Morphotectonics of a high plateau on the northwestern flank of the Continental Rift of southeastern Brazil     

May Christine Modenesi-Gauttieri  Silvio Takashi Hiruma  Claudio Riccomini   《Geomorphology》2002,43(3-4)

Integration of landform and structural analysis allowed the identification of Late Pleistocene–Holocene pulses of tectonic activity in the Campos do Jordão Plateau with ages and regimes similar to the ones from the continental rift. Fault reactivation along Precambrian shear zones give rise to a series of conspicuous morphotectonic features, determine the formation of stream piracy phenomena, and divide the plateau into smaller blocks. Recognition of these tectonic pulses as well as of their effects in landform development—particularly clear on the Campos de São Francisco at the highest area of the SE edge of the plateau—show that besides the climate-related Quaternary environmental changes significant neotectonic instability should be considered in the geomorphic evolution of the Campos do Jordão Plateau.  相似文献   

Integrating Geospatial Technologies in Fifth-Grade Curriculum: Impact on Spatial Ability and Map-Analysis Skills     

May Jadallah  Alycia M. Hund  Jonathan Thayn  Joel Garth Studebaker  Zachary J. Roman  Elizabeth Kirby 《The Journal of geography》2017,116(4):139-151

This study explores the effects of geographic information systems (GIS) curriculum on fifth-grade students' spatial ability and map-analysis skills. A total of 174 students from an urban public school district and their teachers participated in a quasi-experimental design study. Four teachers implemented a GIS curriculum in experimental classes over six weeks while three teachers continued with regular teaching in control classes. Both groups completed pre- and post-tests measuring spatial ability and map-analysis skills. Students in the GIS classes demonstrated more growth over time in spatial ability and map-analysis skills than did their peers in the control classes.  相似文献   

Miocene Gypcretes from the Calama Basin, northern Chile     

Adrian J. Hartley  & Geoffrey May 《Sedimentology》1998,45(2):351-364

Gypcretes of Miocene age are preserved beneath a 9·53 ± 0·36 Ma ignimbrite along the eastern margin of the Oligo-Pleistocene Calama Basin, northern Chile. They are restricted to a single stratigraphic horizon developed within laterally extensive (>35 km) coalesced alluvial fan deposits, developed along the margin of an endorheic basin. Two types of gypcrete are recognized. Type 1 comprises almost completely gypsum-cemented sandstones containing alabastrine nodules and columns, sub-vertical and horizontal veins of fibrous gypsum and 'v-shaped' cracks infilled by clastic material, and are interpreted as surface weathered gypsic crusts. Type 2 gypcretes are composed of massive, reddened poikilitic and mesocrystalline gypsum (up to 80% of the rock) with isolated bedding-parallel, clast-rich lenses (200 × 30 cm) and sub-vertical veins of fibrous gypsum. The massive texture resembles that of well developed B horizons in Quaternary alluvial desert soils. The crystal forms suggest an origin as a subsurface gypsic crust formed by a combination of hydromorphic (poikilitic) and illuvial (mesocrystalline) processes with the fibrous gypsum veins suggestive of periodic surface exposure.
Gypcrete horizons are up to 25 m thick and composed of both gypcrete types. They represent superimposed phases of surface and subsurface gypcrete development. Quaternary gypcretes are developed in arid climatic regimes, but are not considered to develop under hyper-arid climates. An arid climate is considered to have prevailed in the study area up to 9·5 Ma after which a change to hyper-aridity favoured gypcrete preservation.  相似文献   

The effectiveness of trenches in reducing seismic motion     

Thomas W. May  Bruce A. Bolt 《地震工程与结构动力学》1982,10(2):195-210

The effect of placing barriers in the travel path of P, SV and SH seismic waves has been studied using time-domain solutions of plane-strain finite element programs for two-dimensional crustal models. The wavefields considered propagate parallel to the free surface of an elastic medium consisting of a single layer over a halfspace. Barriers take the form of open-air trenches. Effects of damping are assessed by considering representative viscoelastic conditions. Computations are presented as the ratio of spectral energy observed at a point with the barrier system in place in the model to the spectral energy observed at the same point without the barrier system in the model. These spectral ratios are dependent upon the direction of wave propagation. The calculations brought to light the marked role of surficial layering and attenuation properties of the surface rocks or soils on the effectiveness of seismic trench barriers. Barrier models without these features cannot in general reliably predict seismic wavefields at the surface. In the range of cases studied, trench depth d rather than width is the most sensitive parameter. When the ratio d/λ, the ratio of trench depth to the wavelength of shear waves, is greater than about 0·6, power spectral ratios of 0·06 and less are found for SH waves and the vertical component of SV motion for frequencies of 4–6 Hz. By contrast, for frequencies less than 3–4 Hz, power spectral ratios from unity to about two and greater are observed, indicating amplification for the horizontal component of wave motion. Spectral ratios calculated at some locations in front of the barrier system show over two-fold amplification. Spectral ratios also change significantly with the relative location of the free surface observation point.  相似文献   

Small scale heterogeneity of Phanerozoic lower crust: evidence from isotopic and geochemical systematics of mid-Cretaceous granulite gneisses,San Gabriel Mountains,southern California     

Andrew P. Barth  J. L. Wooden  D. J. May 《Contributions to Mineralogy and Petrology》1992,109(3):394-407

An elongate belt of mid-Cretaceous, compositionally banded gneisses and granulites is exposed in Cucamonga terrane, in the southeastern foothills of the San Gabriel Mountains of southern California. Banded gneisses include mafic granulites of two geochemical types: type 1 rocks are similar to high Al arc basalts and andesites but have higher HFSE (high-field-strength-element) abundances and extremely variable LILE (largeion-lithophile-element) abundances, while type 2 rocks are relatively low in Al and similar to alkali rich MOR (midocean-ridge) or intraplate basalts. Intercalated with mafic granulites are paragneisses which include felsic granulites, aluminous gneisses, marble, and calc-silicate gneisses. Type 1 mafic granulites and calcic trondhjemitic pegmatites also oceur as cross-cutting, synmetamorphic dikes or small plutons. Small-scale heterogeneity of deep continental crust is indicated by the lithologic and isotopic diversity of intercalated ortho-and paragneisses exposed in Cucamonga terrane. Geochemical and isotopic data indicate that K, Rb, and U depletion and Sm/Nd fractionation were associated with biotite +/- muscovite dehydration reactions in type 1 mafic granulites and aluminous gneisses during high-grade metamorphism. Field relations and model initial isotopic ratios imply a wide range of protolith ages, ranging from Early Proterozoic to Phanerozoic.  相似文献   

Body and brood sizes of Tenagomysis spp. (Crustacea: Mysida) in southern estuaries in New Zealand     

S Paul  DM May  M Lee  GP Closs 《新西兰海洋与淡水研究杂志》2016,50(3):433-443

Mysids form a large biomass and mediate the benthic–pelagic coupling of numerous estuaries in southern New Zealand. An intra-annual (2011–2012) field survey in the breeding seasons (i.e. austral spring followed by summer) of mysids Tenagomysis chiltoni and Tenagomysis novaezealandiae, examining the body and brood sizes, was conducted. Samples were collected from six open and eight intermittently open/closed estuaries along the Otago coastline. Brood size of gravid females of T. chiltoni was not significantly related to their body size. Brood size of gravid females of T. novaezealandiae showed a significantly positive relationship with body size in spring but not in summer. It appears that brood size of gravid mysids do not always necessarily depend on body size, but may be influenced by breeding season (e.g. spring) and estuarine typology (e.g. intermittently open/closed).  相似文献   

Assessment of the importance of moderate spatial resolution cloud climatology data in solar radiation modeling     

Alexandria Gartside McCombs  May Yuan 《自然地理学》2016,37(5):313-326

Improving solar radiation models is critical for supporting the increase in solar energy usage and modeling ecosystem dynamics. However, coarse spatial resolutions of solar radiation models overlook the impacts resulting from spatial variability of clouds at meso- and micro-scales. To address this problem, Moderate Resolution Imaging Spectroradiometer (MODIS) cloud climatology developed by the National Severe Storms Laboratory was used to relate cloudiness to surface solar radiation observations. We developed a linear regression model between the surface solar radiation and MODIS cloud climatology and used the model to estimate average radiation across Oklahoma. Furthermore, the study compared the average error and coefficient of determination to measured ground radiation. Error analysis of the regression model showed that the differences between observed radiation and estimated radiation were spatially autocorrelated for the Aqua MODIS satellite scan. This suggests cloudiness alone is not sufficient to predict surface solar radiation. This study found that simple cloud datasets alone can account for approximately 50% of the variation in observed solar radiation at 250-m spatial resolution, but additional datasets such as optical depth, elevation, and slope are needed to accurately explain spatial distributions of incoming shortwave radiation.  相似文献   

The generation of stochastic load functions to simulate wind loading on structures     

T. A. Wyatt  H. I. May 《地震工程与结构动力学》1972,1(3):217-224

The simplest form of input required for step-by-step simulation of response of a structure to a gusty wind is a stochastic process having Gaussian distribution and a specified power spectrum. Methods for generating such a process are described in detail, and the extension outlined for generating a number of partially correlated input processes having specified power spectra and cross-spectra.  相似文献   

Metals in sediments and fish from Sea Lots and Point Lisas Harbors, Trinidad and Tobago     

Mohammed A  May T  Echols K  Walther M  Manoo A  Maraj D  Agard J  Orazio C 《Marine pollution bulletin》2012,64(1):169-173

Concentrations of heavy metals were determined in nearshore marine sediments and fish tissue from Sea Lots area on the west coast, at Caroni Lagoon National Park, and in the Point Lisas harbor, Trinidad. The most dominant metals found in sediments were Al, Fe and Zn with mean concentrations highest at Sea Lots (Al-39420 μg/g; Fe-45640 μg/g; Zn-245 μg/g), when compared to sediments from Point Lisas (Al-11936 μg/g; Fe-30171 μg/g; Zn-69 μg/g) and Caroni (Al-0400 μg/g; Fe-19000 μg/g; Zn-32 μg/g), High concentration of Cu, Al, Fe and Zn were also detected in fish tissue from Point Lisas and Caroni. Metal concentrations in fish tissue showed significant correlation with sediment metals concentration, which suggests that tissue levels are influenced by sediment concentration. Of the metals, only Zn, Hg and Cu had a bioaccumulation factor (BAF) greater than one, which suggests a high bioaccumulation potential for these metals.  相似文献   

Use of a Three-Domain Repesentation to Enhance GIS Support for Complex Spatiotemporal Queries   总被引：1，自引：0，他引：1  

May Yuan 《Transactions in GIS》1999,3(2):137-159

As the development of Geographic Information Systems (GIS) proceeds to advanced scientific and societal applications, there is an emerging need to enhance GIS support for complex spatiotemporal queries. Dynamic GIS representations (as opposed to static, map-based representations) that can integrate proper data elements in the production of geographic information are required. This paper demonstrates the use of a three-domain representation that facilitates compilation of higher-level information (such as frequency and rate) from preliminary data records (such as time and location) stored in a database. The three-domain representation is compared with snapshot, space-time composite, and spatiotemporal object models using a sample data set for forest transitions. While the three-domain representation is a normalization of these data models, it offers a conceptual alternative that enables GIS to represent spatiotemporal behaviors of geographic entities, in addition to entities as well as histories at locations as emphasized in most GIS data models. The comparison shows that the three-domain representation has combined the strengths of the space-time composite and spatiotemporal object models. Moreover, it enables aggregations of analytical use along with dynamic mappings between geographic concepts and locations, a distinct capability that takes GIS query processing beyond the level of information support offered by static map-based data models.  相似文献