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1.
Fission tracks and point defects in natural zircon are directly observed by a 1 MV electron microscope at atomic resolution for three types of samples adjusted to the 100 orientation. Lattice planes intersecting the fission tracks at high angles are distorted in a rather irregular manner over a wide region up to more than 100 Å wide. Diameter of the tracks, ranging from 25 Å to 40Å, is much narrower than those so far reported for the U-doped synthetic zircon (100–200 Å), UO2 thin film (100 Å), mica (66 Å, 240 Å) or fluorophlogopite (150 Å). The fact that fairly long tracks thousands of angstroms in length are observed in thin 100-oriented sample hundreds of angstroms in thickness and that some of them are nearly parallel to a low index lattice plane suggest a possible occurrence of channelling in the process of track formation. Parallel tracks often observed in chemically etched specimens support the idea of channelling. Slightly bent tracks are sometimes observed. It is concluded from computer simulation that many contrast anomalies of bright and dark spots in the lattice image are due to point defects of vacancies and interstitial atoms, mainly produced by the direct atomic collision with α-particles or by passage of ionizing nuclear particles. Optimum conditions of the observation of point defects with highest contrast are studied. One interstitial Zr atom or one Zr ion vacancy will give very low contrast and will be not detectable unless the crystal is less than two unit cells thick. A pair of Zr ion vacancies, however, yields extended detectable limit of thickness. Some of the observed defects are in good accordance with those simulated. 相似文献
2.
Kenji Kashiwaya Hideo Sakai Masayuki Ryugo Masae Horii Takayoshi Kawai 《Journal of Paleolimnology》2001,25(3):271-278
Analysis of physical properties in long sediment cores (BDP96) from Academician Ridge in Lake Baikal indicates that major climato-limnological changes during the past 3.5 Myr occurred at about 2.5–2.8, 1.7–1.9, and 0.9–1.2 Ma, which were close to times of major geomagnetic polarity reversals (Matuyama/Gauss, Olduvai, Jaramillo + Matuyama/Brunhes). The principal climato-limnological oscillation has a long-term period of nearly 1,000 kyr, which corresponds to the periodicity of fluctuation in solar insolation. It also seems to be related to geomagnetic field intensity. Other long-term period of 400 kyr corresponds to Milankovitch parameters of eccentricity. These results suggest that changes in solar insolation were closely related to long-term environmental variations in the deep continental interior. 相似文献
3.
Kenji Kashiwaya Masayuki Ryugo Masae Horii Hideo Sakai Toshio Nakamura Takayoshi Kawai 《Journal of Paleolimnology》1999,21(2):143-150
The St.16 core obtained from the Academician Ridge of Lake Baikal in eastern Siberia may span about 260 000 years, and some physical properties of the core samples are closely related to aquatic paleoproductivity and climatic change. The median of grain size, grain density, and water content fluctuate synchronously. They also are connected with change in the abundance of biogenic silica (diatoms). The physical parameters indicate that there were high aquatic productivity periods around interglacial periods (MIS 5 and 7; 70 000-125 000 yr B.P. and 180 000-250 000 yr B.P.). Comparatively large clastics were transported from outside of the lake through various routes (ice rafting, etc.) in addition to fluvial routes during the glacials or 'stadials. There are ca. 20 000 yr, 40 000 yr and 100 000 yr periods in the variations of physical properties. These are related to the three Milankovitch parameters of solar insolation. 相似文献
4.
High-, intermediate-, and low-type zircon crystals of natural origin were investigated using a 1,000 kV high-resolution electron microscope. The lattice images obtained successfully for high zircon were in good accordance with computer simulated ones, and 1.5 Å separations, the nearest distance between zirconium atoms projected along the a axis, were clearly resolved under a certain instrumental condition. The images of fission tracks and surrounding areas show nearly perfect lattice images and that within the fission tracks, with a width of 20 ～ 30 Å and length of ca. 1,000 Å, the structure is heavily disordered, almost amorphous; that both sides of the tracks the lattices are displaced or dislocated, and that in the area adjacent to the tracks, bright and dark spot images occur, corresponding to vacancies and their interstitial atoms. In low zircon, the structure is completely destroyed to show an entirely amorphous state, whereas an intermediate type consists of domains of the order of 50 ～ 100 Å across with nearly regular lattices, along whose boundaries strongly disordered areas with widths of few tens of angstroms appear, but the relative orientations of the neighbouring domains are almost continuous. Thus a whole process of metamictization is visualized on a lattice scale. Metamictization proceeds principally by the formation of fission tracks, the direct result of fast movement of nuclear particles; recoil nuclei therefrom seem to play a less important role in the destruction of the structure. 相似文献
5.
Maki Morimoto Kyoko Kawanobe Osamu Abe Takayoshi Kawai Toshiyuki Kawamura Kunio Shirasawa 《水文研究》2010,24(7):904-916
In winter, lakes and lagoons at high altitudes or high latitudes have interesting hydrological cycles that differ from those in other seasons or in other regions, because water surfaces are covered with ice. Hydrological balances of lakes and lagoons are complex dynamic systems, and to elucidate them, isotopic tracers of water have been used as effective tools along with observations of precipitation, evaporation, inflows, and outflows. Here, to understand hydrological processes during freezing periods in the brackish Saroma‐ko Lagoon, Hokkaido, northern Japan, we examined horizontal and vertical distributions of salinity and isotope compositions of lagoon water and ice in 2005 and 2006. Horizontal and vertical gradients of salinity and isotope compositions were observed from the river mouth to the sea channel, and factors determining these distributions were considered. The mixing of freshwater and seawater and a freezing effect were presumed to be factors in relationships between salinity and isotopes and in relationships between surface waters and ice just above the water. A simple box model for water balance was constructed based on these putative factors to reproduce the distributions of salinity and isotope compositions of surface waters and ice. An evaluation of the model revealed that this hydrological system is controlled primarily by horizontal advection of the epilimnion, freshwater influx, and the ice growth rate. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
6.
Yuan-Gang Zu Wen-Jie Wang Hui-Mei Wang Wei Liu Song Cui Takayoshi Koike 《Climatic change》2009,96(1-2):137-159
With the implementation of the Chinese Natural Forest Conservation Program (NFCP) in 1998, over millions of hectares of forest in northeastern China have been protected through natural restoration (closure of hills). The impact of this program on the carbon budget of soil has not been evaluated until now. This paper presents results from a 6-year study of total CO2 efflux from both soil and litter (R total), CO2 flux from soil (R soil), soil organic matter (SOM), soil microbe density, and litter input and root biomass at an uncut larch (Larix gmelinii) forest and at a natural restoration site. The natural restoration area is a clear-cut site that was formerly part of a continuous portion of the uncut larch forest. Our objectives were to: (1) quantify the magnitude of CO2 efflux from typical sites in northeastern China; (2) explore the changes in thermal conditions, SOM, and annual CO2 flux during the 6-year natural restoration, and (3) evaluate the impact of NFCP on soil carbon processes. The annual R soil at the clear-cut site (58.6–68.2 mol m???2 year???1) was 113.6–228.4% (mean 141.5%) higher than that at the uncut larch site (29.6–58.4 mol m???2 year???1). At the same time, annual CO2 from litter at the clear-cut site (2.0–14.2 mol m???2 year???1) was only 23.5–84.5% (mean 52.5%) of that at the uncut larch site (5.4–16.8 mol m???2 year???1). SOM at the surface layer of the clear-cut site was 75% of that at the uncut larch site, but the soil microbial biomass (carbon) at the clear-cut site was much higher than that at the larch site (p?<?0.05). The percentage of bacteria, fungi and actinomycetes also were largely different between both sites. Natural restoration at the clear-cut site strongly affected thermal conditions. Although the soil temperature (T soil) and effective accumulated $T_{\rm soil} > 0^{\circ}$ C at the clear-cut site was much higher, the temperature sensitivity (Q 10) was much lower than that at the uncut larch site, and their differences decreased linearly from 2001 to 2006 (p?<?0.05). Moreover, Q 10 at the clear-cut site significantly increased with the progress of natural restoration, which diminished the Q 10 difference between the two sites (slope?=???0.2792, r 2?=?0.4744, p?<?0.05). These data imply that the NFCP natural restoration process has positively recovered the thermal condition of the clear-cut site to the level of uncut larch forest during the 6-year period. However, linear regression analysis showed that the 6-year natural restoration only slightly affected the annual soil CO2 efflux and SOM at both sites, and also did not diminish the differences between the two sites (p?>?0.10), indicating that a much longer time is necessary to restore the soil carbon in the clear-cut site. 相似文献
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8.
The statistical technique of functional data analysis (FDA) is applied to a time series analysis of plankton monitoring data. The analysis is focused on revealing patterns in the seasonal cycle to assess interannual variability of several different taxonomic groups of plankton. Cell concentrations of diatom, dinoflagellate and zooplankton abundances from the Bay of Fundy, Canada provide the observations for analysis. FDA was performed on the log-transformed abundance data as a new approach for treating such types of sparse and noisy data. Differences in the seasonal progression were seen, with peak numbers, timings and abundance levels varying for the three groups as determined by curve registration and higher order derivatives using the objectively fit FDA curves. Nonmetric multidimensional scaling was used to capture seasonal variation among years. These results were further assessed in terms of dominant species and the relationships between groups for different seasons and years. It is anticipated that the easy to use, general and flexible technique of FDA could be applied to a wide variety of marine ecological data that are characterized by missing values and non-Gaussian distributions. 相似文献
9.
Phytoplankton cultures occurring in disphotic zone water were conducted to examine dissolved organic carbon (DOC) for possible controlling agent of the initial lag period and growth rate. Culture media of various concentrations of DOC were prepared by mixing low DOC disphotic zone water with high DOC surface water. Natural phytoplankton populations showed strong correlations in their lag period with DOC concentrations in the range from 0.75 mgC·I–1 to 1.2 mgC·I–1 in the water (r=–0.833,n=8) and in their population growth rate () (r=0.899,n=8). Similar tendencies were confirmed with a marine diatom (Skeletonema costatum) dominating in the present disphotic zone water by culture experiments. By reducing DOC concentrations in seawater samples by pretreatments of ultraviolet radiation, charcoal adsorption and Amberlite XAD-2 resin adsorption, lag periods ofS. costatum increased in every case, but their population growth rates were almost identical. These results obviously show that prolonged lag period at least occurs in low DOC water, which can explain the observations by Barber and Ryther (1969) that low photosynthetic carbon uptake rate occurs in newly upwelled low DOC water. It is found that the essential substance to shorten lag periods of phytoplankton cultured in disphotic zone water is a portion of dissolved organic matter, which is poor in disphotic zone water and rich in surface water, and the effect of the substance analogous to Na2EDTA strongly suggests that the substances are organic ligands. 相似文献
10.
Seasonal and areal variation of continental aerosol in the surface air over the western North Pacific region 总被引：1，自引：0，他引：1
Shizuo Tsunogai Toshitaka Suzuki Takayoshi Kurata Mitsuo Uematsu 《Journal of Oceanography》1985,41(6):427-434
Weekly aerosol samples were collected for two years from 1981 at six stations in the western North Pacific region. The samples were analyzed for aluminum to determine the mineral dust concentration in the air. By combining our data with observations in the central and eastern North Pacific by a US research group, the following results and conclusions have been obtained. Spring peaks in atmospheric mineral dust were observed at all the stations accompanied byKosa episodes (hazes due to mineral dust of Chinese origin). The spring peaks, however, varied from year to year. The mean concentration of mineral dust depends not only on the distance from the Asian coast but also on the latitude of the sampling station. The half-decrease distance of the atmospheric mineral dust turned out to be 500–600 km for all latitudes in the western North Pacific. This indicates that the rate of deposition of mineral dust in the western North Pacific is much larger than that in the central and eastern North Pacific. 相似文献