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31.
Alfonso F. Davila Christoph Gross Alberto G. Fairén Thomas Kneissl James M. Dohm 《Icarus》2011,212(2):579-589
Different lines of evidence point to hydrological cycling in the martian past. The extent, duration, and magnitude of this cycling remains unclear, as well as the magnitude of aqueous processes on the surface. Here, we provide geomorphic and mineralogic evidence of a large inter-crater sedimentary basin located in the Terra Sirenum region, which was once covered by a body of liquid water with an areal extent of at least 30,000 km2 and a depth of approximately 200 m. The topographic basin, which is modified by a number of large impact craters, is partly controlled by ancient impact and tectonic structures. As a result of evaporation of the large body of water, salt flats formed in the lowest topographic reaches of the basin. Hydrated phyllosilicates occur in close proximity to the salt flats and in the ejecta and rim materials of small impact craters with stratigraphic relations that suggest that they underlie the evaporite deposits. Crater statistics place the maximum age of aqueous activity during the Late Noachian epoch. The relatively pristine mineral deposits in the basin have a high potential to yield information of the geochemistry and water activity during the ancient Noachian Period when conditions were seemingly more conducive to life. 相似文献
32.
依据南海低纬地区SA09-040孔高分辨率的孢粉记录,自下至上划分了4个孢粉组合带。从孢粉成分的变化,重建了22.25ka B P以来的植被与气候变化历史。结果表明:孢粉主要来源于婆罗洲和周围岛屿,孢粉1带(22.25~16.6ka B P),低山雨林植被发育,为暖热气候,从测年时间看,当时为末次冰期晚期。孢粉2带(16.6~10.82ka B P,为末次冰消期),植被以热带低山雨林和低地雨林为主,针叶的松数量较多,当时的气温比现在低。孢粉3带(全新世早期,10.82~6.43ka B P),植被以热带低山雨林和低地雨林为主,针叶松属数量减少,气温比前期升高,海平面也上升。孢粉4带(全新世中晚期,6.43ka B P至今),全新世中期为炎热、湿润的气候环境,全新世晚期可能与婆罗洲现今的植被景观相近,为热、湿的气候环境。 相似文献
33.
Alejandro Marulanda Aguirre Omar Alfonso Fonseca Tobasura Omar Darío Cardona Arboleda 《水文科学杂志》2013,58(12):2179-2192
ABSTRACTThis paper presents the results of a hydrological study aimed at characterizing flood-prone areas in the urban growth zone in the city of Manizales based on the potential effects of melting of the Nevado del Ruiz glacier, in Caldas, Colombia. These results constitute a basis for decision making regarding possible urban growth zones in Andean areas that face risks from volcanic eruptions producing lahars and floods caused by glacier melt. Conservative estimates of extreme flows in the Chinchiná River in the urban growth area of El Rosario can be obtained by considering the effects of rain triggered by airborne particulate material following a volcanic explosion combined with the effects of glacier melt. The effects of global warming on tropical glaciers contribute to their retreat, leading to their disappearance. Therefore, the worst scenario would take place if these events occurred in the short term as glacier volume decreases with time.
Editor Z.W. Kundzewicz; Associate editor not assigned 相似文献
34.
Maurizio?Romanelli Francesco?Di BenedettoEmail author Laura?Bartali Massimo?Innocenti Gabriele?Fornaciai Giordano?Montegrossi Luca?A.?Pardi Alfonso?Zoleo Fabio?Capacci 《Physics and Chemistry of Minerals》2012,39(6):479-490
A set of raw industrial materials, that is, pure quartz and quartz-rich mixtures, were investigated through electron paramagnetic
resonance and electron spin echo-envelope modulation spectroscopies, with the aim of evaluating the effective role played
by defect centres and of assessing whether they can be used to monitor changes in the physical properties of quartz powders
with reference to their health effects. The obtained results point to two interactions of the Al defect centres with H+, hosted in sites within the channels parallel and perpendicular to the c axis of quartz, respectively. These two Al/H+ (hAl) centres exhibit a weak chemical bond, and their relative amounts appear to be modified/controlled by the thermo-mechanical
processes underwent by powders. Indeed, a mechanically promoted inter-conversion between the two kinds of site is suggested.
As a consequence, the hAl centres are effective in monitoring even modest activations of powders, through thermal or mechanical processes, and they
are also supposed to play a specific, relevant role in quartz reactivity during the considered industrial processes. 相似文献
35.
36.
Glacier recession and human vulnerability in the Yanamarey watershed of the Cordillera Blanca, Peru 总被引:2,自引:0,他引:2
Jeffrey T. Bury Bryan G. Mark Jeffrey M. McKenzie Adam French Michel Baraer Kyung In Huh Marco Alfonso Zapata Luyo Ricardo Jes��s G��mez L��pez 《Climatic change》2011,105(1-2):179-206
Glaciers in the Cordillera Blanca, Peru, are undergoing rapid retreat, in large part due to climate change. These changes are significantly altering water availability in the region and pose critical risks to local populations that are highly dependent on these resources for livelihoods. We examine these issues through an interdisciplinary and linked evaluation of hydrological change and livelihood vulnerability in the Yanamarey watershed. Physical observations of the Yanamarey glacier show acceleration in frontal retreat at a rate of 8 m decade???1 since 1970, accompanied by total volume loss on the order of 0.022 km3. Hydrological and hydrochemical analyses document a possible transformation of stream flow over the past decade as the seasonal storage capacity of the glacier has degraded. Recent stream discharge measurements from the proglacial lake below the glacier are more coincident with the highly variable seasonal precipitation than they were during the 1998?C1999 hydrological year. Local household perceptions of glacier recession and seasonal hydrological variability agree with this trend, which is increasing human vulnerability in the watershed. Household case-study survey results demonstrate that shifting water resources, increasing weather extremes and climate-related threats to tourism are all new vectors of vulnerability for household livelihoods. 相似文献
37.
Andrés García García Carolina Perpiñá Carlos de Alfonso Vicente Hernández 《Earth Science Informatics》2013,6(4):199-207
This paper presents the integration of desktop grid infrastructure with GIS technologies, by proposing a parallel resolution method in a generic distributed environment. A case study focused on a discrete facility location problem, in the biomass area, exemplifies the high amount of computing resources (CPU, memory, HDD) required to solve the spatial problem. A comprehensive analysis is undertaken in order to analyse the behaviour of the grid-enabled GIS system. This analysis, consisting of a set of the experiments on the case study, concludes that the desktop grid infrastructure is able to use a commercial GIS system to solve the spatial problem achieving high speedup and computational resource utilization. Particularly, the results of the experiments showed an increase in speedup of fourteen times using sixteen computers and a computational efficiency greater than 87 % compared with the sequential procedure. 相似文献
38.
Benoît Thibodeau Moritz F. Lehmann Jacqueline Kowarzyk Alfonso Mucci Yves Gélinas Denis Gilbert Roxane Maranger Mohammad Alkhatib 《Estuarine, Coastal and Shelf Science》2010
Water column concentrations and benthic fluxes of dissolved inorganic nitrogen (DIN) and oxygen (DO) were measured in the Gulf of St. Lawrence and the Upper and Lower St. Lawrence Estuary (USLE and LSLE, respectively) to assess the nitrogen (N) budget in the St. Lawrence (SL) system, as well as to elucidate the impact of bottom water hypoxia on fixed-N removal in the LSLE. A severe nitrate deficit, with respect to ambient phosphate concentrations (N*∼−10 μmol L−1), was observed within and in the vicinity of the hypoxic bottom water of the LSLE. Given that DO concentrations in the water column have remained above 50 μmol L−1, nitrate reduction in suboxic sediments, rather than in the water column, is most likely responsible for the removal of fixed N from the SL system. Net nitrate fluxes into the sediments, derived from pore water nitrate concentration gradients, ranged from 190 μmol m−2 d−1 in the hypoxic western LSLE to 100 μmol m−2 d−1 in the Gulf. The average total benthic nitrate reduction rate for the Laurentian Channel (LC) is on the order of 690 μmol m−2 d−1, with coupled nitrification-nitrate reduction accounting for more than 70%. Using average nitrate reduction rates derived from the observed water column nitrate deficit, the annual fixed-N elimination within the three main channels of the Gulf of St. Lawrence and LSLE was estimated at 411 × 106 t N, yielding an almost balanced N budget for the SL marine system. 相似文献
39.
Alfonso Herrera-Bachiller Pedro García-Corrales Carmen Roldán & Juan Junoy 《Marine Ecology》2008,29(S1):43-50
Nemerteans have been recorded in several studies of the sandy beaches, but usually these specimens have been only regarded as members of the Phylum, with no attempt at identification at any taxonomic level. This lack of identification is partly because of the sampling procedures used to collect beach macroinfauna. Nemerteans are fragile and need special care. They must be isolated and observed in vivo before using histological procedures, which must be employed for the taxonomical studies. This study deals with a sandy beach hoplonemertean, Psammamphiporus elongatus ( Stephenson 1911 ), only known for seven specimens from the Firth of Clyde (UK). This species is recorded for the first time from the Galician sandy beaches (NW Spain) where it reaches its maximum abundance. The species is described and illustrated and new data on its morphology and ecology are provided. The species was apparently affected by the 'Prestige' oil spill, and would be a good indicator of beach quality. 相似文献
40.
Esther Molina-Montes Alfonso Hernández-laguna 《Geochimica et cosmochimica acta》2008,72(16):3929-3938
Atomic models involving the dehydroxylation process of dioctahedral phyllosilicates without interlayer charge were used to calculate energies and explore the reaction paths of the possible mechanisms of this reaction at a quantum mechanical level. The geometrical features and electronic structure of a molecular cluster model of two edge-sharing octahedrally coordinated cations coupled to a ring of six silicate tetrahedra was evaluated by ab initio molecular orbital calculations with Hartree-Fock approximation. Two dehydroxylation mechanisms are considered. One mechanism involves two contiguous hydroxyl that are on an octahedron shared edge that joins a pair of octahedral cations. The other model considered involves OH loss from across an octahedral vacant. The substitution effect of Al3+ by Fe3+ in the octahedral sheet on the activation energy and structural transformations is compared by minimization of the critical points of the Potential Energy Surface (PES) for the reactant, transition state and product along the reaction path of the dehydroxylation process. The calculated energy differences and vibration frequencies are according to previous experimental results. The dehydroxylation mechanism involving OH across the octahedral hole, is less energetically favorable and is endothermic. 相似文献