Effect of material ageing and dirt on the behaviour of greenhouse insect-proof screens

The present work examines the variations in the aerodynamic characteristics of four insect-proof screens by means of wind tunnel tests and digital image processing. The tested insect-proof screens were examined in three different conditions: (i) in their new, unused state; (ii) under conditions of accumulated dust and dirt after a period of 3 to 4 years of use; and (iii) under clean conditions after a period of 3 to 4 years of use and a cleaning treatment with high-pressure water. The deterioration of the screens caused the mesh to become less tense, therefore increasing its thickness and improving its aerodynamic behaviour despite a slight increase of the thread diameter and a subsequent decrease of the 2-dimensional porosity. The pressure drop coefficient, Fφ, of the used but clean screens was 1.5% to 8.8% lower (for u=1.0 m/s) than that of the new ones, thus increasing the discharge coefficient, Cd,φ, by between 0.8% and 4.8% as a result of the presence of the screens. On the other hand, comparison of the used screens in their clean and unclean states showed that the accumulation of dirt has a major bearing on their aerodynamic characteristics: Fφ increased by between 16.5% and 61.2% (for u=1.0 m/s) for the unclean screens, resulting in a Cd,φ reduction of between 7.5% and 21.3% and therefore a lower natural ventilation capacity of the greenhouse. A regular cleaning treatment of the insect-proof screens is a simple measure that improves the natural ventilation capacity of the greenhouse.

Growing old with media technology and the material experience of ageing

During the 20th and 21st century, media such as radio, telephone, television, computers and cell phones moved into everyday life as taken-for-granted elements. Based on observations and life-history interviews with 22 older women, this article discusses how media technology is materially involved in the experience of growing old. The analysis reveals two aspects of this. First, different technology stands out from its background presence as problematic because the media no longer enable the experiences they used to. Second, disconnects with and through media technology direct attention towards the declining body. The participants embody ‘old age’ by linking their experience with media to two cultural constructions of material ageing: generation and natural ageing. I argue that inasmuch as everyday life has become mediatized, the experience of growing old also takes place with and through media technology. This article forms part of ‘Media and the Ageing Body’ Special Issue.