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971.
全球导航卫星掩星探测仪(GNOS)是国际首台北斗系统(BDS)和全球定位系统(GPS)双系统兼容掩星探测仪, 2013年9月23日随风云三号卫星C星(FY3 C)发射入轨, 目前已测得大量掩星数据. 介绍了FY3 C-GNOS的组成; 统计了2013年10月12日全天的FY3 C-GNOS掩星事件及其全球分布情况; 通过与GPS精密定轨结果进行对比分析, 测试了BDS在轨实时定位精度, 检验了BDS掩星产品的可靠性和一致性. 初步分析结果表明: 14颗BDS卫星在轨运营的条件下, BDS和GPS兼容掩星探测仪可将掩星事件数提高约33.3%; BDS实时定位平均偏差优于6 m, 标准偏差优于7 m; 5-25 km高度范围内, BDS与GPS内符合精度大气折射率优于2%, 温度优于2 K, 湿度优于1.5 g/kg, 压强优于2%, 电离层峰值密度优于15.6%. GNOS的在轨正常运行及BDS与GPS掩星定位精度及反演产品的一致性为北斗掩星探测的业务化运行奠定了基础. 相似文献
972.
脉冲磁约束线形空心阴极放电形成的大面积等离子体片可应用于等离子体天线、隐身及模拟超音速飞行器表面的等离子体鞘套. 本文首次利用实测等离子体片电子密度时空分布和横向场传播矩阵法, 研究了电磁波在等离子体片中反射率、透射率、吸收率随频率及脉冲放电时间的变化特征. 结果表明: 极化方向平行磁场的电磁波, 在小于截止频率的低频带内具有较高的反射率和吸收率, 增大电流, 反射率增加, 吸收率下降, 在大于截止频率的高频带内反射率和吸收率较低, 增大电流, 透射率下降, 吸收率升高; 极化方向垂直磁场的电磁波在高混杂谐振频率附近存在吸收率明显增强的吸收带, 谐振吸收峰值与放电电流无关; 脉冲放电期间, 电磁波的反射率、透射率与吸收率由不稳定过渡到稳定的时间约为100 μs, 过渡时间随着放电电流的增加而增大, 极化方向垂直磁场、小于截止频率的电磁波在稳定放电阶段谐振吸收较强. 本文的研究成果对利用等离子体片实现对电磁波的稳定高反射作用具有重要意义. 相似文献
973.
974.
975.
Carbon nanodots (C-Dots) have attracted much attention in recent years due to their low cost, ready scalability, excellent chemical stability, biocompatibility and multicolor luminescence. Here, we report a facile strategy for producing highly luminescent, surface-different nitrogen-doped carbon dots (C-Dots) by using different ionic liquids (ILs). Intriguingly, the surface-different C-Dots show different selectivity for Cu2+ and Fe3+. To the best of our knowledge, this is the first example which shows that ILs are excellent precursors for producing luminescent nanomaterial used for detection of different metal ions. The resultant nitrogen-doped C-Dots are highly photoluminescent and can be used for multicolor bioimaging. Most notable, by taking different ILs as precursors, we obtain surface-different C-Dots, which can be directly used for selective detection of Cu2+ and Fe3+ without any modification. These C-Dots based sensors exhibit high sensitivity and selectivity and the sensing process can be easily accomplished with one-step rapid operation. More importantly, compared with other method using QDs, organic dyes and organic solvent, this strategy is much more eco-friendly. This work may offer a new approach for developing low cost and sensitive C-Dots-based sensors for biological and environmental applications. 相似文献
976.
An efficient and stereoselective synthesis of diaza-triquinanes, the skeleton structures of many natural products, has been accomplished by intramolecular 1,3-dipolar cycloaddition of azomethine imine generated from sugar-derived hex-5-enal and pyrazolidin-3-one. 相似文献
977.
A novel metallo‐organically templated pentaborate with layered framework, [Cd(TETA)(C2H3O2)][B5O6(OH)4] ( 1 ) (TETA = triethylenetramine), was synthesized under mild solvothermal conditions. The structure was determined by single‐crystal X‐ray diffraction and further characterized by FT‐IR spectroscopy, elemental analysis, thermogravimetric analysis, and photoluminescence spectroscopy. The structure consists of an isolated polyborate anion [B5O6(OH)4]– and the cadmium complex cation of [Cd(TETA)(C2H3O2)]+, which contains both organic amine and organic acid ligands. The [B5O6(OH)4]– units are connected together by hydrogen bonds, and a 2D sheet‐like framework with rectangle‐like 12‐membered boron rings are formed. The [Cd(TETA)(C2H3O2)]+ complex cations are located in the free space between the layers and connect the adjacent borate layers through hydrogen bonds to form a three‐dimensional supramolecular network. The luminescent properties of the compound were studied for the first time in the series of metallo‐organically‐templated pentaborates, and a blue luminescence occurs with an emission maximum at 468 nm upon excitation at 397 nm. 相似文献
978.
979.
First-principles calculations using the augmented plane wave plus local orbitals method, as implemented in the WIEN2K code, have been carried out to study the A-B intersite charge transfer and the correlated electrical and magnetic properties of the perovskite BiCu(3)Fe(4)O(12), especially as regards the charge transfer. The results indicate that the charge transfer between A-site Cu and B-site Fe is by way of O 2p orbitals, and during this process orbital hybridization plays an important role. More importantly, the charge transfer is of 3d(9) + 4d(5)L(0.75) →3d(9)L + 4d(5) type (here L denotes an oxygen hole or a ligand hole). During this process, the magnetic interaction experiences a transition from Cu-Fe ferrimagnetic coupling to G-type antiferromagnetic coupling within B-site Fe with paramagnetic Cu(3+). As to electrical property, it undergoes a metal to insulator transition. All our calculated results are consistent with the available experimental results. 相似文献
980.
Ma M He Z Yang J Chen F Wang K Zhang Q Deng H Fu Q 《Langmuir : the ACS journal of surfaces and colloids》2011,27(21):13072-13081
In this Article, the morphological evolution in the blend thin film of polystyrene (PS)/poly(ε-caprolactone) (PCL) was investigated via mainly AFM. It was found that an enriched two-layer structure with PS at the upper layer and PCL at the bottom layer was formed during spinning coating. By changing the solution concentration, different kinds of crystal morphologies, such as finger-like, dendritic, and spherulitic-like, could be obtained at the bottom PCL layer. These different initial states led to the morphological evolution processes to be quite different from each other, so the phase separation, dewetting, and crystalline morphology of PS/PCL blend films as a function of time were studied. It was interesting to find that the morphological evolution of PS at the upper layer was largely dependent on the film thickness. For the ultrathin (15 nm) blend film, a liquid-solid/liquid-liquid dewetting-wetting process was observed, forming ribbons that rupture into discrete circular PS islands on voronoi finger-like PCL crystal. For the thick (30 nm) blend film, the liquid-liquid dewetting of the upper PS layer from the underlying adsorbed PCL layer was found, forming interconnected rim structures that rupture into discrete circular PS islands embedded in the single lamellar PCL dendritic crystal due to Rayleigh instability. For the thicker (60 nm) blend film, a two-step liquid-liquid dewetting process with regular holes decorated with dendritic PCL crystal at early annealing stage and small holes decorated with spherulite-like PCL crystal among the early dewetting holes at later annealing stage was observed. The mechanism of this unusual morphological evolution process was discussed on the basis of the entropy effect and annealing-induced phase separation. 相似文献