Recurrent personal exposure to ambient PM_2.5 is associated with adverse human health effects, in particular on the respiratory and cardiovascular systems. Here, we present an assessment of personal exposure and inhalation of PM_2.5 for five modes of transport (walking, cycling, public bus (trolleybus and diesel bus), conventional car (CC) and hybrid-electric car (HEC)) and two routes of similar distance, along a major road in the Mexico City metropolitan area (MCMA). Arithmetic average exposure concentrations ranged from 16.5 ± 6.5 µg m⁻³ for walking to 81.7 ± 9.1 µg m⁻³ for cycling (henceforth shown as average ±1 SD), with no significant differences with geometric averages. The maximum exposure concentration of 110.9 µg m⁻³ was observed for the conventional car. The highest exposure concentrations depended on route and the mode of transport, being observed for cycling and walking. The PM_2.5 measurements showed large spatial heterogeneity in the exposure levels for walking and cycling, while public buses and private transport showed less spatial heterogeneity. The greatest peaks in PM_2.5 coincided with 4-way intersections for all modes of transport, being positively influenced by traffic density. The mass of PM_2.5 inhaled depended mostly on the mode of transport, and ranged between 1.0 ± 0.3 and 30.1 ± 14.2 µg km⁻¹ for the HEC and bicycle, respectively. Local area PM_2.5 increments identified as ‘residuals’ after subtraction of data recorded at the closest fixed monitoring site from exposure concentrations along the studied road suggested that inhalation for bicycle and diesel buses is strongly influenced by vehicular emissions. Residuals estimated for the trolleybus, CC and HEC confirmed a lower inhalation than for the other modes of transport evaluated due to protection by the cabin.

Compound parabolic concentrators are relevant systems used in solar thermal technology. With adequate tailoring, they can be used as an efficient and low-cost alternative in residential water heating applications. This work presents a simulation study using a ray tracing analysis. With this technique, we simulate the interaction between solar rays and solar concentrator to quantify the amount of energy that impinges on the receiver at a particular time. Energy availability is evaluated in a comparison of two configurations throughout the year: static setup at 21° and multi-position setup; tilted with respect to the horizontal, depending on three seasonal positions: 0° for summer, 16° for spring/autumn, and 32° for winter, with the aim to evaluate the amount of available energy in each season. The fact that a tracking system can be dispensed with also represents an economical option for the proposed application. The results showed that at 21°, the proposed solar Compound Parabolic Concentrator (CPC) works satisfactorily; however, by carrying out the selected angular adjustments, the overall energy availability increased by 22%, resulting in a more efficient option. The most effective design was also built and analyzed outdoors. The obtained thermal efficiency was of ~43%. The optical design and its evaluation developed herein proved to be a valuable tool for prototype design and performance evaluation.

In recent years it has been proven that hybrid forms of powertrains in vehicles can lead to substantial reductions in fuel consumption and emissions. In particular, the advent of commercial hybrid electric vehicles proved that improved performance has been achieved by implementing a secondary energy source in a vehicle powertrain. However, the only secondary energy source implemented to date is based on electrochemical batteries, which suffer from technical and economic disadvantages. To overcome this, a novel powertrain based in both mechanical power transmission and mechanical energy storage is proposed. This article presents a brief explanation of flywheel technology as it applies to hybrid vehicles and a qualitative comparison with existing energy storage technologies is also presented. Finally computational simulations will show that the implementation of this powertrain in a vehicle leads to important reductions in fuel consumption while requiring only mechanical components in the system, instead of batteries, motors, generators and power electronics. (8 pages)

Currently, there is limited information regarding the performance of solar heaters in a round-year period under real weather conditions and the determination of their characteristic equation following standard methods. Therefore, this study presents a methodology to determine the characteristic equation of the annual thermal performance under real conditions based on uncertainty and linear regression analysis estimation. With this methodology, it is possible to analyze daily experimental data in a collector that has not been restricted to any particular requirement of evaluation standards. This methodology was applied to evaluate a flat plate solar heater operating in Mexico over a period of one year in two operating modes: thermosyphon and forced circulation. In the case of forced circulation, a small submersible pump was implemented, the activation of which was controlled by using a thermostat, thereby providing an effective control of the flow and temperature of the collector. The results indicated that the methodology was adequate to identify the level of uncertainty in a line of the best fit, which allowed the determination of a characteristic equation that reflects the operation of the heater under real conditions, in a round-year period. As a result of the application of this methodology, it was observed that the use of a submersible pump and a thermostat increases the efficiency throughout a whole year by 0.06, whereas the continuous use of a pump increases efficiency by 0.17, with respect to the operation in the thermosyphon mode.

Compound parabolic concentrators are relevant systems used in solar thermal technology. With adequate tailoring, they can be used as an efficient and low-cost alternative in residential water applications. This work presents a simulation study using a ray tracing methodology. With this technique we simulate the interaction between solar rays and solar concentrator to quantify the amount of energy that impinges on the receiver at a particular time. Energy availability is evaluated in a comparison of two configurations: stationary at 21° throughout the year and multi position setup; tilted with respect to the horizontal depending on three seasonal positions: 0° for summer, 16° for spring / autumn and 32° for winter, with the objective of increasing the amount of available energy in each season. The fact that a tracking system can be dispensed with also represents an economical option for the proposed application. The results showed that at 21°, the proposed system works satisfactorily; however, by carrying out the selected angular adjustments, the overall energy availability increased by 22%, resulting in a more efficient option. The methodology developed herein proved to be a valuable tool for prototype design and performance evaluation.