Comparison of evolutionary rates in the mitochondrial DNA cytochrome b gene and control region and their implications for phylogeny of the Cobitoidea (Teleostei : Cypriniformes)

It is widely accepted that mitochondrial DNA (mtDNA) control region evolves faster than protein encoding genes with few exceptions. In the present study, we sequenced the mitochondrial cytochrome b gene (cyt b) and control region (CR) and compared their rates in 93 specimens representing 67 species of loaches and some related taxa in the Cobitoidea (Order Cypriniformes). The results showed that sequence divergences of the CR were broadly higher than those of the cyt b (about 1.83 times). However, in considering only closely related species, CR sequence evolution was slower than that of cyt b gene (ratio of CR/cyt b is 0.78), a pattern that is found to be very common in Cypriniformes. Combined data of the cyt b and CR were used to estimate the phylogenetic relationship of the Cobitoidea by maximum parsimony, neighbor-joining, and Bayesian methods. With Cyprinus carpio and Danio rerio as outgroups, three analyses identified the same four lineages representing four subfamilies of loaches, with Botiinae on the basal-most clade. The phylogenctic relationship of the Cobitoidea was ((Catostomidae + Gyrinocheilidae) + (Botiinae + (Balitorinae + (Cobitinae + Nemacheilinae)))), which indicated that Sawada's Cobitidae (including Cobitinae and Botiinae) was not monophyletic. Our molecular phylogenetic analyses are in very close agreement with the phylogenetic results based on the morphological data proposed by Nalbant and Bianco, wherein these four subfamilies were elevated to the family level as Botiidae, Balitoridae, Cobitidae, and Nemacheilidae. (c) 2005 Elsevier Inc. All rights reserved.

Sedimentation rates, nitrogen and phosphorus retentions in the largest urban Lake Donghu, China

Sediment core samples were collected in the largest urban Lake Donghu (Stations I and II) in China, and the activities of Pb-210, Ra-226 and Cs-137 were measured by gamma-ray spectrometry. The sedimentation rates, calculated by 210Pb constant rate of supply (CRS) model, ranged from 0.11 to 0.65 (average 0.39) cm(.)y(-1) at Station I, and from 0.21 to 0.78 (average 0.46) cm(.)y(-1) at Station II. Sedimentation rate calculated by Cs-137 as a time marker was 0.55 cm(.)y(-1) at Station II. Based on the average sedimentation rate, we obtained 769 and 147 t(.)y(-1) for nitrogen and phosphorus retentions in Lake Donghu sediments, respectively.

Comparison of cooling rates for hot carriers in GaAs AlAs quantum wells based on macroscopic and microscopic phonon models

By using three analytical phonon models in quantum wells-the slab model, the guided-mode model, and the improved version of the Huang-Zhu model [Phys. Rev. B 38, 13 377 (1998)], -and the phonon modes in bulk, the energy-loss rates of hot carriers due to the Frohlich potential scattering in GaAs/AlAs multiple quantum wells (MQW's) are calculated and compared to those obtained based on a microscopic dipole superlattice model. In the study, a special emphasis is put on the effects of the phonon models on the hot-carrier relaxation process when taking the hot-phonon effect into account. Our numerical results show that, the calculated energy-loss rates based on the slab model and on the improved Huang-Zhu model are almost the same when ignoring the hot-phonon effect; however, with the hot phonon effect considered, the calculated cooling rate as well as the hot phonon occupation number do depend upon the phonon models to be adopted. Out of the four analytical phonon models investigated, the improved Huang-Zhu model gives the results most close to the microscopic calculation, while the guided-mode model presents the poorest results. For hot electrons with a sheet density around 10(12)/cm(2), the slab model has been found to overestimate the hot-phonon effect by more than 40% compared to the Huang-Zhu model, and about 75% compared to the microscopic calculation in which the phonon dispersion is fully included. Our calculation also indicates that Nash's improved version [J. Lumin. 44, 315 (1989)] is necessary for evaluating the energy-loss rates in quantum wells of wider well width, because Huang-Zhu's original analytical formulas an only approximately orthogonal for optical phonons associated with small in-plane wave numbers. [S0163-1829(99)08919-5].