分光光度法测定水稻土中有机酸的研究

本文以三种有机酸为代表,研究并建立了测定水稻土中有机酸的分光光度法。结果表明,三种有机酸的有色络合物具有相同的吸收光谱,且具有相同的最大吸收波长(λ_(mss)=500um)和相近的表观摩尔吸光系数。水分对酯化反应影响很大,含水量达4ml时,吸光值下降85％。酯化温度在10℃以上时,酯化率达最大值且保持稳定。在25℃时,显色反应20min趋干稳定,且在1h内吸光值下降不超过1.2％。土样中的有机酸采用NaCl溶液为提取剂,以3:1的液土比振荡提取30min,NaCl溶液浓度为1％就能达到良好的提取、过滤效果。提取液在烘干前需进行碱化,否则有机酸将损失30％以上。本法平均回收率为92.2％(n=5),标准差为0-0.0478cmol k8~(-1)(n=2-6),平均0.0142cmol kg~(-1)(n=26);变异系数为0—10％(n=2-6),平均4.87％(n=26);线性范围为0—0.0018mol L~(-1)。     

知识经济时代的企业经营与管理

21世纪经济正向着知识经济时代迈进.知识经济不仅对人类的生产方式和生活方式产生着深远影响,而且对企业的经营方式和管理模式也将产生深远的影响.我国企业在知识经济时代下,如何转变和调整经营与管理方式己成为新世纪的重大课题.     

沈阳市烟囱分布对大气污染的影响

本文介绍采用航空遥感技术和实地调查研究相结合的方法,分析了沈阳市烟囱数量、高度、密度以及高、中、低架烟囱的分布状况和特点,同时与大气污染监测结果对照分析了沈阳市煤烟型大气污染的规律及特点,研究了沈阳市烟囱分布对大气污染的影响。最后,提出了沈阳市燃煤污染的防治途径。     

Atmospheric sulfur deposition onto different ecosystems over China

The regional acid deposition model system (RegADMS) was applied to simulate the air sulfur deposition onto different landuse types over China, in which the dry deposition velocities of SO2 and sulfate aerosol (SO4(2-) were estimated by use of a big leaf resistance analogy model and the wet scavenging coefficients were parameterized in terms of precipitation rate. Investigations show that the annual total sulfur deposition over mainland China is 7.24mt (1 mt = 10(6) ton) , in which dry deposition and wet deposition accounts for 56 and 44%, respectively. The sulfur deposition onto agriculture land, grass land, and forest land is 1.09, 3.6 and 1.41 mt, respectively, which sums 6.1 mt and accounts for 84% of the total sulfur deposition. The modeled sulfur deposition was in agreement with the measurement conducted at farmland in Yingtan, a typical read soil region in Jiangxi province of China, during the period of November 1998--October 1999. The total sulfur deposition at the Yingtan site is about 10.3 gm(-2) year(-1) of which 83% is dry deposition. The modeling sulfur deposition at the same site is 8.4 g m(-2) year(-1) Furthermore, the comparison between RegADMS and RAINS-ASIA on modeling regional sulfur deposition shows the consistence of the two models. The correlation coefficient between the simulated sulfur deposition at the medium-large cities reaches 0.72.     

Field Studies on 32P Movement and P Leaching from Flooded Paddy Soils in the Region of Taihu Lake, China

Field experiments were done in two sites, Yixing and Changshu, Jiangsu province, China, to study P movement and leaching in flooded paddy soils. P movement in soil was investigated by using the KH₂ ³²PO₄ tracker method, and the amount of P leached from the soil layer in different depths was estimated by measuring P concentrations in the soil solution and saturated hydraulic conductivities in field. Determination was done about one month after P application. There was 46% and 42% of total ³²P retained in the 0–5cm layer of soil in the Yixing site and in the Changshu site respectively. The ³²P retained in the 25–30 cm layer was only about 1–2% of the total ³²P added. Furthermore, 8.01% of ³²P in the soil of Yixing site and 16.8% of ³²P in the soil of Changshu site was lost from the layer 0–30cm soil. The seasonal amounts of P leached from the top soil layer and from bottom layer are about 4.5–5.8% and 1.6–2.1% of the total P application, respectively. Changes of total P concentrations in soil solutions during rice growth showed that the fertilizer P applied before flooding of the paddy fields suffered a flash leaching loss and a slow leaching loss. We concluded that the fertilizer P could quickly move in the flooded paddy rice field and parts of it can enter into surface water and ground water. Unless the P application is well managed the risk of P loss and consequently environmental pollution exist.     

CuO-ZnO催化剂的XRD和EXAFS研究

用XRD和EXAFS方法研究了CuO-ZnO(50:50)CO_2加氢合成甲醇催化剂的结构.XRD研究发现,在催化剂还原前后,分别存在CuO,ZnO和Cu-ZnO晶相.EXAFS研究发现,在CuO-ZnO中,Cu—O,Cu—Cu键长及Cu的氧配位数、Cu的Cu配位数与纯CuO的十分接近,在Cu-ZnO中,Cu—Wu键长、Cu的Cu配位数与纯Cu的十分接近,说明催化剂在还原前后,CU的近邻结构分别与CuO与Cu的十分接近.纯Cu的活性、选择性很低,而Cu-ZnO的活性、选择性较纯Cu的有很大提高,说明催化剂的性能与催化剂中Cu的近邻结构无关.     

Purification and some properties of β-N-acetyl-D-glucosaminidase from prawn (<Emphasis Type="Italic">Penaeus vannamei</Emphasis>)

The -N-acetyl-D-glucosaminidase (NAGase, EC 3.2.1.52) from prawn (Penaeus vannamei) was purified by extraction with 30% ethanol solution and ammonium sulfate fractionation, then chromatographed on Sephadex G-100 followed by DEAE-cellulose (DE-32) columns. The purified enzyme determined to be homogeneous by polyacrylamide gel electrophoresis (PAGE) and SDS-PAGE. The specific activity of the purified enzyme was 1,560 U mg^–1. Enzyme molecular weight was determined to be 105,000 Da; it contained two subunits of the same mass (45,000 Da). The pI value was calculated to be 4.8 by isoelectric focusing. The optimum pH and optimum temperature of the enzyme for the hydrolysis of pNP--D-GlcNAc (enzyme substrate) were determined to be pH 5.2 and 45°C, respectively. The behavior of the enzyme during hydrolysis of pNP--D-GlcNAc followed Michaelis–Menten kinetics, with K_m=0.254 mM and V_m=9.438 M min^–1, at pH 5.2 and 37°C. The stability of the enzyme was investigated, and the results showed that the enzyme was stable in a pH range from 4.2 to 10.0 and at temperatures <40°C. The effects of metal ions on the enzyme were also studied. Li⁺, Na⁺ and K⁺ had no influence on enzyme activity. Mg²⁺, Ca²⁺ and Mn²⁺ activated the enzyme, while Ba²⁺, Zn²⁺, Co²⁺, Cd²⁺, Hg²⁺, Pb²⁺ Cu²⁺, Fe³⁺ and Al³⁺ showed various degrees of inhibitory effects on the enzyme.Communicated by O. Kinne, Oldendorf/Luhe     

怀来盆地弃耕地自然恢复过程中土壤养分动态

研究了怀来盆地丘陵区弃耕地自然恢复过程中土壤养分的变化规律。采取空间代替时间的方法,确定了代表弃耕地初期阶段、草地阶段和灌丛地阶段的3种样地,通过分层取样测定了土壤有机质、全量养分和速效养分含量。结果表明,全量养分对生态系统恢复的响应与其相应的速效养分明显不同。随着弃耕地的恢复,土壤有机质有明显增加的趋势,P循环和K循环由物质控制向生物控制转换,但速效P在恢复初期增加缓慢。速效N由于耕种期施肥的影响表现出先降低而后增加的特点。全量养分中,只有全N在弃耕地自然恢复中有增加的趋势。灌丛可以在更深的层次上影响土壤养分。植被的恢复与土壤肥力的提高密切相关,这种作用随着植被的恢复而不断增强。     

论注册安全主任制度

为适应市场经济条件下安全生产工作的需要,以广州市建立注册安全主任执业资格制度为背景,概述了作为职业资格制度之一的“执业资格制度”、分析了安全主任执业资格制度产生的社会条件,论述了安全主任知识结构、作用机理等。用以上内容,试图论证：注册安全主任执业资格制度的产生是社会市场经济发展的必然要求     

江苏及邻区地震趋势的极值理论分析

极值理论是概率论中的一个分支,在许多领域已被广泛应用。本文用历史地震资料对江苏及邻区作大震级范围的极值理论分析,用近几十年来的小震资料分别对苏北地区和苏南地区进行了较小震级范围的极值理论分析,对未来按不同的年份进行了缺震估计,并对１９９５年９月２０日的苍山５．２级地震、１９９６年１１月９日的南黄海６．１级地震作了内符检验。