Effect of aeration on steady-state conditions in non- and partially aerated low-loaded biofilter     

A. Albuquerque  A. González-Martínez  F. Osorio 《International Journal of Environmental Science and Technology》2012,9(3):395-408

Excessive growth of biomass and retention of solids associated with air bubbles lead to bed clogging, which affects the biofilters?? performance. Two experiments were carried out in a submerged biofilter at the flow velocity of 0.5?m?h^?1, for an organic loading rate of 51?g C m^?3?h^?1 and a nitrogen loading rate of 13?g NH₄-N?m^?3?h^?1, one with the biofilter not aerated, the other with the biofilter partially aerated. The results showed that the higher head losses occurred in the upper section of the biofilter, where there was a greater biomass development and a higher removal of organic carbon, ammonia and solids, with the maximum allowed head loss being reached in 16 and 8?days. In any case, the steady-state conditions were achieved after 2?days and were interrupted on the tenth day of experiment E1 and on the fifth day of experiment E2. This allowed defining different operating cycles that enabled an average organic removal rate of 12.7?g C m^?3?h^?1 (27?%) and an average ammonia removal rate of 1.1?g NH4-N?m^?3?h^?1 (9?%) without aeration, and of 35.8?g C m^?3?h^?1 (76?%) and 6.3?g NH4-N?m^?3?h^?1 (51?%) with aeration. Regardless of the aeration conditions, more than 90?% of TOC and NH4-N removal occurred in the upper section. After the backwashing cycle, the biofilter returned to steady-state conditions in 6?h (without aeration) and 7?h (with aeration).  相似文献   

Seismic response of a bridge–soil–foundation system under the combined effect of vertical and horizontal ground motions     

Zhenghua Wang  Leonardo Dueñas‐Osorio  Jamie E. Padgett 《地震工程与结构动力学》2013,42(4):545-564

Different levels of model sophistication have recently emerged to support seismic risk assessment of bridges, but mostly at the expense of neglecting the influence of vertical ground motions (VGMs). In this paper, the influence of VGMs on bridge seismic response is presented and the results are compared with the case of horizontal‐only excitations. An advanced finite element model that accounts for VGMs is first developed. Then, to investigate the effect of soil–structure interaction (SSI) including liquefaction potential, the same bridge with soil‐foundation and fixed boundary conditions is also analyzed. Results show that the inclusion of the VGMs has a significant influence on the seismic response, especially for the axial force in columns, normal force of bearings, and the vertical deck bending moments. However, VGMs do not have as much influence on the seismic demand of the pile cap displacements or pile maximum axial forces. Also, the significant fluctuation of the column axial force can reduce its shear and flexural capacity, and a heightened reversal of flexural effects may induce damage in the deck. In addition, relative to the fixed base case, SSI effects tend to reduce response quantities for certain ground motions while increasing demands for others. This phenomenon is explained as a function of the frequency content of the ground motions, the shift in natural vertical periods, and the VGM spectral accelerations at higher modes. Moreover, the mechanisms of liquefaction are isolated relative to SSI effects in nonliquefiable soils, revealing the influence of liquefaction on bridge response under VGMs. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Co-clustering geo-referenced time series: exploring spatio-temporal patterns in Dutch temperature data     

Xiaojing Wu  Raul Zurita-Milla  Menno-Jan Kraak 《International journal of geographical information science》2013,27(4):624-642

Clustering allows considering groups of similar data elements at a higher level of abstraction. This facilitates the extraction of patterns and useful information from large amounts of spatio-temporal data. Till now, most studies have focused on the extraction of patterns from a spatial or a temporal aspect. Here we use the Bregman block average co-clustering algorithm with I-divergence (BBAC_I) to enable the simultaneous analysis of spatial and temporal patterns in geo-referenced time series (time evolving values of a property observed at fixed geographical locations). In addition, we present three geovisualization techniques to fully explore the co-clustering results: heatmaps offer a straightforward overview of the results; small multiples display the spatial and temporal patterns in geographic maps; ringmaps illustrate the temporal patterns associated to cyclic timestamps. To illustrate this study, we used Dutch daily average temperature data collected at 28 weather stations from 1992 to 2011. The co-clustering algorithm was applied hierarchically to understand the spatio-temporal patterns found in the data at the yearly, monthly and daily resolutions. Results pointed out that there is a transition in temperature patterns from northeast to southwest and from ‘cold’ to ‘hot’ years/months/days with only 3 years belonging to ‘cool’ or ‘cold’ years. Because of its characteristics, this newly introduced algorithm can concurrently analyse spatial and temporal patterns by identifying location-timestamp co-clusters that contain values that are similar along both the spatial and the temporal dimensions.  相似文献   

A high resolution stratigraphic framework for the remarkable fossil cetacean assemblage of the Miocene/Pliocene Pisco Formation,Peru     

Leonard Brand  Mario Urbina  Arthur Chadwick  Thomas J. DeVries  Raul Esperante 《Journal of South American Earth Sciences》2011,31(4):414-425

The Miocene/Pliocene Pisco Formation of Peru contains a rich marine vertebrate fossil record, providing a unique opportunity for the study of paleoecology and evolution, along with the sedimentological context of the fossils. The lack of a high-resolution stratigraphic framework has hampered such study. In this paper we develop the needed stratigraphy for the areas in the Pisco Formation where most of the vertebrate paleontological research is occurring. In the Ica Valley and in the vicinity of Lomas, series of lithologically or paleontologically unique marker beds were identified. These were walked out and documented with GPS technology. Measured sections connecting these marker beds provide a stratigraphic framework for the areas studied. GPS locations, maps of the marker beds on aerial photographs, and outcrop photographs allow field determination of the stratigraphic positions of study areas.  相似文献   

Luminosity–metallicity relation for stars on the lower main sequence     

Eira Kotoneva    Chris Flynn  Raul Jimenez 《Monthly notices of the Royal Astronomical Society》2002,335(4):1147-1157

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Hot Subdwarfs: Magnetic, Oscillatory and Other Physical Properties     

R. Oreiro  F. Pérez Hernández  M. Manteiga  A. Ulla  J.M. González Pérez  M.R. Zapatero Osorio  R. GarcÍa López  J. MacDonald  P. Thejll  A. Ferriz-Mas  R.A. Saffer  V. Elkin 《Astrophysics and Space Science》2003,284(1):269-272

Hot subdwarf stars (hot sds) are blue subluminous objects. Only a few determinations areavailable to date regarding the study of such aspects as rotation,microturbulent velocities or the magnetic nature of these objects. Over26 sdBs are known to date to be multiperiodic rapid oscillators. Thisproject presents preliminary results of new observations and models of asample of pulsating and non-pulsating hot sds, includingconsiderations on mass loss and eventual magnetic properties.  相似文献   

The Substellar Population in the Young σ Orionis Cluster, Spatial Distribution     

V.J.S. Béjar  J.A. Caballero  R. Rebolo  M.R. Zapatero Osorio  D. Barrado Y Navascués 《Astrophysics and Space Science》2004,292(1-4):339-346

We review different surveys, in the optical and infrared, conducted in the very young (age 1–8 Myr), nearby (d ～ 350 pc) σ Orionis cluster aimed to characterize the substellar population. We describe spectral characteristics of very low mass stars, brown dwarfs and planetary mass objects in the cluster with spectral types from K7 to T6. We study the spatial distribution of the substellar population detected in a IZJ survey covering an area of 1.12 deg.² We find that the radial distribution of substellar objects can be well fitted by an exponential law (ρ = ρ_o e ^?r/ro ), with a central density (ρ _o ) of 0.26 ± 0.03 objects/arcmin² and a characteristic radius (r _o) of 8.8 arcmin ± 0.6 (equivalent to 0.90 ± 0.06 pc at the distance of the cluster). We discuss the presence of possible inhomogeneities in this distribution due to the existence of subclustering. We also compare the spatial distribution of the substellar population with previously known stars in the cluster. We report the initial mass spectrum in the substellar domain.  相似文献   

Dark halo properties from rotation curves     

Raul Jimenez  Licia Verde  S. Peng Oh 《Monthly notices of the Royal Astronomical Society》2003,339(1):243-259

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The circumstellar disc around the Herbig AeBe star HD169142     

W. R. F. Dent  J. M. Torrelles †  M. Osorio  N. Calvet  G. Anglada 《Monthly notices of the Royal Astronomical Society》2006,365(4):1283-1287

We present 7 mm and 3.5 cm wavelength continuum observations towards the Herbig AeBe star HD169142 performed with the Very Large Array (VLA) with an angular resolution of ≃1 arcsec. We find that this object exhibits strong (≃4.4 mJy), unresolved (≲1 arcsec) 7 mm continuum emission, being one of the brightest isolated Herbig AeBe stars ever detected with the VLA at this wavelength. No emission is detected at 3.5 cm continuum, with a 3σ upper limit of ≃0.08 mJy. From these values, we obtain a spectral index α≳ 2.5 in the 3.5 cm to 7 mm wavelength range, indicating that the observed flux density at 7 mm is most likely dominated by thermal dust emission coming from a circumstellar disc. We use available photometric data from the literature to model the spectral energy distribution (SED) of this object from radio to near-ultraviolet frequencies. The observed SED can be understood in terms of an irradiated accretion disc with low mass accretion rate,     , surrounding a star with an age of ≃10 Myr. We infer that the mass of the disc is ≃0.04 M_⊙, and is populated by dust grains that have grown to a maximum size of 1 mm everywhere, consistent with the lack of silicate 10 μm emission. These features, as well as indications of settling in the wall at the dust destruction radius, led us to speculate that the disc of HD169142 is in an advanced stage of dust evolution, particularly in its inner regions.  相似文献   

Eight Gyr Minimum Disk Age from Hipparcos     

Chris Flynn  Raul Jimenez  Eira Kotoneva 《Astrophysics and Space Science》1999,265(1-4):243-244

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