No abstract

The method of generating x-rays using the pyroelectric effect has garnered interest for applications that desire portability and low power consumption, particularly for real-time in-field and on-line analyses. However, the x-ray intensity produced by this type of x-ray generator is low and inconsistent compared to conventional x-ray tubes. The properties of several pyroelectric materials, including LiTaO3, LiNbO3, and PMN- xPT, were studied and subsequently tested on an in-house developed x-ray generator to explore their suitability for the application. The production of electrons to subsequently generate x-ray relies on the process of ferroelectric electron emission and field ionization to be dominant over charge compensation via the DC conductivity of the pyroelectric material. Given that the time of temperature change occurs faster than the material's charge relaxation time, it was found that the ratio of the pyroelectric coefficient to relative permittivity determined the performance of the x-ray generator. Thus, the x-ray count rates and end-point energies produced by LiTaO3 showed that it continues to be a strong candidate for such x-ray generation applications.

Pelvic spine polymorphism occurs in several species in the stickleback family (Gasterosteidae). Given parallel selection driving similar phenotypic polymorphisms in multiple stickleback species, we sought to determine the extent of parallelism in the ecological consequences of pelvic spine reduction. Based on a metabarcoding analysis of brook stickleback gut contents in two polymorphic populations, we found a shift towards a planktonic diet was associated with pelvic spine reduction. These results contrast with those found in threespine stickleback where pelvic spine reduction is associated with a shift towards a benthic diet. Hence, we found non-parallel consequences of spine polymorphism across species. Furthermore, a change in gill raker morphology has been consistently implicated in the change in diet in pelvic-reduced threespine stickleback. But we found no evidence of any difference in gill raker morphology associated with pelvic spine polymorphism in brook stickleback.