The influence of land use/land cover variability and rainfall intensity in triggering landslides: a back-analysis study via physically based models

Natural Hazards - The objective of this study was to use physically based models to carry out a back-analysis of the set of factors that may have influenced slope instability and the consequent...     

Sampling effects in the emission-line spectra of Hii regions

We show that sampling effects in the initial mass function are very important in the low-mass cluster case. To this aim, we compute photoionization models ionized by realistic clusters made up of various combinations of individual stars and clusters built with a synthesis model. We discuss the differences in the position on diagnostic diagrams, their implications, and future and ongoing applications of the present work.     

MONS OT J004240.69+405142.0: An orphan GRB optical afterglow candidate in Andromeda?

Here we report the serendipitous identification of a bright optical transient in the vicinity of the dwarf elliptical galaxy M 32 (NGC 221). This transient (MONS OT J004240.69+405142.0) was detected using filtered CCD imaging, about 20 arcsec southwest from the core of M 32, at equatorial coordinates α = 00:42:40.69 ± 0.05, δ = +40:51:42.0 ± 0.5, between 04:20:16 and 04:21:46 UT on June 22, 2007. A detailed analysis of the intensity profile of the feature suggests that it is of stellar nature with apparent visual magnitude 9.69 ± 0.15 which gives an absolute magnitude of ?14.7 ± 0.3 if the feature is located in M 31/M 32. Under the assumption of the event reported here being of cosmic origin and although no correlation with GRBs in time or space has been found, the behaviour of the optical transient appears to resemble that of the recently observed GRB 080319B: very fast ascent and decay of several magnitudes within a few minutes. If this interpretation is correct, the afterglow decay was extremely rapid, decreasing by more than 5 mag. in about 2 min, α = 2.4. Given its properties, the event is a possible orphan GRB optical afterglow candidate originated beyond the Local Group. Alternative explanations are also discussed.     

Microclimatic variation of thermal comfort in a district of Lisbon (Telheiras) at night

Summary The microclimatic spatial variation of air temperature, wind speed, radiative fluxes and Physiological Equivalent Temperature (PET) was studied in Telheiras, a northern district of the city of Lisbon. The main goal was to assess how to improve outdoor thermal conditions based on research results. An empirical model was developed to estimate PET in Telheiras under different weather types; the model allows the continuous spatial representation of PET, using a Geographical Information System (GIS) and can be used in other areas of Lisbon. Although there is a small microclimatic variation in air temperature, the PET presents a much stronger variation, due to the influence of wind and radiative fluxes. Urban geometry, expressed by the Sky View Factor (SVF), is the main factor controlling the microclimatic diversity of the neighbourhood. The coolest conditions occur in open areas (centre of large courtyards and marginal areas) and the warmest in streets with low SVF that are sheltered from the wind. Authors’ address: H. Andrade and M.-J. Alcoforado, Centro de Estudos Geográficos, Universidade de Lisboa, Alameda da Universidade, 1600-214 Lisboa, Portugal     

Hydrogeological and mineralogical analysis of the pre‐Romanesque monument of Santa María del Naranco,Asturias, Spain

The church of Santa María del Naranco is an important monument from the pre‐Romanesque period of Asturian art. Here we present research that locates the probable source of travertine used in the construction of a vault within this monument. Since the genesis of this travertine is associated with spring activity, and archival evidence suggests that stone procurement during this period tended to be local, we surveyed existing carbonated aquifers within a 5‐km radius of the monument. We identified a spring (Sopeña) with an associated outcrop of discontinuous travertine that appeared to have been quarried in the past. We conducted X‐ray powder diffraction, electron microprobe, and inductively coupled plasma mass spectrometry analyses of samples extracted from the suspected travertine source, an additional more distant travertine quarry for comparison, and the vault. Matching mineralogy and geochemistry indicate that the Sopeña travertine was the probable source of rock material used in the construction of the vault. This study provides insight into local ancient monument construction and can assist in procuring original stone material for historical restoration. © 2010 Wiley Periodicals, Inc.     

Temporal downscaling: a comparison between artificial neural network and autocorrelation techniques over the Amazon Basin in present and future climate change scenarios

Several studies have been devoted to dynamic and statistical downscaling for both climate variability and climate change. This paper introduces an application of temporal neural networks for downscaling global climate model output and autocorrelation functions. This method is proposed for downscaling daily precipitation time series for a region in the Amazon Basin. The downscaling models were developed and validated using IPCC AR4 model output and observed daily precipitation. In this paper, five AOGCMs for the twentieth century (20C3M; 1970–1999) and three SRES scenarios (A2, A1B, and B1) were used. The performance in downscaling of the temporal neural network was compared to that of an autocorrelation statistical downscaling model with emphasis on its ability to reproduce the observed climate variability and tendency for the period 1970–1999. The model test results indicate that the neural network model significantly outperforms the statistical models for the downscaling of daily precipitation variability.     

Phase separation,fluid mixing,and origin of the greisens and potassic episyenite associated with the Água Boa pluton,Pitinga tin province,Amazonian Craton,Brazil

Based on petrographical data, three types of greisen have been characterized at the western border of Água Boa pluton: siderophyllite–topaz–quartz greisen (greisen 1), fluorite–phengite–quartz greisen (greisen 2) and quartz–chlorite–phengite greisen (greisen 3). Episyenites were also identified.Two fluids of independent origin interacted with the same protolith – a hornblende-biotite alkali feldspar granite – and produced both the greisens and potassic episyenite: (1) an acid, low-salinity (4–12 wt.% NaCl eq.), F-rich, relatively hot (400–350 °C) reduced aqueous-carbonic fluid (CH₄–H₂O–NaCl–FeCl₂ ± KCl), which by immiscibility gave rise to fluid IA (aqueous) and IC (carbonic); and (2) a lower salinity (2–4 wt.% NaCl eq.) and temperature (200–150 °C) aqueous fluid (H₂O–NaCl), which was responsible for all dilution processes. Fluid 1 seems to have had a magmatic-hydrothermal origin, while fluid 2 is probably surface-derived (meteoric water?). An alkaline, F-poorer and diluted equivalent of fluid IA was interpreted to have caused the episyenitization of the granite host rock as well as the formation of phengite-rich greisen 3. The continuos interaction of this fluid with the potassic episyenite produced a moderate- to high-salinity (20–24 wt.% NaCl eq.), low-temperature (200–100 °C) fluid (H₂O–NaCl–CaCl₂ ± KCl), leading to the formation of chlorite-rich zone of greisen 3 and late silicification of potassic episyenite.In the greisen 1, decreasing F-activity and increasing oxygen fugacity, as the system cooled down, favored the formation of a topaz-rich inner zone, which grades into a siderophyllite-rich zone outwardly. Greisen 2 was formed under more oxidizing conditions by fluids poorer in F than those trapped in the siderophyllite-rich zone.The oxidation of aqueous-carbonic fluid took place at three distinct stages: (i) below the FMQ buffer; (ii) between the FMQ and NNO buffers; and (iii) above the NNO buffer.The dissolution cavities generated during the episyenitization process increased the permeability of the altered rocks, resulting in an increase of the fluid/rock ratios at the potassic episyenite and greisen 3 sites.All these fluids were trapped under pressure conditions of <1.0 kbar, representing shallow crustal levels and are consistent with those that have been estimated for the Pitinga tin–granites.The oxygen fugacity, F-activity gradients and salinity variations that occurred during the cooling of the hydrothermal system, in addition to differences in permeability, were important factors in the formation of distinct greisens. They not only controlled the fluid compositional changes, but also caused the cassiterite and sulfide precipitation at the greisen sites.     

A new computational strategy for solving two‐phase flow in strongly heterogeneous poroelastic media of evolving scales

We develop a new computational methodology for solving two‐phase flow in highly heterogeneous porous media incorporating geomechanical coupling subject to uncertainty in the poromechanical parameters. Within the framework of a staggered‐in‐time coupling algorithm, the numerical method proposed herein relies on a Petrov–Galerkin postprocessing approach projected on the Raviart–Thomas space to compute the Darcy velocity of the mixture in conjunction with a locally conservative higher order finite volume discretization of the nonlinear transport equation for the saturation and an operator splitting procedure based on the difference in the time‐scales of transport and geomechanics to compute the effects of transient porosity upon saturation. Notable features of the numerical modeling proposed herein are the local conservation properties inherited by the discrete fluxes that are crucial to correctly capture the fingering patterns arising from the interaction between heterogeneity and nonlinear viscous coupling. Water flooding in a poroelastic formation subject to an overburden is simulated with the geology characterized by multiscale self‐similar permeability and Young modulus random fields with power‐law covariance structure. Statistical moments of the poromechanical unknowns are computed within the framework of a high‐resolution Monte Carlo method. Numerical results illustrate the necessity of adopting locally conservative schemes to obtain reliable predictions of secondary recovery and finger growth in strongly heterogeneous deformable reservoirs. Copyright © 2011 John Wiley & Sons, Ltd.     

New controversies on Columbus' “cosmographic” ideas

This paper examines the spatial distribution of the functional systems in the different belts of settlements around Budapest. The surburban belts have an important role in the capital's labour market, places of employment and recreation with 45 settlements. The paper reviews the structure of the Budapest agglomeration from the core to the three inner, middle and outer belts comprising the suburbs, the semi-urban settlements, the suburban villages, the satellite towns, and the satellite villages. Then the system of the functional urban centres are reviewed, The author establishes the concept of the main, the division, the district and the settlement group centres in the Budapest agglomeration. The different levels of attached functions, such as international, national, regional and local are also described with each centre type. The areal distribution of the centre system of Budapest is shown in maps too.