The impact of silver carp (Hypophthalmichthys molitrix) on the rotifer community in a eutrophic subtropical Chinese lake

From 20 April to 25 June in 1999, an enclosure experiment was conducted in Lake Donghu to assess the impact of planktivorous silver carp on the planktonic rotifer community. We set up four treatments with silver carp biomass at 0, 116, 176, and 316 g m(-2). Total rotifer density was significantly higher in the no-fish enclosure than in fish-present enclosures. Fish predation on the rotifers alleviated zooplankton competition and resulted in dominance of small zooplankton species (Anureaopsis fissa, Trichocerca pusilla and Moina micrura) in fish-present enclosures. However, some relatively larger species (Polyarthra vulgaris, Brachionus angularis, Brachionus calyciflorus, and Asplanchna spp.) showed higher densities in the no-fish enclosure than in fish-present enclosures.

Some nematodes of fishes from central China, with the redescription of Procamallanus (Spirocamallanus)fulvidraconis (Camallanidae)

The present paper comprises a systematic survey of nematodes based on helminthological examinations of 176 specimens of freshwater fishes, belonging to 22 species, from central China (mostly lakes in Hubei Province) collected during the autumn of 2001. The following six species were recorded: Procamallanus (Spirocamallanus) fulvidraconis Li, 1935, Camallanus cotti Fujita, 1927, Dentiphilometra monopteri Moravec et Wang, 2002, Pingus sinensis Hsu, 1933, Proleptinae gen. sp. larv., and Eustrongylides sp. larv. Data on their morphology, morphological variability, host range, prevalence, intensity and distribution are provided. SEM studies of P. fulvidraconis and larval Physalopterinae, used for the first time in these species, revealed some additional morphological details and made it possible to redescribe the former. In contrast to the existing description of P. fulvidraconis, this species was found to possess two spicules and a V-shaped gubernaculum with unequal arms (originally mistaken for the left spicule), as well as deirids, whose location can be considered an important taxonomic feature. Larvae of the Physalopterinae have not previously been reported from fishes in China. The finding of larval Eustrongylides in Paramisgurnus dabryanus represents a new host record. All but one nematode species from this zoogeographically interesting region are briefly described and illustrated.

Experimental study of trophic cascade effect of silver carp (Hypophthalmichthys molitrixon) in a subtropical lake, Lake Donghu: on plankton community and underlying mechanisms of changes of crustacean community

An enclosure experiment was carried out to test trophic cascade effect of filter-feeding fish on the ecosystem: growth of crustacean zooplankton, and possible mechanism of changes of crustacean community structure. Four fish biomass levels were set as follows: 0, 116, 176 and 316 g m(-2), and lake water ( containing ca. 190 g m(-2) of filter-feeding fishes) was comparatively monitored. Nutrient levels were high in all treatments during the experiment. Lowest algal biomass were measured in fishless treatment. Algal biomass decreased during days 21-56 as a function of fish biomass in treatments of low (LF), medium (MF) and high (HF) fish biomass. Crustaceans biomass decreased with increasing fish biomass. Small-bodied cladocerans, Moina micrura, Diaphanosoma brachyurum and Scapholeberis kingii survived when fish biomass was high whilst, large-bodied cladocerans Daphnia spp. and the cyclopoids Theromcyclops taihokuensis, T. brevifuratus, Mescyclops notius and Cyclops vicinus were abundant only in NF enclosures. Evasive calanoid Sinodiaptomus sarsi was significantly enhanced in LF, but decreased significantly with further increase of fish biomass. Demographic data indicated that M. micrura was well developed in all treatments. Our study indicates that algal biomass might be controlled by silver carp biomass in eutrophic environment. Changes of crustacean community are probably affected by the age of the first generation of species. Species with short generation time were dominant and species with long generation time survived less with high fish biomass. Evasive calanoids hardly developed in treatments with high fish biomass because of the ( bottle neck) effect of nauplii. Species abundance were positively related to fish predation avoidance. Other than direct predation, zooplankton might also be suppressed by filter-feeding fish via competition.

Studies on the effects of silver carp (Hypophthalmichthys molitrix) on the Phytoplankton in a shallow hypereutrophic lake through an enclosure experiment

The responses of nutrients, water transparency, zooplankton and phytoplankton to a gradient of silver carp biomass were assessed using enclosure methods. The gradient of four silver carp biomass levels was set as follows: 0, 116, 176 and 316 g m(-2). Nutrients did not show any statistically significant differences among the treatments. An Outburst of Daphnia only occurred in fishless enclosures where phytoplankton biomass was the lowest and water clarity significantly increased. While among fish enclosures, the small-sized Moina micrura dominated throughout the experiment and both zooplankton and phytoplankton biomasses decreased with increased fish biomass. No large colonial cyanobacterial blooms occurred in the fishless enclosures as predicted. This might be due to low water temperature. short experiment time and the occurrence of large bodied Daphnia in our experiment. Cryptophyta was the most dominant group in most of the enclosures and the lake water throughout the experiment. The fishless enclosure had much lower proportion of Cyanophyta but higher proportion of Trachelomonas sp.

Changes in the plankton community following introduction of filter-feeding planktivorous fish

1. We conducted enclosure experiments in a shallow eutrophic lake, in which a biomass gradient of the filter-feeding planktivore, silver carp, Hypophthalmichthys molitrix Valenciennes, was created, and subsequent community changes in both zooplankton and phytoplankton were examined. 2. During a summer experiment, a bloom of Anabaena flos-aquae developed (approximate to 8000 cells mL(-1)) solely in an enclosure without silver carp. Concurrent with, or slightly preceding the Anabaena bloom, the number of rotifer species and their abundance increased from seven to twelve species (1700-14 400 organisms L-1) after the bloom in this fish-free enclosure. Protozoans and bacteria were generally insensitive to the gradient of silver carp biomass. 3. During an autumn experiment, on the other hand, large herbivorous crustaceans were more efficient than silver carp in suppressing the algae, partly because the lower water temperature (approximate to 24 degrees C) inhibited active feeding of this warm-water fish and also formation of algal colonies. Heterotrophic nanoflagellate and bacterial densities were also influenced negatively by the crustaceans. 4. Correspondence analysis (CA) was applied to the weekly community data of zooplankton and phytoplankton. A major effect detected in the zooplankton community was the presence/absence of silver carp rather than the biomass of silver carp, whereas that in the phytoplankton community was the fish biomass before the Anabaena bloom, but shifted to the presence/absence of the fish after the bloom.

ROLE OF PHOSPHORUS CYCLING IN ALGAL METABOLISM AND ALGAL SUCCESSION IN LAKE DONGHU, CHINA

The role of phosphorus cycling in algal metabolism was studied in a shallow lake, Donghu, in Wuhan using the methods of measuring cell quota C, N and P, and calculating nutrients uptake rate by algal photosynthesis. The mean daily phosphorus uptake rate of phytoplankton varied between 0.04-0.11 and 0.027-0.053 g/m2/d in station I and station II respectively. The turnover time of phosphorus in phytoplankton metabolism ranged from 0.75-5.0 days during 1979-1986. The available P was 0.176 (+/- 0.156) g/m3 (mean +/- SD) in 1982 and 0.591 (+/- 0.24) g/m3 in 1986. The relationship between P/B ratio (Y) and TP (X: mg/l) was described by the following regression equation Y = 1.163 + 0.512logX (r = 0.731, P < 0.001). The dynamics of algal biomass and algal species succession were monitored as the indicators of environmental enrichment. The small-sized algae have replaced the blue-green algae as the dominant species during 1979-1986. The small-sized algae include Merismopedia glauca, Cryptomonas ovata, Cryptomonas erosa, several species Cyclotella. There has been drastic decrease in algal biomass and an obvious increase in P/B ratio. A nutrient competition hypothesis is proposed to explain the reason of the disappearance of blue-green algae bloom. The drastic change in algal size and the results in high P/B ratio (reaching a maximum mean daily ratio of 1.09 in 1986) may suggest a transition of algal species from K-selection to r-selection in Lake Donghu.

Parameters determining crystallinity in beta-SiC thin films prepared by catalytic chemical vapor deposition

The effects of deposition gas pressure and H-2 dilution ratio (H-2/SiH4+CH4+H-2), generally considered two of dominant parameters determining crystallinity in beta-SiC thin films prepared by catalytic chemical vapor deposition (Cat-CVD), often called hot-wire CVD method, on the films properties have been systematically studied. As deposition gas pressure increase from 40 to 1000 Pa, the crystallinity of the films is improved. From the study of H-2 dilution ratio, it is considered that H-2 plays a role as etching gas and modulating the phases in beta-SiC thin films. On the basis of the study on the parameters, nanocrystalline beta-SiC films were successfully synthesized on Si substrate at a low temperature of 300degreesC. The Fourier Transform Infrared Spectroscopy (FTIR) and X-ray diffraction (XRD) spectra show formation of beta-SiC. Moreover, according to Sherrer equation, the average grain size of the films estimated is in nanometer-size. (C) 2003 Elsevier B.V. All rights reserved.

mc-Si : H/c-Si solar cell prepared by PECVD

Hetero-junction solar cells with an me-Si: H window layer were achieved. The open voltage is increased while short current is decreased with increasing the mc-Si:H layer's thickness of emitter layer. The highest of V-oc of 597 mV has obtained. When fixed the thickness of 30 nm, changing the N type from amorphous silicon layer to micro-crystalline layer, the efficiency of the hetero-junction solar cells is increased. Although the hydrogen etching before deposition enables the c-Si substrates to become rough by AFM images, it enhances the formation of epitaxial-like micro-crystalline silicon and better parameters of solar cell can be obtained by implying this process. The best result of efficiency is 13.86% with the V-oc of 549.8 mV, J(sc) of 32.19 mA center dot cm(-2) and the cell's area of 1 cm(2).

Unselective regrowth buried heterostructure long-wavelength superluminescent diode realized with MOVPE

A novel unselective regrowth buried heterostructure (BH) long-wavelength superluminescent diode (SLD), which has a grade-strained bulk InGaAs active region, was developed by metalorganic vapor-phase epitaxy (MOVPE). The 3 dB emission spectrum bandwidth of the SLD is about 65 nm with the range from 1596 to 1661 nm at 90 mA and front 1585 to 1650 nm at 150 mA. An output power of 3.5 mW is obtained at 200 mA injection current under CW operation at room temperature. (c) 2006 Elsevier B.V. All rights reserved.

Fabrication of Ge nano-dot heterojunction phototransistors for improved light detection at 1.55 mu m

Heterojunction phototransistors (HPTs) with several Ge/Si nano-dot layers as the absorption region are fabricated to obtain improved light detectivity at 1.55 mu m. The HPT detectors are of n-p-n type with ten layers of Ge(8ML)/Si(45nm) incorporated in the base-collector junction and are grown by an ultrahigh-vacuum chemical-vapor deposition system. The detectors are operated with normal incidence. Because of the good quality of the grown material and fabrication process, the dark current is only 0.71pA/mu m(2) under 5 V bias and the break-down voltage is over 20 V. Compared to the positive-intrinsic-negative (PIN) reference detector with the same absorption layer, the responsivity is improved over 17 times for normal incidence at 1.55 mu m.

Double crystal X-ray diffraction study of MBE self-organized InAs quantum dots

A series of GaAs/InAs/GaAs samples were studied by double crystal X-ray diffraction and the X-ray dynamic theory was used to analyze the X-ray diffraction results. As the thickness of InAs layer exceeds 1.7 monolayer, 3-dimensional InAs islands appear. Pendellosung fringes shifted. A multilayer structure model is proposed to describe the strain status in the InAs islands of the sample and a good agreement is obtained between the experimental and theoretical curves.

Lateral intersubband photocurrent study on InAs/InAlas/InP self-assembled nanostructures

We present lateral intersubband photocurrent (PC) study on self-assembled InAs/InAIAs/InP(001) nanostructures in normal incidence. With the help of interband excitation, a broad PC signal has been observed in the photon energy range of 150-630 meV arising from the bound-to-continuum intersubband absorption in the InAs nanostructures. The large linewidth of the intersubband PC signal is due to the size inhomogeneity of the nanostructures. With the increase of the interband excitation the intersubband PC signal firstly increases with a redshift of PC peak and reaches its maximum, then decreases with no peak shift. The increase and redshift of the PC signal at low excitation level can be explained by the state filling effect. However, the decrease of PC signal at high excitation level may be due to the change of the mobility and lifetime of the electrons. The intersubband PC signal decreases when the temperature is increased, which can be explained by the decrease of the mobility and lifetime of the electrons and the thermal escape of electrons.

伪柔和阴影算法的研究

在计算机图形学领域，阴影的绘制一直是一个热点的研究内容，它对增强场景的真实感有着非常重要的意义。完全物理正确的柔和阴影绘制通常需要耗费大量的时间，于是研究者们提出了各种阴影的近似方法。 本文首先对阴影绘制算法的研究发展历程作了概要性的介绍，特别针对近几年国内外提出的伪柔和阴影算法做了详细的介绍和分析。这些算法主要是根据点光源得到的阴影图[1]和轮廓边进行近似软影绘制的算法，不仅绘制效率高，而且画面真实感比较强。 随着GPU的不断发展，其强大的并行计算能力以及新的可编程着色器，特别是几何着色器[2]的出现，使得基于阴影图的阴影绘制算法中可以加入和场景几何相关的一些计算。本文提出了一个深度剥离[3]和GPU相结合的实时近似软影绘制算法，该算法利用了GPU强大的可编程能力，利用场景物体轮廓信息生成半影图，以此得到伪柔和阴影。实验结果表明本算法是可行的。

基于有序标记的IP包追踪方案

包标记方案是一种针对DoS攻击提出的数据包追踪方案，由于其具有响应时间快、占用资源少的特点，近年来受到了研究者的广泛关注．但由于包标记方案标记过程的随机性，使得受害者进行路径重构时所需收到的数据包数目大大超过了进行重构所必需收到的最小数据包数目，从而导致重构误报率的提高和响应时间的增长．本文提出了一种基于有序标记的IP包追踪方案，该方案通过存储每个目标IP地址的标记状态，对包标记的分片进行有序发送，使得在DoS发生时，受害者重构路径所需收到的标记包的数目大大降低，从而提高了对DoS攻击的响应时间和追踪准确度．该算法的提出进一步提高了包标记方案在实际应用中的可行性．