青藏高原海北高寒湿地土壤呼吸对水位降低和氮添加的响应

近20年来,青藏高原高寒湿地经历了明显的气候变化,从而导致多数湿地水位下降和氮沉降的增加。对于湿地生态系统来说,水位下降意味着土壤通气性能的改善,可能会导致土壤呼吸的增加;而氮沉降的增加可能会降低土壤微生物生物量和pH值,从而可能抑制土壤呼吸。为此,在青海海北高寒草地生态系统国家野外科学观测研究站利用中宇宙(Mesocosm)实验方法,探讨了青藏高原高寒泥炭型湿地土壤呼吸对水位降低和氮添加的响应。结果表明:(1)水位降低显著增强了土壤呼吸,而氮添加对土壤呼吸的影响依赖于水位的变化:对照水位下,氮添加显著抑制土壤呼吸;而水位降低时,氮添加对土壤呼吸速率无显著影响。(2)土壤呼吸速率与地上生物量、枯落物累积量之间呈显著正相关关系,而与根系生物量无显著相关关系。(3)水位降低显著提高了土壤呼吸的温度敏感性,而氮添加对其无显著的影响。因此预测:随着氮沉降的升高,高寒泥炭湿地土壤CO2的排放量将会减少;然而随着暖干化背景下水位的降低,青藏高原高寒湿地会排放更多的CO2

Studies on fabrication of continuous freestanding SiC films from polycarbosilane precursor

以聚碳硅烷(PCS)为先驱体,通过自行设计的喷膜板熔融纺出连续PCS自由薄膜,并对其进行氧化交联与高温裂解烧结可制得连续SiC自由薄膜。用扫描电镜分析薄膜表面和横断面的形貌,通过红外光谱(FTIR)分析氧化交联后薄膜的结构,通过拉曼光谱(Raman spectroscopy)、X射线衍射(XRD)与场发射高分辨透射电子显微镜(HRTEM)对薄膜进行微观分析。结果表明,熔融纺膜与聚碳硅烷先驱体法相结合可制得均匀、致密的连续-βSiC自由薄膜,其厚度可通过调节喷膜板的喷膜口尺寸大小和纺膜速度进行控制,薄膜的厚度大约在10~30μm。Under the technique of the melt spinning of precursor,the uniform and dense continuous freestanding SiC films were successfully fabricated.A special spinneret was designed and manufactured for melt spinning.Polycarbosilane(PCS) was melt spun,cured and pyrolysis treated in the inert gas at high temperature,the initial amorphous PCS green films transformed to polycrystalline β-SiC.The continuous freestanding SiC films were studied for the first time.The microscopic surface and cross-section of resulting freestanding SiC films were investigated by SEM(scanning electron microscope),and their composition and microstructure were characterized by Raman spectrometer,FTIR(fourier transform infrared spectrometer),HRTEM(high resolution transmission electron microscope) and XRD(X-ray diffractometer).The results showed that continuous freestanding SiC films contained amorphous SiOxCy,β-SiC nano-crystals and free carbon.And they could be obtained at thickness from 10-30μm through adjusting the spout size of spinneret and spinning speed.国家自然科学基金重点资助项目(50532010);; 总装预研基金资助项目(91040A12040107QT87

One-pot Synthesis and Characterization of Liquid Polycarbosilanes

[中文文摘]采用"一釜法",以氯甲基三氯硅烷(Cl3SiCH2Cl)和(氯甲基)甲基二氯硅烷(Cl2Si(CH3)CH2Cl)为原料,经过格氏偶联反应和还原反应制备了液态聚碳硅烷(PCS).通过傅立叶变换红外光谱(FT-IR)、核磁共振(NMR)以及凝胶渗透色谱法(GPC)对由此制备的PCS进行表征并证实其具有超支化的分子结构.调节Cl3SiCH2Cl和Cl2Si(CH3)CH2Cl两种共聚单体的比例,可以有效调控聚合物的结构、组成以及分子量.随着Cl2Si(CH3)CH2Cl比例的提高,可以有效降低副反应的发生,但降低了聚合物的分子量和产率.[英文文摘]A liquid polycarbosilane is prepared by one-pot synthesis with chloromethylt richlorosilane and chloromethylmethyldichloro silane as the starting materials ,via Grignard coupling and the subsequent reduction reaction. The as2synthesized PCS with a hyperbranched st- ructure has been characterized by means of gel permeation chromatography( GPC) ,Fourier transform inf rared ( FT2IR)spectroscopy and nuclear magnetic resonance (NMR) spectroscopy. The chemical structure, composition and molecular weights of the PCS can be tuned by the molar ratio of Cl3 SiCH2Cl to Cl2 Si (CH3 ) CH2Cl. The side reaction can be significantly suppressed with the increase of Cl2 Si (CH3 ) CH2Cl ratio in feed ,while the molecular weights and yields of the resultant polymer are decreased.国家自然科学基金重点项目(50532010); 福建省自然科学基金(E0510002)

Preparation of aluminum nitride fibers from alumina gel fibers by nitridation in ammonia

natural science foundation of Fujian province of China [2010J01307]Aluminum nitride (AlN) fibers were prepared from alumina gel fibers and by heat-treatment in ammonia. The influence of silica on the formation of AlN was investigated. It was shown that phase transformation of alumina (gamma-Al2O3 to alpha-Al2O3) and nitridation reaction took place above 1,100 A degrees C for pure alumina fiber. The addition of a small amount of silica (3 wt%) suppressed the formation of alpha-Al2O3 and preserved the highly reactive metastable alumina, and nitridation rate was enhanced. Fine grain (similar to 20 nm) AlN fibers were obtained for pyrolysis at 1,150-1,250 A degrees C for 3 h in ammonia, and AlN was identified as the sole crystalline phase

煤炭解耦燃烧过程N迁移与转化Ⅱ:单组分气相化学反应实验

在理想平推流反应器中进行了模拟热解气对模拟烟气中NO、N2O的还原实验研究,考察了反应温度、过剩空气系数λ、热解气中CH4、CO、H2、NH3浓度、烟气中NO、N2O浓度变化对NO、N2O出口浓度的影响。实验结果表明,当模拟热解气仅含其中一种气体时,在反应温度973～1223 K时热解气中CH4、CO、H2基本不与NO发生反应,当λ小于或等于1.0时可降低N2O浓度0%～30%;热解气中NH3可降低NO 10%～60%,但NH3不与N2O发生反应

煤炭解耦燃烧过程N迁移与转化Ⅲ:多组分气相化学反应实验

在理想平推流反应器中进行了模拟热解气对模拟烟气中NO、N2O的还原实验研究,考察了反应温度、过剩空气系数,模拟热解气中CH4、CO、H2、NH3入口浓度与模拟烟气中NO、N2O入口浓度对NO、N2O与总氮转化率的影响。结果表明,向NH3添加可燃气体CO、H2、CH4可使NO还原窗口向低温方向移动150-200 K,该温度窗口为1 073-1 223 K;但NH3-CO-H2-CH4-O2体系对NO、N2O的还原分解作用依赖于体系的O2浓度,仅在富燃料情形（过剩空气系数λ为0.6）下可分别达60.6%、100%的NO、N2O脱除率;在反应温度1 073-1 223 K及过剩空气系数λ为0.6条件下,较高的热解气CH4、CO、H2浓度可增加NO排放,但有利于还原N2O;增加NH3入口浓度可增加NO分解率

青藏高原高寒草地土壤中脂肪酸的分布特征

脂肪酸作为一种重要的生物标志物,已被广泛用于沉积物和土壤中有机质来源的示踪.青藏高原是世界上海拔最高的高原,也是亚洲许多大河沉积物的主要源.本研究在青藏高原高寒草地选择17个采样点,采集不同土层深度的土壤样品,通过测定土壤样品中总有机质参数和生物标志物脂肪酸的含量与组成,并结合环境要素(气温、降水和土壤理化性质)数据,阐明了青藏高原高寒草地不同土层深度脂肪酸的组成、来源和分布特征.结果表明:脂肪酸呈双峰型分布,以C_(16)和偶碳长链脂肪酸(C_(20)~C_(30))为主,表明土壤微生物和高等植物的混合输入源.源解析结果显示高等植物对青藏高原土壤中脂肪酸含量的贡献至少达40%.脂肪酸的含量随土层深度增加而降低,最大值为(1.08±0.09)mg/g OC(以OC计)出现在0~10cm层,最小值为(0.46±0.12)mg/g OC出现在50~70cm层,植物组织的输入在深层土壤中急剧减少是导致此现象的主要原因.与环境因子的相关性分析表明,脂肪酸总含量与年平均气温(P<0.05),表明降水有助于新鲜有机质来源的脂肪酸在青藏高原土壤中的累积.此外,其他环境因素,如土壤矿物含量(铁、铝氧化物)、微生物群落组成、枯落物的质量和数量等,对青藏高原土壤中脂肪酸保留所起的作用亟待进一步研究,以便更好理解青藏高原高寒草地土壤中脂肪酸的保留机理

Three-Dimensional heat transfer analysis and optimized design of actively cooled strut for scramjet applications

In this paper, a numerical analysis coupling heat transfers of the combustor internal flow, the coolant flow and the strut wall is developed and applied for the optimization of strut cooling using aviation kerosene as coolant at flow conditions corresponding to the combustor entrance condition for Mach 6 scramjet flight. The coupling procedure is tested and proven to be an efficient method of being capable to obtain the converged temperature and heat transfer solutions of the cooled strut within a few iteration steps. Four cooling designs with varied diameter, length and position of the cooling channels are investigated and their improvements on fuel injection and mixing are also verified compared to the wall injection. The kerosene-cooled strut (Strut4) is tested in a Mach 2.5 supersonic tunnel with inlet total temperature and total pressure of 1900K and 1.45MPa respectively for 60 seconds. The damaged part in the upper leading edge of the strut is observed, which is consistent with the result obtained by the numerical analysis

Power system abnormal data identification method

本发明涉及一种电力系统异常数据辨识方法，包括将电力系统正常数据作为训练样本，训练神经网络；将待检测数据输入训练后的神经网络，获得残差序列；基于仿射传播聚类算法对残差训练进行聚类；根据各个类别的特征和类内距离进行异常数据判断。本发明利用混沌粒子群算法来进行神经网络训练，同时采用仿射传播聚类算法来实现数据聚类，能够显著降低计算量，同时不依赖采样分布，有效地提高了电力系统异常数据辨识的准确性