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971.
于2014年中国第6次北极科学考察期间,采集了楚科奇海陆架4根沉积物柱状样,据此开展了其中几种低环的多环芳烃(PAHs)的总体水平调查,并结合~(210)Pb测年,探讨了其垂直分布特征及历史沉降规律。结果表明,楚科奇海陆架沉积物中几种低环PAHs含量变化范围为50—1 553 ng·g~(–1),总体处于较低水平,且与粒径变化关系不明显。楚科奇海陆架区沉积物的沉积速率为0.05—0.19 cm·a~(–1),低环PAHs垂直变化较小,总体受人类影响极少,局部高值可能受到石油渗漏或成岩作用等过程的影响。  相似文献   
972.
In order to solve unsteady incompressible Navier–Stokes(N–S) equations, a new stabilized finite element method,called the viscous-splitting least square FEM, is proposed. In the model, the N–S equations are split into diffusive and convective parts in each time step. The diffusive part is discretized by the backward difference method in time and discretized by the standard Galerkin method in space. The convective part is a first-order nonlinear equation.After the linearization of the nonlinear part by Newton's method, the convective part is also discretized by the backward difference method in time and discretized by least square scheme in space. C~0-type element can be used for interpolation of the velocity and pressure in the present model. Driven cavity flow and flow past a circular cylinder are conducted to validate the present model. Numerical results agree with previous numerical results, and the model has high accuracy and can be used to simulate problems with complex geometry.  相似文献   
973.
Paraconchoeciadiacanthusn.sp.,anewspeciesofplanktonicOstracoda¥ChenRuixiangandLinJinghong(ReceivedApril16,19931acceptedJuly20...  相似文献   
974.
????????????????????????????????????????????б????????????????????????????????????????????????????????????????????????????????????????仯?????????仯???????????????????????????δ??????????????????????????????????????????仯????????????????????????е?????????????????????????????????????????????????????????????С???????????0.01??????????????????1???????????????????????????????Ч???????  相似文献   
975.
In 2009, the Russian Complex Orbital Observations Near-Earth of Activity of the Sun (CORONAS-Photon) spacecraft was launched, carrying the Polish Solar PHotometer In X-rays (SphinX). The SphinX was most sensitive in the spectral range 1.2?–?15 keV, thus an excellent opportunity appeared for comparison with the low-energy end of Ramaty High Energy Solar Spectroscopic Imager (RHESSI) spectra. Common spectral measurements with these instruments cover the range where most of the flare energy is accumulated. We have chosen four consecutive small solar events observed on 4 July 2009 at 13:43 UT, 13:48 UT, 13:52 UT, and 13:55 UT (RHESSI flare peak times) and used them to compare the data and results from the two instruments. Moreover, we included Geostationary Operational Environmental Satellite (GOES) records in our analysis. In practice, the range of comparison performed for SphinX and RHESSI is limited roughly to 3?–?6 keV. RHESSI fluxes measured with a use of one, four, and nine detectors in the 3?–?4 keV energy band agree with SphinX measurements. However, we observed that SphinX spectral irradiances are three times higher than those of RHESSI in the 4?–?6 keV energy band. This effect contributes to the difference in obtained emission measures, but the derived temperatures of plasma components are similar. RHESSI spectra were fitted using a model with two thermal components. We have found that the RHESSI hot component is in agreement with GOES, and the RHESSI hotter component fits the SphinX flaring component well. Moreover, we calculated the so-called thermodynamic measure and the total thermal energy content in the four microflares that we studied. The results obtained show that SphinX is a very sensitive complementary observatory for RHESSI and GOES.  相似文献   
976.
Mayall Ⅱ = G1 is one of the most luminous globular clusters (GCs) in M31. Here, we determine its age and mass by comparing multicolor photometry with theoretical stellar population synthesis models. Based on far- and near-ultraviolet GALEX photometry, broad-band UBVRI, and infrared JHKs 2MASS data, we construct the most extensive spectral energy distribution of G 1 to date, spanning the wavelength range from 1538 to 20 000A. A quantitative comparison with a variety of simple stellar population (SSP) models yields a mean age which is consistent with G1 being among the oldest building blocks of M31 and having formed within ~1.7 Gyr after the Big Bang. Irrespective of the SSP model or stellar initial mass function adopted, the resulting mass estimates (of order 10^7M⊙) indicate that GI is one of the most massive GCs in the Local Group. However, we speculate that the cluster's exceptionally high mass suggests that it may not be a genuine GC. Our results also suggest that G1 may contain, on average, (1.65±0.63) × 10^2L⊙ far-ultraviolet-bright, hot, extreme horizontal-branch stars, depending on the adopted SSP model. In addition, we demonstrate that extensive multi-passband photometry coupled with SSP analysis enables one to obtain age estimates for old SSPs that have similar accuracies as those from integrated spectroscopy or resolved stellar photometry, provided that some of the free parameters can be constrained independently.  相似文献   
977.
The development and utilization of water and land resources in the Shiyang River basin are the highest among the inland rivers in northwestern China. Using GIS and the landscape structure analysis program FRAGSTATS, landscape metrics of a study area in the lake-district in Minqin Oasis in the lower reaches of Shiyang River basin were calculated and analyzed based on TM images from 1987 to 2001 at class level and landscape level, respectively. Transformation matrix of the landscape mosaics was also examined. The driving forces of landscape changes were analyzed, including the dynamics of runoff and groundwater resources and their exploitation, and influences of policies and market economy. The results showed that: (1) Patch number of farmland and desert decreased, but their mean patch area increased, indicating that reclamation and desertification was very serious in the study area. Contagion index for oasis increased and edge density and landscape diversity were reduced. (2) Farmland and desert areas have enlarged by 1,520.46 and 4,941.27 hm2, respectively. This increase was at the cost of woodland and grassland, which shrank by 1,520.46 and 4,941.27 hm2, respectively. (3) The net utilization of surface water decreased by 50% in the last 10 years, and dropped to 22.3 × 106 m3 in the later 1990s. Exploitation of groundwater increased remarkably, up to 80 × 106 m3 per year in the last 5 years. (4) The capability of the economic structure to withstand pressures of the market economy has depressed distinctly because of the simplified planting pattern, which is dominated by salinity-enduring cash crops, such as cotton. Based on the above analysis, strategies of ecological reconstruction in the lake-district were suggested.  相似文献   
978.
Drought analysis in Jordan under current and future climates   总被引:2,自引:0,他引:2  
Droughts have adverse socioeconomic, agricultural, and environmental impacts that can be reduced by assessing and forecasting drought behavior. The paper presents detailed analyses of both meteorological and vegetative droughts over the period from 1970 to 2005. Standardized Precipitation Index (SPI) and Normalized Difference Vegetation Index (NDVI) have been used to quantify drought according to severity, magnitude and spatial distribution at the Hashemite Kingdom of Jordan. Results suggest that the country faced during the past 35 years frequent non-uniform drought periods in an irregular repetitive manner. Drought severity, magnitudes and life span increased with time from normal to extreme levels especially at last decade reaching magnitudes of more than 4. Generated NDVI maps spatial analyses estimate crop-area percentage damage due to severe and extremely severe drought events occurred during October, December, and February of 2000 to be about 10%, 45%, and 30%, respectively. In response to drought spatial extent, the paper suggest the presence of two drought types, local drought acting on one or more geographical climatic parts and national drought, of less common but more severe, that extend over the whole country. Droughts in Jordan act intensively during January, February and March and tend to shift position with time by alternative migrations from southern desert parts to northern desert parts and from the eastern desert parts to highlands and Jordan Rift Valley (JRV) at the west. The paper also investigates the potential use of Global Climate Model’s (GCM) to forecast future drought events from 2010 till 2040. Tukey HSD test indicates that ECHAM5OM GCM is capable to predicted rainfall variation at the country and suggests future droughts to become more intensive at the northern and southern desserts with 15% rainfall reduction factor, followed by 10% reduction at the JRV, and 5% at the highlands.  相似文献   
979.
利用奇异值分解(SVD)方法和山东省26个代表站1951~2000年6~8月降水量、NCEP/NCAR再分析1958~1998年1~12月925~300hPa5层月平均比湿和风场资料,分析了山东夏季降水与前期(冬季、春季)及同期(夏季)南海到西太平洋地区水汽输送之间相关场的分布型,从中找出了遥相关的“关键区”,并对找到的“关键区”的可靠性进行了验证。研究表明,山东夏季降水与前期(冬季、春季)和同期(夏季)南海到西太平洋地区水汽输送相关较好,春季的相关程度最高,冬季次之,夏季最小。  相似文献   
980.
This paper presents the analyses of regional climate change features and the local urbanization effects on different weather variables over Southeast China. The weather variables considered are: daily mean (Tm), minimum (Tmin), and maximum (Tmax) near surface air temperature, diurnal temperature range (DTR), relative humidity (RH), and precipitation (P). With analysis of two datasets (a station dataset for the period from 1960 to 2005 that is mainly used and a grid dataset for the period 1960–2000), this study reveals that the trends in the variations of these weather variables can be separated into two periods, before and after 1984. Before 1984, there were no significant urbanization effects, and Tmin, RH, and P steadily increased but Tmax decreased, resulting in a considerable decrease in DTR and a slight decrease in Tm. After 1984, Tmin and Tmax increased considerably, and the urbanization influence on Tmin, but not Tmax, is observable. The urbanization effect causes an extra increasing trend in Tmin with a rate of about 0.6°C/decade and, accordingly, extra decreasing trends in DTR and RH. The analysis of the seasonal trends reveals that the urbanization influence results in a near-uniform increase of Tmin for all four seasons and a strong decrease of RH in summer and autumn. Moreover, there is no significant change in P at the annual scale and an increasing rate of 11.8%/decade in summer. With the urbanization influence, a considerable increase in P is noticeable at the annual scale; specifically, the increasing rates of 18.6%/decade in summer and 13.5%/decade in autumn are observed.  相似文献   
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