Step-frequency radar applied on thin road layers

In the field of road construction and maintenance, the need for information on the thickness of very thin road layers is not satisfied by means of commercial pulse GPR, due to the inability of such devices to operate over ranges of several gigahertz. As a result, research has focused on the design of a step-frequency radar technique, able to work with very high-frequency synthetic pulses.An ultrawide band antenna, belonging to the family of Vivaldi antennas, has been developed for road applications. It has been created using stripline technology and yields a band width greater than one decade. During an initial step, this antenna was tested on various bituminous concrete samples with a network analyzer. Different parameters were studied, including band width, offset between antennas, and height and shape of the frequency-dependent pulse.A second step involved GPR dynamic measurements. A customized software program enabled recording data from the network analyzer. Several radar profiles were developed from selected road construction and maintenance test sites (e.g. the Circular Pavement Fatigue Test Track, composed of a number of known structures). Results show improved resolution when compared to a commercial impulse GPR system.     

Evolution of 3D tectonic stress field and fault movement in North China

IntroductionThe research on stress field interior the Earth is an either relative old or young branch of geoscience. Early in the 20th century, in order to learn the state of inner stress field, a few scholars had used simple ideal model to analyze big scale tectonic conformations and activities according to tide, gravity, rotation and inner thermal materials. So far, lots of problems on the state of the Earth stress field have not been solved completely yet. The origin of stress field, the d…     

A New Methodology for Singularity Modelling in Flow Simulations in Reservoir Engineering

In this paper, numerical methods for flow simulation in the well vicinity are discussed. Flux truncation errors are analyzed on gridblocks near the well. Due to the singularity of the well, standard numerical schemes are not efficient for near well flow simulations. To improve simulation accuracy, a new methodology, using a change of coordinates to make near well pressure linear, is presented for the singularity modelling. Based on this new approach, two numerical schemes, a two-point flux approximation scheme and a multi-point one, are proposed. These schemes are accurate for the near well modelling and are suitable for any kinds of gridblocks.     

Frequency–volume relation and prediction of rainfall-induced landslides

Rainfall-induced landslides constitute a major public concern in Hong Kong. This paper investigates two aspects of critical importance to landslide hazard and risk assessment and management: magnitude–cumulative frequency relationship for landslides, and relationship between rainfall and the occurrence of landslides. The results indicated that landslides with a failure volume of not less than 4 m³ have a cumulative frequency–size distribution with a power-law dependence on volume of failure. Analysis of rainfall/landslides showed that the 12-hour rolling rainfall is most important in predicting the number of landslides. Failure volume dependency in the relationships between rainfall and the number of landslides is also presented. However, with an increase in failure volume of landslides, the most important rainfall variable may vary from rainfall of short duration (12-h rolling rainfall) to that of relatively long duration (24-h rolling rainfall).     

卫星重力梯度向下延拓的频域最小二乘配置法

本文深入研究频域最小二乘配置法的基本原理及其在求解卫星重力梯度向下延拓问题中的应用。与一般空域最小二乘配置法相比，该方法具有高效稳定的特点，特别适合于大规模重力场数据处理，并为利用卫星重力梯度数据精化局部重力场提供了可供参考的方法。     

复杂地震系统的数字模拟

借用细胞自动机的计算处理方法，对地震孕育过程中整个系统能量输入，积累，释放，传播等进行了数字模拟，并研究了复杂地震系统的整体特征，结果表明，整体调整系统，地震时能量的损耗系数，外部构造应力场的驱动力大小会影响到地震系统中能量积累和释放的状况，影响到Ｇ－Ｒ关系中ｂ值的大小。     

Estimation of quantiles and confidence intervals for the log-Gumbel distribution

The log-Gumbel distribution is one of the extreme value distributions which has been widely used in flood frequency analysis. This distribution has been examined in this paper regarding quantile estimation and confidence intervals of quantiles. Specific estimation algorithms based on the methods of moments (MOM), probability weighted moments (PWM) and maximum likelihood (ML) are presented. The applicability of the estimation procedures and comparison among the methods have been illustrated based on an application example considering the flood data of the St. Mary's River.     

频谱特性优良的高阶标定脉冲

通过理论分析研究和计算机搜寻得到几种频谱特性优良的高价标定脉冲波形，将其与我国台网广泛使用的阶跃脉冲相比较，可大幅度提高通带短周期段的标定精度，与国外使用的平衡二阶或三阶脉冲比较，具有响主尖波形特征，既可提高通带短周期段标定精度，又不降低通带长周期段精度，此外，具有生成较容易，技术难度适中，便于推广使用等特点。     

用改进的时间差分有限分析法模拟地下水非稳定井流方程

提出了一种改进的时间差分有限分析算法,它能够避免在求解水头剧烈变化时用一般有限分析法计算精度较差的缺陷.算法的稳定性好.     

EFFECT OF WATER DEPTH ON WIND-WAVE FREQUENCY SPECTRUM Ⅰ.SPECTRAL FORM

Wen et al.'s odhed dewiogh to obtain wind-wave frequency spectrum in deep was used toderive the spectrum in finite depth water. The spedrum S(ω) (ω bein angular frequency) when normalizedwith the zeroth moment m and peak frequercyω。 contains in adrition to the peakness factor P=ω。S(ω。)/m。, a twth parameter n=(2πm。)_(1/2)d (d being water depPth), so the spatrum behavior can bestudies for different ware growth stages and water depths.