Investigations of MX-1 tridymite by 29Si MAS NMR — Modulated structures and structural phase transitions

MX-1 tridymite is one of the room-temperature polymorphs of SiO₂ tridymite and has an underlying monoclinic structure (Cc) with incommensurate modulations along a ^* and c ^* (Hoffmann et al. 1983; Löns and Hoffmann 1987). With increasing temperature up to 500° C, MX-1 is reported to experience at least five structural phase transitions. However, its structures and the relationships to other tridymite polymorphs are unclear. We present here a ²⁹Si MAS NMR study of the room-temperature incommensurate structure of MX-1 and its structural phase transitions up to 540° C. Our results suggest that at room temperature, all the Si sites in MX-1 tridymite are in positions with similiar ∠Si-O-Si of ～150° and are consistent with the presence of two incommensurate modulations proposed by Hoffmann et al. (1983). Simulations of the spectra yield modulation amplitudes of 1.33 and 0.87 ppm, corresponding to 0.009 and 0.006 Å for Si-Si. The maximum atomic displacements along a and b due to the modulations appear to be ～0.01–0.02 Å. The structural phase transitions of MX-1 are significantly different from those of MC tridymite below 220° C. Our high temperature results confirm that MX-1 tridymite transforms to the H5 phase at about 65° C. The most important transition occurs near 110° C, where the H5 phase transforms to a phase yielding a single, narrow NMR peak, indicating the disappearance of the superstructure and possibly the onset of the dynamic averaging. The NMR lineshapes of H5 are consistent with the metrically orthorhombic unit cell and commensurate superstructure of 2a, 2b and 10c proposed by Graetsch and Flörke (1991). The phase present above 110° C is probably similar to the OC phase, but has a mean ∠Si-O-Si of ～152.0° at 113° C, 152.9° at 185° C and 154.1° at 500° C. The transitions at ～160 and 220° C for MX-1 are subtle and probably due to impurity MC. Analysis of the modulations in the OS phase of MC tridymite indicates that their amplitudes are of the order of 0.02 Å, significantly less than the value 0.3 Å proposed by Nukui et al. (1979).     

Diel vertical migration of the copepod Calanus sinicus before and during formation of the Yellow Sea Cold Bottom Water in the Yellow Sea

To understand the effects of the Yellow Sea Cold Bottom Water(YSCBW)on the diel vertical migration(DVM)of the copepod Calanus sinicus,we surveyed vertical distribution of C.sinicus at a fixed station in the Yellow Sea before(spring)and during(summer)formation of the YSCBW.Cold water(<10 C)was observed in the bottom layer when the water column was thermally stratified in summer,but the water column was thermally well-mixed in spring 2010.Samples were collected from five different layers at 3-h intervals using an opening-closing net.Adult females(1–155 ind./m3)showed a clear normal DVM pattern throughout the entire water column in spring,whereas adult males did not migrate.DVM of copepodite V(CV)individuals was not clear,but the maximum abundance of CI–CIV occurred consistently in the upper 10–20 m layer,where there was a high concentration of chlorophyll-a(Chl-a)(0.49–1.19μg/L).In summer,weak DVM was limited to cold waters beneath the thermocline for adult females(<30 ind./m3),but not for adult males.The maximum abundance of CI–CIV also occurred consistently in the subsurface layer(20–40 m)together with high concentrations of Chl-a(0.81–2.36μg/L).CV individuals(1–272 ind./m3)moved slightly upward nocturnally to the near-surface layer(10–20 m),where the average temperature was 25.74 C,but they were not found in the surface layer(0–10 m;28.31 C).These results indicate that the existence of the YSBCW affected food availability at depth and the vertical temperature distribution,leading to variation in the amplitude and shape of stage-specific vertical distributions(CI to adults)in C.sinicus before and during the formation of cold waters in the Yellow Sea during the study period.     

The feasibility of carbon incentives to private forest management in Korea

Forest management is regarded as one possible approach to reducing greenhouse gases by absorbing carbon at a relatively low cost. In Korea, the forest comprises 64% of the total land area, so forests are expected to play a key role in mitigating climate change on the one hand. On the other hand, since 70% of the forest area is owned by the private sector, there is considerable uncertainty about managing forests for the national carbon sink strategy. The objective of this study is to examine the levels of carbon incentives to private forest management for the purpose of maximizing forests’ carbon absorption. First, in the context of present forest management policies, this study discusses applicable measures for the promotion of carbon sequestration in private forests. Next, considering the implications of policies related to forestry, the study develops a hypothetical carbon incentive scheme to compensate for economic revenue loss derived from accepting a rotation period that maximizes carbon sequestration. Carbon incentive levels are estimated by assessing the difference of financial revenue between a financially optimal rotation plan and a carbon-sink maximizing rotation plan. This study found that for red pine forests, the levels of the carbon incentives vary US$2–6 at 5% discount rate and US$ 34–88 at 7% discount rate while the values for oak forests are differing US$2–22 at 5% discount rate and US$ 20–52 at 7% discount rate. The study concludes that the carbon incentive scheme could be effective for increasing the carbon sink. However, given related governmental policies, it may not be desirable to employ the scheme without considering changes in government policy toward land use and regional development.     

Temporal domain processing for a synthetic aperture array

A method for the synthesis of an aperture with improved bearing resolution and signal gain is described. The proposed method temporally synthesizes data from an overlap correlator, which is obtained by aperture domain averaging of phase differences. Previous studies, such as extended towed array measurements (ETAM), had a restriction in that the overlapped hydrophones between successive measurements of a towed array were required to have identical positions in space. In this paper, however, it is shown that the phase correction factors can be estimated without restriction on the positions of the overlapped hydrophones. This implies that the proposed method is able to utilize more snapshots to extend the towed array. Simulation results showed that the proposed method resulted in higher estimation accuracy than ETAM. In addition, the effects of coherency and other systematic errors on the proposed method were examined     

1810年2月19日清津近海地震--19世纪韩半岛灾害最严重的地震

据《朝鲜王朝实录》记载 ,1810年 2月 19日在朝鲜咸镜道明川、镜城、会宁和富宁府发生地震 ,造成房屋倒塌和人畜死亡以及地面裂陷、喷水冒砂、滑坡等地表破坏。本文引证《承政院日记》、《备边司誊录》、《日省录》等重要历史文献及地方志 ,详细研究了有关史料。此地震造成 4 7户房屋倒塌 ,5人死亡 ,是 19世纪韩半岛震害最严重的地震。清津湾沿岸地区破坏最重 ,烈度达到Ⅷ度 ,砂土液化和地震海啸加重了震害。震中在清津近海域 (N4 1 7°E12 9 8°) ,震级定为M6 。     

Analytical analysis of pullout resistance of the hydraulic expansion rockbolts on a frictionally coupled model

This paper proposes an empirical formula to estimate the shear strength of hydraulic expansion rockbolts. The field experimental results were obtained from eleven pullout tests to evaluate the results computed by the proposed formula. It was found that shear resistance of hydraulic expansion rockbolts significantly depends on the uniaxial compressive strength and elastic modulus of rock, with high correlation coefficients of 0.7651 and 0.8587, respectively. The developed formula enables estimation of the maximum pullout load in an analytical process without pullout tests in the field. Conversely, due to the poor interlocking at the initial pullout load, the measured displacements were higher than the estimated ones. To reduce the interlocking effects between bolt and rock, we recommend preloading of 29.4 kN. Preload allows reducing the distance between the measured and estimated displacement and making two load-displacement curves practically identical with marginal differences of 1.1 to 1.5 mm at the maximum pullout load.     

Granitoids and Their Magnetic Susceptibility in South Korea

Abstract: Magnetic susceptibility (MS) measurements were carried out for 1,120 samples in the Middle Proterozoic to Early Tertiary granitoids so far recognized in South Korea, and the lateral and spatial variation of their magnetic susceptibility, i.e., content of magnetite, is studied. The Middle Proterozoic two mica granitoids related to cassiterite (Sn) deposits in northeastern part of the Sobaegsan Massif show very low MS (less than 0.3 A‐ 10^‐3 SI unit), and the Permo‐Triassic tonalitic to granodioritic and monzonitic rocks which are barren in mineralization, distributed in the middle part of South Korea also show low MS (less than 1 A‐ 10^‐3 SI unit). On the contrary the Late Triassic to Jurassic granitoids (= Daebo granitoids) which were evolved from tonalite through granodiorite to granite, and are most widely distributed in South Korea, show a wide variation on MS. Particularly in the Andong, Igsan, Gimcheon and Geochang areas, the granitoids which are barren in mineralization, are characterized by high MS (more than 10 A‐ 10^‐3 SI unit). The Chuncheon, Jecheon, Namyang and Geumsan plutons related to molybdenite (Mo) and/or wolframite or scheelite (W), and fluorite (F) mineralizations show a little high MS (more than 3 A‐ 10^‐3 SI unit). However, more than 60% of the Daebo granitoids show low MS (less than 3 A‐ 10^‐3 SI unit) and the rest show a little high MS (more than 3 A‐ 10^‐3 SI unit). Heterogeneous distribution of magnetite content in the Daebo granitoids is considered to reflect heterogeneity of redox state of the source materials for these granitoids. The Cretaceous to Early Tertiary granitoids (= Bulgugsa granitoids) in the Gyeongsang Basin had been generally evolved in the order of tonalite, diorite, granodiorite, granite and alkali‐feldspar granites, which are closely related to base metal ore deposits, and mostly show higher MS (more than 3 A‐ 10^‐3 SI unit) than other granitoids mentioned above, although some exceptions are recognized in highly evolved alkali‐feldspar granites (SiO₂ > 76%). In contrast, as most of the highly oxidized or evolved Cretaceous granitoids distributed in areas other than the Gyeongsang Basin show lower MS than those of the Gyeongsang Basin, and appear to be magnetite free, ilmenite‐series granites, but they might be hematite bearing magnetite‐series granitoids. Highly oxidized nature of the Bulgugsa granitoids may be due to high Fe₂O₃/FeO ratio of the source materials and also high level intrusion style of the granitic magma activities. Most of the granitic rocks of the Middle Proterozoic, Permo‐Triassic and more than 60% of the Late Triassic to Jurassic (Daebo granitoids) belong to ilmenite–series, however less than 40% of the Daebo granitoids and most Cretaceous ones are magnetite–series. Thus, the granitic magma intruded in Korean Peninsula became oxidized while the intrusive ages become younger.     

Are Juvenile Manila Clam Ruditapes philippinarum Free from Perkinsus olseni Infection in Korean Waters?

Ocean Science Journal - As a suspension feeder, Manila clam Ruditapes philippinarum (A. Adams and Reeve 1850) plays a crucial role in the coastal soft bottom ecosystem in the temperate region,...     

Effects of several salt marsh plants on mouse spleen and thymus cell proliferation using mtt assay

In the present study, we have tested the effects of 21 salt marsh plants on cell proliferation of mouse immune cells (spleen and thymus) using MTT assay in culture. The methanolic extracts of six salt marsh plants (Rosa rugosa, Ixeris tamagawaensis, Artemisia capillaris, Tetragonia tetragonoides, Erigeron annus, and Glehnia littoralis) showed very powerful suppressive effects of mouse immune cell death and significant activities of cell proliferationin vitro. Especially, the methanolic extract ofRosa rugosa was found to have fifteen times compared to the control treatment, demonstrating that Rosa rugosa may have a potent stimulation effect on immune cell proliferation. These results suggest that several salt marsh plants includingRosa rugosa could be useful for further study as an immunomodulating agent.