排桩冻结法深基坑施工监测与反馈分析

对于润扬大桥南锚碇排桩冻结法深大基坑,冻结作用使基坑的受力过程变得更为复杂,根据排桩冻结法基坑结构和场地工程地质条件,建立了大型安全监测系统。本文介绍了润扬大桥南锚碇场地工程地质条件、排桩冻结法基坑的结构和南锚碇基坑监测方案、分析了南锚排桩冻结法深基坑各项监测数据的变化规律,包括侧向土压力、内支撑轴力、排桩钢筋应力和排桩水平位移随时间变化规律,并基于施工监测进行了反馈分析,保障了南锚碇排桩冻结法深基坑的安全与稳定。监测结果分析表明,排桩冻结法是基坑工程的一种可行的施工工法,润扬大桥南锚碇排桩冻结法深大基坑的成功实践为今后类似工程的建设积累了宝贵经验。     

沙尘气溶胶与气候变化

沙尘气溶胶通过吸收和散射太阳辐射与长波辐射影响地球辐射收支和能量平衡,从而影响气候变化。另一方面,气候变化,土地利用、沙漠化和城市化等人类活动都是可能导致大气中矿物沙尘气溶胶的改变。沙尘气溶胶在全球及区域尺度气候和环境变化中起着十分重要的作用。     

系统论思想在地貌学中的应用

系统论的思潮及其基本原则迅速地向地貌学领域渗透和扩展,改变着地貌学家的知识结构和思维方式。愈来愈显示出地貌学的一个新的生长点——系统地貌学,将以其强大的生命力萌发出来。它将从系统论与控制论的角度,研究地球表面形态结构及其物质组成与自然环境、社会经济环境之间的相互作用,揭示地貌系统的结构、功能及其演化规律性;对地域分异形成的不同地貌景观,分别建立过程-反应模式。为优化人地系统、合理利用自然资源、建立区域发展最优模式的决策提供科学依据。     

Pulsations of microwave emission and flare plasma diagnostics

We consider the modulation of nonthermal gyrosynchrotron emission from solar flares by the ballooning and radial oscillations of coronal loops. The damping mechanisms for fast magnetoacoustic modes are analyzed. We suggest a method for diagnosing the plasma of flare loops that allows their main parameters to be estimated from peculiarities of the microwave pulsations. Based on observational data obtained with the Nobeyama Radioheliograph (17 GHz) and using a technique developed for the event of May 8, 1998, we determined the particle density n≈3.7×10¹⁰ cm^?3, the temperature T≈4×10⁷ K, and the magnetic field strength B≈220 G in the region of flare energy release. A wavelet analysis for the solar flare of August 28, 1999, has revealed two main types of microwave oscillations with periods P₁≈7, 14 s and P₂≈2.4 s, which we attribute to the ballooning and radial oscillations of compact and extended flare loops, respectively. An analysis of the time profile for microwave emission shows evidence of coronal loop interaction. We determined flare plasma parameters for the compact (T≈5.3×10⁷ K, n≈4.8≈10¹⁰ cm^?3, B≈280 G) and extended (T≈2.1≈10⁷ K, n≈1.2≈10¹⁰ cm^?3, B≈160 G) loops. The results of the soft X-ray observations are consistent with the adopted model.     

东北季风与南海海洋环流的相互作用

针对冬、春季南海区风场，表层海流、海温场的季节变化，选用了２＾１／３层海洋模式和简单一层大气边界层模式，研究了冬、春季我作用下南海上层海洋环流的基本形态及其对ＳＳＴ的影响，估算了这种影响对海南风场的反馈效应。研究结果表明，冬、春季东北 与南海五流的相互作用对吕宋岛西部海域的气旋式冷涡的形成和维持有利。冬季（１月）强东北风作用使南海上层为一气旋式环流，上层环流对季风的反馈作用可使南海西北部东北风减弱     

Soil Moisture Parameterization and Its Influences in Weather and Climate Simulation: A Review

The soil hydrological process in land surface models and its influences on weather and climate simulation have got much attention by scholars both at home and abroad. First, this paper traced the definition and determination of soil moisture, and then reviewed its parameterization in different models, including soil-water characteristic curves for different soil types and numerical methods for solving soil moisture equations. Moreover, methods of soil hydrological parameter determination and uncertainties within land surface models were specified. Also, the importance of methods in parameter sensitivity analysis and optimization was emphasized, and the new datasets of soil hydraulic parameters would play a very important role in the improvement of the land surface model and soil moisture simulation. Finally, the research progress of feedback mechanism between soil moisture and precipitation was summarized. Spatial and temporal distribution of soil moisture and its abnormal would cause a positive feedback, and on the contrary, the meso-scale characteristics of soil moisture distribution had a negative feedback. By summarizing the progresses of the uncertainties and problems in soil moisture simulation, the influences of soil moisture on simulating weather and climate were pointed out.     

Critical phenomena in thermal conductivity: Implications for lower mantle dynamics

Microscopic mechanisms for heat transport in dense minerals (phonon scattering and photon attenuation) exhibit aspects of threshold behavior, discussed qualitatively here. For all minerals examined so-far using laser-flash analysis, the lattice component of the thermal conductivity of the mantle asymptotes to a constant above a critical temperature of 1500 K. Radiative transfer calculated from absorption spectra has thresholds in both grain-size and Fe content, and a rather complex dependence on temperature. These critical phenomena impact convection of the lower mantle, because the lattice contribution tends to destabilize the cold boundary layers, whereas radiative transfer mostly promotes stability in the lower mantle, unless the grains are large and Fe-rich, which makes convection chaotic and time-dependent. The specific behavior suggests that flow in the lower mantle is sluggish, whereas flow in the upper mantle-transition zone is time-dependent. The decrease in k_rad as Fe/(Fe + Mg) increases beyond 0.1 may be connected with formation of lower mantle, thermo-chemical plumes through positive feedback.     

Thermal cyclotron radiation from hot coronal loops and peculiarities of the polarization structure of solar microwave emission sources: II. Integrated characteristics

We present our calculations of the expected characteristics of the integrated spectrum of thermal cyclotron radiation from a solar active region with a coronal magnetic loop. A hot torus is considered as a three-dimensional loop model. We show that the hot-loop emission can change appreciably the emission characteristics of the active region at centimeter and decimeter wavelengths. At certain loop parameters, the emission frequency spectrum can have a nonmonotonic and complex pattern with several peaks or contain narrow-band cyclotron lines. The polarization structure of the source with a hot loop is also complex and the polarization is repeatedly reversed over the observed frequency range under certain conditions. The revealed spectral-polarization peculiarities are considered from the standpoint of whether some atypical observed properties of the emission sources associated with solar active regions can be explained.     

AGN effect on cooling flow dynamics

We analyzed the feedback of AGN jets on cooling flow clusters using three-dimensional AMR hydrodynamic simulations. We studied the interaction of the jet with the intracluster medium and creation of low X-ray emission cavities (Bubbles) in cluster plasma. The distribution of energy input by the jet into the system was quantified in its different forms, i.e. internal, kinetic and potential. We find that the energy associated with the bubbles, (pV+γ pV/(γ−1)), accounts for less than 10 percent of the jet energy.     

1986年2月4日耀斑与电流环合并不稳定性

本文收集了１９８６年２月４日大耀斑的Ｈα、微波、Ｘ射线和γ射线全波段的观测资料。利用暗条电流环模型分析了该耀斑的物理过程，测量了活动暗条的上升运动，求解了动量方程和能量方程。结果表明：（１）１９８６年２月４日的３Ｂ／Ｘ３耀斑可能是由暗条电流环之间的合并不稳定性所致；（２）电阻撕裂摸不稳定性是一种有效的耀斑前预热机制；（３）耀斑的高能观测资料进一步表明了电流环合并不稳定性是引起该大耀斑期间所有高能粒