Charged and neutral defect states in a-Si:H determined from improved analysis of the constant photocurrent method

Siebke F, Stiebig H, Abo-Arais A, Wagner H. Charged and neutral defect states in a-Si:H determined from improved analysis of the constant photocurrent method. Solar Energy Materials and Solar Cells. 1996;41-42:529-536.In order to obtain information about the density of localized gap states in a-Si:H, i.e., the valence band tail, the integrated defect density, the energetic defect distribution and the charge state of the defect states, a numerical model has been developed to simulate constant photocurrent method spectra. It takes into account the full set of optical transitions between localized and extended states under sub-bandgap illumination, capture, emission and recombination processes as well as the energetic position of the Fermi level. We compare measured and simulated CPM spectra of doped and undoped a-Si:H. In the annealed state the defect absorption of n- and p-type as well as undoped a-Si:H is dominated by a charged defect states. The simulation reveals that in undoped a-Si:H light soaking, causing an enhanced defect density, does not alter the charged-to-neutral defect ratio

Towards the identification of transmission pathways and early detection of Enterococcus cecorum infection in broiler chickens

Enterococcus cecorum (EC) infection is an emerging endemic disease in UK and global broiler poultry with major economic impact and welfare concerns. There are significant research gaps with regards to EC pathogenesis, source of infection, transmission routes and early detection of disease, which this study aimed to address. In this prospective study, 725 environmental samples were collected from four broiler farms (A-D) the day before chick placement (Day -1) and through the subsequent crop (Days 7, 14 and 21). Cecal swabs were collected from birds that died of natural causes during the study period. A sample of birds that had been found dead or were culled for health reasons, were presented for post-mortem and samples were taken from lesions for EC culture. DNA was extracted from all environmental samples and EC detected using a qPCR and MALDI-TOF. Two EC isolates from diseased birds were inoculated on concrete slabs and incubated at 23°C and 32°C followed by swabbing of concrete culturing and determination of EC cfu at defined time points. Alongside environmental and bird sampling commercially available, smart camera systems were installed in selected houses on each farm to monitor bird activity and distribution. No EC outbreak occurred during the study, however, it was detected by qPCR in 215/725 (29.7 %) of all samples collected. Also, EC DNA was detected on average in 37% of samples collected on day -1, with ∼88% of samples from chick paper being positive. Despite this, it was only cultured from three caeca samples and joint fluids of two infected birds from farm B on days 14 and 21. The survival experiments using isolates from infected chickens showed EC can survive on concrete for at least 21 days. This study provides invaluable insights into transmission pathways and tenacity of EC. Further studies are needed to determine strain characteristics in relation to their ability to cause disease and to further elucidate the sources of infection on poultry farms