RESUMO
Likelihood ratios (LRs) are a useful measure of evidential strength. In forensic casework consisting of a flow of cases with essentially the same question and the same analysis method, it is feasible to construct an 'LR system', that is, an automated procedure that has the observations as input and an LR as output. This paper is aimed at practitioners interested in building their own LR systems. It gives an overview of the different steps needed to get to a validated LR system from data. The paper is accompanied by a notebook that illustrates each step with an example using glass data. The notebook introduces open-source software in Python constructed by NFI (Netherlands Forensic Institute) data scientists and statisticians.
RESUMO
The electrostatic complexation of rigid poly(p-sulfophenylene-terephthalamide) (S-PPTA), which forms needle-like aggregates in solution, with flexible poly(allylamine hydrochloride) (PAH) resulted in the formation of aligned polymer films. Proton conductivities of a 20:1 S-PPTA:PAH complex membrane were found to be strongly dependent on both the temperature and humidity, reaching a value of approximately 0.2 S cm(-1) at 90 degrees C, which surpasses that of Nafion. In order to investigate the influence of PAH on the structure of S-PPTA films, microscopy and X-ray scattering analysis was conducted. Optical polarization microscopy images were less birefringent for the complexed samples than the pure S-PPTA, which appeared to be the result of a reduction in the size of the ordered domains. However, X-ray analysis revealed that PAH complexation has almost no effect on the direction and degree of the rigid polymer alignment in the film: S-PPTA is aligned homeotropically, where the polymer chains are perpendicular to the surface of the film. Proton conductivity and polymer orientation in the film were essentially found to be independent of the complex composition, up to mole ratios of 10:1 S-PPTA:PAH.