Dynamics of Pyridine Adsorption on Gold(111) Terraces in Acid Solution from in-Situ Scanning Tunneling Microscopy under Potentiostatic Control

The adsorption of pyridine (Py) on Au(111) terraces produced from aqueous 0.1 M HClO4 + 10-3 M Py at 298 K was studied in the potential range 0.15 V pzc, the potential of zero charge of the substrate, both ordered and disordered domains can be observed. Ordered domains correspond to vertically adsorbed Py molecules forming a (4 × 4) hexagonal lattice with the nearest neighbor distance d = 0.38 nm, and corrugation z = 0.04 nm. The ordered adsorbate structure disappears for E pzc, but it is recovered several minutes after stepping E backward to E > Epzc, as expected for a reversible potential-step-induced surface process. The surface concentration of adsorbed Py molecules resulting from the (4 × 4) lattice is close to 1 × 10-9 mol/cm2, a figure exceeding the average integral surface concentration value obtained from electroadsorption measurements. Therefore, disordered domains would be related to a mobile diluted Py adsorbate coexisting with ordered Py adsorbate domains leading to a nonhomogeneous Py adsorbate layer at the positively charged Au(111) terraces.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta

Dynamics of Pyridine Adsorption on Gold(111) Terraces in Acid Solution from in-Situ Scanning Tunneling Microscopy under Potentiostatic Control

The adsorption of pyridine (Py) on Au(111) terraces produced from aqueous 0.1 M HClO4 + 10-3 M Py at 298 K was studied in the potential range 0.15 V pzc, the potential of zero charge of the substrate, both ordered and disordered domains can be observed. Ordered domains correspond to vertically adsorbed Py molecules forming a (4 × 4) hexagonal lattice with the nearest neighbor distance d = 0.38 nm, and corrugation z = 0.04 nm. The ordered adsorbate structure disappears for E pzc, but it is recovered several minutes after stepping E backward to E > Epzc, as expected for a reversible potential-step-induced surface process. The surface concentration of adsorbed Py molecules resulting from the (4 × 4) lattice is close to 1 × 10-9 mol/cm2, a figure exceeding the average integral surface concentration value obtained from electroadsorption measurements. Therefore, disordered domains would be related to a mobile diluted Py adsorbate coexisting with ordered Py adsorbate domains leading to a nonhomogeneous Py adsorbate layer at the positively charged Au(111) terraces.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta

New aspects of the surface chemistry of sulfur on Au(111): Surface structures formed by gold-sulfur complexes

Sulfur adsorption on gold surfaces has been extensively studied because of the key role of sulfur species in heterogeneous catalysis, and, more recently, due to the interest in the synthesis of anisotropic gold nanoparticles with potential applications in medicine that involves sulfide reduction. Here we report new surface structures for sulfur on Au(111) by combining in situ scanning tunneling microscopy in aqueous sodium sulfide solutions and density functional theory calculations. Our results show two related lattices, (3√3×3√3) R30° (θ = 0.22) and (√7 × √7) R19.1° (θ = 0.57), that involve AuS3 complexes as building blocks. Gold‑sulfur complexes are formed by the lifting of gold atoms from the substrate surface as revealed by density functional theory calculations. These species, intermediate between adsorbed S in the well-known (√3 × √3)-R30○ lattice and adsorbed polysulfides in organized rectangular structures, explain the surface coverage of gold vacancy islands, a fingerprint of S adsorption on Au(111).Fil: Carro, Pilar. Universidad de La Laguna; EspañaFil: Andreasen, Gustavo Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Vericat, Carolina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Vela, Maria Elena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Salvarezza, Roberto Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentin

Influence of the electric potential on the structure of pyridine adlayers on Au(111) terraces from in-situ scanning tunnelling microscopy imaging

The adsorption and desorption of pyridine (Py) adlayers prepared on Au(111) terraces were studied by in-situ scanning tunnelling microscopy (STM) and conventional voltammetry using an aqueous 0.1 M HClO4+10−4 M Py solution at 298 K. The applied potential covered the range 0.15 V pzc, the potential of zero charge of Au(111). In the range Epzc pzc, the ordered adlayer structure disappears leaving uncovered Au(111) domains. Similarly, for E > 0.96 V, the (4×4) adlayer lattice is removed completely leading to a bare Au(111) surface. By stepping E backwards to a value in the range Epzc < E < 0.96 V, the readsorption of Py takes place and the (4×4) adlayer domains are recovered in a few minutes. STM data offer the possibility of discussing anion adsorption and the early electroformation stages of the OH-containing adlayer on Au(111) terraces.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Dynamics of Pyridine Adsorption on Gold(111) Terraces in Acid Solution from in-Situ Scanning Tunneling Microscopy under Potentiostatic Control

The adsorption of pyridine (Py) on Au(111) terraces produced from aqueous 0.1 M HClO4 + 10-3 M Py at 298 K was studied in the potential range 0.15 V pzc, the potential of zero charge of the substrate, both ordered and disordered domains can be observed. Ordered domains correspond to vertically adsorbed Py molecules forming a (4 × 4) hexagonal lattice with the nearest neighbor distance d = 0.38 nm, and corrugation z = 0.04 nm. The ordered adsorbate structure disappears for E pzc, but it is recovered several minutes after stepping E backward to E > Epzc, as expected for a reversible potential-step-induced surface process. The surface concentration of adsorbed Py molecules resulting from the (4 × 4) lattice is close to 1 × 10-9 mol/cm2, a figure exceeding the average integral surface concentration value obtained from electroadsorption measurements. Therefore, disordered domains would be related to a mobile diluted Py adsorbate coexisting with ordered Py adsorbate domains leading to a nonhomogeneous Py adsorbate layer at the positively charged Au(111) terraces.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta

In situ sequential STM imaging of structural changes resulting from the electrodissolution of silver crystal surfaces in aqueous perchloric acid : The roughening kinetics

Structural changes of silver terrace domains in aqueous perchloric acid solution at constant anodic current density (j) and room temperature were followed by in situ scanning tunneling microscopy sequential imaging. For j-2 silver electrodissolution proceeds at step edges without roughening. Conversely, for j-2 the silver surface becomes progressively rougher to attain, after a certain critical time, a steady roughness. In this case, the dynamic scaling theory applied to STM images indicates that the dissolving silver surface can be described as a self-affine fractal surface with a static roughening exponent α50.9060.06, and a dynamic roughening exponent β50.3660.08. The value of a is consistent with the relevant role played by surface diffusion in the silver electrodissolution mechanism, whereas the value of b is slightly higher than those derived from growth models incorporating surface diffusion. The difference in the value of β would reflect the influence of either the electric field or energetic barriers at step edges on the rate of roughness development.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Sequential <i>in situ</i> STM imaging of electrodissolving copper in different aqueous acid solutions

The dynamics of Cu surfaces immersed in either aqueous HClO4 or H2SO4 solution under galvanostatic conditions at room temperature was studied by in situ scanning tunneling microscopy (STM) sequential imaging. The mobile interface depends considerably on the apparent current density (j) applied to the specimen. At j = 0, the Cu topography turns out to be highly dynamic as mass transport among different domains takes place. Conversely, for j = 6 μA cm−2 an inhomogeneous attack of the Cu surface leading to a remarkable increase in roughness and to the formation of etched pits at certain surface domains can be observed. Etched pit domains drive the mobile interface to an unstable regime. The addition of HCl to those acid solutions to reach concentrations higher than 10−2 M leads to the formation of a Cu2Cl2 layer.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Evaluación agronómica y nutricional de pastos tropicales de corte sometidos a diferentes frecuencias de corte en Yurimaguas, Amazonia peruana

Four tropical grasses were evaluated: Maralfalfa (Pennisetum violaceum Lam), Purple King grass (P. purpureum x P. typhoides), Elephant grass (Pennisetum purpureum, Schumach) and Guatemala grass (Tripsacum laxum, Nash) with two harvest intervals (45 and 70 days), using a factorial experiment with a randomized complete block design. The interaction pastures × cutting frequencies was significant (p&lt;0.05) for the agronomic and nutritional characteristics. Purple King Grass and Guatemala harvested at 70 days produced higher dry matter yield (17.13 and 17.03 t ha-1, respectively) than Maralfalfa, Purple King Grass, Elephant grass, and Guatemala grass harvested at 45 days. Compared with other grasses, the Guatemala grass harvested at 45 days had the highest leaf: stem ratio (4.64). The highest average contents of protein (78.5 g kg-1) and phosphorus (1.22 g kg-1) were obtained at 45 days. It is concluded that the grasses harvested at 70 days showed their productive potential with a moderate nutritional value, which could be used to increase the yield per unit area. In addition, Guatemala grass could be used in studies with grazing animals due to its high leaf: stem ratio and moderate nutritional value.Se evaluaron cuatro pastos tropicales, Maralfalfa (Pennisetum violaceum Lam), pasto Morado (P. purpureum x P. typhoides), Elefante (Pennisetum purpureum, Schumach) y Guatemala (Tripsacum laxum, Nash) con dos intervalos de corte (45 y 70 días), mediante un experimento factorial con diseño de bloques completos al azar. La interacción pastos × frecuencias de corte fue significativa (p&lt;0.05) para las características agronómicas y nutricionales. Pasto Morado y Guatemala cosechados a los 70 días obtuvieron mayor rendimiento de materia seca (17.13 y 17.03 t ha-1, respectivamente) que Maralfalfa, Morado, Elefante y Guatemala cosechados a los 45 días. En comparación con otros pastos, el pasto Guatemala cosechado a los 45 días obtuvo la relación hoja: tallo más alta (4.64). Los mayores contenidos promedio de proteína (78.5 g kg-1) y fósforo (1.22 g kg-1) se obtuvieron a los 45 días. Se concluye que las gramíneas cosechadas a los 70 días demuestran su potencial productivo con un valor nutritivo moderado, lo que podría ser utilizado para incrementar el rendimiento por unidad de área. Además, el pasto Guatemala podría ser utilizado en estudios con animales en pastoreo debido a su alta relación hoja: tallo y valor nutritivo moderado

Plan de acción para el proceso de calidad alimentaria de una empresa de servicios de alimentación en Cali – Valle del Cauca, analizando el estado actual de su Centro de producción frente a la Resolución 2674 de julio 2013

La organización en mención, es una empresa vallecaucana con una trayectoria de más de 18 años, que cuenta con un amplio conocimiento en la actividad de catering, capacidad creativa e innovadora, brindando productos y servicios de alimentación que satisfacen las necesidades y demanda del mercado, en el presente proyecto se desarrolla un estudio que busca identificar las falencias que posee la empresa en el proceso de calidad alimentaria desarrollado en su centro de producción asociado en la ciudad de Cali ¿ Valle, con el fin de generar un plan para el mejoramiento continuo del proceso productivo que conlleve a la plena satisfacción de todos los clientes y stakeholders. Es necesario el desarrollo de un estudio que permita determinar con exactitud todas las inconsistencias referentes al cumplimiento de la normatividad vigente, conocer sus causas específicas y poder así desarrollar un programa de mejora que le permita a la empresa el mejoramiento de sus procesos, y por consiguiente el cumplimiento de la Norma (Resolución 2674 de julio de 2013; Ley 9 de 1979), asociado a una mayor calidad en los productos ofertados. Para el logro de los objetivos propuestos se llevó a cabo una revisión de la Resolución 2674 de Julio de 2013, detallando los apartados de la misma que deben tenerse en cuenta en el desarrollo del proceso de calidad alimentaria; se procedió con revisión documental y trabajo de campo para evaluar las condiciones en las cuales es realmente desarrollado este proceso para así poder identificar las brechas existentes. Entre la normatividad y la realidad de la empresa, además de ello, se procedió finalmente al análisis a profundidad de las causas de las inconsistencias precisadas, pudiendo con ello determinar el plan de acción que debe poner en marcha la empresa para lograr el cumplimiento total de la normatividad vigente sobre calidad alimentaria.Calidad de los alimentos; Servicios de alimentación; Catering; Centro de producción; Planes de mejoramiento; Mejoramiento continuo; Resolución 2674 de 2013; Ley 9 de 1979; Aseguramiento de la calidad; Plan de acción

Parallel evolutionary biclustering of short-term electric energy consumption

Presentación realizada en el marco del Proyecto PINV18-661: Análisis de la eficiencia energética en edificios no residenciales mediante técnicas metaheurísticas y de inteligencia artificial.CONACYT - Consejo Nacional de Ciencias y TecnologíaPROCIENCI