A physically-based method for removing pits in digital elevation models

Spurious pits in digital elevation models (DEMs) are traditionally removed by filling depressions, often creating flat regions that lead to inaccurate estimation of landscape flow directions. In this study, a physical approach based on a simple landscape evolution model is proposed for DEM pit removal. This method, an alternative to traditional geometrical procedures, enforces more realistic slopes and flow directions on topography. The procedure is compared with the method most commonly used in the literature and distributed with commercial GIS software where, generally, elevations of a depression are increased up to the lowest value among neighbouring cells. Several tests are performed and parameters sensitivity is carried out in order to demonstrate the performance of the proposed model as compared to traditional methods.     

The effect of compression on noble gas solubility in silicate melts and consequences for degassing at mid-ocean ridges

The effect of compression on noble gas solubility in silicate melts is still badly understood due to a lack of theoretical guidance. In the experimental literature, noble gases dissolving in liquid silicates are found to concentrate almost linearly with increasing pressure up to several tens of kbar, suggesting that Henry’s law could be valid up to very high pressures, although this law stipulates that the gaseous phase in contact with the liquid must be ideal. Recently, new experiments dealing with the dissolution of argon in synthetic and natural silicate melts have pointed out that the evolution of concentration with pressure exhibits a departure from linearity in the 50-100 kbar range, leading either to a levelling off or to a sudden collapse of the argon concentration above 50 kbar. Here, we investigate by means of liquid state physics how volatile species dissolve into silicate melts under pressure. We use a hard sphere model (the reference fluid in liquid state physics) to describe silicate melts and gas at high pressures. One of our main results is that, when pressure increases, the concurrent compaction of gas and melt explains the almost-linear behaviour of the noble gas concentration up to several tens of kbars, before melt compaction dominates and concentration either levels off or decreases gradually in the 50-100 kbar range. In spite of the existence of a quasi-linear regime over a large pressure range, our work disqualifies the use of the Henry law when dealing with high pressures. The implication of these findings to provide an understanding of degassing at mid-ocean ridges is next investigated. Applying our model to the scenario where CO₂ vesicle generation occurs in the magma at mantle depths during its ascent from melting regions, we evaluate magma vesicularity as well as noble gas concentrations in the basalt melt and in vesicles as a function of pressure at depth. It is stressed that the variable and usually strong noble gas elemental fractionation observed in mid-ocean ridge basalts can be explained by assuming a sequence of several vesiculation stages interrupted by vesicle loss during magma ascent.     

Coordinated monitoring of the eccentric O-star binary Iota Orionis: optical spectroscopy and photometry

With the objective of investigating the windwind collision phenomenon and supporting contemporaneous X-ray observations, we have organized a large-scale, coordinated optical monitoring campaign of the massive, highly eccentric O9 III+B1 III binary Iota Orionis. Successfully separating the spectra of the components, we refine the orbital elements and confirm the rapid apsidal motion in the system. We also see strong interaction between the components during periastron passage and detect phase-locked variability in the spectrum of the secondary star. However, we find no unambiguous signs of the bow shock crashing on the surface of the secondary, despite the predictions of hydrodynamic simulations. Combining all available photometric data, we find rapid, phase-locked variations and model them numerically, thus restricting the orbital inclination to 50° i 70°.     

Exploring the time geography of public transport networks with the gtfs2gps package

Journal of Geographical Systems - The creation of the General Transit Feed Specification (GTFS) in the mid-2000s provided a new data format for cities to organize and share digital information on...     

The use of GIS tools to support decision-making in the expansion of chain stores

This article deals with a network competitive localization problem in which a firm seeks to determine the location of a new facility, which competes with all the facilities operating in the market, both belonging to the same firm and to the competing firms. In this context, two frequently conflicting objectives are involved: maximization of the total market share captured by the firm and minimization of market share losses for its existing facilities due to being captured by the new facility (cannibalization). We formulate the location problem as a multi-objective optimization model. Some GIS tools that provide some maps representing the market share and the cannibalization effect are proposed. This allows for the visualization of the effects produced by the opening of a new facility in the market and the trade-offs between the objectives. Finally, the advantages of using these tools have been shown by means of an application to a real data case.     

Multidisciplinary approach of the hyperarid desert of Pampas de La Joya in southern Peru as a new Mars-like soil analog

The distribution of living organisms, organic matter, and chemical properties in Mars-like environments on Earth can be used as a model to guide the investigation of possible habitable environments on Mars. This work aims to demonstrate that the place known informally as the “Mar de Cuarzo” (Sea of Quartz) in the Pampas de La Joya desert southern Peru (between 16°S and 17°S latitude), contains soils with characteristics similar to those found on the Martian surface. Using a multidisciplinary approach, we studied the environmental data, geology, organic matter content, oxidant activity, and microbiology of this area. Our data show that (1) Mar de Cuarzo is a hyper arid area with a lower concentration of organic matter than those found in the Mars-like soils from Yungay area (Atacama Desert in Chile), while at the same time having, comparable extreme environmental conditions, and very low levels of microorganisms. (2) The detrital components of the soils come essentially from the Andean volcanic chain and local outcrops of Precambrian gneisses and Cretaceous granitic batholiths. (3) The presence of microclimates, geomorphological features, and the high influence of the “El Niño Southern Oscillation (ENSO)” allowed the formation of exotic and heterogeneous chemical deposits in these soils, including iron oxides, sulfates, and other evaporites. (4) Thermal volatilization in these soils (using methods similar to the Viking and Phoenix instruments) shows high oxidant activity. (5) Labeled release experiment (similar to the Viking instrument) shows high degradation of nutrients added in these soils.Altogether, the Mar de Cuarzo area in the Pampas de La Joya is an interesting place for astrobiological studies as a new analog to Mars, and for comparative analyses with other hyperarid analogs as Yungay.     

Basis for a streamflow forecasting system to Rincón del Bonete and Salto Grande (Uruguay)

This paper presents the basis for the design of streamflow prediction systems for the hydroelectric dams of Rincón del Bonete (Uruguay) and Salto Grande (Uruguay–Argentina). The prediction is made, independently, for each reservoir and each month of the year with two methodologies: data-driven statistical models and hybrid downscaling that includes atmospheric predictors. We determine a set of potential predictors and then fit linear models coupled with variable selection techniques, under the hypothesis of perfectly known predictors. The predictive skill of the schemes outperforms the climatological forecast throughout the year in both reservoirs (except August in Rincón del Bonete). This remains the case even when the forecast lead does not allow for the use of preceding flows as predictors. While in Rincón del Bonete it is not possible to distinguish a period of high predictability, in Salto Grande, there is a robust signal in March–May and October–December.     

On the motion of three rigid bodies: Central configurations

In the present paper, the motion of three rigid bodies is considered. With a set of new variables, and the 10 first integrals of the motion, the problem is reduced to a system of order 25 and one quadrature. The plane motions are characterized, and finally, an equation for the existence of central configurations (in particular, Lagrangian and Eulerian solutions) has been found. Besides, the case of three axisymmetric ellipsoids is studied.