Molecular dynamics simulations of complex shaped particles using Minkowski operators

The Minkowski operators (addition and substraction of sets in vectorial spaces) has been extensively used for Computer Graphics and Image Processing to represent complex shapes. Here we propose to apply those mathematical concepts to extend the Molecular Dynamics (MD) Methods for simulations with complex-shaped particles. A new concept of Voronoi-Minkowski diagrams is introduced to generate random packings of complex-shaped particles with tunable particle roundness. By extending the classical concept of Verlet list we achieve numerical efficiencies that do not grow quadratically with the body number of sides. Simulations of dissipative granular materials under shear demonstrate that the method complies with the first law of thermodynamics for energy balance.Comment: Submitted to Phys. Rev.

The entropic origin of disassortativity in complex networks

Why are most empirical networks, with the prominent exception of social ones, generically degree-degree anticorrelated, i.e. disassortative? With a view to answering this long-standing question, we define a general class of degree-degree correlated networks and obtain the associated Shannon entropy as a function of parameters. It turns out that the maximum entropy does not typically correspond to uncorrelated networks, but to either assortative (correlated) or disassortative (anticorrelated) ones. More specifically, for highly heterogeneous (scale-free) networks, the maximum entropy principle usually leads to disassortativity, providing a parsimonious explanation to the question above. Furthermore, by comparing the correlations measured in some real-world networks with those yielding maximum entropy for the same degree sequence, we find a remarkable agreement in various cases. Our approach provides a neutral model from which, in the absence of further knowledge regarding network evolution, one can obtain the expected value of correlations. In cases in which empirical observations deviate from the neutral predictions -- as happens in social networks -- one can then infer that there are specific correlating mechanisms at work.Comment: 4 pages, 4 figures. Accepted in Phys. Rev. Lett. (2010

Photosynthetic treatment of piggery wastewater in sequential purple phototrophic bacteria and microalgae-bacteria photobioreactors

Producción CientíficaNowadays, piggery wastewater (PWW) management still represents an unsolved global environmental problem. Photosynthetic processes have emerged as an innovative biological platform capable of performing a cost-effective treatment of wastewater with a concomitant assimilation of nutrients into biomass. In this work, the performance of a purple phototrophic bacteria photobioreactor (PPB-PBR) coupled with a microalgae-bacteria photobioreactor (MB-PBR) was assessed during the treatment of PWW at an hydraulic retention time (HRT) of 12.2 (stage I) and 6.2 days (stages II–VI) and intensities of near-infrared radiation in the PPB-PBR of 30 W m−2 (stages I–II) and 114 W m−2 (stages III–IV). Maximum removal efficiencies of total dissolved organic carbon (TOC-RE) and total dissolved nitrogen (TN-RE) of 91% and 82%, respectively, were recorded at an HRT of 12.2 days. The decrease in HRT to 6.2 days reduced the TOC-RE and TN-RE in both photobioreactors, but the increase in near-infrared radiation enhanced TOC-RE in the PPB-PBR, contributing to a global carbon recovery of 67% via assimilation in the form of PPB biomass. PPB-PBR was highly efficient in carbon assimilation, while MB-PBR enhanced nitrogen and total suspended solids removals, with a contribution to TN-RE of 63% and a global decrease in TSS of 76%. The culture broth of PPB-PBR was dominated by Rhodopseudomonas sp. up to 54%, supported by the high HRT and the increase in near-infrared radiation, while the sequential MB-PBR favoured the dominance of Mychonastes homosphaera. This work demonstrated, for the first time, the high efficiency of sequentially coupling PPB and microalgae for the treatment of PWW.Junta de Castilla y León - Fondo Europeo de Desarrollo Regional (projects CLU 2017-09 and UIC 315)Comisión Nacional de Investigación Científica y Tecnológica (CONICYT) (grant PFCHA/DOCTORADO BECAS CHILE/2017 – 72180211

Reinforced-concrete cover cracking due to the pressure of corrosion products

Reinforcement corrosion is one of the most important phenomena that reduce the service life of the reinforced concrete structures. Steel corrosion reduces the strength and bond of the reinforcement and the oxides formed cause internal stresses that crack the concrete cover. The prediction of the evolution of these effects is a problem that involves chemical and mechanical aspects. The phenomenon is not well known and quantitative descriptions of development and magnitude of stresses produced by a corroding rebar to concrete are scarce and although there are several models in the literature they do not universally reproduce the experimental results. This work presents a summary of the available experimental evidence on the amount of internal expansion needed at the reinforcement level for concrete cover to crack and formulas to estimate the expansion. Also, results are presented on the pressure needed for concrete cover to crack together with the experimental technique used for the verification of the assumptions and crack propagation analysis

Reestudio de Zanthoxylum Coco Gill

En un reestudio de Zanthoxylum coco Gill. (sinónimoFagara coco Gill. (Engl.)), especie de Bolivia y Argentina de la familia de las Rutáceas, se han aislado la piranoquinolina angular jlindersina y la cumarina prenilada aurapteno. Estos resultados apoyan el criterio que las cumarinas se acumulan también en las especies sudamericanas de Zanthoxylum. La validez de estos datos como marcadores quimiosistemáticos es discutida

Astronomical site selection: On the use of satellite data for aerosol content monitoring

The main goal of this work is the analysis of new approaches to the study of the properties of astronomical sites. In particular, satellite data measuring aerosols have recently been proposed as a useful technique for site characterization and searching for new sites to host future very large telescopes. Nevertheless, these data need to be critically considered and interpreted in accordance with the spatial resolution and spectroscopic channels used. In this paper we have explored and retrieved measurements from satellites with high spatial and temporal resolutions and concentrated on channels of astronomical interest. The selected datasets are OMI on board the NASA Aura satellite and MODIS on board the NASA Terra and Aqua satellites. A comparison of remote sensing and in situ techniques is discussed. As a result, we find that aerosol data provided by satellites up to now are not reliable enough for aerosol site characterization, and in situ data are required.Comment: LaTeX2e MN v2.2, 16 pages with 13 figures. Accepted for Mon. Not. R. Astron. Soc.(2008

Relation Between Corrosion Degree And Pressure Needed To Produce The First Crack And Evolution Of Crack Width In Natural Exposure

Reinforcement corrosion leads into several damage types which influence the structural loadbearing capacity, among which can be mentioned the cracking of concrete cover. This work presents results of crack width generated in concrete elements fabricated in 1990 with chlorides added in the mix and exposed to the natural atmosphere of Madrid-Spain climate. These elements, one T beam and one column. Two expressions have been fitted to the results: w = k Px / (c/φ) and w = k Px / Ro, where w is a crack width in the time, k is a proportional factor, Px is the corrosion penetration in the time, c/φ is the concrete cover/diameter relation and Ro is the original radius of the bar. The expressions were also fitted to results taken from the literature made applying a current. The beam shows larger crack widths than the beam and the accelerated tests give intermediate results. Based in all the results, although the scatter is important, it has been calculated the k and k’ slopes which resulted respectively in values of 9.5 and 35.

From subsistence farming to agribusiness and nonfarm entrepreneurship: Does it improve economic conditions and well-being?

To eradicate poverty, governments across developing countries have adopted programs to promote business ownership, with varying levels of success. The mixed success of such programs underscores the importance of local business and economic conditions. Yet, empirical evidence on how local context shapes outcomes of entrepreneurship-focused poverty initiatives is sparse. In this paper, we use data from the 2015 Smallholder Survey to examine the impact of farming as a business (agribusiness) and nonfarm entrepreneurship (NFE) on household income and economic well-being in Uganda. We find that, in comparison to subsistence farming, engaging in agribusiness and NFE boosts household income and economic well-being, especially in rural areas with high poverty rates. Our research contributes to the literature by offering new evidence on the efficacy of entrepreneurial initiatives in the specific context of a developing country with a large rural and agricultural economy. In terms of policy, our analysis provides support for the promotion of agribusiness and NFE initiatives to reduce poverty and overcome disparities between urban and rural settings