Land-based adaptation to global change: What drives soil and water conservation in western Africa?

Conservation of land resources is a promising strategy for sustainable agricultural intensification in order to adapt dryland farming systems to climate, market and other stresses. At a local level, factors that drive the adoption of conservation measures operate and interact in specific ways. Linking our knowledge of the local specifications of these drivers to regional and global patterns of vulnerability can significantly enhance our understanding of land-based adaptation to global change. However, the factors that influence the adoption of conservation practices remain actively debated. Therefore, this study presents a meta-analysis of case studies that investigate the adoption of soil and water conservation measures, as an important approach to resource conservation. Synthesising 63 adoption cases in the drylands of western Africa, this meta-analysis reveals a multitude of factors that drive the adoption of soil and water conservation practices. The drivers differ strongly between particular practices and methods of analysis used in the case studies. Contributing to the broader debate on resource conservation, the findings highlight the adoption of soil and water conservation measures as an emergent property of farming systems. They demonstrate the need to better understand the socio-ecological foundation of adoption and the pathways along which adoption evolves in space and time. This study concludes with methodological principles to advance future research on the factors that drive the adoption of soil and water conservation measures as a pre-requisite of improving land-based adaptation efforts.     

北京一次大雹天气过程的闪电活动特征分析

由于受闪电监测系统限制,已有研究多局限于强对流天气的地闪(cloud-to-ground lightning,CG)活动特征。本文利用VLF/LF三维闪电监测定位资料,结合雷达观测等资料对北京地区一次典型大雹天气过程的全闪活动特征进行了分析。结果表明:降雹发生前,闪电活动主要分布在对流系统的后部,闪电数较少,且以负地闪活动为主;降雹期间,闪电频数显著增加,云闪(intracloud lightning,IC)及正地闪活动明显加强,该阶段闪电活动主要集中在对流系统强回波中心及其前部雷达反射率因子梯度较大的区域;降雹结束之后,强回波中心基本移出北京,北京范围内的闪电频数明显减少。正闪比例在降雹发生前逐渐增大,在降雹期间稳定维持在较大值,降雹结束后迅速减小;云闪比(云闪频数/总闪频数)表现为降雹发生前和降雹结束后逐渐增大趋势,在降雹期间基本维持稳定少变。闪电的电流强度主要集中在5—50 kA之间,20 kA以下的低雷电流强度的云闪和地闪多发生在降雹期间及降雹结束后,而20 kA以上的高雷电流强度的云闪和地闪在降雹发生前占有很大比例,小于5 kA的云闪在大雹发生期间所占比例明显高于地闪。降雹发生前及降雹结束后云闪发生高度在2-6 km,降雹期间有所抬升,约为2-8km。闪电频数峰值超前于降水峰值5-20 min。     

影响山东热带气旋的频数与太平洋海温的关系

利用1949—2007年热带气旋年鉴资料,对影响山东热带气旋（TC）的频数与太平洋海温的关系进行了分析。结果表明：（1）厄尔尼诺年,影响山东的TC频数较常年明显偏少。厄尔尼诺次年TC频数较常年稍有增加。拉尼娜年影响山东的TC频数较常年显著偏多,增加明显的月份主要是8月和9月,拉尼娜次年,影响山东TC频数偏少。厄尔尼诺事件强度越大,影响山东的TC频数越少。（2）影响山东的TC数和菲律宾以东洋面的海温呈正相关,并具有很好的持续性。（3）影响山东的TC多年,赤道中东太平洋有较强的负距平区;影响山东的TC少年,赤道中东太平洋为正距平区。说明赤道中东太平洋的海温高低对影响山东的TC频数有较好的指示作用。     

利用信号非线性变换进行抗干扰的原理分析与电路设计

介绍了对信号与强噪声干扰所进行的非线性变换，以实现对噪声干扰的抑制，可获得高质量的有用信号     

Site amplification at Avcılar, Istanbul

Avcılar is the suburb of Istanbul that was most heavily damaged during the August 17, 1999 M_w 7.4 Izmit earthquake. Strong ground motion caused fatalities and damage in Avcılar despite being 90 km from the epicenter. We deployed five portable seismograph stations equipped with Reftek 24-bit recorders and L4C-3D seismometers for 2 months, in order to understand why the local site response was different from elsewhere in Istanbul. A reference station was placed on a hard rock site, and the remaining four stations were placed on other geological units, in areas that had experienced varying levels of damage. We calculated frequency-dependent ground amplification curves by taking the ratios of the spectra at soft and hard rock sites. We obtained similar site response curves for most earthquakes at each site in the frequency range of 0.3–1.6 Hz, and observed no significant site amplification beyond 2.0 Hz at any site. The overall characteristics of the recorded S-waveforms and our modeling of the calculated site amplification curves are consistent with amplification as a result of trapping of seismic energy within a 100–150 m thick, low-velocity subsurface layer. We also review the applicability of microtremor measurements to estimate local site effects at Avcılar. For these data, we used ratios of spectra of horizontal to vertical components to obtain each site response. These results are compared with standard spectral ratios. These microtremor measurements provide consistent estimates of the amplification at most sites at the higher end of the frequency band, namely above 1 Hz. The results from both methods indeed agree well in this part of the frequency band. However, the microtremor method fails to detect amplification at lower frequencies, namely <1.0 Hz.     

Consistent transmitting boundary conditions with a reduced number of eigenmodes for wave propagation in elastic media

The consistent transmitting boundary condition is a powerful numerical technique for frequency domain analysis of wave problems in unbounded elastic media. A second-order complex-valued eigen-problem is associated with this method and the computed eigenmodes are used to formulate the nodal forces acting on the lateral boundaries of a Cartesian computational domain. Usually, all eigenmodes are computed and used in the consistent transmitting boundary conditions to simulate the infinite extent of the elastic medium. In this paper, it is demonstrated that by selecting a reduced number of relevant eigenmodes it is possible to produce similar results and consequently reduce the overall computational cost. This is highly desirable for soil–structure interaction problems involving wide ranges of frequencies and large-size domains with many sub-layers. The efficiency of the proposed approach is investigated by considering, first, the case of foundation vibration over rigid bedrock and, second, the effectiveness of a wave barrier to reduce the transmitted vibrations caused by a surface harmonic loading.     

高温超导磁强计的研制及在TEM上的野外试验

文中介绍了高温超导磁强计的工作原理、特点、所研制的高温超导磁强计的性能指标以及在研制高温超导磁强计的过程中所解决的关键问题,定性地分析了高温超导磁强计在瞬变电磁法(TEM)上应用的优势.在河北固安以高温超导磁强计做探头和使用传统感应线圈做探头在瞬变电磁法(TEM)上进行了野外对比试验.试验结果表明,把高温超导磁强计应用于瞬变电磁法(TEM)上能够加大勘探深度.     

娄底大建煤矿区逆冲断裂下找煤获得成功

根据物探、坑探工作以及隔挡式褶皱和逆冲推覆构造的特征,作者确定了大建煤矿区逆冲断裂下存在着隐状煤田,初步计算远储量达８千多万吨。     

高频燃烧-红外吸收光谱法测定钼矿石和镍矿石中的高含量硫

高频燃烧-红外吸收法用于分析矿石中低含量硫的测定结果较为准确,但对于高含量的硫,分析结果的准确度不高。本文采用高频燃烧-红外碳硫分析仪测定钼矿石和镍矿石中的高含量硫,选择纯铁屑和钨粒作助熔剂,高温燃烧分解样品,通过实验优化了样品称样量、助熔剂用量、仪器分析时间等测定条件。用国家标准物质进行验证,方法精密度(RSD,n=9)小于1%,加标回收率为96.0%～101.9%;与传统的硫酸钡重量法进行比对试验,测定值的相对误差小于2%。针对不同的矿石样品,研究了实际样品与标准物质的基体匹配问题,消除了基体效应的影响,对于钼矿石和镍矿石样品中含量在1%～35%范围内的硫,均能够准确测定,解决了钼矿石和镍矿石中高含量硫的快速、准确测定问题。