The response of CO2 flux to rain pulses at a saline desert     

Jie Ma  Xin‐Jun Zheng  Yan Li 《水文研究》2012,26(26):4029-4037

As the substantial component of the ecosystem respiration, soil CO₂ flux is strongly influenced by infrequent and unpredictable precipitation in arid region. In the current study, we investigated the response of soil CO₂ flux to rain pulses at a saline desert in western China. Soil CO₂ flux was measured continuously during the whole growing season of 2009 at six sites. We found that there were remarkable changes in amplitude or diurnal patterns of soil CO₂ flux induced by rainfall events: from bimodal before rain to a single peak after that. Further analysis indicated that there is a significant linear relationship (P < 0.001) between soil CO₂ flux and soil temperature (T_soil). However, a hysteresis between the waveform of diurnal course of CO₂ flux and T_soil was observed: with soil CO₂ flux always peaked earlier than T_soil. Furthermore, a double exponential decay function was fitted to the soil CO₂ flux after rainfall, and total carbon (C) releases were estimated by numerical integration for rainfall events. The relative enhancement and total C release, in association with the rain pulses, was linearly related to the amount of precipitation. According to the size and frequency of rainfall events, the total amount of C release induced by rain pulses was computed as much as 7.88 g C·m^–2 in 2009, equivalent to 10.25% of gross primary production. These results indicated that rain pulses played a significant role in the carbon budget of this saline desert ecosystem, and the size of them was a good indicator of rain‐induced flux enhancement. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Flows within the Ekman layer during spin-up of a thermally stratified fluid     

Jae Min Hyun 《地球物理与天体物理流体动力学》2013,107(1-4):65-79

Abstract

Finite-difference numerical solutions were obtained to present the flow and temperature field details within the transient Ekman layer during spin-up of a thermally stratified fluid in a cylinder. This complements the earlier studies on stratified spin-up which examined the flows in the interior core region. As the stratification increases, the following changes in the flow field are noticeable. The radial velocity in the Ekman layer decreases in magnitude. The azimuthal flows adjust smoothly from the interior region to the endwall boundary, and the Ekman layer in the azimuthal flow field fades. Vertical motions are inhibited, resulting in a weakened Ekman pumping. The axial vorticity field behaves similarly to the azimuthal flows. The temperature deviation from the equilibrium profile decreases, and the heat transfer flux from the endwall to the fluid decreases. The thickness of the thermal layer is larger than the velocity layer thickness. Illustrative comparisons of the relative sizes of the terms in the governing equations are conducted in order to assess the stratification effect in the adjustment process of the fluid.  相似文献   

一个基于AOP的Bean锁算法   总被引：1，自引：1，他引：0  

黄强  李敏  楼新远 《成都信息工程学院学报》2006,21(2):225-228

提出了一种基于Aspect Oriented Programming（AOP）的Bean锁算法，通过将Bean锁抽象成该问题的一个方面（Aspect），通过AOP引擎使用该算法动态生成加锁Bean，大大降低Bean锁代码的重复量，并在基本不影响性能的前提下，提高代码复用率。通过使用基于AOP的Bean锁，Bean可以完全消除锁代码，从而提高Bean代码的可维护性。  相似文献   

The Correlation between Gamma-ray and Radio Emissions in γ-ray Loud Blazars   总被引：4，自引：0，他引：4  

Jiang-He Yang  Jun-Hui Fan Department of Physics  Electronics Science  Hunan University of Arts  Science  Changde  Center for Astrophysics  Guangzhou University  Guangzhou National Astronomical Observatories  Chinese Academy of Sciences  Beijing Physics Institute  Hunan Normal University  Changsha 《中国天文和天体物理学报》2005,5(3):229-237

We collect 119 v-ray-loud blazars (97 flat spectrum radio quasars (FSRQs) and 22 BL Lacertae objects (BL Lacs)), and investigate possible correlations between their γ-ray emission (maximum, minimum and average values) at 1 GeV and the radio emission at 8.4 GHz. Our main results are as follows. For the lower state γ-ray data, there is no correlation between the γ-ray and radio flux density; For the high state γ-ray data, there are good correlations for the whole 119 blazars and 97 FSRQs, and a weak correlation for the 22 BL Lac objects; For the average γ-ray data, there are good correlations. According to our analysis, we propose that the γ-rays are associated with the radio emission from the jet, and that the γ-ray emission is likely from the SSC process in this case.  相似文献   

GPS无线电掩星数据处理系统     

郭鹏徐会作   《中国科学院上海天文台年刊》2006,(1):118-128

GPS无线电掩星技术能提供高精度、高分辨率、全球覆盖的地球电离层和中性层大气剖面。它具有全天候、低费用、无系统长期漂移等优点。从1995年4月至1997年3月,首次GPS／MET试验的成功显示了GPS掩星技术对监测全球大气能够发挥重要的作用,从而成为当前空间探测技术的研究热点之一。该文主要叙述了无线电掩星技术的数据处理系统的有关情况,并介绍了美国UCAR的掩星数据处理系统CDAAC的概况,可作为我国开展无线电掩星计划有关工作的借鉴。  相似文献   

Comparison between Windowed FFT and Hilbert-Huang Transform for Analyzing Time Series with Poissonian Fluctuations: A Case Study     

Dong Han  Shuang-Nan Zhang Department of Engineering Physics & Center for Astrophysics  Tsinghua University  Beijing  Department of Physics & Center for Astrophysics  Tsinghua University  Beijing Key Laboratory of Particle Astrophysics  Institute of High Energy Physics  Chinese Academy of Sciences  Beijing 《中国天文和天体物理学报》2006,6(4)

Hilbert-Huang Transform (HHT) is a novel data analysis technique for nonlinear and non-stationary data. We present a time-frequency analysis of both simulated light curves and an X-ray burst from the X-ray burster 4U 1702-429 with both the HHT and the Windowed Fast Fourier Transform (WFFT) methods. Our results show that the HHT method has failed in all cases for light curves with Poissonian fluctuations which are typical for all photon counting instruments used in astronomy, whereas the WFFT method can sensitively detect the periodic signals in the presence of Poissonian fluctuations; the only drawback of the WFFT method is that it cannot detect sharp frequency variations accurately.  相似文献   

The Influence of Ion-Acoustic Turbulence on the Electron Acceleration in the Reconnecting Current Sheet     

Gui-Ping Wu  Guang-Li Huang  Yu-Hua TangDepartment of Physics  Southeast University  Nanjing  Purple Mountain Observatory  Chinese Academy of Sciences  Nanjing Department of Astronomy  Nanjing University  Nanjing 《中国天文和天体物理学报》2005,5(1):99-109

Through solving the single electron equation of motion and the Fokker-Planck equation including the terms of electric field strength and ion-acoustic turbulence, we study the influence of the ion-acoustic wave on the electron acceleration in turbulent reconnecting current sheets. It is shown that the ion-acoustic turbulence which causes plasma heating rather than particle acceleration should be considered. With typical parameter values, the acceleration time scale is around the order of 10^-6 s, the accelerated electrons may have approximately a power-law distribution in the energy range 20 ～100 keV and the spectral index is about 3～10, which is basically consistent with the observed hard X-ray spectra in solar flares.  相似文献   

相位校准电路原理分析及测试     

王锦清  韦文仁 《中国科学院上海天文台年刊》2006,(1):83-91

该文详细地介绍了相位校准单元的电路和数学原理以及测试结果。在电路原理部分主要介绍相位校准单元的工作原理、各个关键点的波形以及用隧道二极管产生梳状谱的典型电路。数学原理主要阐述了测量梳状谱的数学依据。最后给出了该相位校准单元的测试要求和测试结果。  相似文献   

JXTA安全问题研究     

张莹  徐志根 《成都信息工程学院学报》2004,19(4):496-499

P2P对等网络(Peer-to-Peer network)是近年来引起广泛关注的网络技术,JXTA项目则是构建P2P网络平台的一个典型例子.针对JXTA网络中面临的安全问题及解决方案进行了初步探讨,最后以在JXTA中实现数字签名为例,介绍了目前正在积极开发中的JXTA安全项目.  相似文献   

设计模式及其在J2ME中的应用   总被引：2，自引：0，他引：2  

韩鹏  李成忠 《成都信息工程学院学报》2004,19(3):332-335

设计模式被描述为在一定的环境中解决某一类问题的方案.已成为现代软件系统设计的重要研究对象.介绍了J2ME体系结构,并深入探讨了3种典型设计模式在J2ME开发中的应用.  相似文献