Classification of Glass Fragments Based on Elemental Composition and Refractive Index*

Abstract: The aim of this study was to assess the efficiency of likelihood ratio (LR)‐based measures when they are applied to solving various classification problems for glass objects which are described by elemental composition, and refractive index (RI) values, and compare LR‐based methods to other classification methods such as support vector machines (SVM) and naïve Bayes classifiers (NBC). One hundred and fifty‐three glass objects (23 building windows, 25 bulbs, 32 car windows, 57 containers, and 16 headlamps) were analyzed by scanning electron microscopy coupled with an energy dispersive X‐ray spectrometer. Refractive indices for building and car windows were measured before (RI_b), and after (RI_a) an annealing process. The proposed scheme for glass fragment(s) classification demonstrates some efficiency, although the classification of car windows (c) and building windows (w) must be treated carefully. This is because of their very similar elemental content. However, a combination of elemental content and information on the change in RI during annealing (ΔRI = RI_a?RI_b) gave very promising results. A LR model for the classification of glass fragments into use‐type categories for forensic purposes gives slightly higher misclassification rates than SVM and NBC. However, the observed differences between results obtained by all three approaches were very similar, especially when applied to the car window and building window classification problem. Therefore, the LR model can be recommended because of the ease of interpretation of LR‐based measures of certainty.     

Simultaneous Quantitative Determination of Amphetamines,Opiates, Ketamine,Cocaine and Metabolites in Human Hair: Application to Forensic Cases of Drug Abuse

A method using liquid chromatography–tandem mass spectrometry (LC–MS/MS) to simultaneously quantify amphetamines, opiates, ketamine, cocaine, and metabolites in human hair is described. Hair samples (50 mg) were extracted with methanol utilizing cryogenic grinding. Calibration curves for all the analytes were established in the concentration range 0.05–10 ng/mg. The recoveries were above 72%, except for AMP at the limit of quantification (LOQ), which was 48%. The accuracies were within ±20% at the LOQ (0.05 ng/mg) and between −11% and 13.3% at 0.3 and 9.5 ng/mg, respectively. The intraday and interday precisions were within 19.6% and 19.8%, respectively. A proficiency test was applied to the validated method with z-scores within ±2, demonstrating the accuracy of the method for the determination of drugs of abuse in the hair of individuals suspected of abusing drugs. The hair concentration ranges, means, and medians are summarized for abused drugs in 158 authentic cases.     

Validating TrueAllele® Interpretation of DNA Mixtures Containing up to Ten Unknown Contributors

Most DNA evidence is a mixture of two or more people. Cybergenetics TrueAllele^® system uses Bayesian computing to separate genotypes from mixture data and compare genotypes to calculate likelihood ratio (LR) match statistics. This validation study examined the reliability of TrueAllele computing on laboratory-generated DNA mixtures containing up to ten unknown contributors. Using log(LR) match information, the study measured sensitivity, specificity, and reproducibility. These reliability metrics were assessed under different conditions, including varying the number of assumed contributors, statistical sampling duration, and setting known genotypes. The main determiner of match information and variability was how much DNA a person contributed to a mixture. Observed contributor number based on data peaks gave better results than the number known from experimental design. The study found that TrueAllele is a reliable method for analyzing DNA mixtures containing up to ten unknown contributors.     

A Mixture Model for the Number of Gunshot Residues Found on Suspects' Hands

Quantifying the strength of gunshot residue (GSR) evidence requires scientific knowledge about the number of particles expected to be found on individuals who were or were not involved in a shooting. However, controlled experiments demand expensive resources in terms of microscope time and labor, which restricts the data of most studies to only a small group of individuals. We suggest a novel method that exploits data collected routinely on suspects during the daily work of forensic laboratories. These observational data relate to both persons who were involved in a shooting and innocent individuals. We suggest a mixture approach with different models for the number of gunshot residue particles in each group and develop an iterative algorithm to estimate the probabilities of observing the evidence under the defense proposition that the suspect is innocent and under the prosecution assumption that he is not. The method is applied to data of more than 500 suspects collected by the Israel National Police Division of Identification and Forensic Science. The analysis shows that the probability of finding three or more GSR particles on the hands of innocent suspects is very small, less than 1.5 in 1000 cases. Our new method enables researchers to use data on real cases, possibly supplemented by experimental data, in order to estimate the probabilities of a given GSR finding under the defense and prosecution propositions.     

Objective evaluation of similarity scores derived by Evofinder® system for marks on bullets fired from Chinese Norinco QSZ-92 pistols

In recent years, many studies have been conducted in the field of firearm identification with the objective of providing an objective method of evaluating the comparison of cartridge cases. However, less attention has been paid to the objective evaluation of bullet comparisons. In this study, 1 000 registered Chinese Norinco QSZ-92 pistols were used, and a database of 2 996 bullets was constructed. Both the receiver operating characteristic (ROC) curve and the score-based likelihood ratio method were used to objectively evaluate the similarity scores derived by the Evofinder^® system. The results indicate that this system has excellent ability to discriminate between the selected pistols. This paper proposes an objective evaluation method, which serves as a response to the ongoing debates regarding the foundation of the discipline.     

Uncertainty in probabilistic genotyping of low template DNA: A case study comparing STRMix™ and TrueAllele™

Two probabilistic genotyping (PG) programs, STRMix™ and TrueAllele™, were used to assess the strength of the same item of DNA evidence in a federal criminal case, with strikingly different results. For STRMix, the reported likelihood ratio in favor of the non-contributor hypothesis was 24; for TrueAllele it ranged from 1.2 million to 16.7 million, depending on the reference population. This case report seeks to explain why the two programs produced different results and to consider what the difference tells us about the reliability and trustworthiness of these programs. It uses a locus-by-locus breakdown to trace the differing results to subtle differences in modeling parameters and methods, analytic thresholds, and mixture ratios, as well as TrueAllele's use of an ad hoc procedure for assigning LRs at some loci. These findings illustrate the extent to which PG analysis rests on a lattice of contestable assumptions, highlighting the importance of rigorous validation of PG programs using known-source test samples that closely replicate the characteristics of evidentiary samples. The article also points out misleading aspects of the way STRMix and TrueAllele results are routinely presented in reports and testimony and calls for clarification of forensic reporting standards to address those problems.     

THEMIS紫外光谱成像仪的放大率估计及其图像的长宽比校正

目的 校正THEMIS紫外光谱成像仪图像的长宽比并估计系统放大率参数.方法 制作测试图片,用紫外光谱成像仪拍摄紫外光谱影像集,由图像和测试图片的差异分析出成像缺陷和放大率参数.结果 通过Photoshop测量像素值的方法测量出图像的长宽比差异,并用MATLAB算法校正,同时得出紫外光谱成像仪的放大倍率β.结论 校正后紫外光谱图像恢复了原始比例,且系统放大率β可以在恢复痕迹原始大小时发挥作用,由此获得准确的紫外光谱图像供后续光谱分析检验和研究.     

水泥稳定碎石室外延迟试验研究

延迟时间是水泥稳定碎石基层施工关键控制因素。以北京京承高速公路水泥稳定碎石基层为研究对象,通过室外延迟试验,确定了各相关因素对混合料延迟强度的影响,并提出了具体的施工延迟控制时间,其结果可供同类型工程施工参考、借鉴。     

论裁量余地原则在国际投资仲裁中的运用

当前，国际投资仲裁体系由于过度干预国家主权，因而面临着正当性危机。欧洲人权法院判例中采用的裁量余地原则能够较好地平衡国家主权与人权保护之冲突。目前国际投资仲裁庭对国家规制行为的审查标准不一，进一步影响到投资仲裁体系的正当性问题，因此，可以引入欧洲人权法院判例中的裁量余地作为对国家规制行为的审查标准，同时辅之于比例分析，以解决投资仲裁面临的正当性危机，这将会减少对国家主权的干扰，因而在政治上更加能够容忍。     

储蓄或参保：城镇灵活就业人员养老方式收益比较分析——以广州市为例

虽然我国城镇灵活就业人员的数量正在快速增长,但其却普遍地游离于社会保障体系之外。在市场经济环境中,具备经济理性的灵活就业人员在抉择社会养老保险问题时,不仅会关注社会养老保险本身的投资—收益情况,还会比较各种养老方式总收益额的高低。本文通过测算参保与储蓄两种养老模式总收益额的比例及变化,从加大宣传力度、提高最低缴费年限和完善社保费用补缴办法等方面,对有效地促进灵活就业人员参加社会养老保险和实现我国养老保险制度的可持续发展提出相关建议。