Work sharing in Kerala's fisheries     

Marrit van den Berg  Bart Jan Lensing 《Marine Policy》2007

Earlier studies suggest that once population growth and market integration reach a certain critical level, traditional practices of work sharing tend to degenerate or disappear altogether. Work sharing has, however, survived to date in small-scale fisheries in Kerala, India. Artisanal fishermen strongly favor the system, for ethical reasons as well as for their personal benefit. Besides, boat owners appear not to be hindered by the system. Contrary to observations in crop production, work sharing has not inhibited the introduction of modern technologies like motorization.  相似文献   

The use of SfM-photogrammetry to quantify and understand gully degradation at the temporal scale of rainfall events: an example from the Ethiopian drylands     

Wouter Lannoeye  Cornelis Stal  Etefa Guyassa  Amanuel Zenebe  Jan Nyssen  Amaury Frankl 《自然地理学》2016,37(6):430-451

Abstract

With the recent technological advances offered by SfM-photogrammetry, we now have the possibility to study gully erosion at very high spatial and temporal scales from multi-temporal DEMs, and thus to enhance our understanding of both gully erosion processes and controls. Here, we examine gully degradation and aggradation at a gully headcut and at four re-incisions along a gully reach in Northern Ethiopia. Environmental controls recorded are topography rainfall, runoff, land use and cover, land management, and soil characteristics. The overall vulnerability of the catchment to erosion is low as calculated from the RUSLE (average 11.83 t ha^?1 y^?1). This reflects the successful land management of the past years. The runoff coefficient was on average 7.3% (maximum 18.2%). Runoff events caused most geomorphic change in the gully, but slumping of the gully bank also occurred on dry days. Most geomorphic change was caused by one major rainfall event of 54.8 mm d^?1, and smaller runoff events caused both degradation and aggradation, often asynchronous between studied sites. Although most research focuses on gully heads alone, re-incisions at lower locations can still cause important gully degradation, which ultimately will reach the gully head and cause instability.  相似文献   

Behavior of Fiber Glass Bolts,Rock Bolts and Cable Bolts in Shear     

Xuwei Li  Naj Aziz  Ali Mirzaghorbanali  Jan Nemcik 《Rock Mechanics and Rock Engineering》2016,49(7):2723-2735

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Biotite stability in peraluminous granitic melts: Compositional dependence and application to the generation of two-mica granites in the South Bohemian batholith (Bohemian Massif, Czech Republic)   总被引：2，自引：0，他引：2  

Milo&#x; Ren  Francois Holtz  Cherhui Luo  Oliver Beermann  Jan Stelling 《Lithos》2008,102(3-4):538-553

Crystallization experiments have been conducted in the system Na₂O–K₂O–MgO–FeO–Al₂O₃–SiO₂–H₂O (with 4% normative corundum) in order to constrain the stability of biotite as a function of water activity and the Mg# of biotite [Mg/(Mg +Fe_total)] in equilibrium with peraluminous granitic melts. The temperature at which biotite breakdown starts is strongly dependent on the Mg# of biotite. At 500 MPa, the temperature of biotite breakdown to form orthopyroxene increases from 750 °C to 830 °C, as the Mg# of biotite increases from 0.4 to 0.5. Considering that the system investigated is relevant for Ca-poor peraluminous biotite-bearing rocks (metapelites), the biotite dehydration curves obtained are used to discuss the melting reactions and the temperatures that lead to the formation of two distinct types of two-mica granites found in the South Bohemian batholith (specifically the Eisgarn and Deštná granites). The phase relationships were determined experimentally for the composition of these two granites in order to constrain the composition of the biotite in equilibrium with the melt in the protoliths. We demonstrate that Eisgarn granitic melts may have been generated at temperatures in the range 830–850 °C from melting reactions involving biotite with a Mg# up to 0.5 as a reactant. In contrast, Deštná granitic melts cannot have been generated from dehydration melting reactions involving biotite.  相似文献   

Geological evolution of Mount Etna volcano (Italy) from earliest products until the first central volcanism (between 500 and 100 ka ago) inferred from geochronological and stratigraphic data   总被引：1，自引：0，他引：1  

Stefano Branca  Mauro Coltelli  Emanuela De Beni  Jan Wijbrans 《International Journal of Earth Sciences》2008,97(1):135-152

We present an updated geological evolution of Mount Etna volcano based on new ⁴⁰Ar/³⁹Ar age determinations and stratigraphic data integrating the previous K/Ar ages. Volcanism began at about 500 ka ago through submarine eruptions on the Gela–Catania Foredeep basin. About 300 ka ago fissure-type eruptions occurred on the ancient alluvial plain of the Simeto River forming a lava plateau. From about 220 ka ago the eruptive activity was localised mainly along the Ionian coast where fissure-type eruptions built a shield volcano. Between 129 and 126 ka ago volcanism shifted westward toward the central portion of the present volcano (Val Calanna–Moscarello area). Furthermore, scattered effusive eruptions on the southern periphery of Etna edifice occurred until about 121 ka ago. The stabilization of the plumbing system on the Valle del Bove area is marked by the building of two small polygenic edifices, Tarderia and Rocche volcanoes. Their eruptive activity was rather coeval ending 106 and 102 ka ago, respectively. During the investigated time-span volcanism in Etna region was controlled by a main E–W extensional tectonic related to the reactivation of Malta Escarpment fault system in eastern Sicily. Electronic supplementary material The online version of this article () contains supplementary material, which is available to authorized users. An erratum to this article can be found at  相似文献   

Heat flow variation with depth in Poland: evidence from equilibrium temperature logs in 2.9-km-deep well Torun-1     

Jacek?Majorowicz  Jan??afanda  Torun- Working Group 《International Journal of Earth Sciences》2008,97(2):307-315

High-precision temperature measurements were carried out up to a depth of 2,930 m in the 5.5-km-deep well Torun-1, 26 years after completion of drilling. The temperature log provides equilibrium thermal state information for the Polish Lowland at the western margin of the Precambrian craton. Geothermal gradient calculated from the equilibrium temperature log, together with estimates of thermal conductivity from ‘net rock’ geophysical well logging analysis and available core measurements, yields heat flow in the range 50–60 mW/m² below 2-km depth. Heat flow of 50 mW/m² plus ∼10 mW/m² generated within thick sediments and highly metamorphosed sedimentary wedge is typical for the western margin of the Precambrian East European craton. Heat-flow variations with depth can be explained by a model of surface-temperature changes >10°C (glaciation to Holocene). Torun-1 Working Group: Marta Wróblewska, Jacek Majorowicz, Jan Szewczyk, Jan Šafanda, Vladimír Cermák  相似文献   

Climate change scenarios of heat waves in Central Europe and their uncertainties     

Ond?ej?LhotkaEmail authorView author&#;s OrcID profile  Jan?Kysely  Ale??Farda 《Theoretical and Applied Climatology》2018,131(3-4):1043-1054

The study examines climate change scenarios of Central European heat waves with a focus on related uncertainties in a large ensemble of regional climate model (RCM) simulations from the EURO-CORDEX and ENSEMBLES projects. Historical runs (1970–1999) driven by global climate models (GCMs) are evaluated against the E-OBS gridded data set in the first step. Although the RCMs are found to reproduce the frequency of heat waves quite well, those RCMs with the coarser grid (25 and 50 km) considerably overestimate the frequency of severe heat waves. This deficiency is improved in higher-resolution (12.5 km) EURO-CORDEX RCMs. In the near future (2020–2049), heat waves are projected to be nearly twice as frequent in comparison to the modelled historical period, and the increase is even larger for severe heat waves. Uncertainty originates mainly from the selection of RCMs and GCMs because the increase is similar for all concentration scenarios. For the late twenty-first century (2070–2099), a substantial increase in heat wave frequencies is projected, the magnitude of which depends mainly upon concentration scenario. Three to four heat waves per summer are projected in this period (compared to less than one in the recent climate), and severe heat waves are likely to become a regular phenomenon. This increment is primarily driven by a positive shift of temperature distribution, but changes in its scale and enhanced temporal autocorrelation of temperature also contribute to the projected increase in heat wave frequencies.  相似文献   

The global and local correlation between the Venus gravity field and its topography     

Milan Burša  Zdislav šíma  Jan Kostelecký 《Earth, Moon, and Planets》1992,57(2):123-138

The correlation between the undulations of the equipotential and topography surface of Venus have been investigated over 16 meridional sections as well as, in the global scale. The correlation is, in general high. However, the figure parameters of the ellipsoids best fitting the surface in question differ significantly. The global features like figures of the best-fitting ellipsoids are mutually strange.  相似文献   

Comparative assessment of spatiotemporal snow cover changes and hydrological behavior of the Gilgit,Astore and Hunza River basins (Hindukush–Karakoram–Himalaya region,Pakistan)     

Adnan Ahmad Tahir  Jan Franklin Adamowski  Pierre Chevallier  Ayaz Ul Haq  Silvia Terzago 《Meteorology and Atmospheric Physics》2016,128(6):793-811

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Contamination patterns and molluscan and polychaete assemblages in two Persian (Arabian) Gulf oilfields          下载免费PDF全文

Paolo G. Albano  Nadezhda Filippova  Jan Steger  Hannah Schmidbaur  Adam Tomašových  Michael Stachowitsch  Martin Zuschin 《Marine Ecology》2016,37(4):907-919

This study examined two shallow‐water, offshore oil facilities and their surroundings in the Umm Al Dalkh and Zakum oilfields [United Arab Emirates, Persian (Arabian) Gulf]. The focus was on sediment contamination levels and the detection of disturbance based on two representative invertebrate components of the benthos: molluscs and polychaetes. We tested the hypothesis that significant disturbance to the community has occurred, by examining whether distance from the platform or variation in contaminants explains among‐site variation in the composition of benthic communities. Moreover, we also tested the hypothesis that organic enrichment because of oil input has modified the feeding guild structure by examining whether the relative abundances of filter‐feeders, deposit‐feeders and omnivores are correlated with distance from the platform or with contamination by hydrocarbons. The contamination levels and their spatial distribution in the sediments differed significantly between the two fields, as did their mollusc and polychaete communities. The within‐field variability, however, was much lower: no clear structuring of contamination values and species composition and abundance was detectable in relation to distance from the oil platform. Contamination levels were low, often below detection levels or international guideline values. Variation in contaminant concentrations did not explain variation in taxonomic composition and abundance. The relative abundance of the above‐mentioned feeding guilds did not correlate with either distance from the platform or with contaminant concentrations. These patterns may reflect the long time that has elapsed since drilling (15–20 years), which appears to have allowed contaminants to disperse and degrade and assemblages to recover from the impact, if indeed such a disturbance ever occurred. In contrast to low values of barium and total petroleum hydrocarbons, associated with well drilling, some metals were at their highest concentrations beneath the central platforms. This suggests that production‐related activities (including platform cleaning and maintenance) are currently a more relevant contamination source.  相似文献