The Kjeldahl Titrimetric Finish: On the Ammonia Titration Trapping in Boric Acid

Kjeldahl method using concentrated boric acid is a common practice in many laboratories. A thorough study of the titration with hydrochloric acid of ammonia trapped in a solution of boric acid is made in an attempt to explain the fundamentals of a widely applied standard method. A new potentiometric method for the determination of the end point in the Kjeldahl titrimetric finish is proposed based on the linearization of the titration curve of the ammonia‐boric acid system. The method is strictly based on mole and charge balances, and no approximations are made in deriving the equations. The proposed method has proved very accurate when applied to synthetic titration curves and data. Some problems, however, are experienced in the practice, because the behavior of the experimental system studied is far from the expected one on the basis of the theoretical model. However, a slight modification of the devised method has been applied to the experimental titration of ammonia with hydrochloric acid, in boric acid as trapping solution, getting good results

Indicadores para la planeación del mantenimiento basado en eficiencia energética en redes de intercambiadores de calor

Thanks to the asset management regulations, modern maintenance practices are rapidly getting a more managerial role, and is used to achieve savings and optimize energy use. Therefore, knowing at all times the status of the equipment allows for timely and necessary interventions that generate value to the company, and recover the initial conditions of them. Heat exchanger networks, rather than a productive asset, constitute an energy-saving strategy, to have lower fuel costs, emission control, rational use of energy, etc. in the atmospheric furnaces of the crude distillation units, and other units that perform similar processes. Thus, keeping them in their best conditions, most of the time is necessary. In this paper, we propose a methodology for the diagnosis of the equipment of the network, and the maintenance planning justified by the energy efficiency of them and the economic impact of the intervention. In addition, an indicator is presented to provide an economic justification for maintenance interventions, as well as for briefly showing the results of the application of maintenance mainly on efficiency and the use of the KPI J proposed for programming the maintenance schedule of some of the equipment (pilot test) of the heat exchanger network under study. The methodology developed uses real operation values, and its results provided savings up to USD 150,000.Gracias a las normativas de gestión de activos, Las practicas modernas de mantenimiento están asumiendo cada vez un rol más gerencial, y siendo usadas para lograr ahorros y optimizar el uso de la energía. Así las cosas, conocer en todo momento el estado de los equipos mantenidos, permite realizar las intervenciones oportunas y necesarias que generen valor a la empresa, y recuperar las condiciones iniciales de los equipos o cercanas a estas. Las redes de intercambiadores de calor, más que un activo productivo, constituyen una estrategia de ahorro energético, en pro de tener menores costos de combustible, control de emisiones, uso racional de la energía, etc. en los hornos atmosféricos de las unidades de destilación de crudo, y otras unidades que realizan procesos similares, por lo que mantenerlos en sus mejores condiciones la mayor parte del tiempo es menester. A continuación, se propone una metodología para el diagnóstico de los equipos de la red, y la planeación del mantenimiento justificada por la eficiencia energética de los equipos y el impacto económico de la intervención. Para esto se presentan a) los indicadores clave de desempeño de los intercambiadores, b) un indicador que sirve como justificación económico-energética de las intervenciones de mantenimiento, c) cronograma de mantenimiento de algunos de los equipos (prueba piloto) de la red de intercambiadores de calor en estudio. La metodología desarrollada utiliza valores reales operación y sus resultados están aplicados logrando ahorros de 150.000 USD

Amphibia, Anura, Hylidae, Dendropsophus microcephalus (Boulenger, 1898): distribution extensions

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MEJORAMIENTO DEL PROCESO DE SECADO DE CEREALES EN UNA EMPRESA PRODUCTORA DE ALIMENTO PARA AVES DE CORRAL

A partir de este estudio se creó una propuesta para mejorar el proceso de secado de cereales, teniendo en cuenta que una mala gestión en este proceso, genera retrasos en producción, detrimento de la calidad del producto y por ende riesgos químicos, biológicos y físicos, poniendo en peligro la vida de las aves que se alimentan del producto terminado. Para tal efecto, se realizó un estudio analítico del proceso, encontrándose dos puntos críticos en particular: Una falta de homogeneidad en la humedad de los granos secos y prolongados tiempos de secado. Este estudio ocupó el segundo lugar en la convocatoria de ACAIR

Bioconversion of polyphenols and organic acids by gut microbiota of predigested Hibiscus sabdariffa L. calyces and Agave (A. tequilana Weber) fructans assessed in a dynamic in vitro model (TIM-2) of the human colon

The present work aimed at understanding gut microbiota bioconversion of phenolic compounds (PC) and organic acids in predigested Hibiscus sabdariffa (Hb) calyces and the mixture of Hb and Agave (Agave tequilana Weber) fructans (AF). With this purpose, dried Hb and Hb/AF were predigested with enzymatic treatment, and then fermented in a dynamic in vitro model of the human colon (TIM-2). After HPLC-ESI-QToF-MS analysis of samples taken at 0, 24, 48 and 72 h of fermentation, it was observed that hydroxycinnamic acids, flavanols, flavonols, and anthocyanins were mainly transformed into derivatives of hydroxyphenylpropionic, hydroxyphenylacetic and hydroxybenzoic acids. Moreover, organic acids, such as hydroxycitric and hibiscus acids, were formed along with unidentified lactones and reduced compounds. Interestingly, no differences were observed between microbial-derived metabolites formed after the fermentation of Hb and Hb/AF. In conclusion, colonic fermentation of polyphenol-rich Hb yields a wide range of microbial phenolic metabolites with potential effects on health.RMB and SGSA acknowledge to Science and Technology for Development Program (CYTED) through the Ibero-American Network of Underutilized Autonomous Foods (ALSUB-CYTED, 118RT0543). SGSA acknowledges CONACYT-Mexico for the sabbatical grant 260935. The Spanish Ministry of Science, Innovation and Universities (Project AGL2015-69986-R) is also acknowledged. This research has been made possible with the support of the Dutch Province of Limburg.Peer reviewe

Panhipopituitarismo y diabetes mellitus: el fenómeno de Houssay

Se presenta el caso de una paciente con diabetes tipo 2 de larga evolución que permaneció asintomática, por lo menos durante dos años, debido a la presencia de un panhipopituitarismo (síndrome de Sheehan) adquirido mucho antes

Musashi and Plasticity of Xenopus and Axolotl Spinal Cord Ependymal Cells

The differentiated state of spinal cord ependymal cells in regeneration-competent amphibians varies between a constitutively active state in what is essentially a developing organism, the tadpole of the frog Xenopus laevis, and a quiescent, activatable state in a slowly growing adult salamander Ambystoma mexicanum, the Axolotl. Ependymal cells are epithelial in intact spinal cord of all vertebrates. After transection, body region ependymal epithelium in both Xenopus and the Axolotl disorganizes for regenerative outgrowth (gap replacement). Injury-reactive ependymal cells serve as a stem/progenitor cell population in regeneration and reconstruct the central canal. Expression patterns of mRNA and protein for the stem/progenitor cell-maintenance Notch signaling pathway mRNA-binding protein Musashi (msi) change with life stage and regeneration competence. Msi-1 is missing (immunohistochemistry), or at very low levels (polymerase chain reaction, PCR), in both intact regeneration-competent adult Axolotl cord and intact non-regeneration-competent Xenopus tadpole (Nieuwkoop and Faber stage 62+, NF 62+). The critical correlation for successful regeneration is msi-1 expression/upregulation after injury in the ependymal outgrowth and stump-region ependymal cells. msi-1 and msi-2 isoforms were cloned for the Axolotl as well as previously unknown isoforms of Xenopus msi-2. Intact Xenopus spinal cord ependymal cells show a loss of msi-1 expression between regeneration-competent (NF 50–53) and non-regenerating stages (NF 62+) and in post-metamorphosis froglets, while msi-2 displays a lower molecular weight isoform in non-regenerating cord. In the Axolotl, embryos and juveniles maintain Msi-1 expression in the intact cord. In the adult Axolotl, Msi-1 is absent, but upregulates after injury. Msi-2 levels are more variable among Axolotl life stages: rising between late tailbud embryos and juveniles and decreasing in adult cord. Cultures of regeneration-competent Xenopus tadpole cord and injury-responsive adult Axolotl cord ependymal cells showed an identical growth factor response. Epidermal growth factor (EGF) maintains mesenchymal outgrowth in vitro, the cells are proliferative and maintain msi-1 expression. Non-regeneration competent Xenopus ependymal cells, NF 62+, failed to attach or grow well in EGF+ medium. Ependymal Msi-1 expression in vivo and in vitro is a strong indicator of regeneration competence in the amphibian spinal cord

Entrenamiento Discriminativo Maximizando una Distancia entre Modelos de Clases

En este trabajo se presenta una técnica de entrenamiento discriminativo para modelos ocultos de Markov, orientado a la detección de patologías en señales de voz. La técnica busca maximizar el área que encierra la curva ROC (Receiver Operating Characteristic curve) ajustando los parámetros de modelo, empleando como función objetivo la distancia entre las medias de las funciones de densidad de probabilidad subyacentes asociadas a cada clase. Como resultado se obtiene una mejora en el desempeño del sistema de clasificación comparada con diferentes criterios de entrenamiento.This paper presents an approach that improves discriminative training criterion for Hidden Markov Models, and it is oriented to voice pathological identification. This technique aims at maximizing the Area under the Receiver Operating Characteristic curve by adjusting the model parameters using as objective function the distance between the means of the underlying probability densities functions associated with each class. As result we obtain an improvement in the performance of the classification system compared with different training criteria

Análisis comparativo de las características fisicoquímicas de la cascarilla de arroz.

En este estudio se hace un análisis comparativo de las principales propiedades fisicoquímicas de la cascarilla de arroz obtenida por investigaciones realizadas en las universidades de Canadá, California, RP China y de Ibagué Colombia, como punto de partida para la realización del proyecto de transformación de la biomasa arrocera en energía eléctrica y térmica. Se concluye que existe una igualdad entre los rengos de las características fisicoquímicas de la cascarilla de arroz para regiones tan distantes y diferentes como China, Canadá, Estados Unidos y Colombia; y que en ellas las temperaturas de oxidación alcanzada es del orden de 1200K, liberando alrededor del 67% del valor calórico en la etapa dominante de la combustión correspondiente a la combustión de los volátiles