335,732 research outputs found
Reticulated vitreous carbon as an electrode material
No full textAn illustrated review of reticulated vitreous carbon (RVC) as an electrode material is presented. Early uses of RVC were largely restricted to small-scale (<1 cm3) electroanalytical studies in research laboratories. RVC properties of a high ratio of surface area to volume and minimal reactivity over a wide range of process conditions, combined with low cost and easy handling, have resulted in a steady diversification of its applications both in research laboratories and in industry. The physical structure of RVC (in terms of pores per linear inch, strut length, strut thickness and area of the trigonal strut) is examined for 10, 30, 60 and 100 ppi (pores per linear inch) grades using scanning electron microscopy. The accurate measurement of these geometrical values presents both theoretical (in terms of definition of trigonal strut area, beginning and end of single strand) and practical problems (large differences in strut length and thickness in individual samples). Data are presented to show the relationships between geometrical properties. Applications include electroanalytical studies and sensors, metal ion removal, synthesis of organics and Fenton s reagent, H2O2 production and batteries/fuel cells
Relacion del último viage al estrecho de Magallanes de la fragata de S.M. Santa María de la Cabeza en los años de 1785 y 1786 : extracto de todos los anteriores ... y noticia de los habitantes, suelo, clima y producciones del estrecho
No full textCopia digital. Madrid : Ministerio de Cultura. Subdirección General de Coordinación Bibliotecaria, 2009Aguilar Piñal, VIII, 2443, hace responsable de esta obra a José de Vargas Ponce. Pero, Sempere y Guarinos en "Ensayo de una biblioteca española de los mejores escritores del Reinado de Carlos III", VI, p. 237, dice que José de Vargas fue encargado de "cuidar de la edición, y la enriqueció con muchas noticias y observaciones ... Suyas son la introducción, y toda la segunda parte, que contiene la historia de las expediciones y Viages, hechas antes de éste al Estrecho Magallanico ..."Marca tip. en portSign.: [ ]\p2\s, a\p8\s, b\p1\s, A-X\p8\s, Y\p10\sLas [4] h. pleg. son tablas con datos metereológicos del viajeLa h. de grab. calc.: "Ferdin. Selma delin. et incid. anno 1788", es el retrato de MagallanesLos map. pleg. son grab. calc.: "grabada por Bart. Vazquez", "Pró lo grabó
On an endpoint Kato-Ponce inequality
No full textWe prove that the L∞ end-point Kato-Ponce inequality (Leibniz rule) holds for the fractional Laplacian operators D3 = (-Δ)s/2, Js = (1-Δ) s/2, s > 0. This settles a conjecture by Grafakos, Maldonado and Naibo [7]. We also establish a family of new refined Kato-Ponce commutator estimates. Some of these inequalities are in borderline spaces.link_to_subscribed_fulltex
On Kato–Ponce and fractional Leibniz
No full textWe show that in the Kato–Ponce inequality Js(fg)−fJsgp ∂f∞ Js−1gp + Jsfp g∞, the Jsf term on the right-hand side can be replaced by Js−1∂f. This solves a question raised in Kato–Ponce [14]. We propose a new fractional Leibniz rule for Ds = (−Δ)s/ 2 and similar operators, generalizing the Kenig–Ponce–Vega estimate [15] to all s > 0. We also prove a family of generalized and refined Kato–Ponce type inequalities which include many commutator estimates as special cases. To showcase the sharpness of the estimates at various endpoint cases, we construct several counterexamples. In particular, we show that in the original Kato–Ponce inequality, the L∞-norm on the right-hand side cannot be replaced by the weaker BMO norm. Some divergence-free counterexamples are also included.</p
Geochemical and petrographic characterization of the Bella Rica hydrothermal gold mineralization (Ponce Enriquez, Ecuador)
No full textBella Rica is sited in the Ponce Enriquez mining district (south of Ecuador), one of the most important gold mining areas in Ecuador, active since 1980’s. Gold mesothermal mineralization is hosted within Cretaceous mafic volcanic rocks of Pallatanga Units (Pratt et al., 2005).
The high level of heavy metal(loid)s concentration (As, Cu, Cd, Zn, and Pb) in stream sediments and other matrixes (surface water, soil, and biological) has been discussed in several studies (e.g., Williams et al., 2000; Jiménez-Oyola et al., 2021). The presence of heavy metal(loid)s in the mining district has been considered as due to the superposition of geogenic sources and mining activity. Gold is recovered by leaching with cyanide and flotation in artisanal activity and by a combination of amalgamation with mercury in the illegal mining activity. Despite aforementioned environmental investigations, the studies on the characterization and origin of the Au mineralization are still limited.
With the aim of contributing to the regional geological background, in this study, we present new data on the geochemical and petrographic features of the hydrothermal gold mineralization in the Ponce Enriquez area. Detailed maps of the distribution of selected heavy metal(loid)s are provided. Furthermore, petrologic investigations are carried out with the aim to characterize temperatures and composition of hydrothermal fluids involved in the genesis of Ponce Enriquez ore deposit. These data can help to increase the regional geological knowledge and the promotion of the sustainable development of Ecuador metalliferous mineral sector.
Jimenez-Oyola S., Garcia-Martinez M.-J., Ortega M.F., Chavez E., Garcia-Garizabal I. & Bolonio D. (2021) - Ecological and probabilistic human health risk assessment of heavy metal(loid)s in river sediments affected by mining activities in Ecuador. Environ. Geochem. Health, 43, 4459-4474.
Pratt W.T., Duque P. & Ponce M. (2005) - An autochthonous geological model for the eastern Andes of Ecuador. Tectonophysics, 399, 251-278.
Williams T.M., Dunkley P.N., Cruz E., Actimbay V., Gaibor A., Lopez E., Baez N. & Aspden J.A. (2000) - Regional geochemical reconnaissance of the Cordillera Occidental of Ecuador: economic and environmental applications. Appl. Geochem., 15, 531-550
Origines Gentium. Textes réunis par V. Fromentin et S. Gotteland, 2001
No full textGonzález Ponce Francisco J. Origines Gentium. Textes réunis par V. Fromentin et S. Gotteland, 2001. In: Revue des Études Anciennes. Tome 105, 2003, n°1. pp. 312-314
Puerto Rico, hills near Ponce cultivated with sugarcane
No full textSanto Domingo [Dominican Republic]. Puerto Rico. January 1922. Cane, mts., Wd. Ponce. 4:15. B-. 8 1/25. North.GrayscalePlatt Nitrate Negatives, Box 2
- …
