铂原子高激发态能级自然辐射寿命测量研究

运用时间分辨激光诱导荧光技术和激光诱导等离子体方法测量了铂原子的15条奇宇称高激发态能级的自然辐射寿命.测量结果处于6.1到116 ns之间,且误差低于10%.经比较,与前人结果在误差范围内符合很好.据文献调研所知,结果中有5条高度接近60000 cm~(-1)的高激发态能级的寿命值是未见报道的.     

取代基对N-H…O=C氢键二聚体中氢键强度的影响

使用MP2方法研究了N-H…O=C氢键二聚体的氢键强度,探讨了不同取代基对N-H…O=C氢键强度的影响.研究发现,可以通过改变取代基的供电性或吸电性来调控氢键强度:乙基等供电子基团对N-H…=C氢键强度的调节作用不大;-NO_2等强吸电子基团可极大地改变N-H…=C氢键强度;质子受体分子中的强吸电子基团如-NO_2可使N-H…O=C氢键强度减弱多达2.6 kcal/mol.自然键轨道(NBO)分析表明,N-H…O=C氢键强度越强,参与形成氢键的氢原子电荷越正,氧原子电荷越负,单体分子间电荷转移越多,N-H…O=C氢键中氧原子孤对电子n(O)对N-H反键轨道σ*(N-H)的二阶稳定化能越大.     

Natural rubber nanocomposites using polystyrene-encapsulated nanosilica prepared by differential microemulsion polymerization

In this study, nanocomposites of natural rubber (NR) and polystyrene (PS)-encapsulated nanosilica were prepared by latex compounding method. The nanolatex of PS-encapsulated silica was synthesized via in situ differential microemulsion polymerization. The resulted hybrid nanoparticles showed core-shell morphology with an average diameter of 40 nm. The silica hybrid nanoparticles were subsequently used as filler for the NR nanocomposite. The properties of NR were found to be improved as a result of the incorporation of PS-encapsulated nanosilica at 3 and 3-9 parts per hundred rubber (phr) for tensile strength and modulus at 300% strain, respectively, except the elongation at break, and up to 9 phr for flammability. The results from dynamic mechanical analyzer showed that the elastic properties of NR near the glass transition temperature increased with the inclusion of increasing concentration of the PS-encapsulated nanosilica, causing by the semi-interpenetrating nanostructure in the NR nanocomposites.     

自然冷源在家用冰箱系统应用及性能分析

空气自然冷源已逐渐用于制冷系统中,引入自然冷源能提高冷凝器出口过冷度,或将自然冷源冷却载冷剂经节流直接引入蒸发器,可有效提高系统COP;基于国内冬春季温度≤5℃的自然冷源分布状况,设计了一种引入自然冷源用于家用冰箱的新型制冷系统,并建立热力学计算模型,分析了不同自然冷源工况时冷凝器过冷度在0、5、10、15℃下的系统COP、压缩机指示功率、系统耗电量及冷凝器热负荷,经计算,冬春季时与传统家用冰箱制冷系统相比,系统COP提高了12%,日均系统耗电量节约0.48kWh。     

石油污染水体荧光图谱特征分析

石油类物质对水体吸收系数的影响主要通过黄色物质(CDOM)体现出来,CDOM和石油类物质皆具有荧光基团,如果两者的荧光图谱各自特征明显的话,那么有望利用荧光技术分离出水中石油物质和CDOM各自对水体总吸收系数的贡献,从而提高水体石油类物质含量的遥感反演精度。以大连周边海水和山区水库水为自然水体本底,分别与取自采油污水厂和炼油污水厂的污水进行混合配比,利用试验数据分析了仅含CDOM、含油与CDOM混合、仅含石油三种水样的荧光图谱特征,旨在为利用荧光技术分离出水中石油物质和CDOM各自对水体总吸收系数的贡献提供依据。分析结果表明：(1)自然水体中,海水的CDOM具有三个典型荧光峰,分别位于Ex:225-230 nm/Em:320～330 nm,Ex:280 nm/Em:340 nm和Ex:225-240 nm/Em:430～470 nm,为海水叶绿素碎屑物所致;淡水具有两典型荧光峰,分别位于：Ex：240～260 nm/Em：420～450 nm和Ex：310～350 nm/Em：420～440 nm,为陆源物质所致;(2)用正己烷萃取后的仅含油水样,具有1～3个荧光峰,分别位于Ex: 220～240 nm/Em：320-340 nm,Ex:270～290 nm/Em：310～340 nm和Ex: 220～235 nm/Em：280～310 nm,为各自烃类成分所致;(3)在自然水体中混入油污水后,含油和CDOM的水样荧光图谱呈现出一个非常强的荧光峰,位于Ex：230～250 nm/Em：320～370 nm,为CDOM和石油类物质荧光成分共同作用所致。     

Computational analysis of non-isothermal temperature distribution on natural convection in nanofluid filled enclosures

In this study, the problem of steady state natural convection in an enclosure filled with a nanofluid has been analyzed numerically by using heating and cooling by sinusoidal temperature profiles on one side. The governing partial differential equations, in terms of the dimensionless stream function–vorticity and temperature, are solved numerically using the finite volume method for various inclination angles 0^°≤?≤90^°$0^{°}\le ?\le 90^{°}$, different types of nanoparticles (TiO₂ and Al₂O₃) and fractions of nanoparticles 0≤φ≤0.1$0\le \phi \le 0.1$, whereas the range of the Rayleigh number Ra is 10³–10⁵. It is found that the addition of nanoparticles into water affects the fluid flow and temperature distribution especially for higher Rayleigh numbers. An enhancement in heat transfer rate was registered for the whole range of Rayleigh numbers. However, low Rayleigh numbers show more enhancement compared to high Rayleigh numbers.     

不同生境华东野核桃光合生理特性及叶绿素荧光参数比较

采用LI-6400便携式光合作用系统,于2011年7月下旬的晴朗天气条件下,对浙江省天台山林窗、林缘、林下生境华东野核桃（Juglans cathayensis var. formosana）的光合生理特性及叶绿素荧光参数进行测定,并比较林窗生境中华东野核桃与其伴生植物山胡椒（Lindera glauca）、玉兰（Magnolia denudata）、云锦杜鹃（Rhododendron fortunei）光合日进程的差异. 结果表明：夏季,林窗生境的华东野核桃及主要伴生植物叶片的净光合速率（P_n）日进程均呈“双峰”曲线,有明显的“午休”现象,其“午休”的原因主要是由非气孔限制因素引起的;林下、林缘的P_n日进程均呈“单峰”曲线.林窗生境的华东野核桃与林缘、林下相比,其光补偿点（LCP）低,光饱和点（LSP）高,对光适应的生态幅较宽;并且林窗生境的华东野核桃暗呼吸速率（R_d）低,日均P_n、最大净光合速率（A_max）高,有利于有机物的积累,说明林窗生境适合其生长. 3种生境华东野核桃的PSⅡ最大光化学效率（F_v / F_m）均呈现出“V”型曲线. 林窗生境中华东野核桃的日均P_n均比其他伴生植物高,且差异均极显著（P＜0.01）,说明华东野核桃的光合作用能力较强.     

基于Sentinel-2A影像的玉米冠层叶绿素含量估算

农作物叶片中的叶绿素通过吸收光能参与光合作用产生化学能,及时、准确地估算叶绿素含量对于农作物长势、养分含量监测、品质评价和产量估算具有重要意义。Sentinel-2卫星的重访周期为5 d,空间分辨率为10 m,具有13个光谱波段,其中包括三个波宽仅为15 nm对叶绿素含量变化敏感的红边波段,是叶绿素含量估算的理想数据源。植被指数是基于农作物在不同波段的反射特性,通过不同波段组合方式刻画长势和叶绿素含量的差异,可用于大区域范围内的玉米冠层叶绿素含量快速、精确估算。以Sentinel-2A影像为数据源,开展基于多种植被指数的玉米冠层叶绿素含量估算方法研究。课题组于2016年8月6-11日在河北省保定市（115°29′-116°14′E,39°5′-39°35′N）进行玉米冠层叶绿素含量的实地测量,并在每个采样位置上采用中绘i80 智能RTK(real-time kinematic)测量系统进行定位。Sentinel-2A影像预处理工作包括几何校正、辐射定标和大气校正,其中大气校正使用Sen2Cor模型和SNAP模型。首先,基于预处理后的Sentinel-2A遥感影像,分别计算CI_green(green chlorophyll index), CI_red-edge(red-edge chlorophyll index), DVI(difference vegetation index), LCI(leaf chlorophyll index), MTCI(MERIS terrestrial chlorophyll index), NAVI(normalized area vegetation index), NDRE(normalized difference red-edge), NDVI(normalized difference vegetation index), RVI(ratio vegetation index), SIPI(structure insensitive pigment index)植被指数。然后,建立样方位置上实测叶绿素含量与各植被指数的统计关系,从而构建玉米冠层叶绿素含量估算模型,并以野外实测玉米冠层叶绿素含量为依据,对基于各植被指数的估算结果进行精度评价。最后,利用筛选出的最优叶绿素含量估算模型,估算研究区内的玉米冠层叶绿素含量。研究的目标为：（1）通过比较分析,构建合适的玉米冠层叶绿素含量估算模型,估算精度以决定系数R2、均方根误差RMSE以及相对误差RE作为评价指标;（2）确定最优波段组合方案：在红边波段中选择与可见光、近红外波段组合效果更优的波段组合方案;（3）确定参与植被指数计算的红边波段的最优数量。精度评价结果表明：（1）选用的植被指数与玉米冠层叶绿素含量呈多项式拟合关系,其中使用红边波段计算的植被指数的估算结果明显优于未使用红边波段的估算结果;红边波段引入后明显提高了可见光、近红外波段对叶绿素含量的拟合的精度,CI_{green(560, 705)}指数比CI_{green(560, 842)}的回归模型R2提高0.516,红边波段参与计算的DVI相对于RVI来说,估算结果更稳定。（2）对于不同的植被指数,参与运算的Sentinel-2A影像的两个红边波段,估算精度的提高程度不同。对于可见光波段参与计算的植被指数来说,在红边波段1（中心波长为705 nm）的估算精度较高,如LCI,CI_green,DVI和RVI等;对于近红外波段参与计算的植被指数来说,在红边波段2（中心波长为740 nm）的估算精度较高,如CI_red-edge,NDRE和NAVI等。（3）对于Sentinel-2A影像来说,两个红边波段共同参与叶绿素含量估算时能取得最高的的估算精度。选用的植被指数中,MTCI_{(665, 705, 740)}指数与玉米冠层叶绿素含量估算精度最高,回归模型拟合精度R2为0.803,模型验证R2为0.665,RMSE为3.185,相对误差RE为4.819%。MTCI_{(665, 705, 740)}指数计算中使用了两个红边波段,突出红边波段反射率差值变化,与玉米冠层叶绿素含量表现出很好的相关性。最后,利用优选出的基于MTCI指数的叶绿素含量估算模型,对研究区范围内的叶绿素含量进行估算并完成空间制图。     

Remote Estimation of the Chlorophyll Concentration of Living Trees Using Laser-induced Fluorescence Imaging Lidar

Monthly variation in chlorophyll concentration of living ginko tree leaves 65 m away from a system was remotely estimated by a laser-induced fluorescence imaging lidar. The combination of a pulsed laser and a short-time gated CCD using an image intensifier made it possible to monitor the weak fluorescence signal from the ginko tree leaves as an image. By applying the experimental idea that a ratio of intensity of the chlorophyll fluorescence at 740 nm to that at 685 nm showed a linear correlation to the chlorophyll concentration, the fluorescence image of the ginko tree obtained by the lidar was converted to the chlorophyll concentration distribution image.     

Coupling between aging and convective motion in a colloidal glass of Laponite

We study thermal convection in a colloidal glass of Laponite in formation. Low concentration preparation are submitted to destabilizing vertical temperature gradient, and present a gradual transition from a turbulent convective state to a steady conductive state as their viscosity increases. The time spent under convection is found to depend strongly on sample concentration, decreasing exponentially with mass fraction of colloidal particles. Moreover, at fixed concentration, it also depends slightly on the pattern selected by the Rayleigh Bénard instability: more rolls maintain the convection state longer. This behavior can be interpreted with recent theoretical approaches of soft glassy material rheology.