The statistics of a passive scalar in field-guided magnetohydrodynamic turbulence     

J. Mason  S. Boldyrev  F. Cattaneo  J.C. Perez 《地球物理与天体物理流体动力学》2014,108(6):686-695

A variety of studies of magnetised plasma turbulence invoke theories for the advection of a passive scalar by turbulent fluctuations. Examples include modelling the electron density fluctuations in the interstellar medium, understanding the chemical composition of galaxy clusters and the intergalactic medium, and testing the prevailing phenomenological theories of magnetohydrodynamic turbulence. While passive scalar turbulence has been extensively studied in the hydrodynamic case, its counterpart in MHD turbulence is significantly less well understood. Herein we conduct a series of high-resolution direct numerical simulations of incompressible, field-guided, MHD turbulence in order to establish the fundamental properties of passive scalar evolution. We study the scalar anisotropy, establish the scaling relation analogous to Yaglom’s law, and measure the intermittency of the passive scalar statistics. We also assess to what extent the pseudo Alfvén fluctuations in strong MHD turbulence can be modelled as a passive scalar. The results suggest that the dynamics of a passive scalar in MHD turbulence is considerably more complicated than in the hydrodynamic case.  相似文献   

Removal of Pyridine from Aqueous Solution by Adsorption on an Activated Carbon Cloth     

Pedro Alonso‐Davila  Oliva L. Torres‐Rivera  Roberto Leyva‐Ramos  Raul Ocampo‐Perez 《洁净——土壤、空气、水》2012,40(1):45-53

Pyridine is a very toxic pollutant that has to be removed from wastewater. In this work, adsorption of pyridine on activated carbon cloth (ACC) is studied as a possible alternative for eliminating pyridine from aqueous solution. The ACC was produced from polyacrylonitrile. The adsorption equilibrium data of pyridine on ACC was obtained in a batch adsorber. The experimental data was interpreted with the isotherms of Langmuir, Freundlich, and Prausnitz‐Radke (PR), and the PR isotherm better represented the experimental data. The capacity of ACC for adsorbing pyridine was favored increasing the solution pH from 3 to 6, and this effect was due to the π–π dispersive and electrostatic interactions between the pyridine species in solution and the surface complexes of ACC. The modified Langmuir model fitted reasonably well the influence of pH on the adsorption capacity. In this model was assumed that both neutral pyridine and pyridinium were simultaneously adsorbed on ACC accordingly to the experimental results. The adsorption capacity was almost independent of temperature. The reversibility study revealed that 75% of the pyridine can be desorbed from ACC indicating that part of the pyridine was irreversibly adsorbed, and possibly chemisorbed.  相似文献   

A new approach to multiphase geochemical speciation modeling     

R.J. Perez  R.A. Heidemann  E.C. Perez 《Applied Geochemistry》2012

  相似文献   

Modeling the onset of photosynthesis after the Chicxulub asteroid impact     

Noel Perez  Rolando Cardenas  Osmel Martin  Reinaldo Rojas 《Astrophysics and Space Science》2013,343(1):7-10

We do a preliminary modelling of the photosynthetic rates of phytoplankton at the very beginning of the Paleogene, just after the impact of the Chicxulub asteroid, which decisively contributed to the last known mass extinction of the Phanerozoic eon. We assume the worst possible scenario from the photobiological point of view: an already clear atmosphere with no ozone, as the timescale for soot and dust settling (years) is smaller than that of the full ozone regeneration (decades). Even in these conditions we show that most phytoplankton species would have had reasonable potential for photosynthesis in all the three main optical ocean water types. This modelling could help explain why the recovery of phytoplankton was relatively rapid after the huge environmental stress of that asteroid impact. In a more general scope, it also reminds us of the great resilience of the unicellular biosphere against huge environmental perturbations.  相似文献   

Walking through volcanic mud: the 2,100-year-old Acahualinca footprints (Nicaragua)     

Hans-Ulrich Schmincke  Steffen Kutterolf  Wendy Perez  Juanita Rausch  Armin Freundt  Wilfried Strauch 《Bulletin of Volcanology》2009,71(5):479-493

We present the stratigraphy, lithology, volcanology, and age of the Acahualinca section in Managua, including a famous footprint layer exposed in two museum pits. The ca. 4-m-high walls of the main northern pit (Pit I) expose excellent cross sections of Late Holocene volcaniclastic deposits in northern Managua. We have subdivided the section into six lithostratigraphic units, some of which we correlate to Late Holocene eruptions. Unit I (1.2 m thick), chiefly of hydroclastic origin, begins with the footprint layer. The bulk is dominated by mostly massive basaltic-andesitic tephra layers, interpreted to represent separate pulses of a basically phreatomagmatic eruptive episode. We correlate these deposits based on compositional and stratigraphic evidence to the Masaya Triple Layer erupted at Masaya volcano ca. 2,120 ± 120 a B.P.. The eruption occurred during the dry season. A major erosional channel unconformity up to 1 m deep in the western half of Pit I separates Units II and I. Unit II begins with basal dacitic pumice lapilli up to 10 cm thick overlain by a massive to bedded fine-grained dacitic tuff including a layer of accretionary lapilli and pockets of well-rounded pumice lapilli. Angular nonvesicular glass shards are interpreted to represent hydroclastic fragmentation. The dacitic tephra is correlated unequivocally with the ca. 1.9-ka-Plinian dacitic Chiltepe eruption. Unit III, a lithified basaltic-andesitic deposit up to 50 cm thick and extremely rich in branch molds and excellent leaf impressions, is correlated with the Masaya Tuff erupted ca. 1.8 ka ago. Unit IV, a reworked massive basaltic-andesitic deposit, rich in brown tuff clasts and well bedded and cross bedded in the northwestern corner of Pit I, cuts erosionally down as far as Unit I. A poorly defined, pale brown mass flow deposit up to 1 m thick (Unit V) is overlain by 1–1.5 m of dominantly reworked, chiefly basaltic tephra topped by soil (Unit VI). A major erosional channel carved chiefly between deposition of Units II and I may have existed as a shallow drainage channel even prior to deposition of the footprint layer. The swath of the footprints is oriented NNW, roughly parallel to, and just east of, the axis of the channel. The interpretation of the footprint layer as the initial product of a powerful eruption at Masaya volcano followed without erosional breaks by additional layers of the same eruptive phase is strong evidence that the group of 15 or 16 people tried to escape from an eruption.  相似文献   

Climatic Warming in the Spanish Mediterranean: Natural Trend or Urban Effect     

J. Quereda Sala  A. Gil Olcina  A. Perez Cuevas  J. Olcina Cantos  A. Rico Amoros  E. Montón Chiva 《Climatic change》2000,46(4):473-483

The evolution of the mean annual temperatures recordedin the major historical network of SpanishMediterranean observatories(36°N–45°/60°W–4°E)exhibits a significant warming trend. Analysis of thetrend is difficult and could be biased by non-climaticprocesses such as the urban effect and weather stationrelocation, which also need to be taken intoaccount.The present work examines the effects of non-climaticprocesses and shows that most of the temperature risecould be due to an urban effect. On correcting for theurban effect, the actual rise was found to be zero ornegligible. The assumption of temperature stability inthe Spanish Mediterranean should thereforenot be rejected.  相似文献   

Quantum Instability of Magnetized Stellar Objects     

R. González Felipe  H. J. Mosquera Cuesta  A. Pérez Martínez  H. Pérez Rojas 《中国天文和天体物理学报》2005,5(4):399-411

The equations of state for degenerate electron and neutron gases are studied in the presence of magnetic fields. After including quantum effects in the investigation of the structural properties of these systems, it is found that some hypermagnetized stars can be unstable according to the criterion of stability of pressures. Highly magnetized white dwarfs should collapse producing a supernova type Ia, while superstrong magnetized neutron stars cannot stand their own magnetic field and must implode, too. A comparison of our results with a set of the available observational data of some compact stars is also presented, and the agreement between this theory and observations is verified.  相似文献   

TPH and PAH concentrations in the subsoil of polyduct segments, oil pipeline pumping stations, and right-of-way pipelines from Central Mexico     

Rosario Iturbe  Alejandrina Castro  Guillermina Perez  Carlos Flores  Luis G. Torres 《Environmental Geology》2008,55(8):1785-1795

For the year 1996, 366 incidents related with clandestine poaching of oil-products were reported in Mexico, 159 in 1997, and 240 in 1998. For the year 2003 (the most recently reported figure), there were 136 events. Petroleos Mexicanos (PEMEX), very concerned with the environmental agenda, has developed programs oriented to diminish contamination levels in all of its oil facilities. This work was aimed at characterizing zones around polyduct segments, pipelines, pumping stations, and right-of-way pipelines located in the center of Mexico. The TPH contaminated sites were, in decreasing order, polyduct km 39 + 150 > polyduct km 25 + 020 > Zoquital > Tepetitlan > Catalina > Venta Prieta > Ceiba. Most of the sampled points showed the presence of more than one of the 16 PAHs considered by USEPA as priority pollutants. Except point TEPE 2A, where no PAHs were detected, all the sampled points showed values from low to medium concentrations; however, values found at the sites did not exceed the limits according to the Mexican or the American legislation. The place with the largest contaminated area corresponded to the polyduct km 39 + 150, with 130 m² and 260 m³ to be treated. The least contaminated area was that around the JUAN 4 point at Juandho station, with 20 m² and 22 m³ of contaminated soil. The total area to be treated is about 230 m² and 497 m³.  相似文献   

Fertilization Changes Seagrass Community Structure but not Blue Carbon Storage: Results from a 30-Year Field Experiment     

Jason L. Howard  Alex Perez  Christian C. Lopes  James W. Fourqurean 《Estuaries and Coasts》2016,39(5):1422-1434

Seagrass ecosystems are attracting attention as potentially important tools for carbon (C) sequestration, comparable to those terrestrial and aquatic ecosystems already incorporated into climate change mitigation frameworks. Despite the relatively low C stocks in living biomass, the soil organic carbon pools beneath seagrass meadows can be substantial. We tested the relationship between soil C storage and seagrass community biomass, productivity, and species composition by revisiting meadows experimentally altered by 30 years of consistent nutrient fertilization provided by roosting birds. While the benthos beneath experimental perches has maintained dense, Halodule wrightii-dominated communities compared to the sparse Thalassia testudinum-dominated communities at control sites, there were no significant differences in soil organic carbon stocks in the top 15 cm. Although there were differences in δ¹³C of the dominant seagrass species at control and treatment sites, there was no difference in soil δ¹³C between treatments. Averages for soil organic carbon content (2.57?±?0.08 %) and δ¹³C (?12.0?±?0.3?‰) were comparable to global averages for seagrass ecosystems; however, our findings question the relevance of local-scale seagrass species composition or density to soil organic carbon pools in some environmental contexts.  相似文献   

Decomposition and analysis by atomic absorption photospectrometry of silicate rocks     

J. Saavedra  A.Garcia Sanchez  S.Rodriguez Perez 《Chemical Geology》1974,13(2):135-139

A rapid and simple method of analysis of silicate rocks using gold crucibles and fluoroboric acid as a solvent of the disintegrated material has been developed. The main elements are determined in a single treatment. The results obtained are comparable to the values recommended for samples of eleven standard rocks.  相似文献