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排序方式: 共有76条查询结果,搜索用时 31 毫秒
1.
Federico Ignacio Isla Orlando Mauricio Quiroz Londoño Luis Camilo Cortizo 《Environmental Earth Sciences》2018,77(17):610
The urban growth of the southern neighborhoods of Mar del Plata City provoked significant changes in the groundwater balance of the loessic sequences. These regional loessic levels with a significant portion of volcanic ash layers were reported subject to fluoride and nitrate concentrations. Residential houses pump from sands located 70 m depth and withdraw the sewages to depths less than 5 m. These effects cause significant local and seasonal (summer) increments of the water table outcropping via springs at certain unconformities of the coastal cliffs. A mathematical model was applied to analyze the water level lowering at the productive levels, while there is a decrease in the quality of the upper levels subject to waste discharges. Much of this groundwater flow is concentrated in unconformities between different types of sediments. Human activities have affected the aquifer dynamics increasing the groundwater pumping rates and the return velocity of the sewages. This should be considered in the management strategies of coastal hydric resources. 相似文献
2.
Five spinel lherzolite xenoliths hosted in Neogene alkali basalts from the marginal parts of the Pannonian Basin (Styrian Basin in Austria and Persani Mts. in the Eastern Transylvanian Basin, Romania) contain orthopyroxene–clinopyroxene–spinel clusters, which are believed to represent former garnet in lherzolitic mantle material. 'Palaeo' equilibrium pressure of this former garnet lherzolite was estimated to be equivalent to depths of 90–120 km using calculated garnet compositions and measured orthopyroxene compositions from the clusters. 'Neo' equilibrium pressures of the xenoliths indicate depths of 55–65 km, suggesting c. 50–60 km uprise of the mantle section represented by these xenoliths. This petrological result confirms the observations from previous geophysical studies that significant mantle uplift has occurred beneath the Pannonian Basin. 相似文献
3.
Jaime Orlando Martínez Eduardo López Ramos 《Journal of South American Earth Sciences》2011,31(1):28-44
The sedimentary prism of the central Pacific continental shelf of Colombia was affected by regional folding and faulting, and probably later mud diapirism, from the Late Miocene to the Holocene. Interpretation of high-resolution seismic lines (2 s/dt) revealed that the prism consists of 13 high-resolution seismic units, that can be separated into 5 seismic groups.Deposition of the prism and the associated stacking pattern, are probably the response to variable uplift and subsidence in a fore-arc basin that underwent important tectonic events by the end of the Miocene. Throughout the Pliocene, the continental shelf sedimentation was affected by the growing of a dome structure probable due to mud diapirism. This fact caused peripheral faults both normal and reverse that controlled the distribution of some of the seismic units. During the Late Pleistocene (Wisconsin stage?) a eustatic sea level fall caused the shoreline to advance about 50 km westward of its present position. Because of this eustatic sea level change, a strong fluvial dissection took place and is interpreted as the probable extension of the San Juan River to the south of the present day river mouth. Within this framework it is believed that the Malaga and Buenaventura Bays were the passageways of branches of the old drainage system of the San Juan River. The inner branch circulated through the present Buenaventura Bay and runs southward leaving the mark of an apparent valley identified in the seismic information in the eastern sector of the study area. This old fluvial valley and its filling material located in the present day inner continental shelf front of Buenaventura are postulated as important targets to find placer minerals such as gold and platinum. 相似文献
4.
Melitta Fiebig-Wittmaack Orlando Astudillo Elaine Wheaton Virginia Wittrock César Perez Antonio Ibacache 《Climatic change》2012,111(3-4):819-833
Little is known about climate change and its impacts for the arid coastal and mountainous regions in northern Chile. The Elqui river basin, part of the Norte Chico of Chile between 27oS and 33oS latitude, is located south of the hyper-arid Atacama desert. Despite water scarcity, agricultural development in this region has been enhanced by agronomic practices and the marketing of valuable products. This paper characterizes the actual climate conditions and presents an overview and analyses of past climate variability, and future possible climate trends, emphasizing those relevant to agriculture. Precipitation shows an important decrease during the first decades of the past century. Runoff shows decreasing trends for the first half of the past century and increases for 1960 to 1985. Drought appears to be increasing. Statistical downscaling was accomplished using the Long Ashton Research Station Weather Generator. Both future periods of 2011 to 2030 and 2046–65 showed trends to higher minimum and maximum temperature. The number of hot days (maximum temperature greater than or equal to 30°C) has a strong increasing trend during October to April. Even though the downscaled results for precipitation do not show trends, the continuation of the present trend of low amounts is a concern. We discuss some implications of climatic changes for agriculture and we emphasize the importance of adaptation, especially to deal with water scarcity. 相似文献
5.
Daniel D. Riemer Eric C. Apel John J. Orlando Geoffrey S. Tyndall William H. Brune Eric J. Williams William A. Lonneman James D. Neece 《Journal of Atmospheric Chemistry》2008,61(3):227-242
As part of the 2000 Texas Air Quality Study (TexAQS), we studied the isoprene oxidation process under ambient conditions to
discern the presence of chlorine atom (Cl) chemistry in the Houston, Texas urban area. By measuring chloromethylbutenone (CMBO)
and an isomer of chloromethylbutenal (CMBA), we clearly observed sixteen episodes of active Cl chemistry during the 24-day
experiment. Estimated median Cl concentration during each of these episodes was between the detection limit of ~102 atoms cm−3 and 50 - 30 + 70 ×104 50_{ - 30}^{ + 70} \times {10^4} atoms cm−3. Cl concentration during all the episodes averaged 7.6 - 2.0 + 4.7 ×104 7.6_{ - 2.0}^{ + 4.7} \times {10^4} atoms cm−3 and thus amounted to less than 3% of the OH concentration during the same periods. During the episodes, the fraction of oxidation
chemistry initiated by Cl ranged from 3–43% and was strongly dependent on the quantity and type of hydrocarbons present in
the atmosphere. Because of its intermittent presence and low concentration, Cl is not a broadly influential oxidant in the
Houston, Texas urban area. 相似文献
6.
O. Petruk V. Beshley F. Bocchino S. Orlando 《Monthly notices of the Royal Astronomical Society》2009,395(3):1467-1475
The synchrotron radio maps of supernova remnants (SNRs) in a uniform interstellar medium and interstellar magnetic field (ISMF) are analysed, allowing for different 'sensitivity' of the injection efficiency to the obliquity of the shock. The very-high-energy γ-ray maps arising from inverse Compton processes are also synthesized. The properties of images in these different wavelength bands are compared, with particular emphasis on the location of the bright limbs in bilateral SNRs. Recent High-Energy Stereoscopic System (HESS) observations of SN 1006 show that the radio and inverse Compton γ-ray limbs coincide, and we found that this may happen if (i) injection is isotropic but the variation of the maximum energy of electrons is rather fast to compensate for differences in the magnetic field, or (ii) the obliquity dependence of injection (either quasi-parallel or quasi-perpendicular) and the electron maximum energy are strong enough to dominate the magnetic field variation. In the latter case, the obliquity dependences of the injection and the maximum energy should not be opposite. We argue that the position of the limbs alone, and even their coincidence in radio, X-rays and γ-rays, as discovered by HESS in SN 1006, cannot be conclusive as regards the dependence of the electron injection efficiency, the compression/amplification of the ISMF and the electron maximum energy on the obliquity angle. 相似文献
7.
Yves Noel Raffaella Demichelis Fabien Pascale Piero Ugliengo Roberto Orlando Roberto Dovesi 《Physics and Chemistry of Minerals》2009,36(1):47-59
The structure and vibrational spectrum of boehmite have been investigated at the quantum-mechanical level with the CRYSTAL
code, using a Gaussian-type basis set and the B3LYP Hamiltonian. Three space groups are considered in this study: Cmcm, Cmc21, P21/c. Cmcm turns out to correspond to a transition state, whereas Cmc21 and P21/c are minimum energy structures. The difference among them is the position of H atoms only, the Al-O frame being essentially
the same. Harmonic frequencies at the Γ point have been computed. The comparison between calculated and experimental frequencies
shows a good agreement for the Al-O part of the spectrum (under 790 cm−1). For the Al-OH bending modes (800–1,300 cm−1) an absolute differences of 50–100 cm−1 is observed; for the OH stretching modes (3,200–3,500 cm−1) it increases to 120–200 cm−1: anharmonicity is large because OH groups are involved in strong hydrogen bonds. 相似文献
8.
Thanks to its fitting triumph, the ΛCDM paradigm is assumed to be the most powerful model, for describing the Universe dynamics,
over much the myriad of cosmological models. Unfortunately, the quest of a self-consistent model remains not well explained,
because it is not clear how to solve the problems of fine-tuning and coincidence, afflicting the ΛCDM framework; as a matter
of fact, these theoretical drawbacks do not allow to consider the ΛCDM model, as the final picture of the modern cosmological
scenario. Here, we show that the simplest model, which provides a constant equation of state for the pressure, leads to a
generalization of ΛCDM, reducing to it in a particular case. Moreover, we highlight the physical mechanisms of this model,
describing the thermodynamical reasons why a constant pressure should be negative in an expanding Universe. In addition, we
fit the free parameters of our model by minimizing the chi square through the age differential method, involving a direct
measurement of H. 相似文献
9.
Pinarelli Laura Gioncada Anna Capaccioni Bruno Vaselli Orlando Downes Hilary 《Mineralogy and Petrology》2019,113(1):39-60
Mineralogy and Petrology - Vulcano is part of the Aeolian volcanic arc in the southern Tyrrhenian Sea. Its products were emplaced through multiple episodes of edifice building and collapse since... 相似文献
10.