Comparison of thermal models for ground-mounted south-facing photovoltaic technologies: a practical case study

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X-ray reflectivity measurement of interdiffusion in metallic multilayers during rapid heating

A technique for measuring interdiffusion in multilayer materials during rapid heating using X-ray reflectivity is described. In this technique the sample is bent to achieve a range of incident angles simultaneously, and the scattered intensity is recorded on a fast high-dynamic-range mixed-mode pixel array detector. Heating of the multilayer is achieved by electrical resistive heating of the silicon substrate, monitored by an infrared pyrometer. As an example, reflectivity data from Al/Ni heated at rates up to 200 K s^(−1) are presented. At short times the interdiffusion coefficient can be determined from the rate of decay of the reflectivity peaks, and it is shown that the activation energy for interdiffusion is consistent with a grain boundary diffusion mechanism. At longer times the simple analysis no longer applies because the evolution of the reflectivity pattern is complicated by other processes, such as nucleation and growth of intermetallic phases

Application of the model ‘Heat Source’ to assess the influence of meteorological components on stream temperature and simulation accuracy under heat wave conditions

Stream temperature is one of the most important factors for aquatic organism, but also regulates drinking water quality, which are both threatened by temperature rises. Atmospheric heat fluxes are primary drivers of stream temperature changes, all of them dependent on the rivers' openness to sky.To be able to simulate stream temperature in rivers of complex terrain and shaded by riparian vegetation a deterministic model including all shading processes was used and validated for the application for Eastern Austrian lowland rivers during summer and the heat wave 2–8 August 2013. The global radiation was included as direct input, which lead to an improvement. It is shown, that both net short wave radiation and evaporation are the most influential components under heat wave conditions and that both are subject to the influence of shading by topography and vegetation. The forward propagation of measurement imprecisions of atmospheric input parameters on simulated water temperature was calculated. The total model imprecision caused by measurement errors of sky obstructing elements (+1.24/−1.40 °C) exceeds the error caused by measurement errors of meteorological input parameters (+0.66/−0.70 °C). The most important sky obstructing elements are vegetation height and vegetation density. A total model imprecision caused by measurement errors of meteorological and shading input parameters is calculated with +1.90/−2.10 °C. While the errors caused by meteorological input are expected much smaller under normal conditions, sky view reducing errors are realistic or even underestimated

Occurrence of repeated drought events: can repetitive stress situations and recovery from drought be traced with leaf reflectance?

Abstract Within the last years a lot of effort has been made to improve irrigation efficiency and early drought stress detection by using various remote sensing techniques. In the present study two different species of wheat (Triticum aestivum and Triticum durum), cultivated in a growth chamber, were used to investigate the effects of drought occurring at different phenological stages. Plant physiological traits and spectral leaf reflectance were used to assess the potential of remote sensing techniques. Drought stress was applied either at flowering and/or at grain filling. Subsequently, a treatment following recovery after drought stress at flowering was set up. The effects of drought were traced by following the changes in plant physiological traits (i.e. photosynthetic rate, leaf conductance, relative and actual leaf water content) as well as in leaf reflectance. Drought resulted in a significant reduction of plant physiological traits and water relations, independently of the time of its occurrence. Rewatering plants after the stress period at flowering resulted in a recovery of plant physiological traits. Single leaf reflectance of plants subjected to drought increased over the entire range of the spectrum. However, five spectral regions with relatively high differences were observed: 520–530 nm, 570–590 nm, 690–710 nm, 1410–1470 nm and 1880–1940 nm. Additionally, three spectral indices were tested towards their applicability for tracing drought stress and subsequent recovery, yielding a reasonable relationship with measured leaf water content, photosynthetic rate and leaf nitrogen content

The influence of riparian vegetation shading on water temperature during low flow conditions in a medium sized river

Stream water temperature limits the growth and survival of aquatic organisms; whereby riparian shading plays a key role in inhibiting river warming. This study explains the effects of riparian shading on summer water temperatures at a pre-alpine Austrian river, during heatwave and non-heatwave periods at low flow conditions. A vegetation-shading index was introduced for the quantification of riparian vegetation effects on water temperature. For maximum water temperatures, a downstream warming of 3.9 °C was observed in unshaded areas, followed by a downstream cooling of 3.5 °C in shaded reaches. Water temperature directly responded to air temperature and cloudiness. For an air temperature change of 2 °C we modelled a water temperature change of 1.3 °C for unshaded reaches, but lower changes for intensively shaded reaches. Similar daily variations at shaded reaches were up to 4 °C lower than unshaded ones. This study gives clear evidence that for a medium-sized pre-alpine river, restoration practices should consider that discontinuity of riparian vegetation should be less than 6000 m; with more than 40% dense vegetation in order to minimize water temperature increases due to unshaded conditions

UV Exposure during Cycling as a Function of Solar Elevation and Orientation

Although cycling is the most prevalent means of locomotion in the world, little research has been done in evaluating the ultraviolet (UV) radiation exposure of cyclists. In this study, a volunteer using a men’s bike was equipped with 10 miniature UV-meters at different body sites. Besides erythemally effective irradiance, the ratio of personal UV exposure to ambient UV radiation was determined for solar elevations up to 65°, taking into account different orientations with respect to the sun. This method provides a universal model that allows for the calculation of UV exposure whenever ambient UV radiation and solar elevation are available. Our results show that the most exposed body sites are the back, forearm, upper arm, and anterior thigh, receiving between 50% and 75% of ambient UV radiation on average. For certain orientations, this percentage can reach 105% to 110%. However, the risk of UV overexposure depends on ambient UV radiation. At lower solar elevations (<40°), the risk of UV overexposure clearly decreases

Influence of low ozone episodes on erythemal UV-B radiation in Austria

ISSN:0177-798XISSN:1434-448