Calorimetric study and thermal analysis of crystalline nicotinic acid

As one primary component of Vitamin B-3, nicotinic acid [pyridine 3-carboxylic acid] was synthesized, and calorimetric study and thermal analysis for this compound were performed. The low-temperature heat capacity of nicotinic acid was measured with a precise automated adiabatic calorimeter over the temperature rang from 79 to 368 K. No thermal anomaly or phase transition was observed in this temperature range. A solid-to-solid transition at T-trs = 451.4 K, a solid-to-liquid transition at T-fus = 509.1 K and a thermal decomposition at T-d = 538.8 K were found through the DSC and TG-DTG techniques. The molar enthalpies of these transitions were determined to be Delta(trs)H(m =) 0.81 kJ mol(-1), Delta(fus)H(m) 27.57 kJ mol(-1) and Delta(d)H(m) = 62.38 kJ mol(-1), respectively, by the integrals of the peak areas of the DSC curves.

长白山自然保护区历史森林景观的初步重建

本文在对环境因子 (包括年均温、年降水量、海拔高度、坡度和坡向 )进行空间表达的基础上 ,建立了长白山自然保护区当前森林景观垂直带 (包括阔叶红松林、云冷杉林、岳桦林和苔原 )与这些环境因子间的逻辑斯蒂回归模型 ,然后利用 1 997年各环境因子的空间数字面来反推 1 975年森林景观带的空间分布 ,并根据 1 975年MSS遥感影像计算机监督分类的结果 ,用Kappa指数对模型预测结果进行验证。结果表明 ,苔原、岳桦林、云冷杉林和阔叶红松林 1 975年的预测分布面积分别为 72 4 3.83hm2 、65 1 7.0 8hm2 、1 2 5 5 70 .1 6hm2 和 342 64.80hm2 ,与遥感分类结果相比 ,苔原和云冷杉林的面积分别减少了 2 9.0 4 %和 3.0 5 %;岳桦林和阔叶红松林的面积分别增加了 2 4 6.45 %和 8.6%。用逻辑斯蒂回归模型可以较好地预测苔原在保护区内的分布范围 ,同时在一定程度上也能预测阔叶红松林的分布范围 ,但是对岳桦林和云冷杉林分布范围的预测结果较差。尽管如此 ,作为一种方法性的探讨 ,本文可以为森林景观空间分布和环境因子变化的关系以及森林景观对气候变化的反应研究提供一种新思路。

稠油废水生物处理主要影响因素分析

有机聚合物和石油烃类物质是稠油废水中的主要污染物.应用辽河油田锦采污水处理厂稠油废水中筛选分离出的菌株B0501,分析其在稠油废水生物处理过程中对废水CODCr的去除作用,研究了不同温度,pH,水力停留时间以及添加氮、磷营养盐等条件下微生物对废水CODCr去除的影响.结果表明:稠油废水中投加的外源微生物B0501提高了废水中CODCr的去除率;接种后,废水在30℃,pH为7.5,水力停留时间为216 h,添加氮、磷营养盐(ρ(氮)/ρ(磷)为5.63)的条件下,废水CODCr去除率大幅度提高,其ρ(CODCr)满足国家污水综合排放一级标准(GB 8798-1996).经形态观察和生理生化反应鉴定,菌株B0501为液化金杆菌(Aureobaterium liquefaciens).

云雾山封育草原对表土持水性的影响

应用离心机法测定土壤水分特征,研究黄土高原典型草原带退耕地植被恢复演替过程中土壤持水性能的变化特点及趋势。结果表明:土壤含水量与土壤水吸力之间符合幂函数θ=aSb,参数a的变化随着植被的演替呈增加趋势;由于植被的影响,在同一吸力范围内的土壤含水量不同,植被为顶级长芒草(Stipabungeana)群落时,土壤在各吸力段的含水量最高,坡耕地最低;其它群落土壤含水量随着水吸力的增加变化趋于一致;退耕地植被在演替过程中通过提高土壤有机质含量改善结构,降低容重并增加毛管孔隙度,对土壤的储水和持水性能产生作用。

三种农作物中镉积累与全硫含量的关系

采用田间试验方法,研究了土壤中镉浓度分别为2和5mg·kg-1时,向日葵(Helianthusannuus)、玉米(Zea mays)和大豆(Glycine max)从苗期至成熟期各生长阶段茎叶中镉积累与全硫含量的关系。结果表明,玉米和向日葵各生长时期茎中镉含量与其全硫含量呈极显著相关,叶片中镉含量与硫含量没有相关性,说明硫在植物镉的运输过程中发挥着重要的作用。土壤中镉浓度为2mg·kg-1时,籽实中镉含量从高到低的顺序是:向日葵>大豆>玉米;土壤中镉浓度为5mg·kg-1时,籽实中镉含量从高到低的顺序是:大豆>向日葵>玉米,与籽实中硫含量的高低顺序一致;玉米籽实中镉含量最低,在2个镉浓度处理下平均值仅为0.01和0.03mg·kg-1,低于国家标准食品中镉限量值。

玉米南运的虚拟耕地资源流动及其影响分析

粮食贸易所隐含的虚拟资源流动是20世纪90年代以来提出的,除供需配置和流域配置之外的另一种重要的粮食和农业资源配置形式.本文借鉴"虚拟资源"的概念和方法,分析了中国玉米"北粮南运"的虚拟耕地资源流动,并重点分析了其对于区域耕地资源配置的影响.结果表明,中国每年从北方运往南方的玉米将近4×107t,相当于向南方调运了(5.9~9.5)×106hm2)的虚拟耕地.作为主要调出区,东北地区资源优势明显,玉米流动的资源配置方式较为合理,华北地区的优势则不明显,资源配置欠合理.虽然虚拟耕地资源流动满足中国南方地区的

Controlled release of urea encapsulated by starch-g-poly(L-lactide)

This paper presented a new approach for preparing a new type of slow-release membrane-encapsulated urea fertilizer with starch-g-PLLA as biodegradable carrier materials. By solution-casting and washing rapidly with water the urea was individually encapsulated within the starch matrix modified by L-lactide through in situ graft-copolymerization.

Energy transfer from Tb3+ to Mn2+ in LaMgAl11O19:Tb, Mn phosphors

Luminescent properties of LaMgAl11O19:Tb, Mn phosphors were investigated. It was observed that the energy distributions of the Tb3+-emission bands associated with transitions from the D-5(3) and D-5(4) levels to F-7(J) depend on the Tb3+-concentration, which is due to the cross-relaxation between Tb 31 ions. The emission band at about 516 nm is attributed to the T-4(1) -> (6)A(1) transition of the Mn2+ ions. We observed an energy transfer from the Tb 3, to Mn2+ ions in LaMgAl11O19:Tb, Mn.

Pore-filling membrane for direct methanol fuel cells based on sulfonated poly(styrene-ran-ethylene) and porous polyimide matrix

We have synthesized a porous co-polyimide film by coagulating a polyimide precursor in the non-solvent and thermal imidization. Factors affecting the morphology, pore size, porosity, and mechanical strength of the film were discussed. The porous polyimide matrix consists of a porous top layer and a spongy sub-structure with micropores. It is used as a porous matrix to construct sulfonated poly(styrene-ran-ethylene) (SPSE) infiltrated composite membrane for direct methanol fuel cell (DMFC) application. Due to the complete inertness to methanol and the very high mechanical strength of the polyimide matrix, the swelling of the composite membrane is greatly suppressed and the methanol crossover is also significantly reduced, while high proton conductivity is still maintained. Because of its higher proton conductivity and less methanol permeability, single fuel cell performance test demonstrated that this composite membrane outperformed Nafion membrane.