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21.
22.
Cosmic-ray-produced26Al (t1/2 = 7.05 × 105 years) has been measured in the Apollo 15 long core (surface to 390 g/cm2—218 cm) for study of galactic cosmic ray production profiles, using accelerator mass spectrometry. The results are in general accord with non-destructive counting data obtained earlier, but systematically lower, and significantly higher precision. From this experiment the half-attenuation length for26Al production can be calculated to be 122 g/cm2 (150–400 g/cm2 region) after normalizing the data to average chemical composition. The53Mn (t1/2 = 3.7 × 106 years) production profile in deep cores was also compiled to date. The half-attenuation length for53Mn production was calculated to be 123 g/cm2 (150–400 g/cm2 region).  相似文献   
23.
Two C28H48-pentacyclic triterpanes were isolated from Monterey shale. X-ray crystallography of a crystal containing both compounds proved their structures as 17β,18α,21α(H)-28,30-bisnorhopane and 17β,18α,21β(H)-28,30-bisnorhopane. Several differences are found between 28,30-bisnorhopanes and the regular hopanes. Unlike the regular hopane epimers, for practical purposes the three epimeric 28,30-bisnorhopanes [17α,21β(H)-, 17β,21α(H)-, and 17β,21β(H)-]cannot be distinguished by their mass spectra. Special conditions are needed to separate them by gas chromatography. The diagenetically first-formed epimer is thought to be 17α,21β(H)- because it predominates in immature shales. The order of thermodynamic stability is 17β,2lα(H) < > 17α,21β(H) > 17β,21β(H), and all three epimers are present in petroleum. 25,28,30-Trisnorhopanes can be analyzed in similar fashion and are found to have similar thermodynamic characteristics. The percent of the ring D/E cis epimer of 28,30-bisnorhopane and/or 25,28,30-trisnorhopane is a useful maturation parameter similar to the 20S/20R sterane ratio. Evidence indicates 25-demethylation of 28,30-bisnorhopane to 25,28,30-trisnorhopane during advanced stages of biodegradation. Hence, percent ring DEcis 25,28,30-trisnorhopane has an application to maturation assessment in heavily biodegraded oils.  相似文献   
24.
Cosmic-ray-produced53Mn (t1/2 = 3.7 × 106years) has been measured in twenty Antarctic meteorites by neutron activation analysis.36Cl (t1/2 = 3.0 × 105years) has been measured in fourteen of these objects by tandem accelerator mass spectrometry. Cosmic ray exposure ages and terrestrial ages of the meteorites are calculated from these results and from rare gases.14C (t1/2 = 5740years) and26Al (t1/2 = 7.2 × 105years) data. The terrestrial ages range from 3 × 104 to 5 × 105 years. Many of the L3 Allan Hills chrondrites seem to be a single fall based on these results. In addition,10Be (t1/2 = 1.6 × 106years) and36Cl have been measured in six Antarctic ice samples. The first measurements of10Be/36Cl ratios in the ice core samples demonstrate a new dating method for ice.  相似文献   
25.
The magnetosphere, ionosphere and solar–terrestrial physics community gathered at the Department of Chemistry, University of York from 9–11 April 2001. Neil Arnold and Ian Mann report.  相似文献   
26.
This paper is to examine the impact of satellite data on the systematic error of operational B-model in China.Em-phasis is put on the study of the impact of satellite sounding data on forecasts of the sea level pressure field and 500 hPaheight.The major findings are as follows.(1)The B-model usually underforecasts the strength of features in the sea level pressure(SLP)field,i.e.pressuresare too low near high pressure systems and too high near low pressure systems.(2)The nature of the systematic errors found in the 500 hPa height forecasts is not as clear cut as that of the SLPforecasts,but most often the same type of pattern is seen,i.e.,the heights in troughs are not low enough and those inridges are not high enough.(3)The use of satellite data in the B-model analysis/forecast system is found to have an impact upon the model'sforecast of SLP and 500 hPa height.Systematic errors in the vicinity of surface lows/500 hPa troughs over the oceansare usually found to be significantly reduced.A less conclusive mix of positive and negative impacts was found for allother types of features.  相似文献   
27.
28.
A limited-area seven-layer physical-numerical model for the lower tropospheric region (surface - 1600m) is described. The grid interval, approximately 190km, is half that of the standard numerical weather-prediction grid used in the hemispheric free atmospheric operational model at the Air Force Global Weather Central (AFGWC). This model is an integral part of the complete AFGWC meso-scale (sub-synoptic) numerical analysis and prediction system and is used to provide greater horizontal and vertical resolution in both numerical analyses and forecasts.Important features of this boundary-layer model include: a completely automated objective analysis of input data; the transport of heat and moisture by three-dimensional wind flow; latent heat exchange in water substance phase changes; and eddy fluxes of heat and water vapor.Input data are conventional synoptic surface and upper air reports. Other operational AFGWC prediction models provide input in the form of horizontal wind components at the upper boundary and an estimate of cloudiness above the boundary layer. Forecasts for the lower boundary and surface layer are empirically derived. Despite some approximations which broadly simplify the real planetary boundary-layer processes, operational use for highly weather-sensitive Air Weather Service support indicates that the model is capable of producing accurate detailed forecasts for periods of up to 24h.A modified version of this paper was presented at the IUGG-IAMAP-AMS conference on Planetary Boundary Layers at Boulder, Colo., 18–21 March, 1970, and at the 5th annual Congress of the Canadian Meteorological Society, at Macdonald College, 12–14 May, 1971.  相似文献   
29.
30.
In situ measurements of stratospheric H2SO4 and HSO3vapors using passive chemical ionization mass spectrometry were made in October 1982 after the eruption of volcano El Chichon. Data were obtained between about 20 and 41 km showing [H2SO4 + HSO3] sum concentrations between about 104 and 2 × 105 cm?3 below 29 km and a steep rise above this altitude. Maximum [H2SO4 + HSO3] values of about 3 × 106 cm?3 are reached above 35 km.Partial [HSO3] concentrations increase above 34 km reaching about 4 × 105cm?3 around 40 km. From the measurements it is concluded that H2SO4 and probably HSO3photolysis have an important influence above 34 km leading to the observed increase of [HSO3] and a depletion of H2SO4vapor.It also seems that the data support the view of heterogeneous HSO3 removal. If correct, this would imply that stratospheric aerosols are formed primarily from HSO3 rather than H2SO4vapor.  相似文献   
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