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30 terms

Intro to Forensic Science-chapter 13 Hairs, fibers, and paint

the scale structure covering the exterior of the hair; the scales always point towards the tip of the hair; the scale pattern is useful in species identfication
is an appendage of the skin that grows out of an organ known as the hair follicle; it extends from its root (or bulb) embedded in the follicle, continues into a shaft, and terminates at a tip end; it is not possible to individualize a human hair to any single head or body but it is still physical evidence; can be used for placing a person at a crime scene;
hair shaft
composed of three layers: the cuticle, cortex, and medulla; mDNA can be extracted from the hair shaft
main body of the hair shaft; its major forensic importance is the fact that it is embedded with pigment granules that impart hair with color; the color, shape and distribution of those granules proved the criminalist with important points of comparison among hairs of different individuals
is a cellular column running through the center of the hair; human hair generally has a medullary index of less than 1/3 ; the hair of most animals has an index of 1/2 or greater; may be continuous, interrupted, fragmented, or absent; the presence of the medulla varies from individual to individual and even among hairs of a given individual; it also has different shapes, depending the species.
medullary index
measures the diameter of the medulla relative to the diameter of the hair shaft
provide the tools to produce hair and continue its growth
follicular tag
translucent tissue surrounding the hair's shaft near the root that may stay on hair after it's been pulled from the head; using DNA on this the hair may be individualized
Comparison microscope
used for comparing the morphological characteristics of hair; these tend to be subjective and highly dependent on the skills and integrity of the analyst; as a rule all positive microscopical hair comparisons must be confirmed by DNA analysis
animal hair identification
scale structure, medullary index, and medullary shape; if a medulla exhibits a patterned shape
Factors for comparing human hair
the presence or absence of a medulla; the distribution, shape, and color intensity of the pigment granules present in the cortex; matching the color, length and diameter; only head hair or public hair; 50 full length head hairs from all areas of the scalp for reference sample; minimum of 2 dozen full length public hairs; hair sample are also collected from victims during an autopsy
anagen phase
initial growth phase during which the hair follicle actively produces hair; may last up to six years; probability of detecting DNA is at this stage
catagen phase
a transition stage between the anagen and telogen phases of hair growth; hair continues to grow but at a decreasing rate; can last anywhere from two to three weeks; roots typically take on an elongated appearance
telogen phase
the final growth phase in which hair naturally falls out of the skin; the root takes on a club-shaped appearance; over two to six months the hair is pushed out of the follicle causing the hair to be naturally shed
hair length
3 inches of grown hair can tell if a person has done drugs in the last ten months; hair grows at an avg of 1 cm per month
natural fibers
derived in whole from animal or plant sources; examples: wool, mohair, cashmere, furs, and cotton; animal fibers constitute most of the natural fibers encountered in crime labs; most prevalent plant fiber is cotton; the microscopic view of cotton fiber shows a ribbon like shape with twists at irregular intervals
manufactured fibers
Rayon 1911, nylon 1939; regenerated and synthetic fibers; the fibers are typically made by forcing the polymeric material thought the holes of a spinneret
aka macromolecules are synthetic fibers composed of large numbers of atoms arranged in repeating units known as monomers
regenerated fibers
made from natural raw materials and include rayon, acetate, and triacetate; produced from regenerated cellulose
synthetic fibers
made solely from synthetic chemical and include nylons, polyesters, and acrylics; made from polymers; possess the physical property of birefringence because they are crystalline
Comparison microscope
used on fibers; morphological features that could be important: lengthwise striations on the surface of the fiber, the presence of delustering particles that reduce shine, the cross sectional shape of the fiber
methods for fiber comparison
(1) the visible light micro-spectrophotometer is a convenient way to compare the colors of fibers through spectral patterns;(2) a more detailed analysis of the fiber's dye composition can be obtained through a chromatographic separation;(3) Infrared spectrophotometry is a rapid and reliable method for identifying the generic class of fibers, as does the polarizing microscope.Depending on the class of fiber, each polarized plane of light will have a characteristic index of refraction.
Collection of fibers
place it in a small sheet of paper, fold and label the paper and place the paper packet inside another container
dries into a hard film that is described as consisting of pigments and additives suspended in the binder
automobile paint
one of the most common types of paint examined in the lab; auto makers normally apply a variety of coatings to the body of an automobile; these coatings may include: electrocoat primer (provides corrosion resistance), primer surfacer, basecoat, and clearcoat
Paint comparison
two most important components of dried paint are the color and the layer structure; side by side using a stereoscopic microscope for color, surface texture, and color layer sequence; pyrolysis gas chromatography and infrared spectrophotometry are used to distinguish most paint binder formulations; paints can be individualized to a single source only when they have a sufficiently detailed layer structure
collection of paint
paper druggist folds and glass or plastic vials; paint smeared or embedded in garments or objects required the whole item to be packaged and sent to the lab; standard/reference paint must always be collected; tools can have paint samples on them and must be collected also
two or more atoms held together by chemical bonds
a molecule with a high molecular mass
the basic unit of structure from which a polymer is constructed