Influence of Embankments with Parapets on the Cross-Wind Turbulence Intensity at the Contact Wire of Railway Overheads

Winds as an environmental factor can cause significant difficulties for the railway system operation. The railway overhead has been particularly vulnerable to cross-winds related problems, such as development of undamped oscillations due to galloping phenomenon. The installation of windbreaks to decrease the aerodynamic loads on the train can affect the loads on railway overheads triggering cable galloping. One essential parameter to indicate the influence of the parapet wake on the catenary contact wire is the turbulence intensity. In this paper the results of an experimental analysis of the turbulence intensity due to the presence of parapets carried out in a wind tunnel are reported. Embankments equipped with different parapets have been tested and turbulence intensity has been measured at both contact wire locations, windward and leeward. The relative influence of the parapets is measured through a reduced turbulence intensity, defined as the ratio between the turbulence intensity measured with parapet and the turbulence intensity in the case without any parapet on the embankment. In general the reduced turbulence intensity increases as the height of the parapet increases

Ascorbic Acid Degradation in PVP Solid Dispersions and the Effects of Water and Pre-lyophilization Solution pH On its Chemical Stability

Ascorbic acid (vitamin C) is an essential micronutrient found both naturally in foods as well as supplemented in fortified foods and dietary supplements. In foods, ascorbic acid typically exists in the aqueous or crystalline solid state, but the lyophilization of ascorbic acid polymer solutions has been proven to render ascorbic acid into the amorphous solid state. This study investigated the importance of two matrix effects – the weight ratio of ascorbic acid to PVP and the pre-lyophilization solution pH – on the chemical degradation of ascorbic acid in the amorphous solid state. Amorphous ascorbic acid was generated via lyophilization with PVP and stored at several controlled temperature conditions and 11% relative humidity. Low pH lyophiles (pH 3.0 and pH 3.5) displayed strongly non-additive moisture sorption behavior while higher pH lyophiles (pH 4.0 and pH 4.5) displayed additive moisture sorption. Changes in the pre-lyophilization solution pH caused up to four-fold increases in the extent of ascorbic acid degradation in lyophiles in spite of similar glass transition temperatures and equal relative humidity storage conditions. Modification of the weight ratio of ascorbic acid to PVP caused over six-fold increases in loss of ascorbic acid during storage. Recrystallized ascorbic acid dispersions showed no significant differences in loss during storage regardless of weight ratio, supporting the importance of the physical state of small molecules on their chemical stability. Given the large differences in chemical stability caused by ascorbic acid to PVP weight ratio and pre-lyophilization solution pH, these two matrix effects should be considered important factors in the chemical stability of small molecules in amorphous solid dispersions

Factores de calidad del servicio en el transporte público de pasajeros: estudio de caso de la ciudad de Toluca, México

En este artículo se identifican, ponderan y valoran los factores que intervienen en la percepción de la calidad de servicio del transporte público en un corredor urbano que se caracteriza por una gestión delegada con tarifa fija y competencia en calidad. Mediante un modelo logit con especificación lineal de la función de utilidad, se estiman los coeficientes de cada factor de calidad de servicio para diferentes segmentos y estratos de la población. Los resultados de la estimación econométrica determinan la importancia, peso y valor de cada factor en términos de utilidad. De esta manera se obtiene que los factores principales que determinan la calidad del servicio son: el estado físico de los autobuses, la forma de manejo del conductor, la tarifa (costo del viaje), el tiempo que está dentro del autobús (tiempo de viaje) y el trato al usuario