Fundamentals of Forensic Science - Final Exam Review

Fibers from textiles are constantly being shed and transferred to people, places, and things.

True

What are the differences between fibers?

-chemical nature

-cross-sectional shape

-surface contour

-color

-length

-diameter

What is a textile fiber?

a unit of matter, either natural or manufactured, that forms the basic element of fabrics and other textiles

What is a natural fiber?

any fiber that exists as a fiber in its natural state

What is a manufactured fiber?

any fiber derived by a process of manufacture from any substance which, at any point in the manufacturing process, is not a fiber

Protein fibers are composed of polymers of ______________________.

amino acids

Cellulosic fibers are made of polymers formed from ______________.

carbohydrates

Mineral (inorganic) fibers may be composed of silica obtained from ________________.

rocks or sand

Synthetic fibers are made of polymers that originate from ___________________.

small organic molecules that combine with water and air

What act established the generic names for fibers?

Textile Fiber Products Identification Act

What are filaments?

type of fibers having indefinite or extreme length, such as silk of manufactured fiber

What are staple fibers?

natural fibers or cut lengths of filament typically being 7/8 to 8 inches

Diameter of natural fibers is measures in what?

Micrometers

What is denier?

Weight in grams of 9000m of material fibrous

What is Tex?

the weight in grams of 1,000 meters of fiber or yarn

What is yarn?

-a term for continuous strands of textile fibers, filaments, or material in a form suitable for weaving, knitting, or otherwise entangling to form a textile fabric

-Constructed to have an S- or Z-twist or no twist at all

What is thread?

the product used to join pieces of fabric together

What is plied yarn?

a yarn constructed of a number of smaller single yarns twisted together

What is fabric?

-a textile structure produced by interlacing yarns, fibers, or filaments with substantial surface area in relation to its thickness

-Defined by method of assembly: woven, knitted, or nonwoven

What are woven fabrics?

fabrics composed of two sets of yarns, called warp and weft, and are formed by the interlacing of these sets of yarns

Warp yarn

run lengthwise to the fabric

Weft yarn

run crosswise; referred to as filling, woof, or picks

What are knitted fabrics?

constructed of interlocking series of loops of one or more yarns and fall into two major categories: courses and wales

Courses

rows of loops across the width of the fabric

Wales

rows of loops along the length of the fabric

Knitted fabrics are formed by multiple yarns.

False

What are nonwoven fabrics?

-an assembly of textile fibers held together by mechanical interlocking in a random web or mat, by fusing of the fibers, or by bonding with a cementing medium

-Ex. felt, bandage pads, automotive textiles, and medical fabrics

Characteristics are imparted to manufactured fibers with particular end uses in mind.

True

Crimp

the waviness of a fiber expressed as crimps per unit length

How is color introduced to manufactured fibers?

Dyes or pigments

Natural fibers may be originally ______________.

white, off-white, or a shade of brown

What is cross sectional shape of a fiber?

the shape of an individual filament when cut at a right angle to its long axis

All fibers are chain-link macromolecules called polymers.

True

Over half of the fibers produced each year are_________________.

natural fibers

What makes up most of natural fibers?

Cotton

Where do natural fibers come from?

animals, plants, minerals

Animal fibers

-Come from either mammals (hairs) or from certain invertebrates, such as the silk worm

-Wool-bearing animals, fur-bearing animals

What are the three major sources for fibers derived from plants?

- Seeds (blast fibers)

-Stems

-Leaves

Technical fibers

used in cordage, sacks, mats, etc. or individual cells, as in fabrics or paper

Manufactured fibers

the various families of fibers produced from fiber-forming substances, which may be synthesized polymers, modified or transformed natural polymers, or glass

Synthetic fibers

those manufactured fibers that are synthesized from chemical compounds

How are synthetic fibers made?

by extruding a fiber-forming substance, called spinning dope, through a hole or holes in a shower headlike device called a spinneret

Color is a discriminator of fibers that have been dyed or chemically finished.

True

What two assessments of fiber colors must be part of every fiber comparison?

Visual and analytical

Thermal properties

relate to the softening and melting temperatures for manufactured fibers and the changes the fiber exhibits when heated

What is the primary tool for the identification and analysis of manufactured fibers?

polarized light microscope

Light microscopy provides a slow, indirect, and inaccurate method for the discrimination of similar fibers.

False

Comparison microscope is optional to confirm whether known and questioned fibers have same characteristics.

False

Cross section is an important characteristic and is indicative of end use

True

Delustrants

-finely ground particles of material that are introduced into the spinning dope

-Diffract light and reduce luster

Polarized light microscopy (fibers)

-Easy and quick nondestructive way to determine the generic polymer class of manufactured and synthetic textile fibers

-grants information about the production and finishing of the fiber after spinning

Becke line

describes the interface between the fiber and the mounting medium

If fiber has higher refractive index, the Becke line moves toward the fiber as the working distance is increased.

True

If the mounting medium has the lower index, the Becke line moves toward the medium as the working distance is increased.

False

If refractive index of fiber and mounting medium is the same, the fiber will "disappear".

True

Birefringence

The interference colors seen after crossing the polarizing filters relate to a fiber's material nature, orientation, and crystallinity.

When does fluorescence occur?

when a substance is excited by specific wavelengths of light; light that is not absorbed may be reemitted

Fluorescent components and their response to certain wavelengths of light can be useful in comparing textile fibers.

True

What may degrade fluorescence characteristics?

UV exposure, bleaching, or some other similar means

What is one of the most critical characteristics in fiber comparison?

Color

What makes color one of the most critical characteristics in fiber comparison?

-May indicate end product

-Nearly infinite possibilities and an easy discriminator

Perception of color by a human is subject to what variety of factors?

genetics, age, and environment

Simultaneous contrast

-the perception of color based on context

-Affected by background color or surrounding colors

Chameleon effect

the perception that colors change based upon the surrounding colors

Dye (fiber)

an organic chemical that is able to absorb and reflect certain wavelengths of visible light

Pigment (fiber)

microscopic, water-insoluble particles that are either incorporated into the fiber at the time of production or are bonded to the surface of the fiber by a resin

What are the three main methods of analyzing the color of fiber?

-visual examination,

-chemical analysis,

-instrumental analysis

Visual color assessment

-accomplished with a comparison microscope

-Not always repeatable

Metameric colors

two colors that appear to match in one set of lighting conditions, but not in another

What does chemical analysis of fiber color involve?

extracting the dye and characterizing or identifying its chemistry

TLC (fiber color)

• Addresses type of dye used to color fiber and may help sort out metameric colors

• A destructive method

What method of analysis offers the best combination of strength and the fewest weaknesses of the three methods?

Instrumental

Why is instrumental analysis the best method of color assessment?

• Objective, repeatable

• Quantitative results

• Standardized methods

• Nondestructive and may be repeated

How is instrumental analysis of fiber color accomplished?

Using a microspectrophotometer (MSP)

Microspectrophotometer (MSP)

-an instrument that allows for the color measurement of individual fibers

-A standard spectrophotometer with a microscope attached to focus on the sample

-Compares the amount of light passing through air with the amount passing through or reflected off a sample

-Segregates colored fibers that appear visually the same but are subtly different

Chemical analysis offers a confirmation of microscopic work and may provide additional information about the specific polymer type or types that make up a fiber.

True

What chemical analysis method is preferred in fiber analysis?

FTIR (not destructive)

What are methods of chemical analysis in fiber assessment?

FTIR, PGC, solubility schemes (destructive)

What are considered "common" types of cottons?

White cotton, indigo-dyed cotton (denim), and certain types of black cotton

Fiber evidence is very powerful in demonstrating ________________.

associations

What is toxicology?

the study of any nonfood substance taken by a living organism

What is toxicology concerned with?

how much substance was taken, physiological and psychological effects of substances

Forensic toxicology

-about humans and how they are affected by drugs and poisons

-a branch of pharmacology that is concerned with the harmful effects of drugs on humans

When does a forensic toxicologist's involvement begin in a case?

When a person has died under circumstances

Nonlethal cases mainly involve ______________ and _____________.

ethyl alcohol; driving

Pharmacology

the study of the relationships between drugs and living things

Forensic toxicologist

a scientist who works on cases with suspicious circumstances in which drugs are involved in death, impairment, or injury

Drug

-a chemical or chemical mixture that is designed to have an effect or series of physiological and/or psychological effects upon a person

-manufactured or designed to cause a particular response

-a natural or synthetic substance that is designed to produce a specific set of psychological or physiological effects on the human body or other animals

Poison

a substance that has a toxic effect on a person

What are the tasks that forensic toxicologists must fulfill?

• Determine the identity of all drugs and poisons present in the body

• Determine the quantities of all drugs and poisons present at the time of death

• Determine which metabolites (secondary products of drugs as they are acted on by the liver) of these drugs are present

• Determine what interactions (e.g., synergisms) may exist among the particular combination of drugs that are present

• Help determine the history and patterns of drug use by the person involved and the role that drug dependence or addiction may play

• Help determine the role that tolerance may play

Pharmacokinetics

Study of how drugs move into and out of the body

What are the processes of pharmacokinetics?

-absorption, distribution, metabolism, and elimination

-A dynamic equilibrium of drug within the body is dependent on these processes

Absorption (pharmacokinetics)

-Drugs may be introduced into the body through a number of routes: oral, intramuscular, intravenous, rectal, topical, subcutaneous, and inhalation

-All introduction methods result in passage of drug through a tissue barrier and into the bloodstream

-Chemical nature of the drug dictates how easily the drug can cross the barrier

-Form of the drug can affect its rate of absorption

-Rate of absorption will depend in part upon what else is already in the stomach at the time of ingestion

Distribution (Pharmacokinetics)

• A drug may be distributed locally by diffusion through tissues

• Global distribution through the body is accomplished by way of the bloodstream

• Portion of a drug may bind to blood proteins; must account for this in determining effective concentration

• Concentration of drug is not the same everywhere (more blood in brain, heart, and liver)

Metabolism (Pharmacokinetics)

-A process whereby a drug or other substance is chemically changed to a different form, called a metabolite

Why does the body metabolize drugs?

-Deactivate the drug, so it has fewer or milder effects

-Create more water-soluble products, which are easier to eliminate

-Convert drug to substance that can be used by the body's cells for energy

What organ in the body metabolizes drugs?

Liver

What two things does liver metabolism accomplish?

•Changes drug into less toxic substance

•Changes drug into form that is easier to eliminate in urine

elimination (pharmacokinetics)

• Predominant mechanism is excretion in urine (Drugs must be water soluble)

• Volatile drugs may also be eliminated by respiration, perspiration

Pharmacodynamics

-Study of how drugs act in the body

-Certain organs contain cells that have active sites or receptors

-Drugs are designed to bind to a particular type of receptor