Notas sobre aracnoidismo en El Salvador. Consideraciones sobre su tratamiento La Casampulga – Chiltuca

Es muy extendida la creencia, entre nosotros, los salvadoreños, de que existe entre nuestras múltiples arañas algunas peligrosas por su ponzoña, y particularmente una que es temida por campesinos y ciudadanos, alrededor de la cual se han construido muchas referencias; unas afirmando y exagerando su peligro, otras negándole por completo ese peligro, y atribuyéndolo únicamente a un proceso imaginario, que se hubiese trasmitido de generación en generación, pues entre nuestros antepasados se tenía esa araña como una amenaza de muerte, y al solo descubrirla aparecía un temor muy grande que hacía que la exterminaran inmediatamente

Leonardo's Civil Bridges

Within both aesthetic and history fields, civil engineering occupies a privileged place among arts whose manifestations are based on drawing. In this work, Leonardo’s creativity concerned with civil bridges proyects, have been studied. Leonardo designed ten bridges: eight of them intended for military porposes and only two were purely planned for civil functionaly - “Ponte sul corno d’oro”, infolio 66, manuscript L; and “Ponte a due piani”, represented in the Manuscript B at the Institute of France, infolio 23. There can be no doubt about Leonardo’s intentions when he started on designing these two bridges: his genious for creativy focused on providing both singulary and functionaly to the structures: they should be admired and utilized at the same time, a monument for civil society to be used.The work presented here attemps to make an scientist-historical trip along these Leonardo’s bridges, highlighting their technical, geometrical and aesthetic characteristics, as well as emphasizing Leonardo’s human, scientist and artistic nature

Synthesis of high‐surface area mesoporous SiC with hierarchical porosity for use as catalyst support

Porous SiC with a hierarchical mesoporous structure is a promising material for high‐performance catalytic systems because of its high thermal conductivity, high chemical inertness at high temperature, and oxidation resistance. Attempts to produce high‐surface area hierarchical SiC have typically been made by using porous carbon as a template and reacting it with either Si or SiO2 at high temperature under inert atmosphere. Because the reaction mechanism with Si involves a carbon dissolution step, and the reaction with SiO2 is highly dependent on C‐SiO2 dispersion, the porous structure of the carbon template is not maintained, and the reaction yields nonporous SiC. In this work, mesoporous SiC has been synthesized using a novel hard‐template methodology. SiC was prepared from hierarchical (mesoporous) silica which served as a solid template. Carbon deposition was done by Carbon Vapor Deposition (CVD) using CH4 as carbon precursor, where different temperatures and reaction times were tested to optimize the carbon coating. The synthesized SiC retained 61 (118 m2/g) and 47% (0.3 cm3/g) of the BET surface area and the mesopore volume of the original SiO2, which is 10 times higher than the retention reported for other template methods used to produce high surface area SiC.Financial support from the Generalitat Valenciana under the PhD grant Vali + d and the “Ministerio de Economía y Competitividad” (Grant MAT2017-86992-R), and action Mobility of Alicante University is gratefully acknowledged

Experimental investigation of the initial regime in fingering electrodeposition: dispersion relation and velocity measurements

Recently a fingering morphology, resembling the hydrodynamic Saffman-Taylor instability, was identified in the quasi-two-dimensional electrodeposition of copper. We present here measurements of the dispersion relation of the growing front. The instability is accompanied by gravity-driven convection rolls at the electrodes, which are examined using particle image velocimetry. While at the anode the theory presented by Chazalviel et al. describes the convection roll, the flow field at the cathode is more complicated because of the growing deposit. In particular, the analysis of the orientation of the velocity vectors reveals some lag of the development of the convection roll compared to the finger envelope.Comment: 11 pages, 15 figures, REVTEX 4; reference adde

Leaching of pure chalcocite with reject brine and MnO2 from manganese

Chalcocite (Cu2S) has the fastest kinetics of dissolution of Cu in chlorinated media of all copper sulfide minerals. Chalcocite has been identified as having economic interest due to its abundance, although the water necessary for its dissolution is scarce in many regions. In this work, the replacement of fresh water by sea water or by reject brine with high chloride content from desalination plants is analyzed. Additionally, the effect of adding MnO2 from available manganese nodules in vast quantities at the bottom of the sea is studied. Reject brine shows better results than sea water, and the addition of MnO2 to the brine significantly increases the kinetics of chalcocite dissolution in a short time. H2SO4 concentration is found to be irrelevant when working at high concentrations of chloride and MnO2. The best results, 71% Cu extractions in 48 h, are obtained for reject brine, 100 mg of MnO2 per 200 g of mineral and H2SO4 0.5 mol/L. The results are expected to contribute to a sustainable process of dissolution of chalcocite by using the reject brine from desalination plantsThe authors thank the Scientific Equipment Unit-MAINI of the Universidad Católica del Norte for all the chemical analyses in this work. The authors are grateful for the contribution of the Scientific Equipment Unit-MAINI of the Universidad Católica del Norte for facilitating the chemical analysis of the solutions. Pedro Robles thanks the Pontificia Universidad Católica de Valparaíso for the support provided. Pedro G. Toledo and Ricardo I. Jeldres thank Centro CRHIAM Project Anid/Fondap/15130015

Knotting probabilities after a local strand passage in unknotted self-avoiding polygons

We investigate the knotting probability after a local strand passage is performed in an unknotted self-avoiding polygon on the simple cubic lattice. We assume that two polygon segments have already been brought close together for the purpose of performing a strand passage, and model this using Theta-SAPs, polygons that contain the pattern Theta at a fixed location. It is proved that the number of n-edge Theta-SAPs grows exponentially (with n) at the same rate as the total number of n-edge unknotted self-avoiding polygons, and that the same holds for subsets of n-edge Theta-SAPs that yield a specific after-strand-passage knot-type. Thus the probability of a given after-strand-passage knot-type does not grow (or decay) exponentially with n, and we conjecture that instead it approaches a knot-type dependent amplitude ratio lying strictly between 0 and 1. This is supported by critical exponent estimates obtained from a new maximum likelihood method for Theta-SAPs that are generated by a composite (aka multiple) Markov Chain Monte Carlo BFACF algorithm. We also give strong numerical evidence that the after-strand-passage knotting probability depends on the local structure around the strand passage site. Considering both the local structure and the crossing-sign at the strand passage site, we observe that the more "compact" the local structure, the less likely the after-strand-passage polygon is to be knotted. This trend is consistent with results from other strand-passage models, however, we are the first to note the influence of the crossing-sign information. Two measures of "compactness" are used: the size of a smallest polygon that contains the structure and the structure's "opening" angle. The opening angle definition is consistent with one that is measurable from single molecule DNA experiments.Comment: 31 pages, 12 figures, submitted to Journal of Physics

Why farmers should manage the arbuscular mycorrhizal symbiosis

The Tansley review by Ryan & Graham (2018) provided a welcome critical perspective on the role of arbuscular mycorrhizal (AM) fungi in large‐scale industrial agriculture, with a focus on cereals (wheat, Triticum aestivum). They conclude that there is little evidence that farmers should consider the abundance or diversity of AM fungi when managing crops. We welcome many of the points made in the paper, as they give an opportunity for self‐reflection, considering that the importance of AM fungi in agroecosystems is often taken for granted. However, we suggest that it is too early to draw the overall conclusion that the management of AM fungi by farmers is currently not warranted. We offer the following points to contribute to the discussion. The first point pertains to the overall focus of Ryan & Graham (2018), which strongly determines the recommendations at which the authors arrive. This scope is limited to yield, at the expense of neglecting aspects of sustainability. We then argue that AM fungal communities do respond negatively to aspects of agricultural management, and list evidence for their positive effects to agronomically important traits, including yield in cereals. In our final argument, we advocate for transitioning to agroecosystems that are more AM compatible in order to increasingly take advantage of all the potential services these ancient symbionts, and other soil biota, can provide

Multiparticle Biased DLA with surface diffusion: a comprehensive model of electrodeposition

We present a complete study of the Multiparticle Biased Diffusion-Limited Aggregation (MBDLA) model supplemented with surface difussion (SD), focusing on the relevance and effects of the latter transport mechanism. By comparing different algorithms, we show that MBDLA+SD is a very good qualitative model for electrodeposition in practically all the range of current intensities {\em provided} one introduces SD in the model in the proper fashion: We have found that the correct procedure involves simultaneous bulk diffusion and SD, introducing a time scale arising from the ratio of the rates of both processes. We discuss in detail the different morphologies obtained and compare them to the available experimental data with very satisfactory results. We also characterize the aggregates thus obtained by means of the dynamic scaling exponents of the interface height, allowing us to distinguish several regimes in the mentioned interface growth. Our asymptotic scaling exponents are again in good agreement with recent experiments. We conclude by discussing a global picture of the influence and consequences of SD in electrodeposition.Comment: 15 pages, 20 figures, accepted for publication in Physical Review

Tightness of slip-linked polymer chains

We study the interplay between entropy and topological constraints for a polymer chain in which sliding rings (slip-links) enforce pair contacts between monomers. These slip-links divide a closed ring polymer into a number of sub-loops which can exchange length between each other. In the ideal chain limit, we find the joint probability density function for the sizes of segments within such a slip-linked polymer chain (paraknot). A particular segment is tight (small in size) or loose (of the order of the overall size of the paraknot) depending on both the number of slip-links it incorporates and its competition with other segments. When self-avoiding interactions are included, scaling arguments can be used to predict the statistics of segment sizes for certain paraknot configurations.Comment: 10 pages, 6 figures, REVTeX