Evolution of gravel surfaces in a sediment‐recirculating flume

The assumption of the equilibrium state of gravel surfaces in flume experiments under feeding or recirculating conditions is generally justified by three equilibrium criteria based on sediment transport, slopes, and bed features. When these parameters become stable, an experiment is expected to reach equilibrium. This equilibrium state, however, is based on a one‐dimensional model, the Exner equation, which may not truly reflect the equilibrium state of the system considering the complex flow and sediment processes. In this paper, the evolutionary process of a gravel surface is investigated based on a large‐scale recirculating flume experiment. The performances of the three equilibrium criteria are evaluated first, and then the evolution of the bed morphology is studied. The key findings include the following: (1) the sediment transport rate, slopes of water and bed surfaces, and one‐dimensional morphological features reach equilibrium roughly simultaneously; (2) two‐dimensional morphology continually evolves after these characteristics reach equilibrium, which is confirmed by the characteristics of the sediment transport process; and (3) the results from a numerical simulation suggest that a much longer time is required to reach an equilibrium state. Our results suggest that sufficient experimental time is required to investigate the equilibrium morphological characteristics of gravel surfaces, which is much longer than the equilibrium time reflected by the one‐dimensional equilibrium criteria. Copyright © 2017 John Wiley & Sons, Ltd.     

2℃温升目标下排放空间及路径的不确定性分析

国际社会已就2℃温升目标达成政治共识。将温升目标向累积排放及各国减排目标转换的过程需要基于一致的科学认知。但由于目前地球系统模式、减排路径及减排方案的研究仍然存在不确定性,缺乏建立政治共识所需的科学基础。通过谈判形成一个自上而下的国际气候制度的决策基础尚不具备。目前最有效和务实的方案仍是各国自下而上加大减排力度,并不断进行评估,促进各国持续加强减排力度,最终公平地承担减排义务。     

Disentangling intangible social–ecological systems

Contemporary environmental challenges call for new research approaches that include the human dimension when studying the natural environment. In spite of the recent development of several conceptual frameworks integrating human society with nature, there has been less methodological and theoretical progress on how to quantitatively study such social–ecological interdependencies. We propose a novel theoretical framework for addressing this gap that partly builds on the rapidly growing interdisciplinary research on complex networks. The framework makes it possible to unpack, define and formalize ways in which societies and nature are interdependent, and to empirically link this to specific governance challenges and opportunities using a range of theories from both the social and natural sciences in an integrated way. At the core of the framework is a set of basic building blocks (motifs) that each represents a simplified but non-trivial social–ecological systems (SES) consisting of two social actors and two ecological resources. The set represents all possible patterns of interdependency in a SES. Each unique motif is characterized in terms of social and ecological connectivity, resource sharing, and resource substitutability. By aligning theoretical insights related to the management of common-pool resources, metapopulation dynamics, and the problem of fit in SES with the set of motifs, we demonstrate the multi-theoretical ability of the framework in a case study of a rural agricultural landscape in southern Madagascar. Several mechanisms explaining the inhabitants’ demonstrated ability to preserve their scattered forest patches in spite of strong pressures on land and forest resources are presented.     

多点双流模式在全运会天气会商中的应用

针对早期电视会商系统存在的问题,分析了省级天气预报电视会商过程的应用需求,介绍了借助矩阵和中央控制系统,研究开发的适合电视会商需求的应用模式及其实现的原理和方法。通过对CRESTRON中央控制系统的控制指令进行编程,实现了同一会场内多点双流模式的电脑控制,并对模式实现的程序代码给出释义。经过检验,多点双流模式在省内天气会商、视频会议等应用中,操作简单、性能稳定。该应用模式已在十一届全运会气象保障平台上投入使用。     

省级天气预报电视会商系统基本应用模式的研究

随着公共气象服务理念的推出,各级气象部门对电视会商系统的应用需求不断上升。现在,每天除了定制的中央气象台、省气象台的天气会商之外,气候会商、干旱会商、奥运保障等各类专项任务,也经常使用该系统。但是早期的电视会商系统,运行模式单一,不能满足气象业务日益增加的需求。借助矩阵和中央控制系统,研究满足不同需要的应用模式,是山东省气象部门电视会商系统提升服务支持能力的有效途径。     

Reductive dechlorination of polychlorinated biphenyls is coupled to nitrogen fixation by a legume-rhizobium symbiosis

Chlorinated persistent organic pollutants, including polychlorinated biphenyls(PCBs), represent a particularly serious environmental problem and human health risk worldwide. Leguminous plants and their symbiotic bacteria(rhizobia) are important components of the biogeochemical cycling of nitrogen in both agricultural and natural ecosystems. However, there have been relatively few detailed studies of the remediation of PCB-contaminated soils by legume-rhizobia symbionts. Here we report for the first time evidence of the reductive dechlorination of 2,4,4′-trichlorobiphenyl(PCB 28) by an alfalfa-rhizobium nitrogen fixing symbiont. Alfalfa(Medicago sativa L.) inoculated with wild-type Sinorhizobium meliloti had significantly larger biomass and PCB 28 accumulation than alfalfa inoculated with the nitrogenase negative mutant rhizobium Sm Y. Dechlorination products of PCB 28, 2,4′-dichlorobiphenyl(PCB 8), and the emission of chloride ion(Cl-) were also found to decrease significantly in the ineffective nodules infected by the mutant strain Sm Y. We therefore hypothesize that N2-fixation by the legume-rhizobium symbiont is coupled with the reductive dechlorination of PCBs within the nodules. The combination of these two processes is of great importance to the biogeochemical cycling and bioremediation of organochlorine pollutants in terrestrial ecosystems.     

Resolving rupture processes of great earthquakes: Reviews and perspective from fast response to joint inversion

Resolving rupture processes of great earthquakes has fundamental importance to the study of earthquake physics,rupture dynamics, fault zone structure, and evolving processes. It also plays an essential role in earthquake hazard estimation,emergency response and seismic hazard mitigation. This paper reviews the major progress of the earthquake rupture process studies in the last decades, with an emphasize on the research directions of the department geophysics of Peking University including real-time response, back-projection techniques, geodetic data analysis, joint inversion and inversion in complex earth medium. We discussed the advantages and limitations of tradition methods; proposed a systematic and integrated approach from fast-response to detailed study. We also raised perspectives of using source models for ground motion prediction and the possibility of full-dynamic inversion.     

Relationship between the transition frequency of local fluid flow and the peak frequency of attenuation

Local fluid flow (LFF) at the mesoscopic scale is the main dissipation mechanism of seismic waves in heterogeneous porous media within the seismic frequency band. LFF is easily influenced by the structure and boundary conditions of the porous media, which leads to different behaviors of the peak frequency of attenuation. The associated transition frequency can provide detailed information about the trend of LFF; therefore, research on the transition frequency of LFF and its relationship with the peak frequency of the corresponding attenuation (i.e., inverse of quality factor) facilitates the detailed understanding of the effect of inner structures and boundary conditions in porous media. In this study, we firstly obtain the transition frequency of fluid flux based on Biot’s theory of poroelasticity and the fast Fourier transform algorithm in a sample containing one repeating unit cell (RUC). We then analyze changes of these two frequencies in porous media with different porous properties. Finally, we extend our analysis to the influence of the undrained boundary condition on the transition frequency and peak frequency in porous media with multiple RUCs. This setup can facilitate the understanding of the effect from the undrained boundary condition. Results demonstrate that these two frequencies have the same trend at low water saturation, but amplitude variations differ between the frequencies as the amount of saturation increases. However, for cases of high water saturation, both the trend and the amplitude variation of these two frequencies fit well with each other.     

华南黄陵隆起构造演化及其对页岩气保存的控制作用

近期中国南方页岩气勘查在黄陵隆起南缘的下寒武统和震旦系取得重大突破,本文针对古老地层页岩气构造保存问题,研究黄陵隆起构造演化历史,反演钻井沉积地层埋藏史,通过二维地震剖面解析黄陵隆起南缘的构造学特征,统计分析相关地质年代学数据。认为该区域在约800 Ma经历了花岗岩侵入,形成了以花岗岩为主体的黄陵隆起基底;该区域在800～200 Ma构造较稳定,缺乏这一时期的构造年代学数据;中侏罗世震旦系陡山沱组埋深可达约8 km,晚侏罗世及以后经过多期抬升至现在的构造格局。本研究说明黄陵隆起的古老基底经过元古宙大量花岗岩侵入,可能均质性高而表现为刚性基底,后期所遭受构造改造程度较低,埋深相对较浅。因此,该地区页岩表现为演化程度适中,构造改造弱,后期热事件影响小,有利于页岩气的保存,是目前黄陵隆起南缘获得页岩气勘查突破的关键。并指出南方具有类似构造的雪峰山隆起、神农架背斜和汉南古陆周缘具有良好的下寒武统页岩气勘查潜力。     

青藏高原整体隆升与地壳短缩增厚的物理－力学机制研究（下）

青藏高原整体隆升与地壳短缩增厚的物理－力学机制研究＊（下）滕吉文张中杰胡家富尹周勋刘宏宾万志超杨顶辉张秉铭张慧（中国科学院地球物理研究所）（承接本刊２卷２期１３３页）４青藏高原隆升与地壳短缩的物理－力学机制讨论青藏高原平均高度为４５００ｍ，面积达３０...