Vibrational spectra, principal components analysis and the horseshoe effect

Vibrational spectroscopy studies often generate datasets containing multiple spectra that are categorized into distinct groups according to similarity. Principal components analysis (PCA) is one of the most frequently used multivariate analysis methods for data reduction of vibrational spectra and visualization of potential groupings between subjects. Vibrational spectra usually display unimodal or multimodal distribution patterns of absorbance or transmittance across wavenumbers. PCA, requires that a linear relationship exists between data distributions of the objects under analysis otherwise the method is prone to a serious artifact known as the ‘horseshoe effect’. This artifact, well known in other fields of science, manifests as a serious distortion of the pattern of how objects group according to the most important principal components leading to misinterpretation of the relationships between the samples from which they are derived. In this paper, using a simulated mid-infrared spectral dataset, we investigate for the first time the potential for the PCA horseshoe effect on vibrational spectra and the why this artifact occurs. We show that when comparing large regions of contiguous wavenumbers between multiple spectra there can be a non-linear relationship between distributions of different spectra. Such non-linearity causes the horseshoe effect and we demonstrate that the degree of distortion of how spectra map on the first two components is related to the region size. We further show that reducing the size of spectra analyzed by PCA can minimize the horseshoe effect. We conclude that PCA should be used with caution in the analysis and interpretation of vibrational spectra and the application of more robust methods should be explored

Investigation into the performance of physical developer formulations for visualizing latent fingerprints on paper

Latent fingerprints deposited on commercial photocopy paper were treated using various preparations of silver-based physical developer and the results from each were compared to those obtained with the standard formulation used by the Australian Federal Police. Five redox stock solutions were prepared with altered orders of reagent addition, and a further solution prepared with exchanged iron concentrations, to test the robustness of the method. Three redox solutions were prepared with specific reagents omitted to determine the significance of the role played by each in development. One redox solution was prepared using Tween 20 as the non-ionic surfactant to assess its suitability as a replacement for Synperonic N. An acid prewash was also prepared using malic acid as an alternative to maleic acid. Results showed the method to be robust to alterations in reagent addition, but not to significant concentration changes. The presence of all components was found to be desirable for distinguishable development of fingerprint detail. It was additionally found that Tween 20 gave at least equal performance to Synperonic N on recently deposited fingerprints. Finally, the use of malic acid gave equivalent fingerprint development but higher background in comparison to maleic acid

Forensic science in Seychelles: An example of a micro-jurisdiction forensic delivery system

Forensic science has become an indispensable tool for even the smallest of jurisdictions. However, micro-jurisdictions often face significant challenges with respect to resource availability, administration and local governance. This paper examines the forensic service provision in Seychelles as an example of a micro-jurisdiction forensic delivery system. The impact of limited resources and remote access to consumables or services have prompted the prospective shift to localise commonly utilised forensic services. The need to balance quality and cost for a sustainable forensic service is examined in relation to jurisdictions with more advanced forensic service delivery. Reforms of the legal framework, administration, and governance structures are some of the key underpinnings for an effective forensic delivery system built on a culture of transparent science that promotes justice and creates public confidence in the judicial system

Camoupedia: A Compendium of Research on Art, Architecture and Camouflage

Book Review of Camoupedia: A Compendium of Research on Art, Architecture and Camouflage, by Roy R. Behrens. ISBN 9780971324466. Reviewed by Georgina Lewis

SCAFFOLDING FOR IMPACT: ACTIVE LEARNING IN FORENSIC EDUCATION

Forensic science programs attract students from a range of scientific disciplines including chemistry, biology, psychology and engineering. At the tertiary level, these students are expected to demonstrate a mastery of forensic principles with the ability to apply them in practice. However, there has been little investigation of effective pedagogical approaches to achieve these outcomes in forensic education. Active learning has long been recognised within other scientific disciplines as an effective means of promoting mastery, motivation, and higher-order thinking skills. Despite this, active learning has yet to be systematically evaluated within a forensic context. This project applied a mixed methods approach to evaluate how active learning strategies influence students’ academic achievement and attitudes towards learning in an introductory forensic science unit. The outcomes and implications of these results will be discussed in relation to establishing scholarly practices for forensic education and training

Preliminary studies into the effect of environmental degradation on the characterisation of automotive clear coats by attenuated total reflectance infrared spectroscopy

This paper presents a study into the impact of environmental weathering on the chemometric classification of automotive clear coats. These studies were conducted using attenuated total reflectance infrared spectroscopy, in conjunction with a chemometric model capable of predicting the country of vehicle manufacture for a sample based upon its infrared spectrum. Testing of three samples exposed to environmental conditions found the model to be robust to weathering over at least an eight-month period. However, analysis of 12 samples of unknown prior history found that extreme degradation over at least a 10-year period, or the presence of a post-manufacture (respray) coating, could result in misclassification when relying solely on analysis of the clear coat. It is therefore important that cross-sections comprising the full layer sequence of the paint system are obtained wherever possible, as analysis of the underlying layers may give more comprehensive characterisation

A study into the ageing and dating of blue ball tip inks on paper using in situ visible spectroscopy with chemometrics

This paper presents a study into the potential of visible spectroscopy with chemometrics as an approach to dating blue ball tip inks on paper documents. Analysis of six inks left under various conditions found that the majority of those kept in the dark could still be matched to the source pen after 32 months of ageing. Conversely, the majority of those exposed to light exhibited rapid spectral changes that continued throughout the 32 month period. Partial least squares regression (PLSR) was used to generate dating models for inks aged with exposure to light. Evaluation using an external test set found absolute dating to be challenging for these ink deposits within the first 2-6 months of ageing. However, predictive accuracy was found to improve for long-term ageing, with two-year old samples yielding age estimates with a maximum error of 6 months. This rapid, non-destructive methodology could assist document examiners in the relative ageing or approximate age determination of questioned documents, as well as the identification of document alterations