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991.
The isotopic composition of Ag and the concentration of Ag and Pd have been determined in Canyon Diablo (IA), Grant (IIIB), Hoba, Santa Clara, Tlacotepec and Warburton Range (IVB), Piñon and Deep Springs (anom.). Troilite from Grant and Santa Clara have also been analyzed. All of these meteorites, with the exception of Canyon Diablo, give 107Ag109Ag in the metal phase that is greater than the terrestrial value with the enrichments of 107Ag ranging from ~2% to 212%. These data show that Ag of anomalous isotopic composition is common to all IVB and anomalous meteorites. The results on Grant suggest that the anomalies may be widespread including more common meteorite groups. There is a general correlation of 107Ag109Ag with PdAg except for the data from FeS of Santa Clara. It is concluded that the excess 107Ag is the result of decay of 107Pd, a nuclide that is extinct at present with an abundance of 107Pd108Pd of about 3 × 10?5. The troilite in Grant exhibits normal 107Ag109Ag to within errors, a high Ag concentration and a low ratio of 108Pd109Ag ~0.17. Grant metal has 107Ag109Ag that is ~2% greater than normal and a high ratio of 108Pd109Ag ~ 103. The data from Grant appear to represent a 107Pd-107Ag isochron and indicate that the cooling rate at elevated temperatures was sufficiently rapid to preserve substantial isotopic differences between metal and troilite. Troilite in Santa Clara was found to contain Ag with a very high 107Ag109Ag ratio (108% above normal), an Ag concentration only a factor of three above the metal and a high value of 108Pd109Ag ~1.3 × 104. The troilite has a higher 107Ag109Ag than the metal. These data are not compatible with a simple model of in situ decay and subsequent local Ag redistribution between metal and troilite during cooling. These data suggest that Ag in Santa Clara and possibly other IVB meteorites is made up of almost pure 107Ag produced from 107Pd decay and 109Ag produced by nuclear reactions with only a small amount of “normal” Ag. This indicates an intense energetic particle bombardment history in the early solar system (~1020 p/m2) which occurred after the formation of small planetary bodies. We infer that a T-Tauri activity by the early sun contributed to some late stage “nucleosynthesis” and the heating of a dust cloud. In addition, implications on the early thermal evolution of iron meteorites are presented based on 107Pd decay and models of the cooling history.  相似文献   
992.
In recent years, the desertification of alpine-cold grasslands has become increasingly serious in the Qinghai–Tibet Plateau in China, but it has not received the same amount of attention as has desertification in (semi)arid areas. Little is thus known about the change in soil organic carbon (SOC) during alpine-cold grassland desertification. To quantify the impacts of desertification on vegetation, SOC and its active fractions in alpine-cold grasslands, areas of light desertified grassland, medium desertified grassland, heavy desertified grassland, serious desertified grassland, and nondesertified grassland were selected as experimental sites in the eastern Qinghai–Tibet Plateau in China. The species number, height and coverage of vegetation were surveyed, and the soil particle fractions, SOC and SOC active fractions (including dissolved organic carbon (DOC), microbial biomass carbon (MBC), and labile organic carbon (LOC) were measured to a depth of 0–100 cm. The results showed that alpine-cold grassland desertification resulted in a significant reduction in vegetation cover, plant biomass, fine soil particles, SOC, DOC, LOC and MBC. The decreases in DOC, LOC and MBC were more rapid and apparent than were those in SOC, and the decrease in MBC was the most obvious among them. The rates of reduction in SOC concentrations accelerated as desertification progressed; most of the SOC was lost in the middle and later desertification stages, with lower losses during early desertification. The results indicate that active SOC fractions, particularly MBC, are more sensitive to desertification and can be used as sensitive indicators of desertification. Efforts to limit desertification and reduce SOC loss in alpine-cold grasslands should focus on early desertification stages and adopt strategies to prevent overgrazing and control the erosion of soil by wind.  相似文献   
993.
The results of mineralogical-technological studies of carbonaceous rocks of the Kimkan noble metal occurrence are reported. New typomorphic associations of trace element are revealed using mathematical statistics.  相似文献   
994.
The ability of the SMARA storm surge numerical prediction system to reproduce local effects in estuarine and coastal winds was recently improved by considering one-way coupling of the air–sea momentum exchange through the wave stress, and best forecasting practices for downscaling. The inclusion of long period atmospheric pressure forcing in tide and tide/surge calculations corrected a systematic error in the surge, produced by the South Atlantic Ocean quasi-stationary pressure patterns. The maximum forecast range for the storm surge at Buenos Aires provided by the real-time use of water level observations is approximately 12 h. The best available water level prediction is the 6-h forecast (nowcast) based on the closest water level observations. The 24-h forecast from the numerical models slightly improves this nowcast. Although the numerical forecast accuracy degrades after the first 48 h, the improvement to the full range observation-based prediction is maintained at the inner Río de la Plata area and extends to the first 3 days at the intermediate navigation channels.  相似文献   
995.
Paleomagnetic determinations on lithologieal profiles of two paralleled long drillin gcores covering the past 130 kyr B.P., GT40 and GT60,from the Yanchi Playa in the arid Northwestern China indicate that a series of pronounced paleomagnetic excursions have been documented. By correlating our results with published regional and worldwide reports 4 excursion events out of 10 apparent reversal signals (labeled from GT-1 to GT-10) were identified as excursion events coeval with the Mono Lake Event (28.4 kyr-25.8 kyr), Laschamp Event (43.3 kyr-40.5kyr), Gaotai Event (82.8 kyr-72.4 kyr) and the Blake Event (127.4 kyr-113.3 kyr), respectively. GT-9 correlates with the above-mentioned Gaotai Event,GT-7 and GT-6 correspond to two stages of the Laschamp Event and GT-5 to the Mono Lake Event. It is noteworthy that the so-called Gaotai Event has not been reported as a pronounced paleomagnetic excursion in the Northwestern China. Every magnetic excursion event corresponds to paleointensity minima, anteceding those established abrupt paleoclimatic change events, such as the Younger Drays and the Heinrich Events (H1-H6). Here, we tentatively propose that these geomagnetic excursions/reversals can be viewed as precursors to climate abruptness. During the transitional stages when the earth‘s magnetic field shifted between a temporal normal and a negative period, the earth‘s magnetic paleointensity fell correspondingly to a pair of minima. Although more precise chronology and more convincing rock magnetic parameter determinations are essentially required for further interpretation of their intricate coupling mechanism, these results may have revealed, to some extent, that the earth‘s incessantly changing magnetic field exerts an strong influence on the onset of saw-tooth shaped abrupt climate oscillations through certain feedback chains in arid Central Asia or even North Hemispheric high latitude regions.  相似文献   
996.
Outburst risk of barrier lakes in Sichuan,China   总被引:1,自引:1,他引:1  
34 barrier lakes induced by earthquake have been formed by wedged debris on the river channels after a massive earthquake happening on May 12 in Sichuan, China. Among them, the Tangjiashan Barrier Lake is the largest one. It faces very urgent risk of dam breaking when water level reaches the top and begins overflow in case of storm rainfalls and continually aftershocks, threatening already devastated cities and villages with about 1.5 million people downstream. The outburst of a similar barrier lake occurred in the Minjiang River in 1933, causing a catastrophic flood. Risk analysis indicates that not all barrier lakes are highly dangerous. Only those lakes with very high dams and water to be filled up in short period need to be dealt with immediately.  相似文献   
997.
This study on the distribution features of petroleum hydrocarbon in water and sedi-ment off the Fujian shore using data obtained from the baseline research on oceanic contamination in Fujian showed that:during the research preiod,petroleum hydrocarbon concentrations in water varied from 5.77μg/L to 37.28μg/L,averaged 14.48 μg/L;was lower in the wet seasson than in the dry season;and was highest in the Minjiang Estuary and Jiulong Estuary in both seasons ,The petorleum hydrocarbon concentrations in shore sediment varied from 14.48 mg/kg to 784.36 mg/kg,averaged 133.3 mg/kg ,and was closely related to sediment types (granularity).  相似文献   
998.
Snow depth is a general input variable in many models of agriculture,hydrology,climate and ecology.This study makes use of observational data of snow depth and explanatory variables to compare the accuracy and effect of geographically weighted regression kriging(GWRK)and regression kriging(RK)in a spatial interpolation of regional snow depth.The auxiliary variables are analyzed using correlation coefficients and the variance inflation factor(VIF).Three variables,Height,topographic ruggedness index(TRI),and land surface temperature(LST),are used as explanatory variables to establish a regression model for snow depth.The estimated spatial distribution of snow depth in the Bayanbulak Basin of the Tianshan Mountains in China with a spatial resolution of 1 km is obtained.The results indicate that 1)the result of GWRK's accuracy is slightly higher than that of RK(R~2=0.55 vs.R~2=0.50,RMSE(root mean square error)=0.102 m vs.RMSE=0.077 m);2)for the subareas,GWRK and RK exhibit similar estimation results of snow depth.Areas in the Bayanbulak Basin with a snow depth greater than 0.15m are mainly distributed in an elevation range of 2632.00–3269.00 m and the snow in this area comprises 45.00–46.00% of the total amount of snow in this basin.However,the GWRK resulted in more detailed information on snow depth distribution than the RK.The final conclusion is that GWRK is better suited for estimating regional snow depth distribution.  相似文献   
999.
This paper presents a tramework for road network change detectlon In order to upctate the Canadian National Topographic DataBase (NTDB). The methodology has been developed on the basis of road extraction from IRS-pan images (with a 5.8 m spatial resolution) by using a wavelet approach. The feature matching and conflation techniques are used to road change detection and updating. Elementary experiments have showed that the proposed framework could be used for developing an operational road database updating system.  相似文献   
1000.
Climate change adaptation of coffee production in space and time   总被引:1,自引:0,他引:1  
Savannas constitute the most fire-prone vegetation type on earth and are a significant source of greenhouse gas emissions. Most savanna fires are lit by people for a variety of livelihood applications. ‘Savanna burning’ is an accountable activity under the Kyoto Protocol, but only Australia, as a developed economy, accounts for emissions from this source in its national accounts. Over the past decade considerable effort has been given to developing savanna burning projects in northern Australia, combining customary indigenous (Aboriginal) approaches to landscape-scale fire management with development of scientifically robust emissions accounting methodologies. Formal acceptance by the Australian Government of that methodology, and its inclusion in Australia’s developing emissions trading scheme, paves the way for Aboriginal people to commercially benefit from savanna burning projects. The paper first describes this Australian experience, and then explores options for implementing community-based savanna burning emissions reduction projects in other continental savanna settings, specifically in Namibia and Venezuela. These latter examples illustrate that savanna fire management approaches potentially have broader application for contributing to livelihood opportunities in other fire-prone savanna regions.  相似文献   
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