皖南、赣北奥陶纪笔石立体标本形成环境的初步研究*

皖南、赣东北和赣西北地区奥陶纪笔石地层发育良好,笔石化石丰富。宁国组和胡乐组均为笔石相地层,但笔石的保存特点并不相同。立体保存的黄铁矿化笔石标本主要见于宁国组,而胡乐组的笔石几乎均为薄膜标本。在比较宁国组和胡乐组在岩性、颜色、化石、矿物和元素等方面的特点后发现,两者有较明显的差异。这表明宁国组和胡乐组形成时的环境是不同的,前者为弱还原环境,后者为较强的还原环境,而在研究区内影响笔石体立体保存的主要因素为还原环境和较高的铁含量。在还原环境下,铁可呈Fe~(2+)存在,笔石体内含有硫,死亡后经降解作用可生成H_2S;H_2S和Fe~(2+)结合可使笔石体黄铁矿化,从而使笔石体硬化而呈立体保存下来。宁国组的铁含量明显高于胡乐组,这似可以解释宁国组产有较多笔石立体标本的原因。     

A short history of nuclear activation analysis

The major developments in the field of nuclear activation analysis, from 1936 to 1989, are discussed. The developments are grouped into five consecutive time periods. The impact of various scientists on the development of the field in the first 35 years is also discussed.     

一类阔叶树叶面积的通用公式测算法

本文在观察和测算的基础上,提出了一类阔叶树的叶形方程,并对方程进行积分,求出了计算这类阔叶树叶面积的通用公式。从1980年应用至今证明,用这个通用公式计算这类阔叶树的面积,方便、简捷、精度高,现介绍如下。     

水土保持耕作法是治理黄土高原地区坡耕地的根本措施

坡耕地所造成的土壤侵蚀,已成为全世界共同关注的问题。黄土高原地区,沟壑纵横,地形破碎,沟深坡陡,是世界上水土流失最强烈的地区。坡耕地的水土流失不仅是造成河流水库淤积的一个重要原因,更重要的是每年要丧失大量的肥沃表土,导致农业减产和土壤退化。一遇暴雨,人民的生命财产将遭受到巨大的威胁。黄土高原地区每年水力侵蚀土层深度达0.2—2cm,每1ha 损失表土120t 左右,损失     

辽西半干旱地区春小麦农田水分循环特征的研究

一、研究地区的生态条件概述辽西属暖温带半干旱低山丘陵区,自然条件差,干旱少雨,干燥度为1.2左右,年均降水量为480.1mm,可能蒸散量为551.7mm,水分亏缺严重,而且70—75%的雨水降子6—8月份,春季偏少。舂季气温回升快,风速大,土壤水分蒸发损失严重,因此春旱频繁,并经常     

温度对茶尺蠖核型多角体病毒增殖动态的影响

多角体计数、对流免疫电泳、单向免疫扩散及火箭免疫电泳测定的结果表明:26℃适于茶尺蠖核型多角体病毒(EoNPV)的增殖。多角体含量或其相对值随着时间的推移而增长,并渐趋于平稳,两者间呈Logistic曲线关系。单位体重或单头幼虫所含的多角体数量(y_1或y_2)、扩散环直径(y_3)和火箭峰值(y_4)与时间(t)的关系式分别为:y_1=(8.1481)/(1 EXP(9.4210-0.0608t))×10~9PIB/克;y_2=(6.1596)/(1 EXP(5.4809-0.0376t))×10~8PIB/头,y_3=(1.4)/(1 EXP(2.710-0.015t))cm;y_4=(3.52)/(1 EXP(4.580-0.040t))cm。但30℃下,EoNPV增殖严重受抑制,饲毒后24～168小时内难以测出多角体,其后多角体含量也极显著低于26℃,乃至难以被三种免疫测定法测出。     

放线菌结瘤植物根与根瘤中有机氮化物的组分及其上运形式

杨梅、沙棘和赤杨三种放线菌结瘤植物根瘤、根部有机氮化物的组分中,都含有占总有机氮化物50％以上的尿囊酸,说明在它们的根瘤中合成了大量的酰脲;同时,三种植物结瘤植株的茎木质部提取物中也含有大量的尿囊酸,表明根瘤将其合成的酰脲向植物地上部位运送。三种植物的根瘤还将其合成的特定的氨基酸及酰胺向地上部位转运,其中杨梅根瘤将固定的氮素以Asn和Gln的形式输出,而根部则以Arg的形式向上转运;沙棘根瘤以Ash,Gln及Ser,赤杨根瘤以Cit的形式合成并转运固定的氮素;后两种植物的无根瘤植株,以NH_4~+为氮源时,在转运的氨基酸组分中Arg的比例明显提高。     

Effects of Chronic Ethanol Consumption and Aging on Dopamine, Serotonin, and Metabolites

Abstract: This study examined the hypothesis that chronic ethanol consumption results in significant abnormalities in both the dopaminergic and the serotonergic system of aged rats. Levels of dopamine (DA), serotonin [5-hydroxytryptamine (5-HT)], 3,4-dihydroxyphenylacetic acid (DOPAC), and 5-hydroxyindole-3-acetic acid (5-HIAA) were determined in brain areas of both the nigrostriatal and mesocorticolimbic DA systems in 5-, 14-, and 24-month-old male Fischer 344 rats. Aging was associated with a reduced concentration of DA in the striatum (ST), ventral tegmental area (VTA), and ventral pallidum (VP) and an increased concentration of 5-HIAA in the ST, globus pallidus, nucleus accumbens, frontal cortex, and VP. In addition, there was an increase in the 5-HIAA/5-HT ratio in all brain areas analyzed. Six weeks of ethanol consumption was accompanied by significant changes in mesocorticolimbic brain areas. In the VTA of 5-month-old ethanol-fed rats DA content was decreased to the levels found in aged rats, e.g., 24 months of age. Ethanol also significantly lowered 5-HT and 5-HIAA contents in the VTA and reduced DOPAC and 5-HIAA levels in the VP. In addition, ethanol blunted the normal age-related increase in 5-HIAA/5-HT ratio in the VTA, VP, and substantia nigra. It is interesting that although the age-related changes were found in both nigrostriatal and mesocorticolimbic brain areas, the ethanol-associated effects were found only in brain areas of the mesocorticolimbic system. The changes in DA and 5-HT function that accompany aging and ethanol consumption may contribute to the problems in motor function and ethanol abuse found in the aged.     

Mathematical modelling of runoff and material transport from drainage areas into recipient water bodies

This paper describes a set of mathematical models to calculate runoff, soil erosion and chemical substance yields for drainage areas. The models represent different degrees of complexity and details of describing hydrological and hydrochemical processes. The availability of initial information and the requirements of the task determine the choice of a model for each particular case. These models have been written as PC/AT programs, to enable their use by a wide range of specialists. The models have been tested in different physical and geographical conditions, e.g. in some small watersheds on the Karelian Isthmus, west of Lake Ladoga, and in experimental catchment areas located in the Valdai Hills area in the southern part of Lake Ladoga drainage area. In further applications the drainage area models have been combined with models of the recipient water body, to obtain a single model of a watershed-lake system. The results of tests have proved that the models can be used for evaluation, simulation and forecasting of the processes of rainfall and snowmelt runoff, infiltration, evaporation, water erosion and pollutant wash-off from drainage areas.     

Crustacean zooplankton species richness and associations in reservoirs and ponds of Aguascalientes State, Mexico

We report the species of crustacean zooplankton found in 19 resevoirs and ponds that were sampled at on at least two occasions in Aguascalientes State, Mexico, at a latitude of about 21°30 North Latitude. We collected a total of 33 cladoceran taxa, 15 calanoid and cyclopoid copepods, an Ergasilus copepod, 2 anostracans, one notostracan species and an amphipod. All these taxa had previously been reported in Mexico. As in more temperate areas, there was a significant correlation between the species richness and lake size. The species-area relationship for Aguascalientes was indistinguishable from that of more northerly lakes. The two most common associations of zooplankton species were (1) those small species that occurred with fish: Daphnia parvula, Diaphanosoma birgei, Leptodiaptomus siciloides, Mastigodiaptomus albuquerquensis, and Thermocyclops inversus, and (2) the large Daphnia schodleri that occurred with the predator Notonecta, in the absence of fish. With minor variations, these two associations also occur throughout temperate North America.