Tool mark identification relies on the premise that microscopic imperfections on a tool's working surface are sufficiently unique and faithfully transferred to enable a one-to-one association between a tool and the tool marks it creates. This paper presents a study undertaken to assess the validity of this premise. As part of this study sets of striated tool marks were created under different conditions and on different media. The topography of these tool marks was acquired and the degree of similarity between them was quantified using well-defined metrics. An analysis of the resulting matching and nonmatching similarity distributions shows nearly error-free identification under most conditions. These results provide substantial support for the validity of the premise of tool mark identification. Because the approach taken in this study relies on a quantifiable similarity metric, the results have greater repeatability and objectivity than those obtained using less precise measures of similarity.
Areal Cross Correlation Function, a statistical function of three dimensional surface topography ANOVA Analysis of Variance ATF Bureau of Alcohol, Tobacco, Firearms, and Explosives BF Breech face CCF Cross Correlation Function, a statistical function of two dimensional surface topography DAS Data Acquisition Station, a component of IBIS (below) EEEL Electronics and Electrical Engineering Laboratory, an organizational unit of NIST FP Firing pin
Since the early 1990's, the idea of automated systems for the comparison of microscopic firearms evidence has received considerable attention. The main objective of such systems is to enable the analysis of large amounts of evidence, therefore, transforming the comparison of firearms evidence from an evidence verification tool into a crime-fighting tool. Two such systems have been widely used in United States forensic laboratories; namely, the Integrated Ballistics Identification System (IBIS) (1) and DRUGFIRE (2). Both IBIS and DRUGFIRE have in common the fact that their characterization of a specimen is based on a two-dimensional (2D) representation of the specimen's surface.
Although these systems have provided satisfactory results in the identification of cartridge cases, their performance in the identification of bullets has not yet met firearms examiner's expectations. This project was motivated by the premise that a better characterizations of the bullet's surface should translate into better performance of automated identification systems. A three-dimensional (3D) characterization of the bullet's surface is proposed as an alternative to a 2D characterization. This paper discusses the development and preliminary results obtained with SCICLOPS™, an automated microscopic comparison system based on the use of a 3D characterization of a bullet's surface.
A procedure for automated bullet signature identification is described based on topography measurements using confocal microscopy and correlation calculation. Automated search and retrieval systems are widely used for comparison of firearms evidence. In this study, 48 bullets fired from six different barrel manufacturers are classified into different groups based on the width class characteristic for each land engraved area of the bullets. Then the cross-correlation function is applied both for automatic selection of the effective correlation area, and for the extraction of a 2D bullet profile signature. Based on the cross-correlation maximum values, a list of top ranking candidates against a ballistics signature database of bullets fired from the same model firearm is developed. The correlation results show a 9.3% higher accuracy rate compared with a currently used commercial system based on optical reflection. This suggests that correlation results can be improved using the sequence of methods described here.
This paper describes the design and operation of the Multi-Axis Cartesian-based Arm Rehabilitation Machine (MACARM), a new cable (wire) robot for upper limb rehabilitation. The prototype configuration is comprised of an array of 8 motors mounted at the corners of a cubic support frame that provides, via cables, 6 degree of freedom (DOF) control of a centrally located end-effector. A 6 DOF load cell mounted on the end-effector provides force measurement. Given its relatively simple architecture, the MACARM may provide an attractive alternative to serial robots for use in neurorehabilitation.
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