1000 resultados para 1131
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The first thermodynamic dissociation constants of glycine in 5, 15 mass % glucose + water mixed solvents at five temperatures from 5 to 45-degrees-C have been determined from precise emf measurements of a cell without liquid junction using hydrogen and Ag-AgCl electrodes and a new method of polynomial approximation proposed on the basis of Pitzer's electrolytic solution theory in our previous paper. The results obtained from both methods agree within experimental error. The standard free energy of transfer for HCl from water to aqueous mixed solvent have been calculated and the results are discussed.
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The five complexes (RC5H4)2M(S2CNBz2)Cl (R = H, CH3; M = Ti, Zr, Hf; Bz = CH2C6H5) have been prepared by the reaction of (RC5H4)2MCl2 with anhydrous sodium salts of dibenzyldithiocarbamate in refluxing CH2Cl2. These complexes have been characterized by elemental analysis, IR and H-1 NMR. X-ray crystal structure determination of Cp2Zr(S2CNBZ2)Cl shows the molecule has a five-coordinate bent metallocene geometry in which the zirconium atom is attached to two eta-5-C5H5 groups, one bidentate dibenzyldithiocarbamate ligand and one chlorine [Zr-Cl, 2.549(1) angstrom; Zr-S, 2.734(1), 2.667(1); Cl-Zr-S, 137.6(1)-degrees and 73.3(1)-degrees; S-Zr-S, 64.3(1)-degrees]. The catalytic system Cp2Ti (S2CNBZ2)Cl-NaH exhibits high initial catalytic activity of hydrogenation of hexene-1 under mild conditions.
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通过多步脱乙酰基反应和溶液超声波降解制备了脱乙酰度D.D在49—100%(wt),重均分子量在1.94—25.1×10~5的系列壳聚糖样品,在0.1mol/L CH_3COONa+0.2mol/L CH_3COOH溶剂中和30℃下,用光散射法首次订定出了不同D.D壳聚糖的M-H方程常数K和α值,结果如下:D.D(wt%) K×10~3(ml·g~(-)1) α69 0.104 1.1284 1.424 0.9691 6.589 0.88100 16.800 0.81导致K和α值差别的主要原因是由于壳聚糖大分子链上的胺基(—NH_2)被酸质子化后,失去了形成分子内氢键的能力,减弱了内旋转受阻程度,同时,质子化后形成的阳离子聚电解质分子链链段间以及链段与溶剂之间的相互作用增强,有效电荷密度的增加使得聚电解质溶液粘度增大。
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对西宁市郊主要公路两侧的土壤和植物中的重金属铅含量采用原子吸收光谱进行了测定。结果表明,土壤和植物中铅污染都较严重。铅的含量比清洁对照区高:土壤2.7—4.1倍,杨树枝叶3.0—4.1倍,小麦青苗3.0-3.7倍,蔬菜1.5—2.3倍。土壤、树木和农作物在距路边80—100m处铅含量通常降到当地背景水平。
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本文首先分析了基于 KQML会话的 Multi- Agent系统 ( MAS)构成及其特点 ,然后提出了基于 CORBA、KQML的合同网协议 ( CNP)系统模型及 Agent通信模型 ,并针对此合同网模型 ,结合调度系统实例分析了其中 KQML语言的形式化表达方式
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大气中不断增加的温室气体浓度,将对气候、生态环境和人类活动等一系列问题产生重大影响,因此其“源”﹑“汇”效应备受关注。水库,作为人为活动对大气温室气体浓度影响的一个重要方面,也越来越受到国、内外学者的关注。本论文对贵州省喀斯特地区两个富营养水库(红枫湖、百花湖)中主要温室气体(CO2﹑CH4﹑N2O)在不同月份的水体中的分布规律进行研究,并结合两湖具体水环境条件,分析了影响两湖水体中CO2﹑CH4﹑N2O变化的因素,进而阐明两湖水体中CO2﹑CH4﹑N2O产生与释放的机理。本论文得到的结论如下: 1.由于地理位置和气候条件类似,所以两库水体中pCO2变化规律类似:两库表层水中pCO2在6月、8月明显低于大气CO2分压,其他月份则明显高于大气CO2分压。从全年角度来说,红枫湖表层水pCO2为874.2±774.4µatm,百花湖为1131.7±1164.0µatm,都是大气CO2的“源”。两湖pCO2与Chla之间存在的显著负相关,说明浮游植物光合作用与细菌呼吸作用共同影响是两湖pCO2出现季节变化的主要原因。 2.夏季,水体中光合作用产生的有机质发生降解产生CO2对温跃层中CO2的增加起重要作用;沉积物中有机质降解导致静水层中CO2积累,这种作用在秋﹑冬季有所降低,可能与水温有关。而秋冬季,随着温跃层的消失,在水体混合作用下,夏季水体中积累的CO2重新释放到表层水中使其pCO2升高。 3.通过与国内、外其他地区湖泊(水库)表层水中CO2的比较,发现:(1)由于红枫湖与百花湖地处喀斯特山区,陆源输入的有机碳比北部温带地区少,所以表层水中CO2低,对大气CO2释放的贡献较小。(2)由于富营养化现象,两库夏季表层水体成为大气CO2的“汇”。并且,就全年而言,表层水中CO2低于北部温带地区,说明两库光合作用固定的C返回大气的程度可能较低。 4.两湖表层水中CH4浓度的变化规律为:枯水期>丰水期,但在所有采样期间两湖始终是大气CH4的“源”。就全年而言,红枫湖两采样点HF-N和HF-S表层水中CH4浓度分别为0.19±0.09µmol/L和0.48±0.53µmol/L,百花湖两采样点BH-1和BH-2分别为0.32±0.29µmol/L和0.29±0.20µmol/L。两湖表层水中CH4浓度变化可能由以下几方面原因造成:(1)枯水期,水体滞留时间长,水体中的CH4得到积累;(2)丰水期,藻类初级生产造成表层水中DO含量增加,表层水体中CH4被氧化的程度较高;(3)丰水期,径流及降雨的增加也可能造成表层水体中CH4被稀释。 5.两湖湖底水体中CH4浓度的变化规律为:枯水期〈丰水期。就全年而言,HF-N和HF-S点底层水中CH4浓度分别为16.49±26.16µmol/L和8.80±15.30µmol/L,BH-1和BH-2分别为6.03±7.07µmol/L和4.41±7.00µmol/L。浮游植物光合作用产生的有机物及湖底水温﹑含氧状况是影响CH4产生的主要因素。SO42-也对湖底CH4的产生起一定抑制作用。 6.夏季,两湖湖水表层藻类的初级生产与湖水底层沉积物的降解对水体中CH4产生有影响。而热分层和两湖静水层中缺氧环境使得CH4得到积累。而到了秋冬季节,在水体混合作用下这部分CH4在水体中重新分布,并且由于氧化作用加强而被损耗。 7.两湖表层水中N2O的变化规律为:夏季N2O明显低于其他季节,但在所有采样期间内两湖都是大气N2O的“源”。从全年来看,红枫湖HF-N和HF-S两采样点表层水中N2O浓度分别为;46.31±29.65nmol/L,36.93±18.41nmol/L;百花湖BH-1和BH-2两采样点表层水中N2O浓度分别为102.13±79.53nmol/L,99.51±75.77nmol/L。硝化反应是影响两湖表层水中N2O季节变化的主要原因,并受表层水温﹑DO及NO3-等共同影响。 8.通过比较水体中NO3-﹑NH4+及N2O的分布特征,发现:春季,红枫湖水体中以硝化反应为主;夏季,两湖温跃层以上水体中以硝化反应为主,湖底以反硝化作用为主;秋﹑冬季节,虽然有个别采样点出现硝化或反硝化反应,但总体上两湖水体中N2O以水体混合作用为主。
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Structure from motion often refers to the computation of 3D structure from a matched sequence of images. However, a depth map of a surface is difficult to compute and may not be a good representation for storage and recognition. Given matched images, I will first show that the sign of the normal curvature in a given direction at a given point in the image can be computed from a simple difference of slopes of line-segments in one image. Using this result, local surface patches can be classified as convex, concave, parabolic (cylindrical), hyperbolic (saddle point) or planar. At the same time the translational component of the optical flow is obtained, from which the focus of expansion can be computed.
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Koven, M. (2003). Folklore Studies and Popular Film and Television: A Necessary Critical Survey. Journal of American Folklore. 116(460), pp.176-195. RAE2008
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103 hojas : ilustraciones.
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Geospatial modeling is one of the most powerful tools available to conservation biologists for estimating current species ranges of Earth's biodiversity. Now, with the advantage of predictive climate models, these methods can be deployed for understanding future impacts on threatened biota. Here, we employ predictive modeling under a conservative estimate of future climate change to examine impacts on the future abundance and geographic distributions of Malagasy lemurs. Using distribution data from the primary literature, we employed ensemble species distribution models and geospatial analyses to predict future changes in species distributions. Current species distribution models (SDMs) were created within the BIOMOD2 framework that capitalizes on ten widely used modeling techniques. Future and current SDMs were then subtracted from each other, and areas of contraction, expansion, and stability were calculated. Model overprediction is a common issue associated Malagasy taxa. Accordingly, we introduce novel methods for incorporating biological data on dispersal potential to better inform the selection of pseudo-absence points. This study predicts that 60% of the 57 species examined will experience a considerable range of reductions in the next seventy years entirely due to future climate change. Of these species, range sizes are predicted to decrease by an average of 59.6%. Nine lemur species (16%) are predicted to expand their ranges, and 13 species (22.8%) distribution sizes were predicted to be stable through time. Species ranges will experience severe shifts, typically contractions, and for the majority of lemur species, geographic distributions will be considerably altered. We identify three areas in dire need of protection, concluding that strategically managed forest corridors must be a key component of lemur and other biodiversity conservation strategies. This recommendation is all the more urgent given that the results presented here do not take into account patterns of ongoing habitat destruction relating to human activities.
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p.139-144
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In this paper, we consider what is meant by elearning and contrast the delivery of material with the actual learning process using an analogy derived from Searle. A case study describes an attempt to use a groupware system in a knowledge management course that met with mixed results. The reasons for these are explored with issues regarding extrinsic and intrinsic motivation and scaffolding being considered in the elearning context