Wave dispersion and optimal mass modelling for one-dimensional periodic structures

Discrete analysis methods are frequently used for the study of the structure and soil. However, the assumption of the displacement interpolation function makes the waves dispersive, which means the numerical dispersion. The wave dispersion induced by the discretization depends on the mass modelling. Also, the existence of added lumped masses makes waves dispersive even for the continuum modelling. In order to examine these wave dispersions, a one-dimensional periodic structure is adopted as an analysis model and the dynamic transfer matrix method is applied. A wave solution and a finite element solution are used for the evaluation of the transfer matrix. The phase and group velocities in the structure are explicitly represented. These values are compared among the continuum modelling and the discretization modelling in which several consistent mass ratios are adopted. The optimal consistent mass ratio, which makes the wave velocity of the discrete model the same as that of the continuum model, is newly developed here. The validity of this mass modelling technique is presented by examining the frequency response function and impulse response function.     

Type IIIb radio bursts: 80 MHz source position and theoretical model

We present Culgoora spectrograph and radioheliograph observations as well as a model of type IIIb bursts; the latter are defined as chains of striae of slow or no frequency drift, the chain as a whole drifting like a normal type III burst.The 80 MHz source positions are studied for a group of IIIb bursts, a IIIb precursor and harmonic pairs of 1:2 frequency ratio. It is found that the IIIb position may vary in a IIIb group. No significant difference was found between the source positions of a IIIb precursor and the following III burst. For one event we found that the fundamental IIIb burst showed a high degree of circular polarization (46%), while its second harmonic, a normal type III burst, was unpolarized.We suggest that the main cause for the striae in type IIIb bursts is the existence of filamentary, density irregularities along the path of the electron stream. The denser filaments initially reduce the value of the density gradient along the electrons' path and thereby enhance their emissions over a small range of plasma frequencies. If the radio emission from the filaments dominates the emission from the ambient rarified plasma, striae appear in the spectrum and a type IIIb burst results. This condition is more easily satisfied at the fundamental frequency and for electron streams of relatively high density.Radiophysics Publication RPP 1758, October, 1974, (2nd version).On leave from the Dept. of Astronomy, University of Tokyo, Tokyo, Japan.On leave from the Dept. of Astronomy, Cairo University, Cairo, Egypt.     

A high accuracy method for determining nitrogen, argon and oxygen in seawater

An improved gas chromatographic system was constructed to analyze oceanic dissolved N₂, Ar and O₂ with a higher accuracy and shorter analytical time. To obtain a higher accuracy of N₂, Ar and O₂ measurements, the following was added to the system: (I) an air trapping system; (II) a N₂–CO₂ trapping system after the operation of the air trapping system; (III) an active carbon column system for separating N₂ and CO₂ completely and (IV) the introduction of automatic valves controlling most of the system. Compared to previous studies, the precision of the measurements of N₂, Ar and O₂ concentrations was higher at 0.04%, 0.05% and 0.02%, respectively, and our analytical time was shorter at 600 s. Using the improved analytical technique, concentrations of N₂ (C_N2, 561.69–611.81 μmol/kg) and Ar (C_Ar, 15.126–16.238 μmol/kg), saturation states of N₂ (ΔN₂, − 5.1–0.9%) and Ar (ΔAr, − 7.0 to − 1.1%) from 0 m to 3000 m depth in the western North Pacific were observed during March 2005. Based on these data, we propose a new concept for estimating the amount of bubble injection (B). The total error in calculating B was estimated to be about 20%. We estimated B from 12 to 43 μmol/kg in this region using the observational values of N₂ and Ar. As each water mass had a significantly different value of B even with an error of 20%, it is possible to use it as an index of sea surface state for when each water mass is produced in the sea surface mixed layer. Moreover, based on our values of B, we estimated preformed dissolved oxygen (DO) (C_preDO, 309–332 μmol/kg) and the saturation state of C_preDO (ΔpreDO, − 7.0 to − 1.2%) in this region. Thus, the difference between C_preDO and DO content in the ocean interior may be a more useful index for biogenic organic decomposition in the ocean field compared to Apparent Oxygen Utilization (AOU). Until now, the estimation of oceanic uptake of anthropogenic CO₂ has used AOU as a major parameter. Therefore, it may be necessary to re-evaluate the oceanic uptake of anthropogenic CO₂ based on our new concept of B.     

Estimation of groundwater flow from temperature monitoring in a borehole heat exchanger during a thermal response test

To estimate the groundwater flow around a borehole heat exchanger (BHE), thermal properties of geological core samples were measured and a thermal response test (TRT) was performed in the Tsukuba upland, Japan. The thermal properties were measured at 57 points along a 50-m-long geological core, consisting predominantly of sand, silt, and clay, drilled near the BHE. In this TRT, the vertical temperature in the BHE was also monitored during and after the test. Results for the thermal properties of the core samples and from the monitoring indicated that groundwater flow enhanced thermal transfers, especially at shallow depths. The groundwater velocities around the BHE were estimated using a two-dimensional numerical model with monitoring data on temperature changes. According to the results, the estimated groundwater velocity was generally consistent with hydrogeological data from previous studies, except for the data collected at shallow depths consisting of a clay layer. The reasons for this discrepancy at shallow depths were predicted to be preferential flow and the occurrence of vertical flow through the BHE grout, induced by the hydrogeological conditions.     

Simulation of soil liquefaction distribution in downtown Mashiki during 2016 Kumamoto earthquake using nonlinear site response

Bulletin of Earthquake Engineering - Several sites located between Road No.28 and Akitsu River in downtown Mashiki were liquefied during the mainshock of the 2016 Kumamoto earthquake. According to...     

耦合融雪的分布式流域"降雨-径流"数值模型

针对中国对耦合融雪的"降雨-径流"过程数值计算模型方面的研究较少,本文联合应用能量平衡方程及运动波理论的基础方程式,结合GIS技术构建分布式流域耦合融雪的"降雨-径流"数值计算模型,并应用流域实测资料进行了有效性验证。研究结果表明:在不考虑融雪条件下,实测流量与计算结果之间存在着较大的误差;在考虑融雪条件下,实测流量与计算结果之间的误差在基准允许范围之内(小于3%);在积雪与融雪区,对流域"降雨-径流"过程的数值计算须考虑融雪。该研究为积雪融雪区提供了一种耦合融雪的"降雨-径流"过程数值计算的新方法。     

航空激光雷达用于森林测量的数据处理方法研究

航空激光雷达是最近十几年开发的最新测量技术.利用激光扫描器所获得的高度数据可以建立精密的地形模型,同时可以获得森林生产力的信息.无论是地形测量还是植被估算,在数据处理时都需要将来自地表和植被的信号分离开,即滤波.数据滤波的方法很多,但是都不成熟,而且处于技术保密状态.本文介绍目前主要的信号分类方法,并开发了动态阈值分离法.该方法以森林为解析对象,通过反复运算逐渐逼近,完成地表和植被的分离,从而实现了地形与森林测量的双重目的.通过引入地形因子把原地形转换为理想平地,大大减少了过度滤波或者滤波不充分的情况.本方法基本实现自动处理,容易操作.利用本方法计算的高度误差(均方差,RMS)为0.4-0.5m.本方法还适用于城市地区高程模型的建立.