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781.
环境样品中痕量元素的化学形态分析Ⅱ.砷汞镉锡铅硒铬的形态分析 总被引:2,自引:6,他引:2
环境中元素的生物有效性和毒性依赖于其存在的化学形态。文章依据文献的有关报道介绍砷、汞、镉、锡、铅、硒和铬在环境中的分布、毒性及它们在环境样品如水、土壤、沉积物和生物体中的形态分析方法,包括分析物的保存、提取、分离和检测。引用文献120篇。 相似文献
782.
Georg Bergeton Larsen Stig Syndergaard Per Høeg Martin Bjært Sørensen 《GPS Solutions》2005,9(2):144-155
The Global Positioning System (GPS) radio occultation measurements obtained using the TurboRogue GPS receiver on the Danish satellite Ørsted have been processed using the single frequency method. Atmospheric profiles of refractivity and temperature are derived and validated against numerical weather prediction data from the European Centre for Medium-Range Weather Forecast (ECMWF). Results from the Ørsted GPS measurement campaign in February 2000 indicate that the single frequency method can provide retrievals with accuracy comparable to that of using two frequencies. From comparisons between measured dry temperature profiles and corresponding dry temperature profiles derived from ECMWF analysis fields, we find a mean difference of less than 0.5 K and a standard deviation of 2–4 K between 500 and 30 hPa in height. Above 30 hPa the impact of the ionosphere becomes more dominant and more difficult to eliminate using the single frequency method, and the results show degraded accuracy when compared to previous analysis results of occultation data from other missions using the dual frequency method. At latitudes less than 40° (denoted low latitudes), the standard deviation is generally smaller than at latitudes higher than 40° (denoted high latitudes). A small temperature bias is observed centered at 200 hPa for low latitudes and at 300 hPa for high latitudes. This indicates that the ECMWF analyses do not adequately resolve the tropopause temperature minimum. In the lowest part of the troposphere an observed warm bias is thought to be due to erroneous tracking of the GPS signal in cases of atmospheric multipath propagation. 相似文献
783.
World-wide synthetic tide parameters for gravity and vertical and horizontal displacements 总被引:3,自引:0,他引:3
The response of the Earth’s crust to the direct effect of lunisolar gravitational forcing is known as the body tide. The body tide is superimposed by surface-loading forces due to the pressure of the periodically varying ocean tide acting on the Earth, called ocean tide loading (OTL). Both body tide and OTL can be decomposed into components of the same frequency known as tidal parameters. However, OTL is more complicated than body tides because of the dynamic effects of the ocean. Estimating OTL requires a model of the ocean tides and knowledge of the elastic properties of the solid Earth. Thus, synthetic tide parameters (amplitude factors and phase leads) have been developed here on a world-wide grid for gravity and positional displacements. The body tide contributions were added to the oceanic contribution to provide the Earth tide response. The accuracy and reliability of the synthetic tidal parameters have been estimated by comparing observed gravity and vertical-displacement tide parameters with those interpolated from our synthetic model, which shows good agreement. Tests also indicate that the synthetic tide parameters provide realistic gravimetric and displacements for practical use in tidal prediction. 相似文献
784.
P. K. Joshi G. S. Rawat H. Padaliya P. S. Roy 《Journal of the Indian Society of Remote Sensing》2005,33(3):371-380
The remote sensing technology has been widely used for mapping the vegetation types in the tropical landscapes. However, in
the temperate and alpine arid regions of India very few studies have been conducted using this technique. In the mountainous
temperate arid conditions the vegetation is largely confined to marsh meadows, streams courses, river valleys and moist pockets
close to snowfields. The ground truth collection in these zones are physically challenging due to tough terrain and restricted
mobility. The detailed mapping of vegetation and other land use classes in these areas is therefore, extremely difficult.
This paper describes the use of IRS-ID LISS III sensor for deciphering land cover details Nubra Valley, northern portion of
Ladakh Autonomous Hill Council, Jammu & Kashmir (India). This analysis essentially emphasizes in bringing out various vegetation
classes (speciallyHippophae rhamnoides and other medicinal plant communities) along the narrow river valleys. 相似文献
785.
Takvor H. Soukissian Aristides M. Prospathopoulos Chrysoula Diamanti 《Journal of Atmospheric & Ocean Science》2002,8(2):163-189
In this paper, a statistical analysis on wind and wave buoy measurements and wind and wave model forecasts obtained during a two-year period (1999-2001) is presented with reference to four characteristic near-shore sites of the Aegean Sea. The measurements are a main product of the "POSEIDON" system aiming at the monitoring and forecasting of the state of the Greek seas, operated by the National Centre for Marine Research (NCMR). Although the two-year period is rather short for a thorough analysis of the local wind and wave climate, yet the obtained results, presented herein for the first time, reveal some interesting features of the corresponding wave and wind characteristics. Comparisons between the measurements and the forecast results are also performed at the locations under consideration. It is found that (i) wind speeds obtained from the POSEIDON weather forecasting system are, in general, in agreement with the measurements, except for high wind speeds which are systematically underestimated, (ii) the WAM model can successfully follow the monthly and over year trend of the evolution of wind and wave characteristics, but face significant problems for efficient sea-state forecasting. Finally, the overall pattern of the wind/wave climate for the entire Aegean Sea as obtained from the models is presented by means of the spatial distribution of the mean annual wind and sea-state intensity. 相似文献
786.
Summary ?This study deals with the climatological aspect of seasonal rainfall distribution in the East Asian monsoon region, which
includes China, Korea and Japan. Rainfall patterns in these three countries have been investigated, but little attention has
been paid to the linkages between them. This paper has contributed to the understanding of the inter-linkage of various sub-regions.
Three datasets are used. One consists of several hundred gauges from China and South Korea. The second is based on the Climate
Prediction Center (CPC) Merged Analysis of Precipitation (CMAP). The two sources of precipitation information are found to
be consistent. The third dataset is the NCEP/NCAR reanalysis 850-hPa winds.
The CMAP precipitation shows that the seasonal transition over East Asia from the boreal winter to the boreal summer monsoon
component occurs abruptly in mid-May. From late March to early May, the spring rainy season usually appears over South China
and the East China Sea, but it is not so pronounced in Japan. The summer monsoon rainy season over East Asia commonly begins
from mid-May to late May along longitudes of eastern China, the Korean Peninsula, and Japan. A strong quasi-20-day sub-seasonal
oscillation in the precipitation appears to be dominant during this rainy season. The end date of the summer monsoon rainy
season in eastern China and Japan occurs in late July, while the end date in the Korean Peninsula is around early August.
The autumn rainy season in the Korean Peninsula has a major range from mid-August to mid-September. In southern China, the
autumn rainy season prevails from late August to mid-October but a short autumn rainy season from late August to early September
is noted in the lower part of the Yangtze River. In Japan, the autumn rainy season is relatively longer from mid-September
to late October.
The sub-seasonal rainfall oscillation in Korea, eastern China and Japan are explained by, and comparable to, the 850-hPa circulation.
The strong westerly frontal zone can control the location of the Meiyu, the Changma, and the Baiu in East Asia. The reason that the seasonal sea surface temperature change in the northwestern Pacific plays a critical role
in the northward advance of the onset of the summer monsoon rainfall over East Asia is also discussed.
Received October 5, 2001; revised April 23, 2002; accepted May 11, 2002 相似文献
787.
788.
789.
Summary ?For the LITFASS-98 experiment, from June 1 until June 30, 1998, the spatially resolved insolation at surface could be computed
from NOAA-14 AVHRR data applying the modular analysis scheme SESAT (Strahlungs- und Energiebilanzen aus Satellitendaten). The satellite inferred insolation for this period shows for clear-sky regions a good agreement with surface
based observations with a rms error of 76 Wm−2. For cloudy conditions the insolation is overestimated with respect to ground based observations, with a rms error between
83 and 118 Wm−2, depending on the cloud optical thickness. This overestimation can be explained by the surface heterogeneity, leading to
underestimated cloud optical thickness, and also by a fixed relative humidity below clouds (55%, dry atmosphere) and a fixed
horizontal visibility (50 km, clear atmosphere). A detailed study of comparable scales in space and time, considering the
different observation geometries and sampling intervals, shows that a 30 min ground based observation can be compared with
a 8 × 8 km2 mean by the satellite data.
Received July 12, 2001; revised April 29, 2002; accepted June 7, 2002 相似文献
790.
An experimental study of the initial flow field downstream of a step change in surface roughness is presented. The roughness length of the downstream surface was approximately tenfold that of the upstream roughness and, unlike all previous studies, attention was concentrated on the roughness sublayer region beneath the inertial (log-law) region. The experiments were conducted at a boundary layer Reynolds number of about 6 × 104 (based on layer thickness andfree-stream velocity) and around a longitudinal location where the (downstream) roughness length, zo2, was about 1% of the boundary-layer thickness atthe roughness change point.The thickness of the roughness sublayer was found for the two roughness. It was observed that the vertical profiles of mean velocity and turbulence characteristics started to show similarity after about 160z02 downstream of the roughness change. The presence of a shear stress overshoot is shown to depend strongly on the precise location (with respect to the roughness elements) at which the measurements are made and the thickness of the equilibrium layer is shown to be very sensitive to the way it is defined. It is demonstrated that the growing equilibrium layer has first to encompass the roughness sublayer before any thickness of inertial sublayer can be developed. It follows that, in somepractical cases, like flows across some urban environments, the latter(log-law) region may never exist at all. 相似文献