西沙北部海域海洋环境噪声频谱特性

Ambient noise is very important in the prediction system of a sonar performance, because it determines the detection ranges always in a passive sonar and usually in an active sonar. In the uncertainty issue for the so-nar performance, it is necessary to know this factor＇s statistical characteristics that are only obtained by data processing from the underwater ambient noise measurements. Broad-band ambient noise signals from 16 hydrophones were amplified and recorded for 2 min every 1 h. The results show that the ambient noise is essentially depth independent. The cross correlation of the ambient noise levels （1, 6 and 12 h average） with a wind speed is presented. It was found that the correlation is excellent on the upper frequency band and the noise levels correlate better with high wind speed than with low wind speed.     

随机动态声速重构方法研究

海洋环境对声传播具有重要的影响,海洋温度、盐度、压力决定声速的大小,研究随机动态声速剖面的最优重构可以为声场模型的计算提供良好的基础,为舰艇行动提供最优的辅助决策.然而声速剖面的重构却是一个复杂的过程,涉及到大量的时空分布不规则的数据的计算和处理,提取出合理的时空间系数能够提高声速重构的精度.实验证明,利用合理的时空分...     

Lusotropicalism: Tropical geography under dictatorship, 1926–1974

This article locates Portuguese tropical geography within wider academic debates on ‘tropicality’, contributing to discussion on not only the ‘tropicality of geography’ but also the ‘geography of tropicality’. It traces the role of Portuguese tropical geography in the colonial project and in the production of geographical knowledge, discourses and imaginaries, in particular the emergence of lusotropicality. While noting the underestimated connections with developments in German and British geography, we argue that the genealogy of Portuguese tropical geography lies mostly within contemporaneous French developments. By focusing on the central role of the Lisbon school (i.e. the Centre for Geographical Studies established in 1943), and in particular the tropical research initiated by Orlando Ribeiro (1911–1997), the paper seeks to engage with the ways in which geographical knowledge was produced within the academic discipline in Portugal under military dictatorship associated with the Estado Novo (1926–1974). By decentring the exploration of some of the ways in which the ‘tropics’ have been constructed and revising forms of producing geographical knowledge, the paper hopes to further understandings of the geographical imaginary of the tropics, unravelling the history and the role of geography in colonialism.     

关中平原城市群“交通-产业-环境”耦合协调发展的动态演化特征分析

关中平原城市群是丝绸之路经济带的重要城市群。运用耦合协调度模型定量分析了关中平原城市群2008—2019年交通、产业和环境三系统耦合协调发展关系的变化规律和时空分布特征。结果表明：（1） 城市群交通、产业和环境各子系统发展评价指数差异化提升,交通系统发展增长率远超过其他两系统,产业和环境发展与交通系统的矛盾较为突出。（2） 三系统综合发展指数空间分布单极态势明显,城间发展水平差异加剧,其中西安市和咸阳市作为极热点城市存在,其余城市为外围受辐射冷点区。（3） 城市群耦合协调发展水平整体上趋于优化提升态势,但仍处于濒临失调状态。其中,西安市一直处于高耦合协调的单极态势,但耦合协调度的城间差距逐渐缩小,耦合协调度等级为协调等级的城市逐渐增多,趋于集中连片式分布。研究结果可以明确关中平原城市群交通、产业和环境三系统耦合协调发展存在的问题,为高质量发展相关政策的制定提供一定的参考依据。     

Rotation of Weakly Collisional Plasmas in Tokamaks, Operated with Alfvén Waves

In this paper we consider rotation induced by kinetic Alfvén waves in weakly collisional plasma of slightly rippled tokamaks in plateau and banana regimes. Rippled magnetic field of tokamaks retards the plasma rotation in toroidal direction. Here, we are going to find the quasistationary poloidal and toroidal plasma velocities and the radial electric field taking into account the complete form of ponderomotive forces.     

海洋温度场稳定性与可预报性研究

海洋温度场具有强烈的时空易变性,带有典型的混沌特征,研究其稳定性对改善温度场可预报性具有重要意义。以混沌理论为支撑,改进最大Lyapunov指数算法,基于POM数值模式预报的温度时序为试验样本,研究了东中国海范围内的海洋温度场混沌稳定性分区和特征,并在此基础上针对混沌强弱区做添加观测试验,研究了基于稳定性分区的温度场可预报性。仿真结果表明,在混沌强烈区添加观测相比较弱区对改进预报效果更显著,对混沌强烈区添加观测整体上可以降低预报温度均方根误差0.2~0.7℃左右,证实了在该区域加强观测能在一定程度上改善温度场的可预报性。     

Influence of sedimentary setting on the use of magnetic susceptibility: examples from the Devonian of Belgium

Bulk magnetic susceptibility measurements on sedimentological samples from all geological periods have been used widely in the last two decades for correlations and as a proxy for sea‐level variations. This paper explores the link between magnetic susceptibility, depositional setting and environmental parameters. These environmental parameters include distal–proximal transects, microfacies successions and fourth‐order trends on different carbonate platform types (platform, ramp, carbonate mound or atoll) during different Devonian stages (Eifelian, Givetian and Frasnian). Average magnetic susceptibility values over a distal–proximal‐trending facies succession vary markedly with depositional setting. On carbonate platforms, average magnetic susceptibility generally increases towards the top of shallowing‐upward sequences. On a distal–proximal transect, average magnetic susceptibility is intermediate for the deepest facies, decreases for the reef belts and increases to a maximum in the back‐reef zone. In ramps and atolls, magnetic susceptibility trends clearly differ; average magnetic susceptibility generally decreases towards the top of shallowing‐upward sequences and is highest in the deepest facies. The strong relationship between magnetic susceptibility, facies and sequences implies a strong environmental influence. However, the different responses in the different platform types suggest that sea‐level changes leading to variation in detrital input is not the only parameter controlling average magnetic susceptibility values. Other primary or secondary processes also probably influenced magnetic mineral distribution. Primary processes such as carbonate production and water agitation during deposition are probably key factors. When carbonate production is high, the proportion of magnetic minerals is diluted and the magnetic susceptibility signal decreases. High water agitation during deposition will also selectively remove magnetic minerals and will lead to low average magnetic susceptibility values. These parameters explain the lowest values observed on the reef platform, inner ramp and atoll crown, which are all in areas characterized by higher carbonate production and greater water agitation during deposition. The lowest values observed in the lagoon inside the atoll crown can be related to detrital isolation by the atoll crown. However, other parameters such as biogenic magnetite production or diagenesis can also influence the magnetic signal. Diagenesis can change magnetism by creating or destroying magnetic minerals. However, the influence of diagenesis probably is linked strongly to the primary facies (permeability, amount of clay or organic matter) and probably enhanced the primary signal. The complexity of the signal gives rise to correlation problems between different depositional settings. Thus, while magnetic susceptibility has the potential to be an important correlation tool, the results of this investigation indicate that it cannot be used without consideration of sedimentary processes and depositional environments and without strong biostratigraphical control.     

珊瑚混凝土在海洋环境中氯离子扩散实验

采用自然扩散法研究了珊瑚混凝土在海水环境中的氯离子扩散特性,探讨了养护龄期、暴露时间和环境差异性对珊瑚混凝土表观氯离子扩散系数的影响。结果表明:随着暴露时间的延长,珊瑚混凝土的表观氯离子扩散系数呈幂指数衰减规律;且延长养护龄期可降低珊瑚混凝土的表观氯离子扩散系数;随着强度等级增加,混凝土的表观氯离子扩散系数降低。我国实际海洋工程中珊瑚混凝土结构的表观氯离子扩散系数比实验室条件要提高3个数量级。因此,适当延长养护时间、提高强度等级有助于延长珊瑚混凝土结构在海洋环境的服役寿命。     

西藏高原积雪覆盖空间分布及地形影响

利用2000-2014年MOD10A2积雪产品和数字高程模型DEM数据,以积雪覆盖率为指标,在分析西藏高原积雪空间分布特点的基础上,定量研究了高程、坡度和坡向等地形要素对高原积雪时空分布的影响。主要结论有：① 西藏高原积雪的空间分布差异显著,具有中东部念青唐古拉山和周边高山积雪丰富,覆盖率高,而南部河谷和羌塘高原中西部积雪少,覆盖率低的特点。② 海拔越高积雪覆盖率越高,积雪持续时间越长,年内变化越稳定。海拔2 km以下积雪覆盖率不足4%,海拔6 km以上覆盖率达75%。海拔4 km以下年内积雪覆盖呈单峰型分布特点,海拔越高,单峰型越明显;而海拔4 km以上则为双峰型,海拔越高,双峰型越明显。海拔6 km以下积雪覆盖率最低值出现在夏季,而6 km以上则出现在冬季。③ 总体上,高原地形坡度越高积雪覆盖率越高。不同坡向中,北坡积雪覆盖率最高,南坡最低,年内分布呈双峰型,而无坡向的平地积雪覆盖率要小于有坡向的山地,其年内变化呈单峰型分布特点。