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351.
352.
The climatic potential of maize under dryland farming in Lesotho, southern Africa, was investigated using five suitability indices comprising probability of accumulating heat units of greater than 1,500 growing degree days, probability of a frost-free growing season, probability of seasonal rainfall of more than 500 mm, probability of drought during the flowering to grain-filling stages and the slope of an area. A geographic information system layer was prepared for each of these parameters and the layers overlaid using different weights for each of the climatic suitability indices to obtain an agroclimatic maize suitability map for Lesotho. This analysis yielded different suitability classes. This variability points to prevalence of climatic constraints that need to be acknowledged when attempting to identify management strategies that can optimize the rain-fed maize production in climatically variable environments. 相似文献
353.
Ludovic Puig Kate Isaak Martin Linder Isabel Escudero Pierre-Elie Crouzet Roger Walker Matthias Ehle Jutta Hübner Rainer Timm Bram de Vogeleer Pierre Drossart Paul Hartogh Christophe Lovis Giusi Micela Marc Ollivier Ignasi Ribas Ignas Snellen Bruce Swinyard Giovanna Tinetti Paul Eccleston 《Experimental Astronomy》2015,40(2-3):393-425
354.
355.
Most U.S. metropolitan regions have experienced urban “sprawl,” or the outward spreading of urban development from city centers.
For cities lying in areas prone to severe weather, the sprawl phenomenon exposes greater numbers of developed areas and inhabitants
to a variety of thunderstorm hazards. This study’s principal goal is to determine how urbanization growth patterns affect
a region’s vulnerability to severe weather events. To assess how sprawl may impact vulnerability to tornadoes, hail, and convective
wind events, an analysis examining potential loss may be utilized. This study employs two distinct approaches to examine how
the Atlanta area’s rapid and extensive development during the latter half of the twentieth Century has affected its overall
potential exposure to thunderstorm hazards. First, archived census data are used to estimate overall impacts from hypothetical
significant tornado, nontornadic convective wind, and hail events occurring at different time periods throughout several locations
in the Atlanta metropolitan region. Second, economic factors are integrated into the analysis, which assists in determining
how these hypothetical severe event scenarios may have changed from a cost standpoint if they were to occur in 2006 as opposed
to 1960. 相似文献
356.
Amy J.V. Riches Yang Liu James M.D. Day Igor S. Puchtel Douglas Rumble III Harry Y. McSween Jr. Richard J. Walker Lawrence A. Taylor 《Polar Science》2011,4(4):497-514
We report the petrography, mineral and whole-rock chemistry (major-, trace-, and highly-siderophile element abundances, and osmium and oxygen isotope compositions) of a newly recognized lherzolitic shergottite, Yamato (Y) 984028. Oxygen isotopes (Δ17O = 0.218‰) confirm a martian origin for this meteorite. Three texturally distinctive internal zones and a partially devitrified fusion crust occur in the polished section of Y 984028 studied here. The zones include: 1) a poikilitic region with pyroxene enclosing olivine and chromite (Zone A); 2) a non-poikilitic zone with cumulate olivine, interstitial pyroxene, maskelynite and Ti-rich chromite (Zone B) and; 3) a monomict breccia (Zone C). The pyroxene oikocryst in Zone A is chemically zoned from Wo3–7En76–71 in the core region to Wo33–36En52–49 at the rim, and encloses more Mg-rich olivine (Fo74–70) in the core, as compared with olivines (Fo69–68) located at the oikocryst rim. Constraints from Fe–Mg partitioning between crystals and melt indicate that constituent minerals are not in equilibrium with the corresponding bulk-rock composition, implying that Y 984028 represents a cumulate. The whole-rock major- and trace-element compositions, and initial 187Os/188Os value (0.1281 ± 0.0002) of Y 984028 are similar to other lherzolitic shergottites and this sample is probably launch-paired with Y 793602, Y 000027, Y 000047, and Y 000097. The Os isotopic composition and highly-siderophile element (HSE) abundances of Y 984028 and other lherzolitic shergottites are consistent with derivation from a martian mantle source that evolved with chondritic Re/Os. 相似文献
357.
Donald M. Terndrup Deokkeun An Angela Hansen Ruth C. Peterson Alistair R. Walker Elaine M. Sadler 《Astrophysics and Space Science》2004,291(3-4):247-252
We present a progress report on an extensive survey to find and characterize all types of horizontal-branch stars in the nuclear bulge of the Galaxy. We have obtained wide, shallow imaging in UBV of ≈12 square degrees in the bulge, with follow-up spectroscopy for radial velocities and metal abundance determinations. We have discovered a number of metal-rich blue HB stars, whose presence in the bulge is expected by the interpretation of the extragalactic ultraviolet excess. Very deep images have been obtained in UBV and SDSS u along the bulge minor axis, which reveal a significant number of EHB candidates fainter than B=19, i.e., with the same absolute magnitudes as EHB stars in several globular clusters. 相似文献
358.
359.
Active microwave remote sensing observations of backscattering, such as C‐band vertically polarized synthetic aperture radar (SAR) observations from the second European remote sensing (ERS‐2) satellite, have the potential to measure moisture content in a near‐surface layer of soil. However, SAR backscattering observations are highly dependent on topography, soil texture, surface roughness and soil moisture, meaning that soil moisture inversion from single frequency and polarization SAR observations is difficult. In this paper, the potential for measuring near‐surface soil moisture with the ERS‐2 satellite is explored by comparing model estimates of backscattering with ERS‐2 SAR observations. This comparison was made for two ERS‐2 overpasses coincident with near‐surface soil moisture measurements in a 6 ha catchment using 15‐cm time domain reflectometry probes on a 20 m grid. In addition, 1‐cm soil moisture data were obtained from a calibrated soil moisture model. Using state‐of‐the‐art theoretical, semi‐empirical and empirical backscattering models, it was found that using measured soil moisture and roughness data there were root mean square (RMS) errors from 3·5 to 8·5 dB and r2 values from 0·00 to 0·25, depending on the backscattering model and degree of filtering. Using model soil moisture in place of measured soil moisture reduced RMS errors slightly (0·5 to 2 dB) but did not improve r2 values. Likewise, using the first day of ERS‐2 backscattering and soil moisture data to solve for RMS surface roughness reduced RMS errors in backscattering for the second day to between 0·9 and 2·8 dB, but did not improve r2 values. Moreover, RMS differences were as large as 3·7 dB and r2 values as low as 0·53 between the various backscattering models, even when using the same data as input. These results suggest that more research is required to improve the agreement between backscattering models, and that ERS‐2 SAR data may be useful for estimating fields‐scale average soil moisture but not variations at the hillslope scale. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
360.
A palaeotemperature record based on fossil coleopteran evidence and dated by accelerator mass spectroscopy (AMS) 14C determinations on plant macrofossils has been obtained for the last glacial-interglacial transition from the site of Gransmoor in eastern England. Calibration of the radiocarbon measurements enabled a direct comparison to be made between this palaeotemperature curve and the snow accumulation record from the GISP-2 Greenland ice-core. The similarity between the two data sets suggests a degree of correspondence in the pattern and timing of climatic change in Greenland and the British Isles at the end of the last cold stage. 相似文献