Deep high spectral resolution spectroscopy and chemical composition of ionized nebulae     

C. Esteban  J. García‐Rojas  A. Mesa‐Delgado  L. Toribio San Cipriano 《Astronomische Nachrichten》2014,335(1):73-78

High spectral resolution spectroscopy has proved to be very useful for the advancement of chemical abundances studies in photoionized nebulae, such as H II regions and planetary nebulae (PNe). Classical analyses make use of the intensity of bright collisionally excited lines (CELs), which have a strong dependence on the electron temperature and density. By using high resolution spectrophotometric data, our group has led the determination of chemical abundances of some heavy element ions, mainly O⁺⁺, O⁺, and C⁺⁺ from faint recombination lines (RLs), allowing us to deblend them from other nearby emission lines or sky features. The importance of these lines is that their emissivity depends weakly on the temperature and density structure of the gas. The unresolved issue in this field is that recombination lines of heavy element ions give abundances that are about 2–3 times higher than those derived from CELs – in H II regions – for the same ion, and can even be a factor of 70 times higher in some PNe. This uncertainty puts into doubt the validity of face values of metallicity that we use as representative not only for ionized nebulae in the Local Universe, but also for star‐forming dwarf and spiral galaxies at different redshifts. Additionally, high‐resolution data can allow us to detect and deblend faint lines of neutron capture element ions in PNe. This information would introduce further restrictions to evolution models of AGBs and would help to quantify the chemical enrichment in s‐elements produced by low and intermediate mass stars. The availability of an échelle spectrograph at the E‐ELT will be of paramount interest to: (a) extend the studies of heavyelement recombination lines to low metallicity objects, (b) to extend abundance determinations of s‐elements to planetary nebulae in the extragalactic domain and to bright Galactic and extragalactic H II regions. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Continuous characterization of dynamic soil behavior by Digital Image Correlation in a transparent shear laminar box     

Segaline  Hugo  Sáez  Esteban  Ubilla  Javier 《Acta Geotechnica》2022,17(6):2395-2414

This work characterizes and analyzes the dynamic behavior of a sandy soil due to one-dimensional propagation of mechanical waves into a transparent laminar shear box. The outstanding char acteristic of this laminar box is a transparent front glass, which allows monitoring the soil behavior by a high-speed and high-resolution camera, and then computing the displacement field in the soil by the Digital Image Correlation (DIC) technique. The response of the laminar container was evaluated using ambient vibrations, harmonic signals and Ricker wavelets. Afterward, dynamic soil properties derived from DIC analysis are compared against theoretical and laboratory results. Finally, a numerical simulation is carried out using the finite element method, where the influence of the lateral friction of the glass on the motion is assessed and discussed. It is concluded that the transparent laminar shear box provides a useful tool for studying the continuous dynamic soil behavior; additionally, the transparent boundary has a minor impact on the results and a minimum observable cyclic shear strain of about 10–4 was reached.

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Comments on possible Miocene hominin footprints     

Jeff Meldrum  Esteban Sarmiento 《Proceedings of the Geologists' Association. Geologists' Association》2018,129(4):577-580

Gierlinski et al. (2017) report on what they interpret to be Miocene hominin footprints near the seaside village of Trachilos in western Crete. We review the case made by the authors that these ichnites represent bona-fide footprints, and their conclusion that they were made by bipedal hominins. Gierlinski et al.'s study demonstrates a number of problems with data presentation, e.g. a) substrates corresponding to measured prints are not clearly specified, b) no explanation is given for how prints were identified when the authors' own criteria for print identification were not met, c) no consistent morphological detail among prints is provided that could identify them as originating from the same or a similar agent, or one with bilateral symmetry, d) alternative agents that could have produced the prints are not explored, e) no explanation is given as to how their multivariate analyses of print outlines deals with missing data and why it uses non-homologous landmarks, etc. The evidence they present, therefore, is insufficient to support their arguments and conclusions. We remain unconvinced the ichnites are bona-fide footprints, let alone hominin footprints, but discuss some of the criteria employed for distinguishing and recognizing an early hominin footprint.  相似文献   

Detecting filaments in the ultra-high energy cosmic ray distribution     

Diego Harari  Silvia Mollerach  Esteban Roulet   《Astroparticle Physics》2006,25(6):412-418

We propose and test new statistical tools to study the distribution of cosmic rays based on the use of the minimal spanning tree. The method described is particularly sensitive to filamentary structures, as those expected to arise from strong sources of charged cosmic rays which get deflected by intervening magnetic fields. We also test the method with data available from the AGASA and SUGAR surface detector arrays.  相似文献   

Classification of Tsunami and Evacuation Areas   总被引：3，自引：2，他引：1  

Tomoya Shibayama  Miguel Esteban  Ioan Nistor  Hiroshi Takagi  Nguyen Danh Thao  Ryo Matsumaru  Takahito Mikami  Rafael Aranguiz  Ravindra Jayaratne  Koichiro Ohira 《Natural Hazards》2013,67(2):365-386

On March 11, 2011, a large earthquake that occurred offshore the north-east coast of Japan generated a large tsunami which devastated extensive areas of the Tohoku coastline. Despite Japan being considered a country well prepared for these types of disasters, large casualties were recorded, with numerous discussions amongst the Japanese coastal engineering community ensuing. As a result, two different levels of tsunamis have been proposed and now recognized in Japan, depending on the frequency of such extreme events. The idea that hard measures can protect the lives of inhabitants of coastal areas has been abandoned, and these measures are only considered to be effective in protecting properties against the more frequent but lower magnitude events. Soft measures should always be used to protect against the loss of lives, and to this respect, the authors of the paper propose the introduction of a Classification of Evacuation Areas, to show which of these should be prioritized by residents as they seek to evacuate.  相似文献   

Environmental changes affecting light climate in oligotrophic mountain lakes: the deep chlorophyll maxima as a sensitive variable     

Beatriz Modenutti  Esteban Balseiro  Marcela Bastidas Navarro  Cecilia Laspoumaderes  María Sol Souza  Florencia Cuassolo 《Aquatic Sciences - Research Across Boundaries》2013,75(3):361-371

The North-Patagonian Andean lakes of Argentina are high light, low nutrient environments that exhibit development of deep chlorophyll maxima (DCM) at the metalimnetic layer during summer stratification, at approximately 1 % of surface PAR irradiance. We examined whether the position of DCM changes as a consequence of long-time (global warming: glacial clay input) and short-time (eruption: volcanic ashes) events. We performed different field studies: (1) an interlacustrine analysis of six lakes from different basins, including data of the 2011 volcanic eruption, which caused an unexpected variation in water transparency; and (2) an intralacustrine analysis in which we compared different stations along a transparency gradient in Lake Mascardi caused by glacial clay input at one end of the gradient. In these analyses, we documented changes in DCM depth and its relationship with different parameters. DCM development was not related with thermocline depth or nutrient distribution. In all cases, the only significant variables were Kd 320 nm and Kd PAR. Our study showed that suspended particles (glacial clay and volcanic ashes) can play a crucial role in transparent lakes, affecting lake features such as the phototrophic biomass distribution along the water column. Suspended solid inputs from either glacial clay or volcanic ashes produce a comparable effect, provoking a decrease in light and, consequently, an upper location of the DCM. Thus, the DCM position is highly sensitive to global changes, such as increased temperatures causing glacier recession or to regional changes caused by volcanic eruptions.  相似文献   

Evidence for high velocity gas in giantHii regions     

J. M. Vilchez  C. Esteban  H. Castañeda  M. G. Edmunds 《Astrophysics and Space Science》1989,156(1-2):237-242

Spectroscopy of selected areas of the two GiantHii Regions (GHR) NGC 5471 and NGC 604 shows convincing evidence for the existence of ionised gas at high velocities (1000 km s^–1) from the analysis of the profile of the Balmer (in NGC 604) and the [Oiii] (in NGC 5471) lines. The association of these effects with the presence of WR clusters and possible SNR inside the complex are analysed and the results are compared with previous indications in the literature for 30 Dor (in front of R 136) as well as with recent evidence from high-dispersion spectroscopy for some GHRs in M101.  相似文献   

Chemical composition of the Orion nebula derived from echelle spectrophotometry     

C.Esteban  M.Peimbert  S.Torres-Peimbert  V.Escalante 《Monthly notices of the Royal Astronomical Society》1998,295(2):401-422

We present echelle spectroscopy in the 3500- to 7060-... range for two positions of the Orion nebula. The data were obtained using the 2.1-m telescope at Observatorio Astronómico Nacional in San Pedro Mártir, Baja California. We have measured the intensities of about 220 emission lines, in particular 81 permitted lines of C⁺, N⁺, N⁺⁺, O⁰, O⁺, Ne⁰, Si⁺, Si⁺⁺ and S⁺, some of them produced by recombination only and others mainly by fluorescence. We have determined electron temperatures, electron densities and ionic abundances using different continuum and line intensity ratios. We derived the He, C and O abundances from recombination lines and find that the C/H and O/H values are very similar to those derived from B stars of the Orion association, and that these nebular values are independent of the temperature structure. We have also derived abundances from collisionally excited lines. These abundances depend on the temperature structure; accurate t ² values have been derived comparing the O II recombination lines with the [O III ] collisionally excited lines. The gaseous abundances of Mg, Si and Fe show significant depletions, implying that a substantial fraction of these atoms is tied up in dust grains. The derived depletions are similar to those found in warm clouds of the Galactic disc, but are not as large as those found in cold clouds. A comparison of the solar and Orion chemical abundances is made.  相似文献   

Future typhoon and storm surges under different global warming scenarios: case study of typhoon Haiyan (2013)     

Ryota Nakamura  Tomoya Shibayama  Miguel Esteban  Takumu Iwamoto 《Natural Hazards》2016,82(3):1645-1681

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Impact of diagenesis on reservoir quality in a sedimentary geothermal play: a case study in the Cooper Basin,South Australia          下载免费PDF全文

Antoine Dillinger  Ludovic P. Ricard  Cameron Huddlestone‐Holmes  Lionel Esteban 《Basin Research》2016,28(2):252-272

Geothermal resources hosted within sedimentary basins with high natural permeability have been targeted for the production of energy in Australia. The Hutton Sandstone (Cooper‐Eromanga Basin) – a prolific oil and gas producer known to have good reservoir quality and high reservoir volume – was recently tested for its geothermal potential in the Cooper Region. However, recent exploratory drilling did not produce the anticipated flow rates, raising the question of the impact of diagenesis on the reservoir quality of this sedimentary formation. The combined characterization of the petrology, diagenesis and petrophysical properties of the Hutton Sandstone at Celsius‐1 and other surrounding wells indicates variable reservoir properties in the Cooper Region. This integrated study demonstrates that low formation permeability occurs at geothermal target depth and explains the negligible flow rates obtained at Celsius‐1. These low permeabilities are the results of the preservation of widespread detrital clayey matrix and the extensive occurrence of authigenic kaolinite, illite and silica cements at the top and base of the Hutton Sandstone. This aspect is confirmed by NMR T₂ transversal relaxation time becoming shorter at similar depths. Petrography analysis also reveals that sandstones are affected by diagenetic processes of the eogenetic and mesogenetic phases. However, the Hutton Sandstone at Celsius‐1 is presently at pressure‐temperature conditions that are below the mesogenetic conditions, which suggests a late episode of uplift and cooling from maximum palaeotemperatures.  相似文献