Bankfull width and morphological units in an alpine stream of the dolomites (Northern Italy)

This research examines variations in bankfull cross-sections along a steep stream of the Dolomites (Cordevole stream, Belluno, Northern Italy). Field measurements were conducted to determine variations in the channel top-width at bankfull stage in relation to the drainage area and to the length of the flow path. After grouping the bed morphologies according to the Montgomery and Buffington [Montgomery, D.R., Buffington, J.M., 1997. Channel-reach morphology in mountain drainage basins. Geol. Soc. of Am. Bull. 109 (5) 596–611.] classification, we analyzed the increase in bankfull width for the dominant stream units (cascades, step pools, isolated pools and colluvial reaches at the head of the basin). We observed that the morphologies more related to the drainage area are colluvial reaches and pools; the less adaptable are steps and cascades. These differences likely result from the absence of lateral constriction in the colluvial reaches and pools, whereas the presence of coarser sediments in the bed can affect the transverse adjustments in steps and reaches dominated by cascades. Linkages between cross-section geometry and parameters related to flow (i.e. drainage area and stream power) have been analyzed together with the distribution of surface grain sizes and its coarsening pattern. The existence of distinctive bankfull widths between different morphological units points out the degree of susceptibility to be modeled according to the channel slope, reference diameter (D₉₀), and contributing area.     

用置换法处理桩端沉碴

文章对超出规范规定范围内的桩端沉碴提出用置换法处理的技术方法 ,取得显著效果 ,克服了传统处理方法强度小等缺点 ,也避免了采用跨越处理工期长、造价高的不良后果。     

高压变电站抗震可靠性分析(一)

讨论了高压变电站中电气主接线系统的抗震可靠性分析问题,主要分析了高压变电站中常见的双母线系统的抗震可靠性。通过系统的可靠性关系和建立系统的可靠性分析准则,给出了双母线系统在各个抗震准则条件下的可靠性的表达形式。最后进行了实例分析。     

电渗固结中的界面电阻问题

结合试验对电渗固结中的界面电阻问题进行了详细的分析和探讨,提出了界面电压降假定,在该假定的基础上,经过一系列理论推导,给出了一个简洁的界面电阻表达式,这将有助于我们对电渗固结的电流以及能耗做出更为准确的估计。     

Preconditioned non‐linear conjugate gradient method for frequency domain full‐waveform seismic inversion

We present preconditioned non‐linear conjugate gradient algorithms as alternatives to the Gauss‐Newton method for frequency domain full‐waveform seismic inversion. We designed two preconditioning operators. For the first preconditioner, we introduce the inverse of an approximate sparse Hessian matrix. The approximate Hessian matrix, which is highly sparse, is constructed by judiciously truncating the Gauss‐Newton Hessian matrix based on examining the auto‐correlation and cross‐correlation of the Jacobian matrix. As the second preconditioner, we employ the approximation of the inverse of the Gauss‐Newton Hessian matrix. This preconditioner is constructed by terminating the iteration process of the conjugate gradient least‐squares method, which is used for inverting the Hessian matrix before it converges. In our preconditioned non‐linear conjugate gradient algorithms, the step‐length along the search direction, which is a crucial factor for the convergence, is carefully chosen to maximize the reduction of the cost function after each iteration. The numerical simulation results show that by including a very limited number of non‐zero elements in the approximate Hessian, the first preconditioned non‐linear conjugate gradient algorithm is able to yield comparable inversion results to the Gauss‐Newton method while maintaining the efficiency of the un‐preconditioned non‐linear conjugate gradient method. The only extra cost is the computation of the inverse of the approximate sparse Hessian matrix, which is less expensive than the computation of a forward simulation of one source at one frequency of operation. The second preconditioned non‐linear conjugate gradient algorithm also significantly saves the computational expense in comparison with the Gauss‐Newton method while maintaining the Gauss‐Newton reconstruction quality. However, this second preconditioned non‐linear conjugate gradient algorithm is more expensive than the first one.     

低纹波低功耗自动控制APD偏压电路

全站仪红外测距系统接收电路采用APD雪崩光电二极管作为接收器件,它的精度对后级的信号处理及测量精度起着决定性的影响,针对其高精度要求,提出两种APD偏压电路。前者采用交流反馈网络消除冲击电压,提高了开关管寿命,采用三级滤波网络极大的降低了电路纹波从而提高了测量精度;后者采用专用芯片控制电路电源,使储能电感处于非连续工作状态,大大降低了电路的功耗,同时采用4个变容二极管既升高了电压,又减小了纹波。两种电路均具有可自动控制,且能对APD的内部增益进行全范围补偿的优点。实践证明,电路工作性能理想,提高了测距精度。     

瞬变电磁法感应电压场与B场探测效果的数值计算对比分析

本文通过一维和三维正演程序分别生成了回线源瞬变电磁法的感应电压场和B z场数据,并从多个角度对比了二者的探测效果。通过多个模型对比分析了这两种数据在当前主流硬件的数据采集精度下的最长有效延迟时间;通过全时视电导率计算与一维反演对比分析了两种数据的纵向分辨率和横向分辨率。结果表明,在本文采用的仪器精度水平和测量方式下,只有当模型中存在电导率≥0.036 S/m的高导异常体时,B z场的有效观测延迟时间才可能比感应电压场更长;B z场相比感应电压场虽然能够提前感知到地下异常体,但是在横向和纵向分辨率以及对异常体电导率的呈现程度上均比感应电压场差。在实际野外测量时,不建议仅开展B z场测量,而是在有条件情况下,同时采集感应电压场和B z场,充分利用感应电压场和B z场各自的优势,达到最佳的探测效果。     

基于改进两步移动搜索法的县域医疗卫生服务空间可达性研究

针对县域医疗卫生服务设施的空间布局问题,应用改进两步移动搜索法对德清县医疗卫生服务的空间可达性进行评价。具体改进包括：引入核密度型距离衰减函数对两步移动搜索法进行扩展、考虑医疗设施资源的未充分利用、对不同规模等级医疗机构设置不同服务阈值。计算结果表明：① 浙江省德清县域医疗卫生服务空间可达性呈圈层式空间分布特征,高可达性区域主要集中于县城及邻接区域,边缘地区缺医明显;② 基于改进两步移动搜索法和传统两步移动搜索法的可达性计算结果具有不同的整体特征,但前者可达性计算结果及空间分布更符合实际。     

GNSS连续站阶跃修复及其对数据处理的影响

近年来,由于仪器更换和强震影响,一些长期稳定的GNSS连续站出现了阶跃,严重地影响了参考框架的稳定性和解算精度,理论上这些测站不能再选为参考框架点。针对GNSS连续站阶跃修复及其对数据处理的影响进行了分析,结果表明：1）如果选用未修复阶跃的测站为框架点,将会扭曲解算结果;2）QOCA能够较为便捷地修复测站阶跃;3）修复测站阶跃能够保证参考框架点的稳定性,并能一定程度提高解算精度。     

基于AT89C51的小功率调频调压电源设计

为满足钻井导向系统非接触供电单元开发设计需要,设计一种小功率调压、调频电源.采用智能控制芯片AT89C51作为控制核心部件,自振式反激变换器实现调压模块设计,全桥逆变电路实现调频模块设计,通过IR2110芯片实现驱动.控制芯片产生PWM控制信号,控制开关管的导通并在直流侧加入合适的整流电容使电压平稳输出,经隔离驱动电路实现电能的通断控制,实现电源电压、频率和幅值可调.实验结果表明:该电源具有过电流、过电压保护功能,设计结构合理,成本低廉,控制精度较高,达到设计要求.