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The formation and release under gravity of blood droplets from simulated weapon tips has been investigated experimentally and the results analysed and interpreted using established theoretical models for detached pendent drops. Droplets were produced from a series of conical nozzles, manufactured with a range of cone angles and including a set of un-bored conical tips, under conditions where the tip was either non-wetted or pre-wetted with blood. For the former, radius-limited case, detached droplet volumes were found to agree well with the predictions of both the pendent drop weight and drop shape models. For pre-wetted tips, droplet volumes were found to increase with increasing cone angle and to be independent of whether the blood flow was through an orifice at the tip or across the tip surface itself for un-bored tips. Such angle-limited, detached droplet volumes were predicted well by applying the same contact angle correction factor as for a flat surface. The maximum droplet volume, formed from a horizontal flat surface, was found to be around 150μL for horse blood. Similar theoretical approaches were then extended to droplets released under centrifugal force appropriate to swing cast-off activity and evaluated using previously published experimental data. Order of magnitude agreement for droplet diameters was fairly good but, more importantly, these were found to be proportional to the inverse of the tangential velocity thereby supporting a model where the blood droplet is released directly from a blood mass itself, such as a ligament, rather than from being pinned to some surface feature or orifice on the weapon. This work provides a sound theoretical and experimental understanding of blood droplet release under these conditions that can underpin both future research and the interpretation of blood evidence in case-work., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Cuticular hydrocarbons were extracted daily from the larvae of two closely related blowflies Calliphora vicina and Calliphora vomitoria (Diptera: Calliphoridae). The hydrocarbons were then analysed using Gas Chromatography-Mass Spectrometry (GC-MS), with the aim of observing changes within their chemical profiles in order to determine the larval age. The hydrocarbons were examined daily for each species from 1day old larvae until pupariation. The results show significant chemical changes occurring from the younger larvae to the post-feeding larvae. With the aid of a multivariate statistical method (Principal Component Analysis and Artificial Neural Networks), samples were clustered and classified, allowing for the larval age to be established. Results from this study allowed larvae to be aged to the day with at worst, 87% accuracy, which suggests there is great potential for the use of cuticular hydrocarbons present on larvae to give an indication of their age and hence potentially a valuable tool for minimum PMI estimations., (Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.)

Calliphoridae are known to be the most forensically important insects when it comes to establishing the minimum post mortem interval (PMImin) in criminal investigations. The first step in calculating the PMImin is to identify the larvae present to species level. Accurate identification which is conventionally carried out by morphological analysis is crucial because different insects have different life stage timings. Rapid identification in the immature larvae stages would drastically cut time in criminal investigations as it would eliminate the need to rear larvae to adult flies to determine the species. Cuticular hydrocarbon analysis on 1st instar larvae has been applied to three forensically important blowflies; Lucilia sericata, Calliphora vicina and Calliphora vomitoria, using gas chromatography-mass spectrometry (GC-MS) and principal component analysis (PCA). The results show that each species holds a distinct "fingerprint" hydrocarbon profile, allowing for accurate identification to be established in 1-day old larvae, when it can be challenging to apply morphological criteria. Consequently, this GC-MS based technique could accelerate and strengthen the identification process, not only for forensically important species, but also for other entomological samples which are hard to identify using morphological features., (Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.)

In analytical chemistry large datasets are collected using a variety of instruments for multiple tasks, where manual analysis can be time-consuming. Ideally, it is desirable to automate this process while obtaining an acceptable level of accuracy, two aims that artificial neural networks (ANNs) can fulfil. ANNs possess the ability to classify novel data based on their knowledge of the domain to which they have been exposed. ANNs can also analyse non-linear data, tolerate noise within data and are capable of reducing time taken to classify large amounts of novel data once trained, making them well-suited to the field of analytical chemistry where large datasets are present (such as that collected from gas chromatography-mass spectrometry (GC-MS)). In this study, the use of ANNs for the autonomous analysis of GC-MS profiles of Lucilia sericata larvae is investigated, where ANNs are required to estimate the age of the larvae to aid in the estimation of the post mortem interval (PMI). Two ANN analysis approaches are presented, where the ANN correctly classified the data with accuracy scores of 80.8% and 87.7% and Cohen's Kappa coefficients of 0.78 and 0.86. Inspection of these results shows the ANN to confuse two consecutive days which are of the same life stage and as a result are very similar in their chemical profile, which can be expected. The grouping of these two days into one class further improved results where accuracy scores 89% and 97.5% were obtained for the two analysis approaches., (Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.)

The spreading of bloodstains on matt, vinyl silk and gloss painted surfaces, following both perpendicular and non-perpendicular impact, has been studied with a view to understanding whether surface-specific properties affect the size and shape of the final stain. In all cases the dimensions of the stains on the rougher, matt paint are up to 5% less than on the other painted surfaces though this difference decreases with impact velocity. Both the diameter of circular stains and the width of elliptical stains have been successfully modelled as a function of the perpendicular component of impact velocity vn using a modification of the energy conservation approach through the inclusion of a single, empirical constant characteristic of the surface itself. By further development of this theory, the characteristic dynamical length parameter which governs the spreading has been modified to be dependent on angle thus enabling the length of elliptical stains to be predicted independently for the first time. For all these surfaces, experiment shows that the impact angles, calculated using the conventional trigonometric formula, are in deficit by around 1° at high vn increasing to around 5° at lower vn. By modelling this deficit independently using the theoretical expressions for stain width and length, this variation with vn has been successfully explained. This work has demonstrated some of the fundamental systematic sources of error in using the conventional formula for interpreting elliptical stains and established some of the basic theory on which to develop the interpretation of casework stains on surfaces, in the future., (Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.)

A detailed understanding of blood droplet impact dynamics and stain formation is an essential prerequisite to the interpretation of both individual bloodstains and spatter patterns. The current literature on theoretical models for the spreading and splashing of liquid drops on surfaces relevant to the forensic context of bloodstain formation has been reviewed. These models have been evaluated for a paper substrate using experimental data obtained as function of droplet size, impact velocity and angle. It is shown that for perpendicular impact there are fairly simple mathematical models for the spreading diameter and the number of scallops or spines formed around the stain though these have quite limited ranges of validity in their basic form. In particular, predictions for the diameter are best for small droplets impacting at high velocity and the number of spines saturates for higher impact velocities. In the case of spreading, a modification to the energy conservation model is found to provide excellent agreement with experimental stain diameters across a wide range of impact velocities. For non-perpendicular impact, the width of stains is found to depend principally on the normal component of impact velocity and may be predicted by an appropriate modification to the expression for the perpendicular case. Limitations in the calculation of impact angle from the stain aspect ratio are identified and a theoretical basis for the prediction of spines around an elliptical stain is proposed. Some key issues for future research are identified which include a systematic, quantitative study of the effect of surface properties on bloodstain formation., (Copyright © 2011 Elsevier Ireland Ltd. All rights reserved.)

A novel approach to the non-destructive discrimination of black, ball-point pen ink-lines on paper, has been developed which uses a standard luminescence spectrometer coupled with multivariate statistical analysis. The application of Principal Component Analysis (PCA) to these data-sets, followed by linear regression of the loadings, not only facilitates separation of the ink luminescence from that of the paper, but also allows a direct comparison between two ink lines on documents. This data reduction means that such a comparison can be done on an effectively univariate basis whereby a straightforward statistical comparison is made between two numbers, each characteristic of an ink. Thus the question, in the forensic context, of whether two ink-lines are indistinguishable may be answered with a particular statistical confidence and the method shows significantly better discrimination, for the pens studied, than conventional forensic investigative techniques involving the luminescence imaging of writing using filtered light.

The technique of principal component analysis has been applied to the UV-vis spectra of inks obtained from a wide range of black ballpoint pens available in the UK market. Both the pen ink and material extracted from the ink line on paper have been examined. Here, principal component analysis characterised each spectrum within a group through the numerical loadings attached to the first few principal components. Analysis of the spectra from multiple measurements on the same brand of pen showed excellent reproducibility and clear discrimination between inks that was supported by statistical analysis. Indeed it was possible to discriminate between the pen ink and the ink line from all brands examined in this way, suggesting that the solvent extraction process may have an influence on these results. For the complete set of 25 pens, interpretation of the loadings for the first few principal components showed that both the pen inks and the extracted ink lines may be classified in an objective manner and in agreement with the results of parallel thin layer chromatography studies. Within each class almost all inks could be individualised. Further work has shown that principal component analysis may be used to identify a particular ink from a database of reference UV-vis spectra and a strategy for developing this approach is suggested.