ABSTRACT
For high-performance thermoplastic materials, material behavior results from the degree of crystallization and the distribution of crystalline phases. Due to the less stiff amorphous and the stiffer and anisotropic crystalline phases, the microstructural properties are inhomogeneous. Thus, imaging of the microstructure is an important tool to characterize the process-induced morphology and the resulting properties. Using focusing ultrasonic transducers with high frequency (25 MHz nominal center frequency) enables the imaging of specimens with high lateral resolution, while wave propagation is related to the elastic modulus, density and damping of the medium. The present work shows experimental results of high-frequency ultrasonic spectroscopy (HF-US) applied to injection-molded polyether-ether-ketone (PEEK) tensile specimens with different process-related morphologies. This work presents different analysis procedures, e.g., backwall echo, time of flight and Fourier-transformed time signals, facilitating the mapping of gradual mechanical properties and assigning them to different crystalline content and morphological zones.
ABSTRACT
BACKGROUND: The dramatic mass mortalities amongst hibernating bats in Northeastern America caused by "white nose-syndrome" (WNS) continue to threaten populations of different bat species. The cold-loving fungus, Geomyces destructans, is the most likely causative agent leading to extensive destruction of the skin, particularly the wing membranes. Recent investigations in Europe confirmed the presence of the fungus G. destructans without associated mass mortality in hibernating bats in six countries but its distribution remains poorly known. METHODOLOGY/PRINCIPAL FINDINGS: We collected data on the presence of bats with white fungal growth in 12 countries in Europe between 2003 and 2010 and conducted morphological and genetic analysis to confirm the identity of the fungus as Geomyces destructans. Our results demonstrate the presence of the fungus in eight countries spanning over 2000 km from West to East and provide compelling photographic evidence for its presence in another four countries including Romania, and Turkey. Furthermore, matching prevalence data of a hibernaculum monitored over two consecutive years with data from across Europe show that the temporal occurrence of the fungus, which first becomes visible around February, peaks in March but can still be seen in some torpid bats in May or June, is strikingly similar throughout Europe. Finally, we isolated and cultured G. destructans from a cave wall adjacent to a bat with fungal growth. CONCLUSIONS/SIGNIFICANCE: G. destructans is widely found over large areas of the European continent without associated mass mortalities in bats, suggesting that the fungus is native to Europe. The characterisation of the temporal variation in G. destructans growth on bats provides reference data for studying the spatio-temporal dynamic of the fungus. Finally, the presence of G. destructans spores on cave walls suggests that hibernacula could act as passive vectors and/or reservoirs for G. destructans and therefore, might play an important role in the transmission process.
