Numerical analysis of gas diffusion in drilled hollow–core photonic crystal fibres

Hollow-Core Photonic Crystal Fibres (HC-PCFs) have emerged as an area of interest for fibre-optic based distributed gas sensing. In order to allow the gas to enter the hollow core of the fibre, various techniques such as lateral drilled side holes have been investigated in the literature. However, it is essential to understand the mechanisms of gas flow in HC-PCFs with drilled side holes in order to determine the optimum design parameters of the sensor such as the size and spacing of drilled side holes. This study aims to analyse the gas flow behaviour and determine the response time of HC–PCFs with drilled side holes by developing and applying a numerical model based on gas diffusion in a microchannel. The model is validated against the results of two different experimental studies. The model is then applied to determine the response time is a function of the length, the number and spacing of side holes and the gas type (methane and acetylene). It is found that an inverse relationship exists between the effects of number and spacing of side holes on the response time and the optical loss, suggesting that an optimum design point exists

Spatial distribution and volume of dead wood in unmanaged caspian beech (Fagus orientalis) forests from northern Iran

Unmanaged forests are remnants of natural ecosystems that provide a basis for close-to-nature silvicultural research and applications. These forests have high amounts of dead wood, and although this material is being increasingly studied, the diversity of dead wood in terms of different diameters, decay stages, and spatial distribution patterns is as important as its volume for understanding forest dynamics. Here, we study natural forests in northern Iran to investigate the spatial distribution, decay stages, and volume of dead wood in unmanaged temperate forests at different developmental stages. Three stem-mapped sampling plots (100 m × 100 m) were established in uneven-aged stands dominated by Caspian beech (Fagus orientalis Lispsky). The total dead wood ranged from 37 to 119 m2 ha-1. Our results imply a spatial distribution shift from aggregation to randomness for dead trees in Caspian beech forest succession. We detected significant spatial interactions (attraction) between living and dead trees at short to medium spatial scales (1-20 m) in the plot with the earlier successional stage, suggesting that intra-specific competition is a prevailing force causing tree mortality at the stem-exclusion phase. By contrast, as trees become dominant with the mortality of other trees, the random tree-mortality pattern prevails. The spatial distribution and volume of dead wood may serve as a management target in near-to-natural Caspian beech forest. On the basis of our results, conservation-oriented management strategies should take into account the increasing amount of dead wood, particularly of large diameter in a late stage of decay. © 2013 by the authors.The authors would like to thank the Forest, Range and Watershed Organization of Iran for the financial support of the project. Jesús Julio Camarero acknowledges the support of ARAID. David Nesbitt looked over the English of this manuscript.Peer Reviewe

An interpretive study of food, snack and beverage advertisements in rural and urban El Salvador

© 2015 Amanzadeh et al.; licensee BioMed Central.Background: Globalization and increased marketing of non-nutritious foods and beverages are driving a nutrition transition in developing countries, adversely affecting the health of vulnerable populations.

Mathematical modelling of gas flow in a hollow-core optical fibre

Hollow-Core Photonic Crystal Fibres (HC PCFs) provide a microscale cell for fast response optical gas sensing. This paper presents a computational simulation of flow behaviour of methane and hydrogen gases in HC-PCFs under ambient pressure and temperature. A mathematical model has been developed to study the gas diffusion time in different structures and lengths of HC-PCF. The results show the relation of gas concentration over time along the length of HC-PCF’s core