Redshift-space limits of bound structures     

Rolando Dünner  reas Reisenegger  rés Meza †  Pablo A. Araya  Hernán Quintana 《Monthly notices of the Royal Astronomical Society》2007,376(4):1577-1587

An exponentially expanding Universe, possibly governed by a cosmological constant, forces gravitationally bound structures to become more and more isolated, eventually becoming causally disconnected from each other and forming so-called 'island universes'. This new scenario reformulates the question about which will be the largest structures that will remain gravitationally bound, together with requiring a systematic tool that can be used to recognize the limits and mass of these structures from observational data, namely redshift surveys of galaxies. Here we present a method, based on the spherical collapse model and N -body simulations, by which we can estimate the limits of bound structures as observed in redshift space. The method is based on a theoretical criterion presented in a previous paper that determines the mean density contrast that a spherical shell must have in order to be marginally bound to the massive structure within it. Understanding the kinematics of the system, we translated the real-space limiting conditions of this 'critical' shell to redshift space, producing a projected velocity envelope that only depends on the density profile of the structure. From it we created a redshift-space version of the density contrast that we called 'density estimator', which can be calibrated from N -body simulations for a reasonable projected velocity envelope template, and used to estimate the limits and mass of a structure only from its redshift-space coordinates.  相似文献   

The limits of bound structures in the accelerating Universe     

Rolando Dünner  Pablo A. Araya  rés Meza †  Andreas Reisenegger 《Monthly notices of the Royal Astronomical Society》2006,366(3):803-811

According to the latest evidence, the Universe is entering an era of exponential expansion, where gravitationally bound structures will get disconnected from each other, forming isolated 'island universes'. In this scenario, we present a theoretical criterion to determine the boundaries of gravitationally bound structures and a physically motivated definition of superclusters as the largest bound structures in the Universe. We use the spherical collapse model self-consistently to obtain an analytical condition for the mean density enclosed by the last bound shell of the structure (2.36 times the critical density in the present Universe, assumed to be flat, with 30 per cent matter and 70 per cent cosmological constant, in agreement with the previous, numerical result of Chiueh & He). N -body simulations extended to the future show that this criterion, applied at the present cosmological epoch, defines a sphere that encloses ≈99.7 per cent of the particles that will remain bound to the structure at least until the scale parameter of the Universe is 100 times its present value. On the other hand, (28 ± 13) per cent of the enclosed particles are in fact not bound, so the enclosed mass overestimates the bound mass, in contrast with the previous, less rigorous criterion of, e.g. Busha and collaborators, which gave a more precise mass estimate. We also verify that the spherical collapse model estimate for the radial infall velocity of a shell enclosing a given mean density gives an accurate prediction for the velocity profile of infalling particles, down to very near the centre of the virialized core.  相似文献   

Structural Setting of Northern Tunisia Insights from Gravity Data Analysis Jendouba Case Study     

Imen Hamdi Nasr  Adnen Amiri  Mohamed Hédi Inoubli  Abdelhmid Ben Salem  AbdelHak Chaqui  Said Tlig 《Pure and Applied Geophysics》2011,168(10):1835-1849

Detailed gravity data in conjunction with available surface geology are analyzed to infer the organization of the underlying structures in Jendouba area. Gravity data analysis benefits from the gravity Bouguer anomaly, upward continuations, residual distribution, derivatives and Euler deconvolved maps. The main results display a positive amplitude gravity anomaly as the response of Triassic evaporitic bodies and important NE trending features at the boundaries between the Triassic outcrops and their enveloping strata. Integration of gravity, geological and structural maps let to the identification of major structural directions and trends of the study area. It confirms some structural elements gathered from outcrops. It defines also new ones.  相似文献   

Advantages of using the kriging interpolator to estimate the gravity surface, comparison and spatial variability of gravity data in the El Kef-Ouargha region (northern Tunisia)     

Mohamed Arfaoui  Mohamed Hédi Inoubli 《Arabian Journal of Geosciences》2013,6(8):3139-3147

A comparative study on two interpolator methods for Bouguer anomaly mapping was performed in the El Kef-Ouargha region, Tunisia. In particular, we compare the results of minimum curvature gridding and kriging. We undertake a geostatistical study using both anisotropic and isotropic analysis for studding the spatial variability and kriging the random variable: “Bouguer anomaly”. The model parameters of each method are calculated to compare the results. The anisotropic analysis most closely approximates the measured data. Consequentially, the Bouguer anomaly and vertical gradient maps using anisotropic kriging have the best correlation with the geological map, best represent density distributions at depth and most closely approximate the measured anomaly amplitudes.  相似文献   

The potential for photosynthesis in hydrothermal vents: a new avenue for life in the Universe?     

Noel Perez  Rolando Cardenas  Osmel Martin  Leiva-Mora Michel 《Astrophysics and Space Science》2013,346(2):327-331

We perform a quantitative assessment for the potential for photosynthesis in hydrothermal vents in the deep ocean. The photosynthetically active radiation in this case is from geothermal origin: the infrared thermal radiation emitted by hot water, at temperatures ranging from 473 up to 673 K. We find that at these temperatures the photosynthetic potential is rather low in these ecosystems for most known species. However, species which a very high efficiency in the use of light and which could use infrared photons till 1300 nm, could achieve good rates of photosynthesis in hydrothermal vents. These organisms might also thrive in deep hydrothermal vents in other planetary bodies, such as one of the more astrobiologically promising Jupiter satellites: Europa.  相似文献   

GEONTO-MET: an approach to conceptualizing the geographic domain     

Miguel Torres  Rolando Quintero  Marco Moreno-Ibarra  Rolando Menchaca-Mendez  Giovanni Guzman 《International journal of geographical information science》2013,27(10):1633-1657

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Moisture transport and seasonal variations in the stable isotopic composition of rainfall in Central American and Andean Páramo during El Niño conditions (2015–2016)     

Germain Esquivel‐Hernndez  Giovanny M. Mosquera  Ricardo Snchez‐Murillo  Adolfo Quesada‐Romn  Christian Birkel  Patricio Crespo  Rolando Clleri  David Windhorst  Lutz Breuer  Jan Boll 《水文研究》2019,33(13):1802-1817

High‐elevation tropical grassland systems, called Páramo, provide essential ecosystem services such as water storage and supply for surrounding and lowland areas. Páramo systems are threatened by climate and land use changes. Rainfall generation processes and moisture transport pathways influencing precipitation in the Páramo are poorly understood but needed to estimate the impact of these changes, particularly during El Niño conditions, which largely affect hydrometeorological conditions in tropical regions. To fill this knowledge gap, we present a stable isotope analysis of rainfall samples collected on a daily to weekly basis between January 2015 and May 2016 during the strongest El Niño event recorded in history (2014–2016) in two Páramo regions of Central America (Chirripó, Costa Rica) and the northern Andes (Cajas, south Ecuador). Isotopic compositions were used to identify how rainfall generation processes (convective and orographic) change seasonally at each study site. Hybrid Single Particle Lagrangian Integrated Trajectory model (HYSPLIT) air mass back trajectory analysis was used to identify preferential moisture transport pathways to each Páramo site. Our results show the strong influence of north‐east trade winds to transport moisture from the Caribbean Sea to Chirripó and the South American low‐level jet to transport moisture from the Amazon forest to Cajas. These moisture contributions were also related to the formation of convective rainfall associated with the passage of the Intertropical Convergence Zone over Costa Rica and Ecuador during the wetter seasons and to orographic precipitation during the transition and drier seasons. Our findings provide essential baseline information for further research applications of water stable isotopes as tracers of rainfall generation processes and transport in the Páramo and other montane ecosystems in the tropics.  相似文献   

Predictive potential of Perzyna viscoplastic modelling for granular geomaterials     

Maria Lazari  Lorenzo Sanavia  Claudio di Prisco  Federico Pisanò 《国际地质力学数值与分析法杂志》2019,43(2):544-567

This paper reappraises Perzyna-type viscoplasticity for the constitutive modelling of granular geomaterials, with emphasis on the simulation of rate/time effects of different magnitude. An existing elasto-plastic model for sands is first recast into a Perzyna viscoplastic formulation and then calibrated/validated against laboratory test results on Hostun sand from the literature. Notable model features include (1) enhanced definition of the viscous nucleus function and (2) void ratio dependence of stiffness and viscous parameters, to model the pycnotropic behaviour of granular materials with a single set of parameters, uniquely identified against standard creep and triaxial test results. The comparison between experimental data and numerical simulations points out the predicative capability of the developed model and the complexity of defining a unique viscous nucleus function to capture sand behaviour under different loading/initial/boundary and drainage conditions. It is concluded that the unified viscoplastic simulation of both drained and undrained response is particularly challenging within Perzyna's framework and opens to future research in the area. The discussion presented is relevant, for instance, to the simulation of multiphase strain localisation phenomena, such as those associated to slope stability problems in variably saturated soils.  相似文献   

Three dimensional steady-state locus for dry monodisperse granular materials: DEM numerical results and theoretical modelling     

Irene Redaelli  Claudio di Prisco 《国际地质力学数值与分析法杂志》2019,43(16):2525-2550

In this paper, steady-state conditions for ideal monodisperse dry granular materials are both theoretically and numerically analysed. A series of discrete element (DEM) numerical simulations have been performed on a periodic cell by imposing stress paths characterized by different Lode angles, pressures, and deviatoric strain rates. The dependence of the material response on both inertial number and loading path has been discussed in terms of void ratio, fabric, and granular temperature. DEM numerical results have been finally compared with the prediction of an already conceived model based on both kinetic and critical state theories, here suitably modified to account for three-dimensional conditions.  相似文献   

Exploring Mars and its terrestrial analogues     

Enrico Flamini  Gian Gabriele Ori  Simonetta di Pippo  Gordon Osinsky 《Planetary and Space Science》2009,57(5-6):509

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