization charge densities of the AlGaN barrier layer for Ni Schottky contacts with different areas on strained Al0.3Ga0.7N/GaN heterostructures are different corresponding to different Ni Schottky contact areas. As a result, the conclusion can be made that Schottky contact metals on strained AlGaN/GaN heterostructures have an influence on the strain of the AlGaN barrier layer. (C) 2008 American Institute of Physics.

Scanning electron microscopy observation of in-device InAs/AlAs quantum dots by selective etching of capping layers

Self-assembled InAs/AlAs quantum dots embedded in a resonant tunneling diode device structure are grown by molecular beam epitaxy. Through the selective etching in a C6H8O7 center dot H2O-K3C6H5O7 center dot H2O-H2O2 buffer solution, 310 nm GaAs capping layers are removed and the InAs/AlAs quantum dots are observed by field-emission scanning electron microscopy. It is shown that as-fabricated quantum dots have a diameter of several tens of nanometers and a density of 10(10) cm(-2) order. The images taken by this means are comparable or slightly better than those of transmission electron microscopy. The undercut of the InAs/AlAs layer near the edges of mesas is detected and that verifies the reliability of the quantum dot images. The inhomogeneous oxidation of the upper AlAs barrier in H2O2 is also observed. By comparing the morphologies of the mesa edge adjacent regions and the rest areas of the sample, it is concluded that the physicochemical reaction introduced in this letter is diffusion limited.

Fabrication and optical optimization of spot-size converters with strong cladding layers

A silicon-on-insulator (SOI) optical fiber-to-waveguide spot-size converter (SSC) overlaid with specially treated silica is investigated for integrated optical circuits. Unlike the conventional process of simply depositing the hot silica on silicon waveguides, two successive layers of silicon dioxide were grown on etched SSC structures by PECVD (plasma-enhanced chemical vapor deposition). The two layers have 0.8% index contrast and supply stronger cladding for an incident light beam. Additionally, this process is able to reduce the effective refractive index of the input mode to less than 1.47 (extremely close to that of the fiber), substantially weakening the unwanted back reflection. Exploiting this technology, it was demonstrated that the SSC showed a theoretical low mode mismatch loss of 1.23 dB for a TE-like mode and has an experimental coupling efficiency of 66%.

Spin states in InAs/AlSb/GaSb semiconductor quantum wells

We investigate theoretically the spin states in InAs/AlSb/GaSb broken-gap quantum wells by solving the Kane model and the Poisson equation self-consistently. The spin states in InAs/AlSb/GaSb quantum wells are quite different from those obtained by the single-band Rashba model due to the electron-hole hybridization. The Rashba spin splitting of the lowest conduction subband shows an oscillating behavior. The D'yakonov-Perel' spin-relaxation time shows several peaks with increasing the Fermi wave vector. By inserting an AlSb barrier between the InAs and GaSb layers, the hybridization can be greatly reduced. Consequently, the spin orientation, the spin splitting, and the D'yakonov-Perel' spin-relaxation time can be tuned significantly by changing the thickness of the AlSb barrier.

Spin splitting of conduction subbands in Al0.3Ga0.7As/GaAs/AlxGa1-x As/Al0.3Ga0.7As step quantum wells

By means of the transfer matrix technique, interface-induced Rashba spin splitting of conduction subbands in Al0.3Ga0.7As/GaAs/AlxGa1-xAs/Al0.3Ga0.7As step quantum wells which contain internal structure inversion asymmetry introduced by the insertion of AlxGa1-xAs step potential is investigated theoretically in the absence of electric field and magnetic field. The dependence of spin splitting on the well width, step width and Al concentration is investigated in detail. We find that the sign of the first excited subband spin splitting changes with well width and step width, and is opposite to that of the ground subband under certain conditions. The sign and strength of the spin splitting are shown to be sensitive to the components of the envelope function at three interfaces. Copyright (C) EPLA, 2009

Molecular Beam Epitaxy of GaSb on GaAs Substrates with AlSb Buffer Layers

We investigate the molecular beam epitaxy growth of GaSb films on GaAs substrates using AlSb buffer layers. Optimization of AlSb growth parameter is aimed at obtaining high GaSb crystal quality and smooth GaSb surface. The optimized growth temperature and thickness of AlSb layers are found to be 450 degrees C and 2.1 nm, respectively. A rms surface roughness of 0.67 nm over 10 x 10 mu m(2) is achieved as a 0.5 mu m GaSb film is grown under optimized conditions.

Determination of the tilt and twist angles of curved GaN layers by high-resolution x-ray diffraction

The full-width at half-maximum (FWHM) of an x-ray rocking curve (XRC) has been used as a parameter to determine the tilt and twist angles of GaN layers. Nevertheless, when the thickness of GaN epilayer reaches several microns, the peak broadening due to curvature becomes non-negligible. In this paper, using the (0 0 l), l = 2, 4, 6, XRC to minimize the effects of wafer curvature was studied systematically. Also the method to determine the tilt angle of a curved GaN layer was proposed while the Williamson-Hall plot was unsuitable. It was found that the (0 0 6) XRC-FWHM had a significant advantage for high-quality GaN layers with the radius curvature of r less than 3.5 m. Furthermore, an extrapolating method of gaining a reliable tilt angle has also been proposed, with which the calculated error can be improved by 10% for r < 2 m crystals compared with the (0 0 6) XRC-FWHM. In skew geometry, we have demonstrated that the twist angles deriving from the (2 0 4) XRC-FWHM are in accord with those from the grazing incidence in-plane diffraction (IP-GID) method for significantly curved samples.