Noisy clocks and silent sunrises: measurement methods of daily activity pattern

From insects to mammals, many animals engage in behaviours known to follow cyclic patterns over days (e.g. singing, diving or foraging behaviours). Many of them are regulated by external factors, such as light intensity, and are thus associated with sunrise, sunset or zenith. However, these astronomical events do not occur at the same time everyday: they vary with both the time of the year and the latitude. Logically, therefore, behaviour timing should be recorded relative to these events. Yet, in the field, recording the timing of behaviour is much less difficult with a clock, which is often deemed a suitable common proxy. In this paper, we assess the potential methodological problems associated with analyzing behaviours on the basis of clock time rather than with the actual position of the sun. To demonstrate the important difference between these methods of analysis, we first simulated a behaviour set at sunrise and compared the time of occurrence with the two methods. We then used a dataset, based on a long-term monitoring of hunting behaviour of African wild dogs, Lycaon pictus, to reveal how using clock time can result in erroneous assumptions about behaviour. Finally, we investigated the occurrence of sun time records in published field studies. As a majority of them did not take into account the relevance of astronomical events, it is probable that many result in faulty behavioural timings. The model presented can change clock-recorded time into actual deviation from astronomical events to assist current protocols as well as correct the already recorded datasets

On the evolution of online tourism communities - Network battle or longtail niches?

Even though the emergence or respectively the construction of online communities is of great interest for scientists and community engineers, only few empirical data has been presented on community growth. This article starts with a reflection on possible growth curves of virtual communities. It contrasts a network externality perspective that produces clear winners and losers in a market with a long tail perspective that also allows small niche products to be successful. These considerations are empirically tested with a sample of 74 travel communities whose numbers of registered members were recorded at two measure points. The results show that online travel communities develop into an archetypical long tail. A very small number of communities with exceedingly high numbers of members are accompanied by a vast amount of communities with only few members. An analysis of the long tail, however, reveals that the community tail is not dead but is populated by a large number of especially regional communities that show considerable growth rates

Low radiation dose in computed tomography: the role of iodine

Recent approaches to reducing radiation exposure during CT examinations typically utilize automated dose modulation strategies on the basis of lower tube voltage combined with iterative reconstruction and other dose-saving techniques. Less clearly appreciated is the potentially substantial role that iodinated contrast media (CM) can play in low-radiation-dose CT examinations. Herein we discuss the role of iodinated CM in low-radiation-dose examinations and describe approaches for the optimization of CM administration protocols to further reduce radiation dose and/or CM dose while maintaining image quality for accurate diagnosis. Similar to the higher iodine attenuation obtained at low-tube-voltage settings, high-iodine-signal protocols may permit radiation dose reduction by permitting a lowering of mAs while maintaining the signal-to-noise ratio. This is particularly feasible in first pass examinations where high iodine signal can be achieved by injecting iodine more rapidly. The combination of low kV and IR can also be used to reduce the iodine dose. Here, in optimum contrast injection protocols, the volume of CM administered rather than the iodine concentration should be reduced, since with high-iodine-concentration CM further reductions of iodine dose are achievable for modern first pass examinations. Moreover, higher concentrations of CM more readily allow reductions of both flow rate and volume, thereby improving the tolerability of contrast administration