Molecular systematics of Xenocyprinae (Teleostei : Cyprinidae): Taxonomy, biogeography, and coevolution of a special group restricted in east Asia

We surveyed mitochondrial DNA (mtDNA) sequence variation in the subfamily Xenocyprinae from China and used these data to estimate intraspecific, interspecific, and intergeneric phylogeny and assess biogeographic scenarios underlying the geographic structure of lineages. We sequenced 1140 bp of cytochrome b from 30 individuals of Xenocyprinae and one putative outgroup (Myxocypris asiaticus) and also sequenced 297 bp of ND4L, 1380 bp of ND4, 68 bp of tRNA(His), and 69 bp of tRNA(Ser) from 17 individuals of Xenocyprinae and the outgroup (M. asiaticus). We detected high levels of nucleotide variation among populations, species, and genera. The phylogenetic analysis suggested that Distoechodon hupeinensis might be transferred to the genus Xenocypris, the taxonomic status of the genus Plagiognathops might be preserved, and species of Xenocypris and Plagiognathops form a monophyletic group that is sister to the genus Distoechodon and Pseudobrama. The introgressive hybridization might occur among the populations of X. argentea and X. davidi, causing the two species to not be separated by mtDNA patterns according to their species identification, and the process and direction of hybridization are discussed. The spatial distributions of mtDNA lineages among populations of Xenocypris were compatible with the major geographic region, which indicated that the relationship between Hubei + Hunan and Fujian is closer than that between Hubei + Hunan and Sichuan, From a perspective of parasite investigation, our data suggested that the fauna of Hexamita in Xenocyprinae could be used to infer the phylogeny of their hosts. (C) 2001 Academic Press.

Peak identification for PCDD/Fs in environmental samples at different temperature programs

A method has been developed for peak recognition of 136 polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) at different temperature programs. Their retention behaviours are predicted on the basis of an identification database of retention values (A, B) of gas chromatography. By the retention times of C-13 labelled 2,3,7,8-substituted PCDD/F internal standards, the retentions of all PCDDs and PCDFs can be calculated. After comparison with the retentions of practical environmental samples, the predicted values have been proved to be very accurate. (C) 2000 Elsevier Science Ltd. All rights reserved.

Biological evaluation of running waters in Korea, with special reference to bioassessment using the PFU system

A total of six stations in the Han River system were selected for establishing polyurethane foam units (PFUs) to collect protozoans, including phytomastigophorans, zoomastigophorans, amoebas and ciliates, in July 1993. In the bioassessment of microbial communities using the PFUs, the number of species decreased as pollution intensity increased. The diversity index values calculated at the main stations generally agreed with the pollution status of the stations. Anyang-Chon (Chon means stream) showed the lowest diversity value (1.89), and all stations, except Masok and Anyang-Chon, showed diversity index values ranging from 3.15 to 3.93. The highest heterotrophic index (HI) value was detected in Anyang-Chon followed by Masok-Chon. The number of species at the main stations reached a maximum on day 11 of being exposed to PFUs. The results of S-eq, G and T-90% all suggest that bioassessments using the PFU system were well matched with pollution status of the water. All microbial variables were significantly correlated with comprehensive chemical pollution indices, P-a and P-b, with correlation coefficients ranging from r=0.87 to r=0.96.

NUMERICAL ANALYSIS OF A NOVEL 980nm MICROCAVITY SEMICONDUCTOR OPTICAL AMPLIFIER WITH HIGH GAIN AND LOW NOISE

A novel microcavity semiconductor optical amplifier ( MCSOA) was proposed by incorporating top and bottom distributed Bragg reflectors ( DBRs) into the waveguide structure of conventional traveling-wave semiconductor optical amplifiers(TW-SOAs). The incoming( outgoing) light beam incidented onto (escaped from) the waveguide structure at a oblique angle through two optical windows, where the top DBR was etched away, and anti-reflection coating was deposited. The light beams inside the optical cavity were reflected repeatedly between two DBRs and propagated along waveguide in a zigzag optical path. The performance of the MCSOA was systematically investigated by extensive numerical simulation based on a traveling-wave model by taking into account the comprehensive effects of DBRs on both the amplification of signals and the filtering of spontaneous emission( SE). Our results show that the MCSOA is capable of achieving a fiber-to-fiber gain as high as 40dB and a low noise figure is less than 3.5dB.

Electrical control of dynamic spin splitting induced by exchange interaction as revealed by time-resolved Kerr rotation in a degenerate spin-polarized electron gas

Manipulation of the spin degree of freedom has been demonstrated in a spin-polarized electron plasma in a heterostructure by using exchange-interaction-induced dynamic spin splitting rather than the Rashba and Dresselhaus types, as revealed by time-resolved Kerr rotation. The measured spin splitting increases from 0.256 meV to 0.559 meV as the bias varies from -0.3 V to -0.6 V. Both the sign switch of the Kerr signal and the phase reversal of Larmor precessions have been observed with biases, which all fit into the framework of exchange-interaction-induced spin splitting. The electrical control of it may provide a new effective scheme for manipulating spin-selected transport in spin FET-like devices. Copyright (C) EPLA, 2008.

Spin dynamics in the second subband of a quasi-two-dimensional system studied in a single-barrier heterostructure by time-resolved Kerr rotation

Spin dynamics in the first and second subbands have been examined simultaneously by time resolved Kerr rotation in a single-barrier heterostructure of a 500 nm thick GaAs absorption layer. By scanning the wavelengths of the probe and pump beams towards the short wavelength in the zero magnetic field, the spin coherent time T-2(1)* in the 1st subband E-1 decreases in accordance with the D'yakonov-Perel' (DP) spin decoherence mechanism. Meanwhile, the spin coherence time T-2(2)* in the 2nd subband E-2 remains very low at wavelengths longer than 810 nm, and then is dramatically enhanced afterwards. At 803 nm, T-2(2)* (450 ps) becomes ten times longer than T-2(1)* (50 ps). A new feature has been discovered at the wavelength of 811nm under the bias of -0.3V (807nm under the bias of -0.6V) that the spin coherence times (T-2(1)* and T-2(2)*) and the effective g* factors (vertical bar g*(E-1)vertical bar and vertical bar g*(E-2)vertical bar) all display a sudden change, presumably due to the "resonant" spin exchange coupling between two spin opposite bands. Copyright (C) EPLA, 2008.

Dispersion-compensating photonic crystal fibers with special characteristics

Based on the modified dual core structure, three kinds of special photonic crystal fibers are presented, which are extremely large negative dispersion, super-broad bond, and large area made field dispersion-compensating photonic crystal fibers (DCPCF). For extremely large negative dispersion DCPCF, the peak of negative dispersion reaches -5.9 x 10(4) ps/(mn km). Super-broad bond DCPCF has broadband large negative dispersion and the dispersion value varies linearly from -380 ps/(nm km) to -420 ps/(nm km) in the C band. The designed large area made field DCPCF has a peak dispersion of -1203 ps/(nm km) with the inner core mode area of 47 mu m(2) and outer core mode area of 835 mu m(2). Furthermore, for the large area mode field DCPCF, the experimental result is also obtained. (C) 2008 Wiley Periodicals, Inc.

Transport properties in a gated heterostructure with a trapezoidal AlxGa1-xAs barrier layer

By replacing the flat (Ga1-xAlx)As barrier layer with a trapezoidal AlxGa1-xAs barrier layer, a conventional heterostructure can be operated in enhancement mode. The sheet density of two-dimensional electron gas (2DEG) in the structure can be tuned linearly from N-2D = 0.3 x 10(11) cm(-2) to N-2D = 4.3 x 10(11) cm(-2) by changing the bias on the top gate. The present scheme for gated heterostructures is easy to fabricate and does not require the use of self-alignment photolithography or the deposition of insulating layers. In addition, this scheme facilitates the initial electrical contact to 2DEG. Although, the highest electron mobility obtained for the moment is limited by the background doping level of heterostructures, the mobility should be improved substantially in the future. (C) 2009 Elsevier B.V. All rights reserved.

High responsivity resonant-cavity-enhanced InGaAs/GaAs quantum-dot photodetector for wavelength of similar to 1 mu m at room temperature

The characteristics of a resonant cavity-enhanced InGaAs/GaAs quantum-dot n-i-n photodiode with only a bottom distributed Bragg reflector used as the cavity mirror, are reported. To suppress the dark current, an AlAs layer is inserted into the device structure as the blocking layer. It turns out that the structure still possesses the resonant coupling nature, and makes Rabi splitting discernible in the photoluminescence spectra. The measured responsivity spectrum of the photocurrent shows a peak at lambda = 1030 nm, and increases rapidly as the bias voltage increases. A peak responsivity of 0.75 A/W, or equivalently an external quantum efficiency of 90.3%, is obtained at V-bias = -1.4 V.