Meet the Narco: increased competition among criminal organisations and the explosion of violence in Mexico

Several previous studies have found that interventions by security forces against criminal organisations result in increased violence related to organised crime. However, much less is known about how and why this effect occurs. Our study not only identifies the causal mechanisms that explain this outcome, but also evaluates the empirical validity of these mechanisms. Employing a novel data set, we find that following security-force intervention, the number of criminal organisations increases, and such greater fragmentation in turn raises the incidence of violence among criminal organisations as the relative power of the organisations changes. We employ a mediation model to verify the existence of these causal mechanisms. In addition, we find a decreasing rate of rise in levels of violence as the number of organisations increases.     

Contextual Stress and Health Risk Behaviors Among African American Adolescents

This study examined the longitudinal association between contextual stress and health risk behaviors and the role of protective factors in a community epidemiologically-defined sample of urban African American adolescents (N = 500; 46.4% female). Structural equation modeling was used to create a latent variable measuring contextual stress (community violence, neighborhood disorder, and experiences with racial discrimination). Contextual stress in 8th grade was associated with aggressive behavior and substance use 2 years later for boys. For girls, contextual stress predicted later substance use, but not aggressive behavior. High academic competence and self-worth reduced the impact of contextual stress on substance use for boys. Implications for intervention and directions for future research on health risk behaviors among African American adolescents are discussed.     

Quantification of human mitochondrial DNA using synthesized DNA standards

Successful mitochondrial DNA (mtDNA) forensic analysis depends on sufficient quantity and quality of mtDNA. A real-time quantitative PCR assay was developed to assess such characteristics in a DNA sample, which utilizes a duplex, synthetic DNA to ensure optimal quality assurance and quality control. The assay's 105-base pair target sequence facilitates amplification of degraded DNA and is minimally homologous to nonhuman mtDNA. The primers and probe hybridize to a region that has relatively few sequence polymorphisms. The assay can also identify the presence of PCR inhibitors and thus indicate the need for sample repurification. The results show that the assay provides information down to 10 copies and provides a dynamic range spanning seven orders of magnitude. Additional experiments demonstrated that as few as 300 mtDNA copies resulted in successful hypervariable region amplification, information that permits sample conservation and optimized downstream PCR testing. The assay described is rapid, reliable, and robust.     

Comparison of glass fragments using particle-induced X-ray emission (PIXE) spectrometry

A procedure has been developed to analyze the trace element concentrations in glass fragments using particle-induced X-ray emission (PIXE) spectrometry. This method involves using accelerated protons to excite inner-shell electronic transitions of target atoms and recording the resultant X-rays to characterize the trace element concentrations. The protocol was able to identify those glass fragments that originated from different sources based on their elemental analyses. The protocol includes specific approaches to calculating uncertainties and handling measurements below the level of detection. The results indicate that this approach has increased sensitivity for several elements with higher atomic number compared with X-ray fluorescence methods. While not as sensitive as laser-ablation or inductively coupled plasma mass spectrometry methods of dissolved samples, it is entirely nondestructive and entails a much simpler sample preparation process that may be used to presort glass fragments for more comprehensive elemental analysis. As such, the technique described may have a niche role in forensic glass analysis.     

Evaluation of maxillary sinus dimensions in gender determination using helical CT scanning

Gender determination is an important step in identification in forensic medicine. CT measurements of maxillary sinuses may be useful to support gender identification. This study was undertaken to study the accuracy and reliability of maxillary sinus dimensions measurement in gender classification through the use of reconstructed helical CT images. Eighty-eight patients (43 men and 45 women) with age range from 20 to 49 years were selected in this study. The width, length, and height of the maxillary sinuses in addition to the total distance across both sinuses were measured. Data were subjected to discriminant analysis for gender using multiple regression analysis. Maxillary sinus height was the best discriminant parameter that could be used to study sexual dimorphism with an overall accuracy of 71.6%. Using multivariate analysis, 74.4% of male sinuses and 73.3% of female sinuses were sexed correctly. The overall percentage for sexing maxillary sinuses correctly was 73.9%. It can be concluded that reconstructed CT image can provide valuable measurements for maxillary sinuses and could be used for sexing when other methods of sexing are not conclusive.