Environment enhanced fatigue of advanced aluminum alloys and composites

The objective is to characterize and understand the environmental fatigue crack propagation behavior of advanced, high stiffness and strength, aluminum alloys and metal matrix composites. Those gases and aqueous electrolytes which are capable of producing atomic hydrogen by reactions on clean crack surfaces are emphasized. Characterizations of the behavior of new materials are sought to provide data for damage tolerant component life prediction. Mechanistic models are sought for crack tip damage processes which are generally applicable to structural aluminum alloys. Such models will enable predictions of cracking behavior outside of the data, metallurgical improvements in material cracking resistance, and insight on hydrogen compatibility

Environment enhanced fatigue of advanced aluminum alloys and metal matrix composites

The environmental fatigue crack propagation behavior of advanced Al-Li-Cu based alloys and metal matrix composites is being characterized. Aqueous NaCl and water vapor, which produce atomic hydrogen by reactions on clean crack surfaces, are emphasized. The effects of environment sensitive crack closure, stress ratio, and precipitate microstructure are assessed. Mechanistic models are sought for intrinsic crack tip damage processes to enable predictions of cracking behavior outside of the data, metallurgical improvements in material cracking resistance, and insight on hydrogen compatibility

Planned perception within concurrent mapping and localization

The fundamental requirement of truly autonomous mobile robots is navigation. Navigation is the science of determining one's position and orientation based on information provided by various sensors. Mobile robot navigation, especially autonomous vehicle navigation, is confronted with the problem of attempting to determine the structure of an a priori unknown environment, while at the same time using this information for navigation purposes. This problem is referred to as concurrent mapping and localization (CML). This thesis addresses the question of how to improve CML performance through smarter sensing strategies affecting robot behavior. Planned perception is the process of adaptively determining the sensing strategy of the mobile robot. The goal of integrating planned perception within concurrent mapping and localization is to attempt to answer the question of how a mobile robot should behave so as to attempt to optimize CML performance. This thesis demonstrates in simulation how the CML framework could be improved with planned perception by motivating changes in robot pose and hence, sensing locale.http://archive.org/details/plannedperceptio109451102

Self-induced laser line sweeping in double-clad Yb-doped fiber-ring lasers

International audienceExperimental observation of the self-induced laser line sweeping (SLLS) in fiber ring lasers is presented. The SLLS with the same gain fiber is studied in Fabry-Perot cavity for comparison. The SLLS effect manifests itself as a laser wavelength drift with speed of the order of nanometer per second from shorter to longer wavelengths across several nanometers and fast backward jump. Recently, the dynamics of the SLLS in a Fabry-Perot cavity fiber laser was qualitatively described by a dynamic grating induced by spatial-hole-burning in the ytterbium doped fiber where the lifetime of the grating was related to the self-sustained relaxation oscillations. In this paper we address possible discrepancies between the published theoretical model and earlier observations of SLLS, particularly in fiber-ring lasers.We show that the qualitative theoretical model developed for explaining SLLS in the Fabry-Perot cavity can be used also to explain the SLLS effect we observed earlier in fiber-ring lasers

Ecology, behaviour and management of the European catfish

The extreme body sizes of ‘megafishes’ associated with their high commercial values and recreational interests have made them highly threatened in their native range worldwide by human-induced impacts such as overexploitation. Meanwhile, and because of the aforementioned interests, some megafishes have been introduced outside of their native range. A notable exampled is the European catfish (Silurus glanis), one of the few siluriforms native from western Europe and among the 10 largest freshwater fish worldwide, attaining a total length over 2.7 m and a documented mass of 130 kg. Its distinct phylogeny and extreme size imply many features rare among other European fish such as peculiar behaviours (massive aggregations, beaching), consumption of large bodied prey, fast growth rate, long lifespan, high fecundity, nest guarding and large eggs. The spread of the species is likely to continue due to illegal introduction coupled with natural range extension due to current and future climate change. Based on these attributes and potential future risks, this introduced giant predator in European fresh waters could provide a novel model species of high utility for testing aspects of ecological and invasion theory and associated hypotheses. Here, we reviewed the most recent knowledge on the current distribution and the ecology of the species to understand how this can help advance our understanding of biological invasions. We also identified key research questions that should help stimulating new research on this intriguing, yet largely unknown, species and, more generally, on the ecology of invasive species

49 Gbit/s Direct-Modulation and Direct-Detection Transmission over 80 km SMF-28 without Optical Amplification or Filtering

We demonstrate direct-modulation of a discrete mode laser using Discrete Multi-Tone modulation for transmission distances up to 100 km in the 1550 nm band. A large operational temperature range (0-65ºC) is also demonstrated

Simple geometric interpretation of signal evolution in phase-sensitive fibre optic parametric amplifier

Visualisation of complex nonlinear equation solutions is a useful analysis tool for various scientific and engineering applications. We have re-examined the geometrical interpretation of the classical nonlinear four-wave mixing equations for the specific scheme of a phase sensitive one-pump fiber optical parametric amplification, which has recently attracted revived interest in the optical communications due to potential low noise properties of such amplifiers. Analysis of the phase portraits of the corresponding dynamical systems provide valuable additional insight into field dynamics and properties of the amplifiers. Simple geometric approach has been proposed to describe evolution of the waves, involved in phase-sensitive fiber optical parametric amplification (PS-FOPA) process, using a Hamiltonian structure of the governing equations. We have demonstrated how the proposed approach can be applied to the optimization problems arising in the design of the specific PS-FOPA scheme. The method considered here is rather general and can be used in various applications