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排序方式: 共有149条查询结果,搜索用时 15 毫秒
31.
Adakitic lavas in the Central Luzon back‐arc region,Philippines: lower crust partial melting products? 总被引:6,自引:0,他引:6
Graciano P. Yumul JR Carla Dimalanta Herve Bellon Decibel V. Faustino Joel V. De Jesus Rodolfo A. Tamayo JR Ferdinand T. Jumawan 《Island Arc》2000,9(4):499-512
Abstract Volcanism in the back-arc side region of Central Luzon, Philippines, with respect to the Manila Trench is characterized by fewer and smaller volume volcanic centers compared to the adjacent forearc side-main volcanic arc igneous rocks. The back-arc side volcanic rocks which include basalts, basaltic andesites, andesites and dacites also contain more hydrous minerals (ie, hornblende and biotite). Adakite-like geochemical characteristics of these back-arc lavas, including elevated Sr, depleted heavy rare earth elements and high Sr/Y ratios, are unlikely to have formed by slab melting, be related to incipient subduction, slab window magmatism or plagioclase accumulation. Field and geochemical evidence show that these adakitic lavas were most probably formed by the partial melting of a garnet-bearing amphibolitic lower crust. Adakitic lavas are not necessarily arc–trench gap region slab melts. 相似文献
32.
The dependence of the ellipticity of nearby optical galaxies associated with extragalactic radio sources on the type of radio galaxy is considered. It is shown that elliptical galaxies identified with radio galaxies of the FRI type and with radio sources having a radio image with a small elongation have a smaller ellipticity, on the average, than those associated with radio galaxies of the FRII type and with radio sources with greater elongation. As one possible explanation for this phenomenon, one can assume that the optical galaxies associated with radio galaxies of type FRI and with radio sources of small elongation are oriented in space so that they are observed edge-on relatively rarely. 相似文献
33.
Rainfall variability,rainfed agriculture and degree of human marginality in North Guanajuato,Mexico
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Rebeca Granados Jesus Soria Moises Cortina 《Singapore journal of tropical geography》2017,38(2):153-166
Mexico has a heterogeneous climate due to its geographical location. Half of the Mexican territory is dryland, mostly in the centre and north of the country, within which agriculture is the main activity in the primary production sector. At present, climate variability has a strong impact on Mexican agriculture. This study analysed rainfall variability, its impact on the agricultural productivity in terms of harvested quantity and productivity of 1996‐2014, and in parallel, the role that socioeconomic development plays on the well‐being of the population who live in areas with rainfed agriculture and a semi‐dry climate. The data obtained were analysed with the Statistical Analysis System. A positive correlation was found between rainfall and productivity (r = 0.76 for maize; r = 0.711 for beans). Rainfall variations therefore have a great impact on agricultural productivity, on food security and on the economy. Besides production losses, a parallel consequence is marginalization of the population because producers' income is increasingly reduced due to smaller crop volumes. 相似文献
34.
Wolske Kimberly S. Raimi Kaitlin T. Campbell-Arvai Victoria Hart P. Sol 《Climatic change》2019,152(3-4):345-361
Climatic Change - Carbon dioxide removal (CDR) describes a suite of controversial approaches to mitigating climate change that involve removing existing carbon dioxide from the atmosphere. Through... 相似文献
35.
Solé M García de la Parra LM Alejandre-Grimaldo S Sardá F 《Marine pollution bulletin》2006,52(12):1708-1716
There is a lack of information on monitoring neurotoxicity in offshore commercial species. To help fill this gap, we sampled hake (Merluccius merluccius) and Norway lobster (Nephrops norvegicus) in fishing grounds off the coast of l’Ametlla de Mar (NW Mediterranean) in June 2005 at a depth of 100 m and 400 m. Additionally, at 400 m depth, two other fish species, Micromesistius poutassou and Phycis blennoides were included. Neurotoxicity markers such as Colinesterases (ChEs), namely acethyl- (AChE), butyryl- (BChE), propionyl- (PrChE) and carboxilesterase (CbE) were measured in muscle. Lipid peroxidation (LP), a marker of oxidative damage, was also included. The results are discussed in relation to the animal’s sex, size and fishing depth. A comparison of esterases and LP levels between muscle and liver of hake and between muscle and hepatopancreas of Norway Lobster was made.
AChE was dominant in muscle and CbE in hepatopancreas. No differences between fish species were seen for AChE. However, N. norvegicus, presented lower levels of ChEs and LP. A size-dependence in ChEs was seen for M. merluccius, with larger animals showing significantly lower activities (p < 0.05). Sex-dependence was seen in N. norvegicus for most esterases, except AChE, with males displaying higher activities (p < 0.05). A sampling-depth effect was also seen in the crustacea, with animals from 100 m generally presenting lower esterase activities and higher LP levels. 相似文献
36.
lvaro Peliz Ana Teles-Machado Patrick Marchesiello Jesus Dubert Jesus Garcia Lafuente 《Dynamics of Atmospheres and Oceans》2009,46(1-4):36-45
We present a case study of the generation of a cold filament rooted off the southwestern edge of the Strait of Gibraltar (Atlantic side) during the summer of 2000. The event is successfully simulated using high-resolution atmospheric and oceanic numerical models. It is shown that a sharp filament may develop oceanwards with little modification of the Atlantic inflow into the Mediterranean, contrary to usual expectations. The filament is essentially driven by the surface layer response to Gap winds occurring during Levanter conditions. The easterly wind funnelling in the Strait generates a strong wind jet and intense wind curl which impacts the oceanic surface layer through Ekman pumping and mixing processes. The generation and fate of the filament is very similar to the Gulf of Tehuantepec case, where strong Gap wind events produce asymmetric deformation and erosion of the thermocline that tends to favour anticyclonic mesoscale circulations. Our observations and model results from both realistic and idealized experiments suggest that similar phenomena are present in the Gulf of Cadiz, but they are altered by the persisting Atlantic inflow, so that the response to Gap winds is not as dramatic. 相似文献
37.
A model for the conservation of geological remains as documents 总被引:1,自引:0,他引:1
Geological remains are conserved mainly either together with living beings for the sake of the integrity of nature or for
their economical or aesthetic value. However, they also have scientific value for the geologist to reconstruct the earth's
past. For this reason we propose a model which is an application of marginal utility theory in economics and takes into account
the informational utility of geological remains. Informational utility of geological remains ranges over their geological significance which is induced by the importance of the geological processes that produce them, and over their spatial extensiveness. Our model takes into account also the cost and budget of conservation and proposes to solve the differential equations of informational utility and cost simultaneously in order
to obtain the optimum quantity of the remains to be conserved.
Received: 9 January 1998 · Accepted: 4 February 1998 相似文献
38.
Hélène Sol 《Journal of Astrophysics and Astronomy》2018,39(4):52
During the last decade, very high energy astrophysics emerged as a new branch of astronomy with major discoveries achieved by the present ground-based gamma-ray Cherenkov telescopes. The sample of cosmic sources firmly detected at very high energy (VHE) now exceeds two hundred objects, including active galactic nuclei (AGN), pulsar wind nebulae, and several other types of sources of which a significant number are unidentified ones. The scientific return from recent VHE data is particularly interesting for AGN science, shedding new light on particle acceleration and emission processes around supermassive black holes, and probing the intergalactic space by the analysis of VHE photons propagating from bright remote sources to the Earth. The perspectives of this research field are promising with new generation VHE instruments such as CTA, a project of open observatory at extreme energies at the horizon 2023, allowing a deep analysis of the sky in the highest part of the electromagnetic spectrum, from 20 GeV to 300 TeV. 相似文献
39.
Francisco J. Fernández Helder I. Chaminé Paulo E. Fonseca José M. Munhá António Ribeiro Jesus Aller Mercedes Fuertes-Fuentes Frederico S. Borges 《地学学报》2003,15(2):96-103
ABSTRACT The study of a garnet-bearing quartzite from a major suture zone in Iberia reports an unusual high-T fabric. Quartz c -axis patterns were plotted using shaped garnet as reference axis for the finite stretch ( X -axis). The pole figures are characterized by a dominant single maximum around X together with other point maxima along the XY plane (mylonitic foliation). These patterns suggest that dominant < c > prism slip and subordinated < a > prism slip operated during quartz plastic deformation in agreement with P–T conditions for syntectonic garnet growth (4–5 kbar and 700 ± 50 °C) and, pre-dating the well-known (late) Variscan D1 event (<6 kb and 600 ± 30 °C). The geotectonic framework suggests that the fabrics were formed along the western shear margin of the Ossa-Morena Zone during the early stages of the Variscan orogeny. 相似文献
40.
Joeri van Leeuwen Robert D. Ferdman Sol Meyer Ingrid Stairs 《Monthly notices of the Royal Astronomical Society》2007,374(4):1437-1440
Low-mass white dwarfs can be produced either in low-mass X-ray binaries by stable mass transfer to a neutron star, or in a common envelope phase with a heavier white dwarf companion. We have searched eight low-mass white dwarf candidates recently identified in the Sloan Digital Sky Survey for radio pulsations from pulsar companions, using the Green Bank Telescope at 340 MHz. We have found no pulsations down to flux densities of 0.6–0.8 mJy kpc−2 and conclude that a given low-mass helium-core white dwarf has a probability of <0.18 ± 0.05 of being in a binary with a radio pulsar. 相似文献