Co-occurrence and microhabitat of Ancyrocephalus mogurndae (Monogenea) and Henneguya weishanensis (Myxosporea) on gills of the mandarin fish, Siniperca chuatsi

Seasonal variations in a population of the monogenean Ancyrocephalus mogurndae Gussev, 1955 were investigated on gills of cage-cultured mandarin fish, Siniperca chuatsi (Basilewsky), during the period from April 1994 to April 1995. The abundance of A. mogurndae peaked in late spring and summer. Prevalence was high (75-100 %) throughout the study period, and did not vary significantly between months. More than 50 % of all monogeneans were found on the first and second gill arches, except one occasion when the fourth gill arch had the majority in April 1995. The niche breadths were significantly correlated with the population abundance. A coexistent parasitic myxosporean, Henneguya weishanensis Hu, 1965, on the gills of the fish was found to have little influence on the gill-arch preference of the monogenean, although the monogenean abundance was higher in those fish infected with the myxosporean.

Double synaptic weight neuron theory and its application

In this paper, a novel mathematical model of neuron-Double Synaptic Weight Neuron (DSWN)(l) is presented. The DSWN can simulate many kinds of neuron architectures, including Radial-Basis-Function (RBF), Hyper Sausage and Hyper Ellipsoid models, etc. Moreover, this new model has been implemented in the new CASSANN-II neurocomputer that can be used to form various types of neural networks with multiple mathematical models of neurons. The flexibility of the DSWN has also been described in constructing neural networks. Based on the theory of Biomimetic Pattern Recognition (BPR) and high-dimensional space covering, a recognition system of omni directionally oriented rigid objects on the horizontal surface and a face recognition system had been implemented on CASSANN-II neurocomputer. In these two special cases, the result showed DSWN neural network had great potential in pattern recognition.

Gal(1-x)Mn(1-x)Sb grown on GaSb with mass-analyzed low-energy dual ion beam deposition

The Ga1-xMnxSb samples were fabricated by the implantation of Mn ions into GaSb (1 0 0) substrate with mass-analyzed low-energy dual ion beam deposition system, and post-annealing. Auger electron spectroscopy depth profile of the Ga1-xMnxSb samples showed that the Mn ions were successfully implanted into GaSb substrate. Clear double-crystal X-ray diffraction patterns of the Ga1-xMnxSb samples indicate that the Ga1-xMnxSb epilayers have the zinc-blende structure without detectable second phase. Magnetic hysteresis-loop of the Ga1-xMnxSb epilayers were obtained at room temperature (293 K) with alternating gradient magnetometry. (c) 2005 Elsevier B.V. All rights reserved.

Structure optimization of field-plate AlGaN/GaN HEMTs

AlGaN/GaN high electron mobility transistors (HEMTs) on 6H-SiC with varying field-plate length and gate-drain spacing were fabricated and analyzed. The classical small signal FET model and the well-known ColdFET method were used to extract the small signal parameters of the devices. Though the devices with field plates exhibited lower better f(T) characteristic, they did demonstrate better f(max), MSG and power density performances than the conventional devices without field plate. Besides, no independence of DC characteristic on field-plate length was observed. With the increase of the field-plate length and the gate-drain spacing, the characteristic of f(T) and f(max), degraded due to the large parasitic effects. Loadpull method was used to measure the microwave power performance of the devices. Under the condition of continuous wave at 5.4 GHz, an output power density of 4.69 W/mm was obtained for device with field-plate length of 0.5 mu m and gate-drain length of 2 mu m. (c) 2006 Elsevier Ltd. All rights reserved.

Evolution of mosaic structure in InN grown by metalorganic chemical vapor deposition

Mosaic structure in InN layers grown by metalorganic chemical vapor deposition at various temperatures has been investigated by X-ray diffraction (XRD). With a combination of Williamson-Hall measurement and fitting of twist angles, it was found that variation of growth temperature from 450 to 550 degrees C leads to the variation of the lateral coherence length, vertical coherence length, tilt and twist of mosaic blocks in InN films in a, respectively, monotonic way. In particular, mosaic tilt increases whereas mosaic twist decreases with elevating temperature. Atomic force microscopy shows the morphological difference of the InN nucleation layers grown at 450 and 550 degrees C. Different coalescence thickness and temperature-dependent in-plane rotation of InN nuclei are considered to account for the XRD results. (c) 2006 Elsevier B.V. All rights reserved.

Field-aided collection in GaInP2 top solar cells

This paper reports the study on a field-aided collection in p-on-n GaInP2 top cells. The cells were produced by metalorganic vapor phase epitaxy at a low gas pressure. In order to optimize the device configuration, numerical simulations have been performed for the impacts of field-aided collection on the performance of the top cells. On the basis of the modeling results, a modified p(+)-p(-)-n(-)-n(+) configuration is introduced for GaInP2 top cells. This modification has brought out improved photovoltaic performance of the top cells, with conversion efficiency EFF = 14.26% (AM0, 2 x 2 cm(2), 25degreesC). (C) 2003 Elsevier B.V. All rights reserved.

Fabrication of improved FD SOIMOSFETs for suppressing edge effect

FD SOI MOSFETs with MESA and Irradiated FD SOI MOSFETs with LOCOS isolation usually show the edge effect, that is, the leakage current called hump is generated in the subthreshold region. According to different reasons for generating the edge effect, rounded corner process and BTS structure are applied to improve device performance. The results indicate that the above two methods are effective to reduce the edge effect and qualified devices are fabricated successfully.

黄土高原环境异质性与植被的恢复与重建

黄土高原是一个独特的地理区域,由于对其原生植被的不同认识,自然区划历来富有争议。为因地制宜地进行植被建设,在辨析植被属性有关论点(黄土无林、草原次生等)的基础上,主要由现代植被证据进一步讨论黄土高原的自然地带。分析了生物气候条件在不同地域之间的分异性,阐述了植被地带特征。为充分说明植被地带性,还从历史的角度探讨了植被建设的效果。表明黄土高原环境的非均质性可表征为森林、草原等地带,不能认为黄土高原不具有森林发育的地带性环境。相对于森林地带北界森林线,森林草原地带北界应为树木线。植被建设不应局限于一种土地利用模式,不能无视疏林及稀疏灌丛在森林草原地带的客观存在。

稀土分离过程的平衡反应和动力学研究

本论文共分六章，论文首先综述了近年稀土溶剂萃取最新出现的一些萃取体系及萃取方法，然后用溶剂萃取法系统研究了新萃取剂 PT-2 萃取稀土(III)、Cyanex 923 和 Cyanex 925 萃取铈(IV)、钍和稀土(III)的性质，推导层流型恒界面池的理论基础并用恒界面池法研究 Cyanex 272、PT-2 萃取稀土动力学，用高效离心分配色层仪(HPCPC) PT-2、Cyanex 302 和 Cyanex 272-P507 混合体系分离稀土(III)的规律，本论文还在大量实验数据的基础上，提出从氟碳铈矿中提取稀土的具有创新性的绿色工艺流程。论文第一章综述了近年衡土溶剂萃取的研究成果，为探求优于应用于工业生产的萃取稀土(III)的 P507 体系以及萃取钇的环烷酸体系，人们合成大量的有机磷类、羧酸类、苯胲类萃取剂并研究了它们萃取稀土的性能，将现有的萃取剂进行优化组合得到许多稀土的协同萃取体系，还将结晶反萃、还原反萃等方法应用于稀土分离过程。第二章用两相滴定法在测定 PT-2 的 K_d、K_2 等基本常数基础上，研究了 PT-2 的正庚烷溶液在盐酸、硝酸介质中萃取 15 个稀土离子（除了 Pm 外）的分配规律及萃取机理，同硫酸体系、高氯酸体系萃取平衡进行了对比，得到一些在理论上和实际上很有价值的结果。首次发现高位阻的酸性膦酸类萃取剂 PT-2 萃取轻、重稀土(III)时存在不同的机理，在盐酸、硝酸和硫酸体系中， PT-2 萃取轻稀土(III)为阳离子交换机理， PT-2 萃取重稀土时，阳离子交换机理和溶剂缔合机理共存；高氯酸介质中，由于高氯酸根离子难以同稀土(III)形成络合物， PT-2 萃取稀土(III)的机理符合一般的酸性膦酸酯的萃取规律，为阳离子交换机理。第三章探求了多种纯化 Cyanex 923 和 Cyanex 925 的途径，得出了较为行之有效的纯化方法，系统地研究了 Cyanex 923 从硫酸和硝酸介质中萃取 Ce(IV)、Th、La 和 Gd的规律，确定了萃合物的组成，计算了 lgK、ΔG、ΔH、ΔS 等热力学常数。 Cyanex 923 对 Ce(IV)、 Th(IV)的萃取在高酸度时随酸度的增大而降低，而 Ce(IV)、 Th(IV)同时萃取时， Th(IV)的萃取受到 Ce(IV)的抑制。发现 Cyanex 923 是一种良好 Ce(IV)的萃取剂，可用于铈从稀土(III)、钍中的分离、富集，具有很好的应用前景。第四章在层流型恒界面池的传质过程理论研究基础上，研究了二 (2,4,4-三甲基戊基)膦酸(HBTMPP)、PT-2 萃取 Er(III)的动力学，测定了流体线性流速、有机相浓度、水相浓度和酸度、温度及界面面积等因素对萃取速率的影响，对萃取的控制模式作出判断，为 Cyanex 272、 PT-2 在稀土湿法冶金中的应用提供基础参数。推导出层流型恒界面池中扩散控制模式下的萃取过程善于传质量和扩散层厚度两个基本公式。PT-2 萃取 Er(III)的过程属于扩散控制模式，在不同参数（温度、线性流速、界面面积、两相组成等）条件下，以 ln[(1/β + 1)C_b~a/C_(b,0)~a - 1/β] 对时间 t 作图得到都为直线，这些参数的变化对萃取的控制模式没有影响。萃取速率随温度、线性流速、界面面积等的变化规律也表明，该萃取过程为一扩散控制模式。根据萃取速率随线性流速、界面面积和温度的影响推断 HBTMPP 萃取 Er(III)为扩散控制和化学反应共同作用的混合控制模式。利用稳态法推导出该萃取过程的初始速率方程，该速率方程能和实验结果较好吻合。第五章用 HPCPC 研究 PT-2、Cyanex 302 及 Cyanex 272-P507 体系分离重稀土元素，评估 HPCPC 的性能及萃取剂的萃取性能，考察了流动相的流速、 pH 及 HPCPC 的转速等对分离效率的影响，并对这些体系萃取重稀土(III)的机理进行了探讨。发现流速对 HPCPC 的分离效率有显著的影响，随流速的增大，理论板数降低，分离度减小；理论塔板数和分离度随转速的变化无明显的变化；在 D 值相同时， Vs/Vm 越小，理论塔板数 N 越大；pH 越高，D 越大，理论塔板数则越低；萃取剂的浓度越高，理论塔板数越低。用 HPCPC 梯度洗脱法在 Cyanex 302 体系中只经过一次运行可将轻、重稀土混合物 La(III)、Sm(III)、Dy(III)和 Tm(III)分离。第六章针对攀西稀土矿 冶炼工艺中存在由于稀土收率低、放射性钍未得到分离和利用、存在二个放射性废渣和放射性废水等问题，采用溶剂萃取法，从攀西矿氧化焙烧－硫酸浸出液中萃取分离钍和铈(IV)。研究了 N1923 从氟碳铈矿硫酸浸出液中萃取分离钍和铈(IV)的工艺，并在此基础上提出从攀西矿中萃取分离铈(IV)、钍和提取氯化稀土的流程 I。用 N1923 萃取铈(IV)、钍，稀硫酸为洗液，形成含四价铈及钍的有机相和含三价稀土元素的萃余液，实现铈、钍与三价稀土的萃取分离。由于用含过氧化氢的硫酸溶液反萃铈(IV)困难，用含过氧化氢的硝酸溶液反萃铈(IV)、钍，再以 Cyanex 923 萃取钍，实现钍和铈(III)的分离。还研究了用 S501 萃取萃取铈(IV)工艺，以稀硫酸为洗液，用含过氧化氢的硫酸溶液为反萃取液反萃铈(IV)。解决了萃取过程铈(IV)的还原性问题；探明了氟离子对萃取过程的影响以及在料液、洗液、反萃取液中加入硼酸的作用，在大量数据的基础上提出了工艺的各成分的组成。