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61.
Sosuke Otani Yasunori Kozuki Ryoichi Yamanaka Hiromitsu Sasaoka Tetsu Ishiyama Yoshihito Okitsu Hajime Sakai Yoji Fujiki 《Estuarine, Coastal and Shelf Science》2010,86(3):434-440
The objective of this study is to elucidate the burrow structure and to clarify the role of burrows in material cycle in the tidal flat. In our work, we focused on the dominant species in muddy tidal flat, crab Macrophthalmus japonicus.Burrow structure of Macrophthalmus japonicus was investigated on a Katsuura river tidal flat in Tokushima prefecture, Japan, using in situ resin casting. Sampling was conducted in August 2006, and a total of 48 burrow casts were obtained. Burrows consisted mainly of J-shaped structures (98%) while the rest belonged to U-shaped structures (2%). The maximum measured burrow volume was 120 cm3 and wall surface area was 224 cm2, while maximum burrow length and depth were 23.2 cm and 16.5 cm, respectively. Burrow volume and surface area were strongly correlated with carapace width of M. japonicus. Investigation of the individual number of M. japonicus in 13 quadrats (50 × 50 × 20 cm) was conducted using 2 mm sieve. The number of M. japonicus was 15–31 ind./m2. Using cohort analysis we estimated that surface area of burrows was 0.07–0.15 m2/m2.CO2 emission rate was measured at the surface sediment during the period from June to December 2008. Results varied from 13.8 ± 2.2 to 49.4 ± 3.2 mg CO2/m2/h, and organic carbon decomposition was 3.8 ± 0.6–13.5 ± 0.9 mg C/m2/h. This leads the increase of organic carbon decomposition by 1.1 times, because of the expansion of the tidal flat surface area by burrowing activity. Organic carbon decomposition in burrow walls therefore contributed to organic matter decomposition in the tidal flat. These results indicated that in situ activities of Macrophthalmus japonicus significantly influence the material cycle and it is important to consider the existence of burrow in order to understand the fluxes of materials and to evaluate the purification function of the tidal flat. 相似文献
62.
Tomonori Kume Kyoichi Otsuki Sheng Du Norikazu Yamanaka Yi‐Long Wang Guo‐Bin Liu 《水文研究》2012,26(8):1161-1168
In this study, we aimed to clarify spatial variations in xylem sap flow, and to determine the impacts of these variations on stand‐scale transpiration (E) estimates. We examined circumferential and radial variations in sap flow velocity (Fd) measured at several directions and depths in tree trunks of black locust (Robinia pseudoacacia) and native oak (Quercus liaotungensis), both of which have ring‐porous wood anatomy, in forest stands on the Loess Plateau, China. We evaluated the impacts of circumferential variations in Fd on stand‐scale transpiration estimates using a simple scaling exercise. We found significant circumferential variations in Fd in the outermost xylem in both species (coefficients of variation = 20–45%). For both species, Fd measured at the inner xylem was smaller than that of the outermost xylem and the Fd at the depth of > 10 mm was almost zero. The simple exercises showed that omitting circumferential variations in Fd affected the E estimate by 16–21%, which was less than the effects of omitting within‐tree radial and tree‐to‐tree variations in Fd in both species. These results suggest that circumferential variations in Fd can be a minor source of error for E estimates compared with within‐tree radial and tree‐to‐tree variations in Fd, regardless of the significant circumferential variations. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
63.
Space observations of solar flares such as those from Yohkoh, SOHO, TRACE, and RHESSI have revealed a lot of observational
evidence of magnetic reconnection in solar flares: cusp-shaped arcades, reconnection inflows, plasmoids, etc. Thus it has
been established, at least phenomenologically, that magnetic reconnection does occur in solar flares. However, a number of
fundamental questions and puzzles still remain in the physics of reconnection in solar flares. In this paper, we discuss the
recent progresses and future prospects in the study of magnetic reconnection in solar flares from both theoretical and observational
points of view. 相似文献
64.
65.
Mst. Hawa Bibi Faruque Ahmed Hiroaki Ishiga Takashi Asaeda Takeshi Fujino 《Environmental Earth Sciences》2010,60(3):655-670
Geochemical analyses of lakebed and core sediments from Lake Sambe on the outskirts of Oda City in Shimane prefecture in southwestern
Japan were carried out in order to assess the water quality and the concentration and distribution patterns of sixteen elements.
The lake water showed a stratified condition with respect to dissolved O2, and As, Fe, and Mn concentrations in the bottom layers which increased in the summer. The chemical composition of the sediments,
as measured by X-ray fluorescence, included major and trace elements (P, Ca, Sc, Ti, V, Cr, Fe, Ni, Cu, Zn, As, Sr, Zr, Pb,
and Th), and total sulfur (TS). Elevated values of As, Zn, V, Fe, P, and TS were present in several layers of the upper cores
(from 0 to 5 cm) and other surface sediments. Increases in the abundances of these metals in lake sediments are probably related
to the reducing condition of the sediments, fine-grained organic rich sediments, and post-depositional diagenetic remobilization.
Moreover, correlations between the concentrations of trace metals and iron in the sediments suggest their adsorption onto
Fe (oxy)hydroxides, whereas correlations with sulfur indicate that they were precipitated as Fe-sulfides. The average abundances
of As, Pb, Zn, and Cu exceeded the lowest effect level and Interim Sediment Quality Guideline values that the New York State
Department of Environmental Conservation and the Canadian Council of Ministers of the Environment determined to have moderate
impact on aquatic organisms. In addition, concentrations of As and Zn exceeded the Coastal Ocean Sediment Database threshold
value, indicating potentially toxic levels. Therefore, the presence of trace metals in the lake sediments may result in adverse
effects on biota health. 相似文献
66.
Abstract: K–Ar datings and oxygen isotope analyses revealed a cooling history of the Uchiyama granitic pluton, which is genetically related to the Pb-Zn deposits (Taishu mine) in the Tsushima Islands, Japan. The pluton intrudes into the Paleogene Taishu Group to form the biotite-hornfels zone, while the Taishu vein-type Pb–Zn deposits occur in fissures developed in the non-hornfels zone about 1 to 3 km westward from the contact. Amphibole and biotite K-Ar ages of the pluton have a wide range from 19 to 13 Ma. Oxygen isotopes of the biotite and coexisting quartz grains indicate that isotopic exchange reactions have occurred under subsolidus conditions, and that the K-Ar ages are affected by various cooling rates in the pluton. The mineralization age of the Taishu ore deposits is obtained for the first time to be 15.40.8 Ma by a K-Ar age of 2 M 1 –muscovite in a calcite–quartz–muscovite–chlorite veinlet of the Shintomi orebody. Whole rock K-Ar ages of biotite-hornfels near the pluton represent similar ages to the ore deposits. Using blocking temperature calculated from reported diffusivity for argon, the pluton was cooled from 560 to 350C in the period of 17 to 14 Ma. The vein formation took place after the time when temperature in wall rocks of the pluton had dropped below the brittle-plastic transition (about 400C). These results imply that the cooling of the pluton has caused injection of magmatic fluids into meteoric hydrothermal systems, and the Pb-Zn mineralization has occurred due to this mixing at the age of about 15 Ma. 相似文献
67.
Geochemical study of the Holocene sediments of the Meghna River Delta, Chandpur, Bangladesh was conducted to investigate the distribution of arsenic and related trace and major elements. The work carried out includes analyses of core sediments and provenance study by rare earth element (REE) analysis. Results showed that the cores pass downward from silty clays and clays into fine to medium sands. The uppermost 3 m of the core sediments are oxidized [average oxidation reduction potential (ORP) + 230 mV], and the ORP values gradually become negative with depths (−45 to −170 mV), indicating anoxic conditions prevail in the Meghna sediments. The REE patterns of all lithotypes in the study areas are similar and are comparable to the average upper continental crust. Arsenic and other trace elements (Pb, Zn, Cu, Ni, and Cr) have greater concentrations in the silts and clays compared to those in the sands. Positive correlation between As and Fe was found in the sediments, indicating As may be adsorbed on Fe oxides in aquifer sediments. 相似文献
68.
Hiroshi Tsuno Atsuyuki Ohta Hiroyuki Kagi Noboru Imai Hiroaki Tao Masaharu Nomura 《Geostandards and Geoanalytical Research》2006,30(1):55-62
The oxidation states of chromium in GSJ JSO-2 (artificially contaminated soil) and three other geochemical reference materials (GSJ JSO-1, JLS-1 and JMS-1) were observed using X-ray near edge structure (XANES). For comparison, other artificially contaminated soil materials (mimic-JSO-2) were prepared by adding Cr(VI) into JSO-1. Their oxidation states of chromium were determined using XANES. The chromium contents were 1118 μg g-1 for JSO-2, 1352 μg g-1 for mimic-JSO-2 and 69-113 μg g-1 for the other reference materials. Most chromium was present as hexavalent in mimic-JSO-2. No hexavalent species were detected in other samples. These results for chromium oxidation state in JSO-2 and mimic-JSO-2 obtained with XANES resembled those obtained from a chemical extraction method. The present JSO-2 has no trace of Cr(VI), although Cr(VI) was added as a major species during preparation. On the other hand, the content of Cr(VI) obtained in mimic-JSO-2 agreed with the original Cr(VI) content. A time-elapse study showed that Cr(VI) contents in mimic-JSO-2 decreased gradually to 70% of the original abundance during 240-day preservation in dry conditions. Moreover, the abundance of Cr(VI) decreased markedly to 15% after 240 days in the wet mimic-JSO-2 containing 20% m/m of water. These experiments suggested that soil humidity enhanced the reduction of Cr(VI) and that Cr(VI) was reduced even in dry conditions. Consequently, it is reasonable to infer that Cr(VI) doped into JSO-2 was completely reduced to Cr(III) during the preservation period of 5 years. The certification of the long-term stability of the chemical form in reference materials will be much more important in future. 相似文献
69.
Taku Tsuchiya Takamitsu Yamanaka Masanori Matsui 《Physics and Chemistry of Minerals》1998,25(2):94-100
A two-body interatomic potential model for GeO2 polymorphs has been determined to simulate the structure change of them by semi-empirical procedure, total lattice energy
minimization of GeO2 polymorphs. Based on this potential, two polymorphs of GeO2; α-quartz-type and rutile-type, have been reproduced using the molecular dynamics (MD) simulation techniques. Crystal structures, bulk moduli, volume thermal expansion coefficients and enthalpies of these
polymorphs of GeO2 were simulated. In spite of the simple form of the potential, these simulated structural values, bulk moduli and thermal
expansivities are in excellent agreement with the reliable experimental data in respect to both polymorphs. Using this potential,
MD simulation was further used to study the structural changes of GeO2 under high pressure. We have investigated the pressure-induced amorphization. As reported in previous experimental studies,
quartz-type GeO2 undergoes pressure-induced crystalline-to-amorphous transformation at room temperature, the same as other quartz compounds;
SiO2, AlPO4. Under hydrostatic compression, in this study, α-quartz-type GeO2 transformed to a denser amorphous state at 7.4 GPa with change of the packing of oxygen ions and increase of germanium coordination.
At higher pressure still, rutile-type GeO2 transformed to a new phase of CaCl2-type structure as a post-rutile candidate.
Received: 29 July 1996 / Revised, accepted: 30 April 1997 相似文献
70.
Ore value-tonnage diagrams for resource assessment 总被引:4,自引:0,他引:4
An ore value-tonnage diagram has been proposed for assessing mineral resources. Diagrams of W+Mo, and Pb+Zn deposits show
a good linearity between ore value and logarithms of cumulative ore tonnage. Diagrams of the massive sulfide, orthomagmatic,
placer, porphyry, replacement, and stratabound types are also linear. It is assumed, therefore, that deposits of each of these
commodities and these types belong to a single population. In contrast, the ore value-tonnage relations of all the deposits
analyzed here is approximated by the combination of two exponential functions. The same feature is seen for deposits of the
Cu+W+Mo, Cu+Pb+Zn, and Au+Ag commodities, and of the vein and unconformity-related types. This suggests that deposits belonging
to each of such categories are divided into the high and low value groups. We can expect, accordingly, to find high value
deposits of such categories. 相似文献