Theoretical analysis and experimental study of the space-charge-screening effect in uni-traveling-carrier photodiode

A new optimized structure of an UTC (uni-traveling-carrier) photodiode is developed and epitaxied by metal-organic chemical vapor deposition. We fabricated a UTC photodiode of 30 mu m in diameter. Theoretical simulation based on drift-diffusion model was used to analyze the space-charge-screening effect in UTC photodiode primarily in two aspects: the carrier concentrations and the space electric field. The simulation results were generally in agreement with the experimental data.

Grey screening-photovoltaic soliton-induced waveguides

This paper shows that waveguides induced by grey screening-photovoltaic solitons are always single mode for all intensity ratios, which are the ratio between the peak intensity of the soliton and the dark irradiance. It finds that the confined energy near the centre of the grey soliton and the propagation constant of the guided mode increase monotonically with increasing intensity ratio. On the other hand, when the soliton greyness increases, the confined energy near the centre of the grey soliton and the propagation constant of the guided mode reduce monotonically. When the bulk photovoltaic effect is neglected for short circuits, these waveguides become waveguides induced by grey screening solitons. When the external bias field is absent, these waveguides become waveguides induced by grey photovoltaic solitons.

Waveguides induced by screening-photovoltaic solitons in biased photorefractive-photovoltaic crystals

We investigate theoretically waveguides induced by screening-photovoltaic solitons in biased photorefractive-photovoltaic crystals. We show that the number of guided modes in a waveguide induced by a bright screening-photovoltaic soliton increases monotonically with the increasing intensity ratio of the soliton, which is the ratio between the peak intensity of the soliton and the dark irradiance. On the other hand, waveguides induced by dark screening-photovoltaic solitons are always single mode for all intensity ratios and the confined energy near the centre of a dark screening-photovoltaic soliton increases monotonically with the increasing intensity ratio. When the bulk photovoltaic effect is neglectable, these waveguides are those induced by screening solitons. When the external field is absent, these waveguides predict those induced by photovoltaic solitons.

A colorimetric assay for screening microcystin class compounds in aquatic systems

Secondary metabolites produced by water-blooming cyanobacteria in eutrophic waters include some potent hepatotoxins, These compounds also have tumour-promoting properties, attributable to their inhibition and activation of protein phosphatases and kinases respectively. The inhibitory effect of these toxins on protein phosphatases have been employed in a commonly used radiometric assay, involving the use of a P-32-labeled substrate, for the detection and quantitation of these compounds. This paper investigates and describes a colorimetric method in which the activity of protein phosphatase 2A is determined by measuring the rate of colour production from the release of yellow p-nitrophenol using p-nitrophenyl phosphate as the substrate. Results of this study suggest that the colorimetric protein phosphatase inhibition assay is a simple, inexpensive tool for screening substances that may have tumour-promoting characteristics in aquatic systems. The detection limit of the colorimetric method is comparable to the radiometric assay. (C) 1998 Elsevier Science Ltd. All rights reserved.

镉、铅排异大白菜品种的筛选和鉴定及安全生产调控技术

随着工农业的快速发展，土壤重金属尤其Cd和Pb污染日益严重。筛选和培育具有重金属低积累特性的农作物排异品种被认为是当前应对土壤重金属污染最为合理和有效的途径之一。本文通过盆栽试验、大田试验和砂培试验，研究了大白菜品种对Cd和Pb的吸收和积累的品种差异、对Cd、Pb胁迫的响应以及大白菜安全生产的调控技术，得出以下结论： 1) 盆栽梯度试验中，80种大白菜地上部对Cd的吸收存在显著差异(p < 0.05)。在3种Cd处理下(1.0, 2.5和5.0 mg/kg)，80种大白菜Cd含量浓度范围分别为(mg/kg) 0.22–2.46, 0.90–14.10和2.03–18.01, 其平均值分别为 0.79, 3.76 和6.79 mg/kg DW。大白菜对Cd胁迫具有较强的耐性。大田试验中，15种大白菜的富集系数和转运系数与盆栽梯度试验的结果基本一致。排异植物的筛选和鉴定标准包括：(1)该植物的地上部和根部的Cd含量都很低或者可食部位低于有关标准；(2) 富集系数(BF) < 1.0；(3) 转运系数(TF) < 1.0；(4)该植物具有较高的Cd耐性，在较高的Cd污染下能够正常生长且生物量无显著下降。采用此标准，结合盆栽梯度试验和大田试验结果，北京新3号、绿星70和丰源新3号可鉴定为Cd排异品种。秋傲和赛新5号具有排异Cd特性，但其对Cd的耐性较差。 2) 盆栽梯度试验中，在Pb投加浓度为500和1500 mg/kg处理下，30种大白菜地上部对Pb的吸收存在显著差异 (p < 0.05)，其Pb浓度的范围分别为：0.52–8.68 和1.86–16.20 mg/kg, 其平均值分别为3.01 和6.87 mg/kg DW。并且，随着Pb浓度的增加，白菜地上部Pb含量有随之增加的趋势。大白菜对Pb具有较强的耐性。低浓度的Pb处理对大白菜的生物具有一定的促进作用。结合盆栽试验和大田试验的结果，秋傲、世博秋抗和福星80可鉴定为Pb排异大白菜品种。 3) 砂培试验中，在Cd和Pb胁迫下，大白菜地上部的丙二醛(MDA)含量增加，随着Cd处理浓度的增加，超氧化物歧化酶(SOD)活性呈现先下降后上升接着下降的趋势，酸菜王的SOD活性要高于北京新3号SOD的活性。随着Pb处理浓度的增加，福星80地上部的SOD活性随之增加，而绿星大棵菜地上部的SOD活性先下降后增加。在不同梯度的Cd处理下，大白菜地上部的可溶性蛋白(SP)含量未见显著降低，甚至有所增加，而在不同梯度的Pb处理下，大白菜地上部的SP含量有所降低。 4) 施用改良剂可升高土壤的pH值和降低土壤中的有效态Cd，从而对大白菜的生长具有促进作用。施用改良剂可显著降低大白菜对Cd和Pb的吸收和累积。