Elastic properties of the incommensurate phase of akermanite,Ca2MgSi2O7

The crystal structure of akermanite, Ca₂Mg-Si₂O₇, consists of mixed tetrahedral sheets formed by [MgO₄] tetrahedra and [Si₂O₇] groups interleaved along the c axis with Ca²⁺ ions in eight-fold coordination. Above 358 K, the structure is tetragonal , and below it is incommensurate with modulations parallel to [110] and . The elastic stiffness moduli, C ^ij of the incommensurate phase at room temperature were measured from wave velocities in the 20–75 MHz carrier frequency range by the ultrasonic phase comparison method using optically clear synthetic single crystal plates (3×3×2 mm) oriented parallel to (100), (001), (110) and (101) planes. The C _ij values (GPa) are: C ₁₁ 159.40, C ₃₃ 149.43, C ₄₄ 30.26, C ₆₆ 58.10, C ₁₂ 76.58 and C ₁₃ 57.80. In (010) and (001) planes, the compressional modulus, V ²(L) from the longitudinal wave, L is considerably larger than the shear moduli, V ²(T₁, T ₂) both from the in-plane and perpendicular-to-plane shear waves, T ₁ and T ₂. The relatively small values of the shear moduli indicate the ease of tetrahedral rotations in response to in-plane and perpendicular-to-plane shears and may provide preconditions for structural changes involving shear-type atomic movements.     

Material characteristics and building technique for the rammed earth wall of the 13th Korean fortress in Ganghwa

This study identifies the technique applied for building the rammed earth wall of the 13th Korean fortress, Ganghwa Jungseong, by analyzing its physical, mineralogical, granulometric, and geochemical characteristics. Furthermore, mutual homogeneities between the rammed earth wall and host rock, top soil, and sub-surface soil collected around the fortress were interpreted. The ground of the rammed earth wall was not created artificially but made via soil preparations containing loamy soils from weathered bedrock. The foundation part was built using various layers of soils having different colors, magnetic susceptibilities, particle sizes, and organic components. In particular, a layer of loamy saprolite was generated to enhance the stability of the foundation and improve ventilation and draining throughout the structure. The body of the wall is composed of silty loam at the bottom and silty loam to loam from the middle to the top. Techniques that alternately harden soils using different particle sizes enable external shock absorption and prevent crack formation owing to temperature changes during winter and summer. The rammed earth wall and the soils around the fortress contained related rock-forming materials had similar magnetic susceptibilities and geochemical characteristics, which indicated that they have a genetically common source. Moreover, the rammed earth wall was built using the soil weathered from the banded gneiss because it was correlated to the banded gneiss constituting the bedrock around the fortress.     

Hydrogeochemical Anomalies in the Springs of the Chiayi Area in West-central Taiwan as Possible Precursors to Earthquakes

Water samples from both hot and artesian springs in Kuantzeling in west-central Taiwan have been collected on a regular basis from July 15, 1999 to the end of August 2001 to measure cation and anion concentrations as a tool to detect major earthquake precursors. The data identify chloride and sulfate ion anomalies few days prior to major quakes and lasting a few days afterward. These anomalies are characterized by increases in Cl^- concentrations from 34.9% to 41.2% and 71.5% to 138.1% as well as increases in SO₄^2- concentrations from 232.7% to 276.8% and 100.0% to 155.1% above the means in both hot and artesian springs. The occurrence of these anomalies is probably explained first as stress/strain-induced pressure changes in the subsurface water systems which then generate precursory limited geochemical discharges at the levels of subsurface reservoirs. Therefore, finally leading to the mixing of previously separated subsurface water bodies occurs. This suggests that the hot and artesian springs in the Kuantzeling area are possible ideal sites for recording strain changes serving well as earthquake precursors.     

Stratigraphy of Quaternary inner-shelf sediments in Tai O Bay, Hong Kong, based on ground-truthed seismic profiles

High-resolution boomer profiles from Tai O Bay, Hong Kong SAR, were ground-truthed using ten discontinuously sampled boreholes penetrating bedrock with a maximum length of 82.1 m. The relationship between depth below seabed and seismic profiles was established through the measurement of two borehole compressional-wave velocity profiles. In departure from previous interpretations, nine Quaternary seismic units were identified, which can be divided into eight systems tracts formed by cycles of fourth-order sea-level fluctuations dating back at least to marine isotope stage (MIS) 7 (ca. 190–245 ka). These consist of two lowstand systems tracts, two transgressive systems tracts, and four highstand systems tracts. Secondary unconformities within the highstand deposits are interpreted to document fifth-order sea-level fluctuations. Lowstand deposits are less common because, as soon as the sea level drops by a few metres, Tai O Bay becomes sub-aerially exposed, leading to widespread non-deposition or erosion. At the same time, extensive fluvial erosion and channel incision take place. Filling of the fluvial channels occurs during rising sea level. Lowstand sediments (if present) are generally landslide deposits laid down on a basal alluvial plain. Uncorrected accelerator mass spectrometry (AMS) radiocarbon dates of mollusc shells show that the depositional environment was marine since 6.2 ka, becoming gradually more brackish as a result of progradation of the Pearl River delta. The computed average sedimentation rate for the period 6.2–4.1 ka is 4.4 m/1,000 year, and approximately 1 m/1,000 year since 4.1 ka.     

ENC不一致性问题分类及其对策

ENC作为一种独特的地理空间信息产品,广泛应用于ECDIS(电子海图显示与信息系统)。由于多方面原因,海员在ECDIS使用过程中可发现ENC中存在一些不一致性现象,不仅影响了ENC的数据质量和可信度,而且容易使海员对海上地理要素产生混淆和误判,最终影响船舶海上航行安全。由于海图编绘资料的多源性以及以单幅数据进行生产的作业模式,数据生产者在数据质量评价时都将关注点放在单幅数据的检校,却忽视了数据之间的不一致问题。为此,对各类不一致问题进行梳理分类,按照出现位置不同,将不一致问题分为"ENC内部不一致性"、"邻接ENC之间不一致性"和"重叠ENC之间不一致性"等3大类,分别进行了原因分析和示例说明,最后给出了解决ENC不一致性的途径,为ENC不一致问题的进一步研究指明了方向。     

Validating the turbulence parameterization schemes of a numerical model using eddy dissipation rate and turbulent kinetic energy measurements in terrain-disrupted airflow

A number of turbulence parameterization schemes are available in the latest version (6.0) of the Regional Atmospheric Modelling System (RAMS). Chan in Meteorol Atmos Phys 103:145–157, (2009), studied the performance of these schemes by simulating the eddy dissipation rate (EDR) distribution in the vicinity of the Hong Kong International Airport (HKIA) and comparing with the EDR measurements of remote-sensing instruments at the airport. For the e-l (turbulent kinetic energy ? mixing length) scheme considered in that study, the asymptotic mixing length was assumed to be a constant. This assumption is changed in the present paper, a variable asymptotic mixing length is chosen and simulations of EDR fields are repeated for terrain-disrupted airflow in the vicinity of HKIA. It is found that, with a variable asymptotic mixing length, the performance of the e-l scheme is greatly improved. With suitable choice of the empirical constants in the turbulence closure, the accuracy of the EDR profile (in comparison with LIDAR and wind profiler measurements) is found to be comparable with that predicted by the Deardorff scheme. A study on the sensitivity of the simulation results to these empirical constants has also been performed. Moreover, as a follow-up of the previous study of Chan in Meteorol Atmos Phys 103:145–157, (2009), case studies have been conducted on the following issues of the model simulation of turbulence for aviation application: (a) the effect of vertical gridding on the simulation results, (b) possibility of false alarm (such as over-forecasting of EDR value) in light turbulence cases, and (c) the performance in the simulation of other turbulence intensity metric for aviation purpose, e.g. TKE.     

In‐situ gamma‐ray spectrometric study of weathered volcanic rocks in Hong Kong

In‐situ gamma‐ray spectrometry (GRS) measurements were conducted at 35 sites in Hong Kong where volcanic rocks with varying extent of weathering were exposed. Elemental analyses using X‐ray fluorescence spectrometry and inductively coupled plasma–mass spectrometry were carried out on samples collected from these 35 plus 22 other locations to assess the feasibility of using the GRS method to quantify the extent of weathering. The Parker weathering index, varying within a range of 0·0–0·8 for the samples studied, was used as a geochemically based reference scheme for correlating the gamma‐ray spectrometric results with the extent of weathering. For the former 35 sites, the concentrations of the three major radioelements, K, U and Th, determined by in‐situ GRS were compared to laboratory‐determined values from the samples. The study reveals that no significant change occurs to the contents of the three radioelements during the initial state of weathering. But once the rocks become highly weathered, further progression of weathering is accompanied by a systematic removal of K and an increased dispersion of U and Th. The results show that K content, which is indicative of the extent of weathering, can be retrieved reliably with the gamma‐ray spectrometry technique. The study has given support to the potential use of the downhole spectral gamma method for evaluation of weathering grade and the detection of subsurface clay‐rich levels. Copyright © 2002 John Wiley & Sons, Ltd.     

The role of MJO and mid-latitude fronts in the South China Sea summer monsoon onset

Previous studies have suggested that the South China Sea (SCS) summer monsoon onset is concurrent with the arrival of a 30–60-day northward-propagating trough. On the other hand, from a synoptic viewpoint, some studies pointed out that the arrival of a mid-latitude front may be the triggering mechanism of the SCSSM onset. This study attempts to link these two viewpoints and to investigate their relative role in inducing the SCSSM onset. Composites of low-level zonal winds, geopotential heights and temperatures during the 1991–1999 SCSSM onsets based on the European Centre for Medium Range Weather Forecast ERA-40 data indicate that both the Madden and Julian Oscillation (MJO)/Kelvin waves and mid-latitude trough are apparently involved in the onset. The MJO/Kelvin waves play a major role in inducing the large-scale easterly-westerly shift over the central SCS, while the effect of the acceleration of westerlies ahead of the mid-latitude trough is limited to the northern SCS only. Numerical experiments using a regional climate model further demonstrate that the MJO/Kelvin waves control the timing of the onset by changing the background meridional geopotential height gradient over the SCS. When the MJO is at its peak phase over the Maritime continent, it imposes a positive meridional geopotential height gradient over the SCS such that easterly winds are induced, which significantly reduces the strength of a mid-latitude trough. After the equatorial convection has dissipated, a Rossby-wave response is induced, leading to the formation of a northward-moving trough. When this trough moves northward, the meridional geopotential height gradient is reversed and westerly winds are induced. At the same time, if a mid-latitude trough arrives in south China, the westerlies associated with the mid-latitude trough will strengthen because of the background meridional geopotential height gradient, which gives the impression that both the northward-moving trough and mid-latitude trough are in phase and work together to induce the onset.     

Wave characteristics past a flexible fishnet

The scattering of surface waves by a flexible fishnet is studied analytically. The fishnet is modelled as a porous flexible barrier displaced solely by hydrodynamic force like a catenary. The objective is to investigate how a flexible permeable barrier affects the passing waves in the way they are transmitted and reflected, as observed by the fact that the water inside a fishfarm surrounded by fishnets is significantly calmer than that outside. The boundary value problems are solved by defining the reflection coefficient in terms of velocity potential and then the full solutions are obtained by suitable application of the eigenfunction expansion method and the least squares approximation method. The variations of the reflection coefficient, hydrodynamic pressure, barrier deformation and surface wave elevation are determined with respect to the barrier length, porosity and stiffness. It is observed that as the fishnet gets more flexible, its deformation increases and the reflection coefficient decreases, whereas as the fishnet gets more porous, more water can pass through it and thus the reflection coefficient, barrier deformation and the hydrodynamic force are reduced. The flexibility of the barrier behaves like its porosity by allowing more wave energy to act on it through its deformation and hence reduce the reflection and hydrodynamic force of the incident waves acting on the barrier.     

Characteristics of vertical ozone distribution in the lower troposphere in the Yangtze River Delta at Lin’an in the spring of 2001

Deterioration of air quality as a result of rapid eco- nomic development in the Yangtze River Delta (YRD) has attracted much scientific and public attention[1―7]. To explore the air quality of a region, measurement of pollutants in locations reflecting the “background” atmospheric conditions of the region is essential. The Regional Baseline Air Quality Monitoring Station of the Chinese Academy of Meteorological Sciences (CAMS) at Lin’an is located in such an area in Zhe- jiang Pro…