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We developed a systematic experimental method to demonstrate that damage threshold fluence (DTF) for fused silica changes with the number of femtosecond laser (800 nm, $65\pm 5~\text{fs}$ , 10 Hz and 600 Hz) pulses. Based on the experimental data, we were able to develop a model which indicates that the change in DTF varies with the number of shots logarithmically up to a critical value. Above this value, DTF approaches an asymptotic value. Both DTF for a single shot and the asymptotic value as well as the critical value where this happens, are extrinsic parameters dependent on the configuration (repetition rate, pressure and geometry near or at the surface). These measurements indicate that the power of this dependence is an intrinsic parameter independent of the configuration. [ABSTRACT FROM AUTHOR]

Omnivory, feeding at more than one trophic level, is a prevalent feature of freshwater ecosystems. Understanding where and when omnivory is important, its relevance for sustaining diversity, and the effect it may have on ecosystem responses to disturbances, are necessary for effective management of freshwater ecosystems., The many theoretical predictions of the effects of omnivory are often contradictory, and empirical studies aimed at understanding omnivory have been difficult and contingent on a number of factors. Here, I synthesise theoretical evidence to generate five predictions of where omnivory will be most important in freshwater ecosystems, how it is maintained and the effect it will have on communities., First, theory indicates that, while strong omnivorous interactions are destabilising, weak omnivorous interactions usually enhance stability. Therefore, mechanisms which decrease the strength of omnivorous interactions should favour their occurrence and increase stability of food webs. Secondly, omnivorous interactions which are theoretically unstable may be found in stable food webs due to stabilising features of the web as a whole. Thirdly, omnivory is likely to persist primarily at intermediate productivity levels and be more common in disturbed environments. Fourthly, omnivory is likely to decrease the strength of trophic cascades. Finally, omnivores should generally make more successful invaders., These predictions are important for effective freshwater management because actions which decrease the strength of omnivorous interactions, such as maintaining habitat refuges for consumers (e.g. woody debris and aquatic plants), may be essential for sustaining biodiversity. In addition, if omnivores make better invaders, effective invasion management may benefit from focussing resources on omnivorous invaders to limit their spread and impact., Overall, this synthesis of theoretical and empirical studies indicates that, while their predictions may be frequently at odds, with deeper investigation they are largely reconcilable and can be used to make practical suggestions for the careful management of omnivory in freshwater food webs. [ABSTRACT FROM AUTHOR]

Given current levels of biodiversity loss and environmental change, studies of how food webs respond to disturbance should broaden their focus beyond short-term disturbances to explore the effects of long-term, "press" disturbances. Press disturbances often disproportionately impact one or a few species, but these impacts invariably propagate to the remaining species in the food web. Additionally, the way species interact with each other within the food web influences the impact they have on the rest of the food web if it is disturbed. Here, we investigate the effect of species-level press disturbances in a large set of model food webs. We simulated disturbances as a reduction in growth rate of a single species within the food web, which is analogous to a targeted disturbance such as selective fishing. In these simulations, we were particularly interested in the resistance of the food web—the magnitude of disturbance it could tolerate before any species went extinct. We found that more highly connected and biodiverse food webs had lower resistance and were more likely to lose species at a low level of disturbance than sparsely connected food webs with few species. Food-web complexity also influenced which species were likely to go extinct due to the disturbance. At low species richness and/or low connectance, food webs could tolerate a large disturbance, and it was usually the focal species which went extinct. In contrast, webs were less stable at higher levels of complexity and a small disturbance rapidly propagated and caused the extinction of a non-focal species. Lastly, the disturbed species' traits were also important: Disturbance of a species with few interactions usually resulted in its own extinction, while disturbance of a species with many interactions more often caused the extinction of the disturbed species' predator(s). Likewise, the trophic level of the disturbed species influenced which species went extinct, although this was modulated by the complexity of the food web. Overall, our study indicates that both the traits of disturbed species and the complexity of the food web need to be considered in attempts to predict or manage the ecological impact of press disturbances. [ABSTRACT FROM AUTHOR]

Novel laser-powered accelerating structures at the miniaturized scale of an optical wavelength open a pathway to high repetition rate, attosecond scale electron bunches that can be accelerated with gradients exceeding 1 GeV/m. Although the theoretical and computational study of dielectric laser accelerators dates back many decades, recently the first experimental realizations of this novel class of accelerators have been demonstrated. We review recent developments in fabrication, testing, and demonstration of these micron scale devices. In particular, prospects for applications of this accelerator technology are evaluated. [ABSTRACT FROM AUTHOR]

Using a vertical undulator, picometer vertical electron beam emittances have been observed at the Australian Synchrotron storage ring. An APPLE-II type undulator was phased to produce a horizontal magnetic field, which creates a synchrotron radiation field that is very sensitive to the vertical electron beam emittance. The measured ratios of undulator spectral peak heights are evaluated by fitting to simulations of the apparatus. With this apparatus immediately available at most existing electron and positron storage rings, we find this to be an appropriate and novel vertical emittance diagnostic. [ABSTRACT FROM AUTHOR]