961 resultados para 1700-1750
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以沈阳城区昭陵古油松为样本,建立了古油松标准化年表、差值年表和自回归年表.结果表明,年表与沈阳1月和4月的极端最低气温显著相关;与2月的降水量、年均水汽压分别为显著和极显著相关,年表对4、5、9和10月的水汽压响应较强,且均与自回归年表显著相关.年表与相对湿度的年指标,4、5、6、9、10和11月月指标的相关性较高,其中与年值和5月值分别为显著相关(差值年表除外)和极显著相关.蒸发与油松的生长在全年和绝大部分月份呈负相关,其中5月最明显,而1月的蒸发量与油松年表呈正相关.年表的窄化突变佐证了1700年以来32次历史资料记录的主要旱灾年.沈阳地区的油松生长也受全球或半球尺度温度波动的影响.3种年表对以往太阳黑子的变化和地磁的活动呈现明显负相关,其中与太阳黑子活动存在显著的11年、23年和50年左右的公共周期,与地磁指标在10.5年、20年和45年左右存在共同的周期变化.
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在历史旱涝记载资料可靠性检验的基础上,重建了湖北省3个区域近500年来的干湿气候变化序列,并比较分析了各区域干湿气候变化的趋势特征、准周期性及跃变现象。结果表明:在3个区域中,鄂东区1570~1770、1890~1950年两个时段偏湿,1470~1520、1790~1830年则偏干;鄂北区偏湿时期主要在1470~1530、1710~1750、1850~1910年三个时段,1470~1530、1770~1830年则偏干;鄂西南区有1550~1610、1650~1710、1830~1890、1930~1990
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历史时期的土地利用与土地覆被变化是影响陆地生态系统碳循环的重要因素.过去300年间,我国土地利用与覆被发生了较大变化,林地面积迅速减小,垦殖扩张明显,均对陆地生态系统的碳循环产生了重要的影响.采用通过第一手历史文献资料重建的历史土地数据,分析了过去300年我国土地利用变化的主要特征,研究表明:在研究时段,耕地面积持续增加,从清前期1661年的60.78×106hm2增加到20世纪末的96.09×106hm2;森林面积从1700年的248.13×106hm2降至1949年的109.01×106hm2.受土地
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利用二进小波变换对华北地区1300~1996年的强震时间序列进行了多尺度分解,并据此划分了不同的地震活动期。认为公元1300年之后,华北地区的强震存在两个平静期(1350~1450年、1700~1780年)和两个活跃期(1450~1700年、1780~1996年)。与以往华北强震的活动期划分方案进行比较,本文的结果在总体规律上与以前的研究差别不大,但在第三、第四地震活动期中活跃期起始界限的划分上比其它方法略有提前,而在平静期的划分上相对较短。文中采用32a尺度的小波分析信号进行分析,既考虑了较大尺度上地震
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黑白仰鼻猴(Rhinopithecus bieti)目前分布在金沙江和澜沧江之间横断山脉的一个狭小的区域范围内(26o14’N-29o20’N,99o15’E-99o37’E),海拔2 600 m(南部) - 4 200 m(北部)之间;目前大约有15 群,数量估计约1700 个体。是我国特有的灵长类之一,为国家Ⅰ级保护动物,在IUCN(世界自然保护联盟)2007 受威胁物种红皮书中被列为濒危物种并处于小种群、高度片断化状态(ENC 2a)。西藏是黑白仰鼻猴分布的北端,约有300 个体。基于前人的野外调查和报道确认,暗针叶林和针阔叶混交林是其适宜栖息地,人们在低海拔和高海拔砍伐或者火烧暗针叶林和针阔叶混交林的产物-农田和夏季牧场正在逐渐侵蚀着其适宜栖息地。尽管当地藏族村民信奉佛教,禁止猎杀任何野生动物,但是近些年来,黑白仰鼻猴栖息地不断丧失,这与牧场和农田扩张、当地人们薪柴采集等活动有关。黑白仰鼻猴西藏种群主要在原始暗针叶林和和针阔叶混交林里活动。为了评估该物种的栖息地现状和变化情况,我们通过野外调查工作,应用GIS 和RS 技术,分别解译了1986 年、1992 年、1997 年、2001 年和2006 年的Landsat TM/ETM+ 冬季卫星影像,并对解译结果进行了计算和分析,得到了以下西藏种群栖息地的主要结果: 1)现有暗针叶林(包括原始针叶林和针阔混交林)面积是30 500 hm2 ,夏季牧场面积是13 100 hm2 ,农田面积是6 400 hm2 ;2)在过去20 年间(1986-2006 年),暗针叶林面积减少了14.6%(5 200 hm2 ),夏季牧场面积增加了47.2%(4 200 hm2 ),农田面积增加了14.3%(800 hm2 );3)在过去20 年间,暗针叶林的斑块数量增加了68.4%,平均斑块面积下降了49.3%(从1986 年的15.1 hm2 下降到2006 年的7.6 hm2 ),最大的斑块指数下降了54.9%;景观丰富度并没有变化,但Shannon 多样性指数和Shannon 均匀度指数分别增加了2.7%。这都表明栖息地丧失和破碎化程度越来越严重。在上述结果的基础上,我们进一步对栖息地变化的主要原因进行了初步分析和探讨。通过暗针叶林面积、夏季牧场面积和农田面积和当地各乡村的家庭户数、人口数量、平均家庭人口数和牲畜存栏数等统计数据的Spearman秩相关分析表明,暗针叶林面积变化分别与当地的人口数量、家庭户数和平均家庭人口数呈显著负相关,与牲畜存栏数呈负相关;而夏季牧场面积和农田面积都分别与人口数量、家庭户数和平均家庭人口数呈显著正相关,与牲畜存栏数呈正相关。这意味着在目前当地传统生产方式基本未发生改变的情况下,因人口数量增加所带来的生产等活动强度的增加是黑白仰鼻猴栖息地丧失与破碎化加剧的主要原因(R2 = 0.972);当地人类经济活动的增加,如牧场和农田扩张,牲畜存栏数增加以及薪材采集和木质建筑等导致了栖息地丧失、退化和破碎化。但另一方面,当地一妻多夫的婚配制度(仅在西藏部分地区仍有保留)对黑白仰鼻猴的栖息地保护有积极的作用,因为大家庭(家庭人口数)的人均资源消耗,如薪柴需求、房屋数量、牧场和农田等,都比小家庭低。在过去20 年中(1983-2003 年),当地家庭户数的增加比人口数量增加要慢,这对黑白仰鼻猴的栖息地保护起到了一定的积极作用。因此,西藏种群作为单独的遗传亚种群,其保护工作任重而道远。
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A novel diamine, 3,3'-bis(N-aminophthalimide) (BAPI), was prepared from 3,3'-bis(N-phenylphthalimide). Its structure was determined via IR, H-1 NMR, N-15 NMR, elemental analysis, and single-crystal X-ray diffraction analysis. A series of homo- and copolyimides were synthesized by a conventional one-step method in p-chlorophenol. The characteristic IR absorption bands of hydrazine-based imide groups were near 1780, 1750, 1350, 1100, and 730 cm(-1). The polymers showed good solubility in polar aprotic solvents and phenols at room temperature. The temperatures of 5% weight loss (T-5%) of the polyimides ranged from 495 to 530 degrees C in air. DMTA analyses indicated that the glass-transition temperatures (Tgs) of the polyimides were in the range 371-432 degrees C. These polymers had cutoff wavelengths between 350 and 400 nm. The polyimide films of 6FDA/BAPI and 4,4'-HQPDA/BAPI were colorless; other films were pale yellow or yellow.
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In this work, a novel substitutional solid solution (W0.8Al0.2)C was synthesized by mechanically activated high-temperature reaction. X-ray diffraction was used for phase identification during the whole reaction process. Environment scanning electronic microscopy-field emission gun and energy dispersive x-ray were used to investigate the microstructure and the quantitative material composition of the specimen. (W(0.8)A(10.2))C was found to crystallize in the WC-type, and the cell parameters were a = 2.907(1) angstrom and c = 2.837(1) angstrom. The hardness of (W0.8Al0.2)C was tested to be 19.3 +/- 1 GPa, and the density was 13.19 +/- 0.05 g cm(-3).
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醛缩酶C是生命代谢过程中重要糖酵解同工酶之一.应用二维凝胶电泳分离卵巢癌细胞中高表达的果糖二磷酸醛缩酶C,并通过基质辅助激光解吸电离飞行时间串联质谱对其进行分析与鉴定,结果表明应用高分辨二维凝胶电泳分离,结合生物质谱联用技术分析和鉴定未知蛋白具有简单快捷的特点.
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The graft copolymerization of butyl acrylate onto poly(vinyl alcohol) with eerie ammonium nitrate as redox initiator in a aqueous medium has been investigated. The formation of graft copolymer was confirmed by means of IR, scanning electron microscopy (SEM), and wide-angle X-ray diffraction (WAXD). The percentage of mononer conversion and percentage of grafting varied with concentrations of initiator, nitric acid, monomer, macromolecular backbone (X-n = 1750, M = 80 000), reaction temperature and reaction time. Some inorganic salts and organic solvents have a great influence upon grafting. The reaction mechanism has been explored, and rate equations for the reaction are established. (C) 2000 John Wiley & Sons, Inc.
Reaction and formation of crystalline silicon oxynitride in Si-O-N systems under solid high pressure
Resumo:
Oxidized amorphous Si3N4 and SiO2 powders were pressed alone or as a mixture under high pressure (1.0-5.0 GPa) at high temperatures (800-1700 degreesC). Formation of crystalline silicon oxynitride (Si(2ON)2) was observed from amorphous silicon nitride (Si3N4) powders containing 5.8 wt% oxygen at 1.0 GPa and 1400 degreesC, The Si2ON2 coexisted with beta -Si3N4 with a weight fraction of 40 wt%, suggesting that all oxygen in the powders participated in the reaction to form Si2ON2. Pressing a mixture of amorphous Si3N4 of lower oxygen (1.5 wt%) and SiO2 under 1.0-5.0 GPa between 1000 degrees and 1350 degreesC did not give Si2ON2 phase, but yielded a mixture of alpha,beta -Si3N4, quartz, and coesite (a high-pressure form of SiO2). The formation of Si2ON2, from oxidized amorphous Si3N4 seemed to be assisted by formation of a Si-O-N melt in the system that was enhanced under the high pressure.
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The crystallization and phase transformation of amorphous Si3N4 ceramics under high pressure (1.0-5.0 GPa) between 800 and 1700 degreesC were investigated. A greatly enhanced crystallization and alpha-beta transformation of the amorphous Si3N4 ceramics were evident under the high pressure, as characterized by that, at 5.0 GPa, the amorphous Si3N4, began to crystallize at a temperature as low as 1000 degreesC (to transform to alpha modification). The subsequent alpha-beta transformation occurred completed between 1350 and 1420 degreesC after only 20 min of pressing at 5.0 GPa. In contrast, under 0.1 MPa N-2, the identical amorphous materials were stable up to 1400 degreesC without detectable crystallization, and only a small amount of a phase was detected at 1500 degreesC. The crystallization temperature and the alpha-beta transformation temperatures are reduced by 200-350 degreesC compared to that at normal pressure. The enhanced phase transformations of the amorphous Si3N4, were discussed on the basis of thermodynamic and kinetic consideration of the effects of pressure on nucleation and growth.
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The curing temperature, pressure, and curing time have significant influence on finished thermosetting composite products. The time of pressure application is one of the most important processing parameters in the manufacture of a thermosetting composite. The determination of the time of pressure application relies on analysis of the viscosity variation of the polymer, associated with curing temperature and curing time. To determine it, the influence of the time of pressure application on the physical properties of epoxy-terminated poly(phenylene ether ketone) (E-PEK)-based continuous carbon fiber composite was studied. It was found that a stepwise temperature cure cycle is more suitable for manufacture of this composite. There are two viscosity valleys, in the case of the E-PEK system, associated with temperature during a stepwise cure cycle. The analysis on the effects of reinforcement fraction and defect content on the composite sheet quality indicates that the width-adjustable second viscosity valley provides a suitable pressing window. The viscosity, ranging from 400 to 1200 Pa . s at the second viscosity valley, is the optimal viscosity range for applying pressure to ensure appropriate resin flow during curing process, which enables one to get a finished composite with optimal fiber volume fraction and low void content. (C) 1997 John Wiley & Sons, Inc.
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Using a molal conductance method, ion solvation and ion association in polytriethylene glycol dimethacrylate (PTREGD)-LiClO4 gel electrolytes with amorphous ethylene oxide-co-propylene oxide (EO-co-PO, <(M)over bar (n)>, = 1750) as the plasticizer were investigated. It was found that the fraction of solute existing as single ions (alpha(i)) and ion pairs (alpha(p)) decreases, while that of triple ions (alpha(t)) increases linearly with increasing salt concentration. The dependence of these fractions on molecular weight of plasticizer was also examined. It was shown that alpha(i) and alpha(t) increase and alpha(p) decreases with increasing molecular weight. The result of temperature dependence of these fractions was very interesting: when the temperature is lower than 55 degrees C, alpha(i) increases while alpha(p) and alpha(t) decrease with increasing temperature; however, when the temperature is higher than 55 degrees C, the reverse is true.