分类： 地球科学 >> 空间物理学 提交时间： 2017-10-31
摘要： The thermal structure and energy balance of upper atmosphere are dominated by solar activity. The response of Cold-Point-Mesopause(CPM) to solar activity is an important form. This article presents the response of Temperature-of-CPM(T-CPM) to solar activity using fourteen-year SABER data series over 80°S–80°N regions. These regions are divided into 16 latitude zones with 10° interval, and the spatial areas of 80°S—80°N,180°W—180°E are divided into 96 lattices with 10°(latitude)×60°(longitude) grid. The annual-mean values of T-CPM and F10.7 are calculated. The least squares regression method and correlation analysis are applied to these annual-mean series. First, the results show that the global T-CPM is significantly correlated to solar activity at the 0.05 level of significance with correlation coefficient of 0.90. The global solar response of T-CPM is 4.89±0.67K/100 Solar-Flux-Units(SFU). Then, for each latitude zone, the solar response of T-CPM and its fluctuation are obtained. The solar response of T-CPM becomes stronger with increasing latitude. The fluctuation ranges of solar response at middle latitude regions are smaller than those of equator and high latitude regions, and the global distribution takes on W-shape. The co-relationship analysis shows that the T-CPM is significantly correlated to solar activity at the 0.05 level of significance for each latitude zone. The correlation coefficients at middle latitude regions are higher than those of equator and high latitude regions, and the global distribution takes on M-shape. At last, for each grid cell, the response of T-CPM to solar activity and their correlation coefficient are presented.
分类： 地球科学 >> 大气科学 提交时间： 2017-10-31
摘要： The Trends of the Cold-Point Tropopause CPT are presented using high-resolution radiosonde observations from 77 stations over China during 1979—2014. The latitude region from 18°N to 53°N is divided into 7 latitude zones with every 5° intervals and the spatial area of 18°N—53°N 75°E—135°E is divided into 27 lattices with 5°×10° grids. The annual-mean values of Height-of-CPT H-CPT and Temperature-of-CPT T-CPT are obtained. First by using the least squares regression method it is found that the H-CPT increases with rate of 273m/decade and overall significant cooling rate of -0.70K/decade for the T-CPT over China. Then the trends and latitude distribution of H-CPT and T-CPT for each latitude zone are reached. The change rates even the change direction of H-CPT H-CPT show obviously latitude distribution characteristics. The characteristic difference of H-CPT among latitude distribution is reducing year by year and corresponding T-CTP is enlarging. The H-CPT displays uplift trend between 28°N—53°N latitude region with the positive change rates and corresponding it has decline trend between 18°N—28°N latitude region with the negative change rates. The change rates of T-CPT are negative values for all latitude zones. Third the spatial latitude-longitude distribution of long-term trends of H-CPT T-CPT for each grid are obtained. The change rates of H-CPT T-CPT are not only dependent on latitude but also on longitude. At last the spatial structure of annual fluctuation of H-CPT T-CPT for each grid are obtained. The fluctuation of standard deviations of T-CPT is not only related to spatial distribution but also to economic belt of China.
分类： 动力与电气工程 >> 工程热物理学 提交时间： 2017-10-31 合作期刊: 《工程热物理学报》
摘要： 本文利用CFD数值模拟软件对当量直径为200 μm的不同孔隙率的叉排圆形微针肋热沉的流动和传热特性进行了数值模拟。模拟结果表明，随着雷诺数的增加，针肋尾部出现不同形态的涡。不同孔隙率的通道中，由于后排针肋的影响，针肋尾迹区的涡的形态、大小出现不同。对不同孔隙率的微针肋热沉，热流密度的变化对热沉的努赛尔数Nu的影响不同，孔隙率较小时热流密度对热沉的努赛尔数Nu影响不大，孔隙率较大时热流密度升高，热沉的努赛尔数Nu升高。
分类： 动力与电气工程 >> 工程热物理学 提交时间： 2017-10-31 合作期刊: 《工程热物理学报》
摘要： 采用显微实验与理论分析相结合的方法，对直流电场作用下水滴破裂前的拉伸过程及其时间特征进行了系统研究。结果表明，电毛细数和表面活性剂浓度是影响水滴拉伸过程的关键因素，而油水粘度比和电导率比的影响并不显著。拉伸时间对低电毛细数和高表面活性剂浓度体系更为敏感。在实验范围内，直流电场作用下球形水滴经拉伸并破裂的最小时间为10 ms。基于此，提出了一种可有效提高水滴静电聚并效率并抑制电分散现象的脉冲电场设计方法。
分类： 动力与电气工程 >> 工程热物理学 提交时间： 2017-10-31 合作期刊: 《工程热物理学报》
摘要： 本文基于多源X射线层析成像技术及联合代数重建算法(SART)首次重构出粘性B类颗粒流化时局部气泡的三维形态，并结合压力脉动分析技术获得了丰富的全局流态化信息。实验结果表明，粘性力的增加强化了气泡间的合并作用，导致气泡的尺寸上升，频率和速度下降，当床温超过35°C后，节涌状态被激发，并与自由流化状态交替产生。而且，粘性力越大，节涌在流化过程中所占的时间比例越长。
分类： 动力与电气工程 >> 工程热物理学 提交时间： 2017-10-31 合作期刊: 《工程热物理学报》
摘要： 本文对变质量流率蒸汽浸没射流压力振荡特性开展了实验研究，发现蒸汽质量流率随时间延长呈指数规律下降。蒸汽射流凝结经历了稳定凝结、振荡凝结、过渡和喘振四个阶段，射流初始水温越高，各个凝结区域转换点对应的蒸汽质量流率越高。在不同的凝结区域，蒸汽质量流率和过冷水温度对振荡特性的影响程度不同。相同蒸汽质量流率时，初始水温越高振荡频率越小。振荡强度均方根值和峰值均在凝结振荡区达到最大，且初始水温越高，最大值对应的蒸汽质量流率越高，振荡强度峰值最高可达70 kPa。
分类： 动力与电气工程 >> 工程热物理学 提交时间： 2017-10-31 合作期刊: 《工程热物理学报》
摘要： 本文基于离焦测距原理，提出一种利用单镜头双相机测量运动颗粒三维速度的方法。入射光经分束立方体分别进入两个工业相机，通过调节分束立方体与相机间的垫圈厚度获取同一对象两幅不同模糊度的图片，根据其模糊差实现运动颗粒在三维场中的定位，再结合单帧多曝光方法，获取其三维速度。通过拍摄慢速搅拌水流中颗粒运动并分析处理不同运动情况的颗粒图片得到了运动颗粒的三维速度，经计算与实验考察证明了其可行性。该方法解决了离焦二义性问题与速度方向二义性问题，为三维速度的测量提供了新的方向。
分类： 动力与电气工程 >> 工程热物理学 提交时间： 2017-10-31 合作期刊: 《工程热物理学报》
摘要： 风扇转子工作在高压比、高转速、高负荷的级环境中，实际流动中存在风扇的长叶片与流体间强烈的耦合作用。针对风扇实际工作中存在的流固耦合问题，本文通过基于时域推进的双向流固耦合方法对风扇转子的流固耦合问题进行求解，并在此基础上对该转子的超声速非失速颤振现象进行研究。分析结果表明，考虑耦合效应的转子特性线整体向大流量方向偏移0.7%，效率降低约0.76%，总压比基本保持不变，稳定工作裕度略有减小；转子在设计转速下近效率最大点处，可能会发生基于叶片一阶固有模态振动的超声速非失速颤振现象。
分类： 材料科学 >> 材料化学 提交时间： 2017-10-31
摘要： Incorporating noble metal nanoparticles on the surface or inner side of semiconductors to form a hybrid nanostructure is an effective route to improve the gas sensing performance of these semiconductors. In this study, we present novel Au-decorated ZnO nanospheres (Au-ZnO NSs) obtained by laser irradiation of liquids. Structural characterization indicated that the Au-ZnO NSs consisted of single crystalline ZnO NSs with few Au nanoparticles decorated on their surfaces and abundant encapsulated Au nanoparticles with relatively small sizes. Laser irradiation-induced heating–melting–evaporating processes are responsible for the formation of unique Au-ZnO NSs. Gas sensing properties of the Au-ZnO NSs, as gas sensing materials, were investigated and compared with those of pure ZnO NSs. The former showed lower working temperature, higher sensitivity, better selectivity, and good reproducibility. The response values of Au-ZnO NSs and pure ZnO NSs sensors to ethanol of 100 ppm were 252 and 75 at working temperature of 320 °C and 360 °C, respectively. The significant enhancements in gas sensing performance should be attributed to the electronic sensitization induced by the depleted layers between encapsulated Au nanoparticles and ZnO and chemical sensitization originating from the catalytic effects of Au nanoparticles decorated on the surfaces that dissociated molecular oxygen.
分类： 材料科学 >> 材料化学 提交时间： 2017-10-31
摘要： A general and straightforward strategy was developed for fabricating transition metal carbide (TMC)/carbon (C) core/shell nanospheres (NSs) by laser ablation of transition metals in acetone/ethanol liquid. Various TMC/C core/shell NSs such as TaC/C, NbC/C, HfC/C, and MoC/C core/shell NSs were successfully fabricated, highlighting the generality of this method. Crucially, this approach is green, facile, catalyst-free, and especially can be operated under ambient environments. Interestingly, all of the as-synthesized TMCs in the NS cores showed a cubic phase and structures similar to that of NaCl-type. The cores were further encapsulated by amorphous carbon shell with different thickness. As an example of the functional properties of these compound materials, the TaC/C core/shell NSs obtained were investigated as a supercapacitor electrode, which showed a large specific capacitance, excellent rate capability and remarkable cycling ability, revealing that the NSs could be used as new electrode materials for electrochemical energy storage. The photoluminescence of TaC/C core/shell NSs exhibited strong emission under the specific excitation wavelength at room temperature, showing potential biomedical applications due to the good biocompatibility of carbon shell. Besides, the basic physical and chemical reactions involved in the unique formation mechanism under highly nonequilibrium states induced by ultrafast laser ablation were discussed.
分类： 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间： 2017-10-31
摘要： Catalysts are the foundation of sustainable and renewable energies to address the depletion of natural fossil fuels problem. Because the catalysts’ activity is surface chemistry dependent, those “naked”, so-called ligand-free catalysts with more active sites exposing to the reactants are more preferable. With ligand-free, highly surface charged nanomaterials as the innate products, a newly emerging technique―laser synthesis and processing in liquids―is gaining increasing attention. The priority of laser-synthesized ligand-free metallic catalysts over chemically-synthesized counterparts has been confirmed by increasing groups through comparative studies on their catalytic activities. Besides the ligand-free metallic catalysts, this technique also excels at synthesis of bimetallic-alloy, core-shell and defect-rich semiconductor catalysts, and show good compatibility with other techniques (e.g., hydrothermal treatment and electrophoresis) to develop advanced catalysts such as ternary oxide, doped semiconductor, supported composite, nanoparticle-polymer matrix and film catalysts. Following the concept of why to choose, how to synthesize and where to use, in this review, we first introduce the advantages of this technique and the synthesized catalysts, secondly show how to develop complex catalysts using the laser-generated particles as the building blocks, and finally present the exciting application examples for photodegradation, water splitting and fuel cells.
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