High-resolution mm interferometry and the search for massive protostellar disks: the case of Cep-A HW2     

Claudia Comito  Peter Schilke  Ulrike Endesfelder  Izaskun Jiménez-Serra  Jesus Martín-Pintado 《Astrophysics and Space Science》2008,313(1-3):59-63

The direct detection of accretion onto massive protostars through rotating disks constitutes an important tile in the massive-star-formation-theory mosaic. This task is however observationally very challenging. A very interesting example is Cepheus A HW2. The properties of the molecular emission around this YSO seems to suggest the presence of a massive rotating disk (cf. Patel et al. in Nature 437:109, 2005). We have carried out sub-arcsec-resolution PdBI observations of high-density and shock tracers such as SO₂, SiO, CH₃CN, and CH₃OH towards the center of the outflow. A detailed analysis of the spatial distribution and of the velocity field traced by all observed species leads us to conclude that, on a ∼700 AU scale, the Cep-A “disk” is actually the result of the superposition of multiple hot-core-type objects, at least one of them ejecting an outflow at a small angle with respect to the line of sight. Together with the well-known large-scale outflow ejected by HW2, this setup makes for a very complex spatial and kinematic picture. Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).  相似文献   

The 2D Steady Hydraulic Head Field Surrounding a Pumping Well in a Finite Heterogeneous Confined Aquifer     

Carl L. Axness  Jesus Carrera 《Mathematical Geology》1999,31(7):873-906

We present a second-order analytic solution [in terms of a heterogeneous log-transmissivity Y(r) = ln T(r)] for the hydraulic head field in a finite 2D confined heterogeneous aquifer under steady radial flow conditions assuming fixed head boundary conditions at the well and at a circular exterior boundary. The solution may be used to obtain the gradient used in calculation of solute transport to a well in a heterogeneous transmissivity field. The solution, obtained using perturbation methods coupled with Green's function techniques, leads us to postulate a more general form of the head for arbitrarily large-variance fields and may be used to obtain moment relations between the log-transmissivity and head under convergent flow conditions when Y(r) is expressed as a random space function. We present expressions for the mean head field when the log-transmissivity is Gaussian and conditioned on the transmissivity value at the well for an arbitrary ln T covariance. Finally, we look at the effect of parameter variations on the mean head behavior and present numerical simulations verifying the second-order mean head expressions.  相似文献   

Multiple Iron-Rich Spinel Phases and Hematite in a Magnetic Soil Developing on Tuffite     

A. T. Goulart  M. F. Jesus Filho  J. D. Fabris  J. M. D. Coey 《Physics and Chemistry of Minerals》1997,25(1):63-69

A dusky red Latosol developing on tuffite was examined in detail in order to characterize its iron oxide mineralogy. Magnetic separation and selective chemical treatment were employed. The mineralogical analyses were carried out by powder X-ray diffraction and Mössbauer spectroscopy, with the electron microprobe technique being used to assess the chemical composition of selected grains. Results reveal that iron-rich spinel-structure phases from this pedosystem are rather variable in chemical composition and lattice parameters, and can be grouped in at least three major populations: the first group consisting of the iron-richest phase, with very low Ti and Cr and virtually no Mg content and high Al; the second group presenting Ti>Mg>>Al>Mn contents but no Cr and the third group related to the Mg-richest phase with Mg>Ti>>Al>Mn. Two major populations of hematite were also identified: one with ～15 mol% Al and other practically Al-free. The first group is thought to be a product of neoformation in an Al-rich pedogenic medium whereas the second is likely to be transformed directly from maghemite. Though chemical treatment along with physical techniques provide a powerful way to characterize iron oxides of tropical soils, some methodological difficulties still remain, particularly those concerned with (i) the characterization and quantification of maghemite in presence of relatively large amount of hematite in the soil mixture, particularly by Mössbauer spectroscopy, and (ii) the allocation of the isomorphous substituents for iron in the cation sites of the spinel structure. Possible mechanisms of alteration of iron-rich phases in this pedosystem are discussed.  相似文献   

Air–sea carbon dioxide fluxes in the coastal southeastern tropical Pacific     

Gernot E. Friederich  Jesus Ledesma  Osvaldo Ulloa  Francisco P. Chavez 《Progress in Oceanography》2008,79(2-4):156

Comprehensive sea surface surveys of the partial pressure of carbon dioxide (pCO₂) have been made in the upwelling system of the coastal (0–200 km from shore) southeastern tropical Pacific since 2004. The shipboard data have been supplemented by mooring and drifter based observations. Air–sea flux estimates were made by combining satellite derived wind fields with the direct sea surface pCO₂ measurements. While there was considerable spatial heterogeneity, there was a significant flux of CO₂ from the ocean to the atmosphere during all survey periods in the region between 4° and 20° south latitude. During periods of strong upwelling the average flux out of the ocean exceeded 10 moles of CO₂ per square meter per year. During periods of weaker upwelling and high productivity the CO₂ evasion rate was near 2.5 mol/m²/yr. The average annual fluxes exceed 5 mol/m²/yr. These findings are in sharp contrast to results obtained in mid-latitude upwelling systems along the west coast of North America where the average air–sea CO₂ flux is low and can often be from the atmosphere into the ocean. In the Peruvian upwelling system there are several likely factors that contribute to sea surface pCO₂ levels that are well above those of the atmosphere in spite of elevated primary productivity: (1) the upwelling source waters contain little pre-formed nitrate and are affected by denitrification, (2) iron limitation of primary production enhanced by offshore upwelling driven by the curl of the wind stress and (3) rapid sea surface warming. The combined carbon, nutrient and oxygen dynamics of this region make it a candidate site for studies of global change.  相似文献   

Asymptotic solution for the two-body problem with constant tangential thrust acceleration   总被引：1，自引：0，他引：1  

Claudio Bombardelli  Giulio Baù  Jesus Peláez 《Celestial Mechanics and Dynamical Astronomy》2011,110(3):239-256

An analytical solution of the two body problem perturbed by a constant tangential acceleration is derived with the aid of perturbation theory. The solution, which is valid for circular and elliptic orbits with generic eccentricity, describes the instantaneous time variation of all orbital elements. A comparison with high-accuracy numerical results shows that the analytical method can be effectively applied to multiple-revolution low-thrust orbit transfer around planets and in interplanetary space with negligible error.  相似文献   

Evaluation and analysis of surface deformation in west Chapala basin,central Mexico     

Martin Hernandez-Marin  Jesus Pacheco-Martinez  Alejandro Ramirez-Cortes  Thomas J. Burbey  Jose A. Ortiz-Lozano  Mario E. Zermeño-de-Leon  Jacobo Guinzberg-Velmont  German Pinto-Aceves 《Environmental Earth Sciences》2014,72(5):1491-1501

Vertical deformation was measured at 14 benchmarks within the urban area of Jocotepec Mexico using first-order leveling methods and then spatially analyzed in relation to land subsidence and soil discontinuity patterns. The study area is located within the western portion of the Chapala basin, middle-west Mexico. Observations of vertical surficial deformation were made at each benchmark (September and November 2012) relative to a fixed station and compared to an initial survey of each benchmark (April 2012). Results indicate that a maximum subsidence of 7.16 cm over the 8-month measurement interval occurs near downtown coincident with the largest levels of drawdown and translates to a maximum subsidence rate of 0.89 cm/month for the sampling period. Two benchmarks located northwest and southeast of the urban area exhibited uplift of 2.8 and 0.76 cm, respectively, suggesting a complex mechanical response between the sedimentary soil units and the factors causing deformation. A potential spatial relationship exists between subsidence patterns and soil discontinuities. Four separate cones of groundwater depression were observed with two being coincident with subsidence bowls downtown and south of the urban area; however, there is no clear relationship between drawdown and subsidence in the remaining areas. Hydrogeologic reconstructions reveal alternating sequences of alluvial aquifers and highly deformable lacustrine aquitards. An analysis of the soil discontinuities reveals that they are directly aligned with the patterns of vertical deformation.  相似文献   

Stream-stage response tests and their joint interpretation with pumping tests   总被引：1，自引：0，他引：1  

Rötting TS  Carrera J  Bolzicco J  Salvany JM 《Ground water》2006,44(3):371-385

Hydraulic head response to stream-stage variations can be used to explore the hydraulic properties of stream-aquifer systems at a relatively large scale. These stream-stage response tests, also called flooding tests, are typically interpreted using one- or two-dimensional models that assume flow perpendicular to the river. Therefore, they cannot be applied to systems that are both horizontally and vertically heterogeneous. In this work, we use the geostatistical inverse problem to jointly interpret data from stream-stage response and pumping tests. The latter tests provide flow data (which are needed to resolve aquifer diffusivity into transmissivity and storage coefficient) and may supply supplementary small-scale information. Here, we summarize the methodology for the design, execution, and joint numerical interpretation of these tests. Application to the Aznalcóllar case study allows us to demonstrate that the proposed methodology may help in responding to questions such as the continuity of aquitards, the role and continuity of highly permeable paleochannels, or the time evolution of stream-aquifer interaction. These results expand the applicability and scope of stream-stage response tests.  相似文献   

Blind Estimation of the Ocean Acoustic Channel by Time–Frequency Processing     

Nelson E. Martins Srgio M. Jesus 《Oceanic Engineering, IEEE Journal of》2006,31(3):646-656

A blind estimator of the ocean acoustic channel impulse response envelope is presented. The signal model is characterized by a deterministic multipath channel excited by a highly nonstationary deterministic source signal. The time-frequency (TF) representation of the received signal allows for the separation between the channel and the source signal. The proposed estimator proceeds in two steps: First, the unstable initial arrivals allow for the estimation of the source signal instantaneous frequency (IF) by maximization of the radially Gaussian kernel distribution; then, the Wigner-Ville distribution (WV) is sequentially windowed and integrated, where the window is defined by the previously estimated IF. The integral gives the channel impulse response envelope, which turns to be an approximation to the blind conventional matched filter (MF). The blind channel estimator (CE) is applicable upon the following conditions: that the multipath channel contains at least one dominant arrival well separated from the others, and that the IF of the source signal is a one-to-one function. Results obtained on real data from the INternal TIde Measurements with Acoustic Tomography Experiments (INTIMATE'96), where the acoustic channel was driven by an linear frequency modulation signal, show that the channel's envelope detailed structure could be accurately and consistently recovered, with the correlation of the estimates ranging from 0.796 to 0.973, as compared to the MF result  相似文献   

Efficient execution of the WRF model and other HPC applications in the cloud     

Hector A. Duran-Limon  Jesus Flores-Contreras  Nikos Parlavantzas  Ming Zhao  Angel Meulenert-Peña 《Earth Science Informatics》2016,9(3):365-382

There are many scientific applications that have high performance computing (HPC) demands. Such demands are traditionally supported by cluster- or Grid-based systems. Cloud computing, which has experienced a tremendous growth, emerged as an approach to provide on-demand access to computing resources. The cloud computing paradigm offers a number of advantages over other distributed platforms. For example, the access to resources is flexible and cost-effective since it is not necessary to invest a large amount of money on a computing infrastructure nor pay salaries for maintenance functions. Therefore, the possibility of using cloud computing for running high performance computing applications is attractive. However, it has been shown elsewhere that current cloud computing platforms are not suitable for running some of these kinds of applications since the performance offered is very poor. The reason is mainly the overhead from virtualisation which is extensively used by most cloud computing platforms as a means to optimise resource usage. Furthermore, running HPC applications in current cloud platforms is a complex task that in many cases requires configuring a cluster of virtual machines (VMs). In this paper, we present a lightweight virtualisation approach for efficiently running the Weather Research and Forecasting (WRF) model (a computing- and communication-intensive application) in a cloud computing environment. Our approach also provides a higher-level programming model that automates the process of configuring a cluster of VMs. We assume such a cloud environment can be shared with other types of HPC applications such as mpiBLAST (an embarrassingly parallel application), and MiniFE (a memory-intensive application). Our experimental results show that lightweight virtualisation imposes about 5 % overhead and it substantially outperforms traditional heavyweight virtualisation such as KVM.  相似文献   

Determination of oxadiazon residues in the field treated soil with and without organic matter incorporated     

Kassio Ferreira Mendes  Marcelo Rodrigues dos Reis  Ana Beatriz Rocha de Jesus Passos  Miriam Hiroko Inoue  Antônio Alberto Silva  Daniel Valadão Silva 《Environmental Earth Sciences》2016,75(3):222

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