利用主成分分析改善土地利用变化的遥感监测精度——以珠江三角洲城市用地扩张为例

近年来,珠江三角洲由于经济的快速发展,城市用地急剧增加,利用多时相的遥感图,可以定量地监测这种城市化的现象。但理,由一般的遥感动态监测方法所得的结果往往夸大变化的程度,以及获得一些不合理的结论．该文提出主成分分析的方法来改善遥感动态监测的精度。将该方法应用应用于珠江三角洲发展最快的东莞市,获得了较满意的结果。     

Flux determination over a smooth surface under strongly unstable conditions

Careful micrometeorological measurements on an empty parking lot allowed determination of the surface fluxes of sensible heatH and of momentum by applying profile equations derived from Monin-Obukhov similarity theory with two sets of the stability correction function for momentum _m and sensible heat _h . These fluxes were compared with reference values ofH independently determined by means of an eddy correlation technique. In general, better agreement was found betweenH values derived from profiles with the stability functions of Brutsaert (1992) and referenceH values, than when the Businger-Dyer functions were used to deriveH. The disagreement in the latter comparison was especially serious under strongly unstable conditions, with the value ofy=–z/L (wherez is the height andL is the Obukhov length) larger than 10. A closer look at the procedure for calculatingH from the profiles revealed that the large differences between theH values derived with these two different versions of the stability correction functions were caused by the small differences of the _h values, and not by the larger differences of the _m values. This result stems from the strong sensitivity of the resultingH values on the choice of _h .     

Periodic orbits of an electric charge in a magnetic dipole field

Periodic orbits in the Stormer problem are studied using the symmetry lines of the Poincaré map introduced by De Vogelaere. Many known facts are explained by mean of these lines. The dynamics of four special symmetry lines when the Stormer parameter ₁ changes is presented, and we obtain a clear global view of the structure of the simple periodic orbits and their bifurcations, including the asymmetrical ones. New asymmetrical multiple periodic orbits are obtained.     

地震前水氡短临异常判别指标及预报三要素的方法探讨

本文分析了中国大陆(重点是南北地震带北段)水氧异常变化,深入研究了有震与无震异常的时空分布特征、异常总频次、起始异常时间差等,发现有震异常往往呈现“同步性”或“群体性”特征,而大部分“零散性”异常则属于非地震异常。根据上述研究,本文还提出了利用水氡异常预报地震的发震时间、地点和震级的初步方法。     

Structural similarity and variety at the tips in a wide range of strike–slip faults: a review

Strike–slip faults are often accompanied by a variety of structures, particularly at their tips. The zones of additional fracturing are classified as tip‐damage zones. These zones can be subdivided into several different damage patterns based on the nature and orientation of faults and fractures developed. Damage zones at the ends of small strike–slip faults (mode II tips) develop wing cracks, horsetail splays, antithetic faults, synthetic branch faults and solution surfaces. Similar tip‐damage patterns are also commonly observed at larger (regional) scales, but with a dominance of faulting over tensile cracks and solution surfaces. Wing cracks and horsetail splays developed at small‐scale faults are replaced by normal faults in large‐scale faults. Antithetic faults and synthetic branch faults are observed at small and large scales. Thrust faults are developed at large scales, in a similar pattern to solution surfaces at a small scale. All these structures may show slightly different angular relationships to the master fault at small and large scale, but develop in response similar stress distribution and mechanics around the fault. Thus, mode II tip‐damage zones show similar patterns over a wide range of fault scales.     

Study of geothermal water intrusion due to groundwater exploitation in the Puebla Valley aquifer system, Mexico

Significant intrusion of geothermal water into fresh groundwater takes place in the Puebla Valley aquifer system, Mexico. The decline in the potentiometric surface due to the overexploitation of the groundwater induces this intrusion. This hydrological system comprises three aquifers located in Plio-Quaternary volcanic sediments and Mesozoic calcareous rocks. The hydraulic balance of the aquifer shows that the annual output exceeds the natural inputs by 12 million m³. Between 1973 and 2002, a drop in the potentiometric surface, with an 80 m cone of depression, was identified in a 5-km-wide area located southwest of the city of Puebla. Chemical analyses performed on water samples since 1990 have shown an increase in total dissolved solids (TDS) of more than 500 mg/L, coinciding with the region showing a cone of depression in the potentiometric surface. A three-dimensional flow and transport model, based on the hydrogeological and geophysical studies, was computed by using the MODFLOW and MT3D software. This model reproduces the evolution of the aquifer system during the last 30 years and predicts for 2010 an additional drawdown in the potentiometric surface of 15 m, and an increase in the geothermal water intrusion.     

Food Deserts in the Prairies? Supermarket Accessibility and Neighborhood Need in Edmonton,Canada*

The U.S. and U.K. literatures have discussed “food deserts,” reflecting populated, typically urban, low‐income areas with limited access to full‐service supermarkets. Less is known about supermarket accessibility within Canadian cities. This article uses the minimum distance and coverage methods to determine supermarket accessibility within the city of Edmonton, Canada, with a focus on high‐need and inner‐city neighborhoods. The results show that for 1999 both of these areas generally had higher accessibility than the remainder of the city, but six high‐need neighborhoods had poor supermarket accessibility. We conclude by examining potential reasons for differences in supermarket accessibility between Canadian, U.S., and U.K. cities.     

库车坳陷侏罗系煤成气动力学模拟研究

应用黄金管—高压釜封闭体系热模拟实验与GC、GC-IRMS分析技术,结合KINETICS专用软件,对库车坳陷侏罗系煤成气进行了动力学模拟研究。库车坳陷侏罗系煤具有高的产气性,在高演化阶段主要产甲烷气;侏罗系煤热解气甲烷碳同位素为-36‰～-25‰,乙烷碳同位素为-28‰～-16‰;甲烷、C2-C5气态烃的生成活化能分别为(47～64k)calm/ol、(55～72k)calm/ol,频率因子各为5.265×1013s-1、5.388×1018s-1。在此基础上,进一步探讨了克拉2气田天然气的成因。研究认为,克拉2气田天然气属阶段捕获的煤成气,主要聚集了5～1Ma时期的天然气,其成熟度Ro分布范围为1.3%～2.5%。     

Land-Parcel Land-Use History as a Key to Site Selection for Documenting Soil Contamination Risk： a Case Study from Australian Suburbia

In that orcharding in early-to-mid twentieth century southeastern Australia involved use of certain heavy metal and As compounds in regular pest-control spray procedures, some interest attaches to the possibility that these landparcels are underlain by soils with above-background Cu, Pb and As levels. Interpreta- tion of Land-cover changes allowed land parcels previously occupied by orchards to be identified in the 1950s through time-series air-photos. A comparison of soil analysis results referring to soil samples from control sites, and from land parcels formerly occupied by orchardists, shows that contamination （above-background） levels of cations in the pesticides can be found in the top 6 cm of former orchard soils. It is clear that digital spatial data handling and culturally-informed air photo interpretation has a place in soil contamination studies, land-use planning （with particular reference to re-development） and in administration of public health.     

禹州煤田泉店井田构造特征及对其二1煤层的影响

对泉店井田的地质构造进行了分析研究,阐明了断层及褶曲的分布,探讨了井田的构造演化,分析了构造特别是断层对二1煤层的影响,为今后煤矿开发生产提供了可靠的地质依据.