Freshwater testate amoebae of nine Yunnan Plateau lakes, China

The testate amoebae from nine major lakes in the Yunnan Plateau, southwest China were investigated from August to October 2003. Ninety-four species and subspecies belonging to 21 genera were found, and six species were new to the testate amoebae fauna of China. The most diverse genera were Difflugia (28 species), Centropyxis (22 species), Arcella (12 species), and Euglypha (seven species), while the predominant genera were Centropyxis (42.0%), Difflugia (21.4%), Arcella (9.7%), and Euglypha (8.2%). The most diverse testate amoebae fauna was found in a mesotrophic lake, Lake Yilong (57 species). The lowest species richness was recorded in the two hypereutrophic lakes, Lake Dianchi (7 species) and Lake Xingyun (11 species). The results suggest that the lake trophic status plays an important role in shaping community structure and in determining species diversity of testate amoebae.

The temporal and spatial distribution, composition and abundance of Protozoa in Chaohu Lake, China: Relationship with eutrophication

Systematic investigations into the temporal and spatial distribution, composition and abundance of protozoa in two regions with different trophic levels in Chaohu Lake, a large, shallow and highly eutrophic freshwater lake in China, were conducted during 2002-2003. A total of 114 species of protozoa, including phytomastigophorans, zoomastigophorans, amoebae and ciliates, were identified from 120 polyurethane foam unit (PFU) samples exposed at four stations and from various types of natural substrates. Of the 114 taxa, 36 core species were found on PFU substrates and 23 of these were found on natural ones. Protozoan abundance and chemical physical parameters at nine sampling stations, four in the western lake and five in the eastern part, indicate trophic gradient changes along the lake. Seasonal variations in the species composition of major groups at littoral PFU sampling stations illustrate the effect of a severe algal bloom on the protozoan community structure. Temporal and spatial distributions of individual abundance as functions of water temperature and trophic status were revealed. This study demonstrates again that the PFU artificial substrate method samples protozoan communities more effectively than routine natural substrate methods. (c) 2005 Elsevier GmbH. All rights reserved.

Phylogenetic relationships among Trichodinidae (Ciliophora : Peritricha) derived from the characteristic values of denticles

The phylogenetic relationships among trichodinids remain obscure. As an important diagnostic marker, the morphology of the denticles in the adhesive disc as well as the adoral spiral has been widely used in generic discrimination and species identification of trichodinids. We studied the characters of denticles of the ten genera of Trichodinidae and the sole genus Urceolaria of Urceolariidae by using a quantitative method. The characteristic values were used to generate Manhattan distance, on which the dendrogram was based to construct with the Unweighted Paired Group Method using the Arithmetic mean (UPGMA). The investigations show that all the genera of the family Trichodinidae were clearly separate from the outgroup Urceolaria, and within the Trichodinidae: (i) Dipartiella grouped with Trichodinella and Tripartiella and lay in the closest position to the outgroup with a low dissimilarity, suggesting Dipartiella might be the most primitive genus in the family; (ii) Hemitrichodina clustered in a single clad and lay in the farthest position to the outgroup with the highest dissimilarity, indicating that it might be the most advanced genus; and (iii) the other 6 genera, Trichodina, Paratrichodina, Semitrichodina, Vauchomia, Pallitrichodina and Trichodoxa clustered in a big clad with very low dissimilarity, showing that they are closely related to each other. We discuss the evolutionary trend of the denticle and conclude that the denticles of the adhesive disc should be an apomorphic feature of the trichodinids and their changes could reflect the evolutionary tendencies of these ciliates.

Testate amoebae (Protozoa : Rhizopoda) from northwest Yunnan, China

A survey of the testate amoebae of northwest Yunnan in the Hengduan Mountains region of southwest China revealed 151 species belonging to 29 genera. Of these, three genera and 27 species were new to the testate amoebae fauna of China. The widely distributed and dominant species were Centropyxis aculeata aculeata, C aerophila aerophila, C. sylvatica, Difflugia elegans, D. globulosa, D. pristis, D. pulex, Phryganella hemisphaerica, Trinema enchelys, and T lineare. The most diverse genera were Difflugia (41 species), Centropyxis (31 species), Arcella (18 species), and Euglypha (11 species). The number of species in each sample varied greatly. It appears that species diversity of testate amoebae is related not only to macro-environments (e.g., geographic zonation) but also to microenvironments (e.g., microhabitats).

Use of PFU protozoan community structural and functional characteristics in assessment of water quality in a large, highly polluted freshwater lake in China

Structural and functional parameters of protozoan communities colonizing on PFU (polyurethane foam unit) artificial substrate were assessed as indicators of water quality in the Chaohu Lake, a large, shallow and highly polluted freshwater lake in China. Protozoan communities were sampled 1, 3, 6, 9 and 14 days after exposure of PFU artificial substrate in the lake during October 2003. Four study stations with the different water quality gradient changes along the lake were distinguishable in terms of differences in the community's structural (species richness, individual abundance, etc.) and functional parameters (protozoan colonization rates on PFU). The concentrations of TP, TN, COD and BOD as the main chemical indicators of pollution at the four sampling sites were also obtained each year during 2002-2003 for comparison with biological parameters. The results showed that the species richness and PFU colonization rate decreased as pollution intensity increased and that the Margalef diversity index values calculated at four sampling sites also related to water quality. The three functional parameters based on the PFU colonization process, that is, S-eq, G and T-90%, were strongly related to the pollution status of the water. The number of protozoan species colonizing on PFU after exposure of 1 to 3 days was found to give a clear comparative indication of the water quality at the four sampling stations. The research provides further evidence that the protozoan community may be utilized effectively in the assessment of water quality and that the PFU method furnishes rapid, cost-effective and reliable information that may be useful for measuring responses to pollution stress in aquatic ecosystems.

Redescription of Difflugia tuberspinifera Hu, Shen, Gu et Gong, 1997 (Protozoa : Rhizopoda : Arcellinida : Difflugiidae) from China

The freshwater testate amoeba Difflugia tuberspinifera Hu et al. 1997 collected from pond and lake in China, is investigated by light and scanning electron microscopy. This little known taxon is redescribed and its morphology, biometry and ecology are supplied. After carefully comparison with other six similar species including Difflugia bartosi Stepanek, D. corona Wallich, D. corona cashi Deflandre, D. corona tuberculata Vucetich, D. muriformis Gauthier-Lievre et Thomas and Netzelia tuberculata (Wallich) Netzal we believe that the sub-spherical to spherical shell, the mulberry-shaped appearance, the 7-10 apertural tooth-like structures, the short collar and the conical spines numbering from 4 to 8 at the upper equatorial region in D. tuberspinifera set it apart from other species. Besides, statistical analysis indicates that D. tuberspinifera is a size-monomorphic species characterized by a main-size class and a small size range and the shell height is significant correlated with other morphometric characters at p < 0.05 excepting the number of aperture tooth-like structures and the number of spines. Moreover, D. tuberspinifera inhabits not only lotic but also lentic environment.

Phylogenetic relationships of the subclass Peritrichia (Oligohymenophorea, Ciliophora) inferred from small subunit rRNA gene sequences

The phylogenetic relationships among peritrichs remain unresolved. In this study, the complete small subunit rRNA (SSrRNA) gene sequences of seven species (Epistylis galea, Campanella umbellaria, Carchesium polypinum, Zoothamnium arbuscula, Vaginicola crystallina, Ophrydium versatile, and Opercularia microdiscum) were determined. Trees were constructed using distance-matrix, maximum-likelihood and maximum-parsimony methods, all of which strongly supported the monophyly of the subclass Peritrichia. Within the peritrichs, 1) E. galea grouped with Opercularia microdiscum and Campanella umbellaria but not the other Epistylis species, which indicates that the genus Epistylis might not be monophyletic; 2) the topological position of Carchesium and Campanella suggested that Carchesium should be placed in the family Zoothammidae, or be elevated to a higher taxonomic rank, and that Campanella should be independent of the family Epistylididae, and probably be given a new rank; and 3) Opisthonecta grouped strongly with Asty/ozoon, which suggested that Opisthonecta species were not the ancestors of the stalked peritrichs.

Growth and production of free-living heterotrophic nanoflagellates in a eutrophic lake - Lake Donghu, Wuhan, China

In situ growth of heterotrophic nanoflagellates (HNF) in Lake Donghu, a eutrophic shallow lake in mainland China, was studied from January 1999 to March 2000 using a modified Weisse protocol. The study results indicated that the growth rates of HNF showed pronounced seasonal variation (-0.37-1.25 d(-1)), reaching the maximum during spring to early summer. When the water temperature was higher than 25.5 degreesC, HNF growth was inversely proportional to water temperature. There was an effect by bacterial abundance and autotrophic picoplankton on HNF growth that depended on location. HNF biomass was the highest in late spring, and the HNF production ranged from -2.25 to 35.45 mg l(-1) d(-1) with mean of 3.17 mg l(-1) d(-1). When considered in the context of biomass and production data for zooplankton in Lake Donghu, it was evident that HNF contributed significantly to the total zooplankton production in Lake Donghu. These in situ studies indicate that temperature and food supply are the major determinants of HNF abundance and productivity.

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Submitted by zhangdi (zhangdi@red.semi.ac.cn) on 2009-04-13T11:45:31Z

Doped polycrystalline 3C-SiC films deposited by LPCVD for radio-frequency MEMS applications

Polycrystalline 3C-SiC films are deposited on SiO2 coated Si substrates by low pressure chemical vapour deposition (LPCVD) with C3H8 and SiH4 as precursors. Controlled nitrogen doping is performed by adding NH3 during SiC growth to obtain the low resistivity 3C-SiC films. X-ray diffraction (XRD) patterns indicate that the deposited films are highly textured (111) orientation. The surface morphology and roughness are determined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The surface features are spherulitic texture with average grain size of 100 nm, and the rms roughness is 20nm (AFM 5 x 5 mu m images). Polycrystalline 3C-SiC films with highly orientational texture and good surface morphology deposited on SiO2 coated Si substrates could be used to fabricate rf microelectromechanical systems (MEMS) devices such as SiC based filters.

Preferential orientation growth of AIN thin films on Si (111) substrates by LP-MOCVD

Aluminum nitride (AIN) thin films were deposited on Si (111) substrates by low pressure metalorganic chemical vapor deposition system. The effects of the V/III ratios on the film structure and surface morphology were systematically studied. The chemical states and vibration modes of AIN films were characterized by X-ray photoelectron spectroscopy and Fourier transform infrared spectrometer. The optical absorption property of the AIN films, characterized by ultraviolet-visible-near infrared spectrophotometer, exhibited a sharp absorption near the wavelength of 206 mm. The AIN (002) preferential orientation growth was obtained at the V/III ratio of 10,000 and the preferential growth mechanism is presented in this paper according to the thermodynamics and kinetics process of the AIN growth.

Preferred growth of nanocrystalline silicon in boron-doped nc-Si : H Films

Preferred growth of nanocrystalline silicon (nc-Si) was first found in boron-doped hydrogenated nanocrystalline (nc-Si:H) films prepared using plasma-enhanced chemical vapor deposition system. The films were characterized by high-resolution transmission electron microscope, X-ray diffraction (XRD) spectrum and Raman Scattering spectrum. The results showed that the diffraction peaks in XRD spectrum were at 2theta approximate to 47degrees and the exponent of crystalline plane of nc-Si in the film was (220). A considerable reason was electric field derived from dc bias made the bonds of Si-Si array according to a certain orient. The size and crystalline volume fraction of nc-Si in boron-doped films were intensively depended on the deposited parameters: diborane (B2H6) doping ratio in silane (SiH4), silane dilution ratio in hydrogen (H-2), rf power density, substrate's temperature and reactive pressure, respectively. But preferred growth of nc-Si in the boron-doped nc-Si:H films cannot be obtained by changing these parameters. (C) 2004 Elsevier Ltd. All rights reserved.

Epitaxial SiC grown on silicon-on-insulator substrate with ultra-thin silicon-over-layer

We report on the comparative studies of epitaxial SiC films grown on silicon-on-insulator (SOI) and Si bulk substrates. The silicon-over-layer (SOL) on the SOI has been thinned down to different thicknesses, with the thinnest about 10 nm. It has been found that the full-width-at-half-maxim in the X-ray diffraction spectrum from the SiC films decreases as the SOL thickness decreases, indicating improved quality of the SiC film. A similar trend has also been found in the Raman spectrum. One of the potential explanations for the observation is strain accommodation by the ultra-thin SOI substrate. (c) 2005 Elsevier B.V. All rights reserved.

Effect of ion flux on recrystallization and resistance lowering in phosphorus-implanted (0001)-oriented 4H-SiC

High-dose ion implantation of phosphorus into 4H-SiC (0001) has been investigated with three different ion fluxes ranging from 1.0 to 4.0 x 10(12) P(+)cm(-2.)s(-1) and keeping the implantation dose constant at 2.0 x 10(15) P(+)cm(-2). The implantations are performed at room temperature and subsequently annealed at 1500 degrees C. Photoluminescence and Raman scattering are employed to investigate the implantation-induced damages and the residual defects after annealing. The electrical properties of the implanted layer are evaluated by Hall effect measurements on the sample with a van der Pauw configuration. Based on these results, it is revealed that the damages and defects in implanted layers can be greatly reduced by decreasing the ion flux. Considering room temperature implantation and a relatively low annealing temperature of 1500 degrees C, a reasonably low sheet resistance of 106 Omega/square is obtained at ion flux of 1.0 x 10(12) P(+)cm(-2.)s(-1) with a donor concentration of 4.4 x 10(19)cm(-3).

Electrical properties and electroluminescence of 4H-SiC p-n junction diodes

Homoepitaxial growth of 4H-SiC on off-oriented Si-face(0001) substrates was performed by using the step-controlled epitaxy technique in a newly developed low-pressure hot-wall CVD (LP-HWCVD) system with a horizontal air-cooled quartz tube at around 1500 degreesC and 1.33 x 10(4) Pa by employing SiH4 + C2H4 + H-2. In-situ doping during growth was carried out by adding NH3 gas into the precursor gases. It was shown that the maximum Hall mobility of the undoped 4H-SiC epilayers at room temperature is about 430 cm(2) (.) V-1 (.) s(-1) with a carrier concentration of similar to 10(16) cm(-3) and the highest carrier concentration of the N-doped 4H-SiC epilayer obtained at NH3 flow rate of 3 sccm is about 2.7 x 10(21) cm(-3) with a mobility of 0.75 cm(2) (.) V-1 (.) s(-1). SiC p-n junctions were obtained by epitaxially growing N-doped 4H-SiC epilayers on Al-doped 4H-SiC substrates. The C - V characteristics of the diodes were linear in the 1/C-3 - V coordinates indicating that the obtained p-n junctions were graded with a built-in voltage of 2.7 eV. The room temperature electroluminescence spectra of 4H-SiC p-n junctions are studied as a function of forward current. The D-A pair recombination due to nitrogen donors and the unintentional, deep boron center is dominant at low forward bias, while the D-A pair recombination due to nitrogen donors and aluminum acceptors are dominant at higher forward biases. The p-n junctions could operate at temperature of up to 400 degreesC, which provides a potential for high-temperature applications.