1999-2007年中国粮食安全的关键影响因素

选取耕地保护“新政”时期的1999-2007年为研究时段,以耕地面积与粮食产量变化的分歧原因—耕地生产力变化为切入点,通过比较分析、空间与计量分析探寻粮食安全的关键影响因素.结果表明:农民种粮积极性变化决定着耕地集约利用是影响粮食安全的关键;2003-2007年农民种粮积极性的持续提高主要来自市场粮价的上涨;粮食直补仅在开始实施的年份激发了农民对种粮收益的预期.此外,本文从提高农民种粮积极性、优化粮食生产投入及改进耕地保护模式3方面,提出了耕地保护发展的政策建议.     

海底管线冲刷悬空及其抑制技术研究综述

海底管线作为海洋工程的重要组成部分,其安全性受到广泛关注。本文简单回顾了国内外学者通过物理实验、理论分析与数值模拟等方法研究海底管线冲刷悬空及防护问题的成果,并对工程中应用较广泛的防护方法的优缺点进行了简单对比,为该领域的进一步研究提供参考。     

基于图像方向性信息测度的图像水印技术

数字水印是图像信息版权保护的一种新兴的技术手段,水印的不可感知性和鲁棒性是相互制约的两个对立面.结合人类的视觉系统特性,提出了一个新的图像水印方案——基于图像方向性信息测度的图像水印,在水印嵌入时根据图像块的局部特性,自适应地调整水印的嵌入强度,达到了在鲁棒性和不可感知性之间的较好折衷.最后结合实例说明了算法的实用性.     

深孔纳米复合水泥基护壁堵漏材料研究

本文围绕深部钻探技术中护壁堵漏材料性能的实际需要,研制了一种深孔纳米复合水泥基护壁堵漏新材料。首先,通过分析100 ℃条件下2种水泥材料的基本性能,确定了G级油井水泥为胶凝材料;然后,基于深孔钻探护壁堵漏材料的性能缺陷,采用特种纤维、纳米材料针对性改善水泥基浆液的力学性能,并优选早强剂（ZQ）、减水剂（GB）作为外加剂进行正交实验,进而研制出纳米复合水泥基护壁堵漏材料优化配方;最后,对其主要性能进行分析评价。结果表明该材料在深孔钻探中浆液流动性好,力学性能优异,综合性能满足深孔钻探护壁堵漏需求。     

Stochastic Modelling of the Impact of Flood Protection Measures Along the River Waal in the Netherlands

River flooding is a problem of international interest. In the past few years many countries suffered from severe floods. A large part of the Netherlands is below sea level and river levels. The Dutch flood defences along the river Rhine are designed for water levels with a probability of exceedance of 1/1250 per year. These water levels are computed with a hydrodynamic model using a deterministic bed level and a deterministic design discharge. Traditionally, the safety against flooding in the Netherlands is obtained by building and reinforcing dikes. Recently, a new policy was proposed to cope with increasing design discharges in the Rhine and Meuse rivers. This policy is known as the Room for the River (RfR) policy, in which a reduction of flood levels is achieved by measures creating space for the river, such as dike replacement, side channels and floodplain lowering. As compared with dike reinforcement, these measures may have a stronger impact on flow and sediment transport fields, probably leading to stronger morphological effects. As a result of the latter the flood conveyance capacity may decrease over time. An a priori judgement of safety against flooding on the basis of an increased conveyance capacity of the river can be quite misleading. Therefore, the determination of design water levels using a fixed-bed hydrodynamic model may not be justified and the use of a mobile-bed approach may be more appropriate. This problem is addressed in this paper, using a case study of the river Waal (one of the Rhine branches in the Netherlands). The morphological response of the river Waal to a flood protection measure (floodplain lowering in combination with summer levee removal) is analysed. The effect of this measure is subject to various sources of uncertainty. Monte Carlo simulations are applied to calculate the impact of uncertainties in the river discharge on the bed levels. The impact of the “uncertain” morphological response on design flood level predictions is analysed for three phenomena, viz. the impact of the spatial morphological variation over years, the impact of the seasonal morphological variation and the impact of the morphological variability around bifurcation points. The impact of seasonal morphological variations turns out to be negligible, but the other two phenomena appear to have each an appreciable impact (order of magnitude 0.05–0.1 m) on the computed design water levels. We have to note however, that other sources of uncertainty (e.g. uncertainty in hydraulic roughness predictor), which may be of influence, are not taken into consideration. In fact, the present investigation is limited to the sensitivity of the design water levels to uncertainties in the predicted bed level.     

对太白山旅游资源开发与保护的探讨

太白山具有丰富而独特的地质、生物和自然景观,气势磅礴、变化万千,而为古今中外科学家和文人学士所向往。太白山第四纪冰川遗迹保存完整;生物资源丰富多彩,仅珍稀动物如熊猫、金丝猴、羚牛、大鲵(娃娃鱼)等就有10多种。太白山已被列为国家级自然保护区。对该区旅游资源必须在切实加强保护的前提下合理开发利用,为此,本文对其开发与保护规划提出探讨性意见。     

南海海岛自动气象站防护应用技术探索

立足海南及南海的自然条件,结合海岛自动气象站在南海高温、高湿、高盐雾、强辐射、强风等恶劣气候环境下使用情况,通过对历年来海岛自动气象站故障及失效模式的统计和分析,总结分析故障原因。根据设备维护人员多年气象设备保障工作积累总结的经验,从海岛自动气象站结构和防护要求出发,集成应用市场上优质材料、先进工艺和多种成熟、关键设备防护技术,形成一些气象设备防护的有效方法措施,以提高海岛自动气象站对海洋环境的适应性和性能,延长设备使用寿命。     

基于雷电临近预警技术的主动防雷应用

为了使雷电临近预警技术在雷电灾害防御业务中更好地发挥作用,针对电子系统的雷电灾害特点,在传统被动防雷技术基础上,提出基于雷电临近预警的主动防雷技术,应用雷电临近预警和远程控制等技术,开发以B/S结构为架构的雷电临近预警应用系统。对2013年8月—2014年8月福建省泉州市4个无线电监测站的主动防雷应用效果进行两种方法的预警效果检验。检验结果表明:主动防雷技术是对被动防雷技术的一个较好的完善和补充。采用闪电数量对比分析,4个监测站的有效预警率为69%,采用预报评分方法对比分析,4个监测站的平均准确率为53%,对雷电活动发生较为集中的区域预警效果较好,对雷电活动发生较为零散的区域预警效果有所降低。     

福建省高速公路沿线雷电活动特征分析

为了揭示福建省高速公路沿线雷电活动特征,做好高速公路机电设施的防雷工作,本文利用2015 2018年福建省三维闪电监测数据以及福建省高速公路路网资料进行统计分析.分析了高速公路沿线地闪的月、日活动特征,得出地闪活动主要分布在5 9月和14:00 18:00.根据高速公路沿线地闪密度绘制雷电活动等级分布图,结果表明高速公...     

野外组装可移动式防直击雷装置的研究

通过对9m×9m的实际接地网进行计算,对于二类和三类防雷建筑物,可以应用当环形接地网的等效面积大于78.5m2后,采取不计接地网接地电阻的设计方法来实现野外可移动式接地网设计,并将避雷针和避雷线组合的接闪器设计成标构件,方便组装,实现野外组装可移动式防直击雷装置.