Comparison of stationary acoustic monitoring and visual observation of finless porpoises

The detection performance regarding stationary acoustic monitoring of Yangtze finless porpoises Neophocaena phocaenoides asiaeorientalis was compared to visual observations. Three stereo acoustic data loggers (A-tag) were placed at different locations near the confluence of Poyang Lake and the Yangtze River, China. The presence and number of porpoises were determined acoustically and visually during each 1-min time bin. On average, porpoises were acoustically detected 81.7 +/- 9.7% of the entire effective observation time, while the presence of animals was confirmed visually 12.7 +/- 11.0% of the entire time. Acoustic monitoring indicated areas of high and low porpoise densities that were consistent with visual observations. The direction of porpoise movement was monitored using stereo beams, which agreed with visual observations at all monitoring locations. Acoustic and visual methods could determine group sizes up to five and ten individuals, respectively. While the acoustic monitoring method had the advantage of high detection probability, it tended to underestimate group size due to the limited resolution of sound source bearing angles. The stationary acoustic monitoring method proved to be a practical and useful alternative to visual observations, especially in areas of low porpoise density for long-term monitoring.

Improvement and observation of immunoelectron microscopic method for the localization of frog Rana grylio virus (RGV) in infected fish cells

In this paper, to understand the roles of amorphous structures which were observed within the viromatrix of Rana grylio virus (RGV), an improved immunoelectron microscopy (IEM) method was developed to detect the localization of RGV in carp Epithelipma papulosum cyprinid (EPC) cells. Infected EPC cells were fixed with 4% paraformaldehyde-0.25% glutaraldehyde mixture, dehydrated completely, and embedded in LR White resin. This method allowed good ultrastructural preservation and specific labeling with anti-RGV antibodies. The results of IEM showed that colloidal gold mainly bound to the capsids of viral particles at the stage of viral assembly, while during the viral maturation colloidal gold bound to the envelop of virions. In addition, within the viromatrix, the amorphous structures, including dense floccules, membranous materials and tubules, also had strong colloidal gold signals, revealing that those amorphous structures were participated in RGV assembly. In contrast, no significant gold labeling signals were obtained in negative controls. The present study not only provided further evidence that amorphous structures within the viromatrix were involved in the process of RGV assembly, but also developed an improved IEM method for studying the interaction between iridovirus and host cells. (C) 2006 Elsevier Ltd. All rights reserved.

A passive acoustic monitoring method applied to observation and group size estimation of finless porpoises

The present study aimed at determining the detection capabilities of an acoustic observation system to recognize porpoises under local riverine conditions and compare the results with sighting observations. Arrays of three to five acoustic data loggers were stationed across the main channel of the Tian-e-zhou Oxbow of China's Yangtze River at intervals of 100-150 m to record sonar. signals of free-ranging finless porpoises (Neophocaena phocaenoides). Acoustic observations, concurrent with visual observations, were conducted at two occasions on 20-22 October 2003 and 17-19 October 2004. During a total of 42 h of observation, 316 finless porpoises were sighted and 7041 sonar signals were recorded by loggers. The acoustic data loggers recorded ultrasonic signals of porpoises clearly, and detected the presence of porpoises with a correct detection level of 77.6% and a false alarm level of 5.8% within an effective distance of 150 m. Results indicated that the stationed passive acoustic observation method was effective in detecting the presence of porpoises and showed potential in estimating the group size. A positive linear correlation between the number of recorded signals and the group size of sighted porpoises was indicated, although it is faced with some uncertainty and requires further investigation. (C) 2005 Acoustical Society of America.

Structure of macrozoobenthos of the East Dongting nature reserve, with emphasis on relationships with environmental variables

Ecological survey of macrozoobenthos assemblages was carried out at 32 sites in the East Dongting Nature Reserve, located in the northern region of the East Dongting Lake in the middle basin of the Yangtze River, China. All total 51 taxa including 18 oligochaetes, 15 mollusks, 14 insects and four other animals were recorded. Mollusks composed the dominant group and accounted for more than 70% of the total abundance. Assemblages were composed mainly of scrapers (66.7%) and collector-gatherers (nearly 20%), and to a lesser extent collector-filterers (roughly 12%), predators (ca. 7%), and shredders (ca. 6%). Two-way indicator species analysis, detrended correspondence, and canonical correspondence analysis (CCA) were employed to identify the relationships between macrozoobenthos assemblages and environmental variables. Thirty-two sites were separated into four site groups based on composition and relative abundance of benthic macroinvertebrates. CCA detected that water depth, pH, conductivity, SiO2, total nitrogen, total phosphorus, alkalinity, hardness, and Ca2+, were significant environmental factors influencing the pattern of macozoobenthos. In this minimal subset, water depth, pH, alkalinity and hardness were the most influential variables.

Selection and ultrastructural observation of a high-CO2-requiring mutant of cyanobacterium Synechococcus sp PCC7942

A high-CO2-requiring mutant of Synechococcus sp. PCC7942 las been isolated after chemical mutagenesis of ethyl methane sulphonate (EMS). It was able to grow at 4% CO2, but not under ambient CO2. The initial screening of the mutant showed that the genetic reversion rate was about 10(-7) and death occurred 2 -3 days after being transferred from 4% CO2 to the ambient air. Its photosynthetic dependence on external dissolved inorganic carbon was higher than that of the wild type cells, but its carbonic anhydrase activity was comparatively low. In the ultrastructural level, various types of aberrant carboxysomes appeared in the mutant cells: rod-shaped carboxysomes, irregular carboxysomes and the "empty-inclusion carboxysomes" with increasing number of glycogen granules surrounding the thylakoids. All these alterations indicated that the mutant was defective in utilizing the external CO2. The induction of carboxysomes by lower levels of CO2 and the biogenesis of carboxysomes are herein discussed.

Direct observation of excitonic polaron in InAs/GaAs quantum dots

We report a direct observation of excitonic polaron in InAs/GaAs quantum dots using the photoluminescence (PL) spectroscopy. We observe that a new peak s' emerges below the s-shell which has anomalous temperature dependence emission energy. The peak s' anticrosses with s at a certain temperature, with a large anticrossing gap up to 31 meV. The behavior of the new peak, which cannot be interpreted using Huang-Rhys model, provides a direct evidence for strong coupling between exciton and LO phonons, and the formation of the excitonic polaron. The strong coupling between exciton and phonons opens a way to coherently control the polaron states.

Direct observation of coherent spin transfer processes in an InGaAs/GaAs quantum well via two-color time-resolved Kerr rotation measurements

A two-color time-resolved Kerr rotation spectroscopy system was built, with a femtosecond Ti:sapphire laser and a photonic crystal fiber, to study coherent spin transfer processes in an InGaAs/GaAs quantum well sample. The femtosecond Ti:sapphire laser plays two roles: besides providing a pump beam with a tunable wavelength, it also excites the photonic crystal fiber to generate supercontinuum light ranging from 500 nm to 1600 nm, from which a probe beam with a desirable wavelength is selected with a suitable interference filter. With such a system, we studied spin transfer processes between two semiconductors of different gaps in an InGaAs/GaAs quantum well sample. We found that electron spins generated in the GaAs barrier were transferred coherently into the InGaAs quantum well. A model based on rate equations and Bloch-Torrey equations is used to describe the coherent spin transfer processes quantitatively. With this model, we obtain an effective electron spin accumulation time of 21 ps in the InGaAs quantum well.

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.

Nature of interfacial defects and their roles in strain relaxation at highly lattice mismatched 3C-SiC/Si (001) interface

Misfit defects in a 3C-SiC/Si (001) interface were investigated using a 200 kV high-resolution electron microscope with a point resolution of 0.194 nm. The [110] high-resolution electron microscopic images that do not directly reflect the crystal structure were transformed into the structure map through image deconvolution. Based on this analysis, four types of misfit dislocations at the 3C-SiC/Si (001) interface were determined. In turn, the strain relaxation mechanism was clarified through the generation of grow-in perfect misfit dislocations (including 90 degrees Lomer dislocations and 60 degrees shuffle dislocations) and 90 partial dislocations associated with stacking faults. (C) 2009 American Institute of Physics. [doi:10.1063/1.3234380]

Observation of the current-voltage plateau-like structure of resonant tunnelling diode with prewells under different magnetic fields

We have grown resonant tunnelling diodes (RTDs) with different sized emitter prewells and without a prewell. The current-voltage (I-V) characteristics of them in different magnetic fields were investigated. Two important phenomena were observed. First, a high magnetic field can destroy the plateau-like structure in the I-V curves of the RTD. This phenomenon is ascribed to the fact that the high magnetic field will demolish the coupling between the energy level in the main quantum well and that in the emitter quantum well or in the prewell. Secondly, the existence and size of the prewell are also important factors influencing the plateau-like structure.

Observation of antiphase states in a passively Q-switched multimode microchip Yb : YAG laser with a GaAs saturable absorber

Antiphase dynamics has been observed experimentally for the laser modes operation in a laser-diode-pumped Q-switched microchip Yb:YAG laser with GaAs as a saturable absorber in the presence of spatial hole-burning. The Q-switched pulses sequences of two modes at different pump power have been obtained. The experimental results have shown that the pulses sequences displayed classic antiphase dynamics. (C) 2003 Elsevier B.V. All rights reserved.

Experimental observation of resonant modes in GaInAsP microsquare resonators

GaInAsP-InP microsquare resonators with InP pedestals are fabricated by two-step chemical etching, and obvious mode peaks are observed in the photoluminescence spectra of the resonators. The mode Q-factors about 500 are obtained for a microsquare resonator with the side length of 7 mu m. The experimental mode interval is in agreement with that predicted by the light ray method based on the cavity length, instead of that of the whispering-gallery (WG)-like modes, which has mode interval twice of that determined by the cavity length. The finite-difference time-domain simulation shows that a little asymmetry may greatly reduce the difference of the Q-factors between the WG-like modes and the other modes.

Observation of intershell and hybridized energy states in InAs/GaAs quantum dots

We have investigated the evolution of exciton state filling as a function of excitation power density in InAs/GaAs quantum dots (QDs). In addition to the emission bands of exciton recombination corresponding to the atom-like S, P, and D, etc. shells of quantum dots, it was observed that some extra states, P-' (between the S and P shells) and D-' (between the P and D shells), appear in the spectra with increasing number of excitons occupying the QDs. The emergence of these intershell excitonic levels is an experimental demonstration of strong exciton-exciton exchange interaction and coupling as well as state mixing and hybridization of a multiexciton system in quantum dots.

Observation of electric current induced by optically injected spin current

Linearly polarized light at normal incidence injects a spin current into a strip of two-dimensional electron gas with Rashba spin-orbit coupling. The authors report observation of an electric current when such light is shed on the vincinity of the junction in a crossbar-shaped InGaAs/InAlAs quantum well Rashba system. The polarization dependence of this electric current was experimentally observed to be the same as that of the spin current. The authors attribute the observed electric current to the scattering of the optically injected spin current at the crossing. (c) 2007 American Institute of Physics.