FINAL 317

Trace Evidence

Evidence occurring in sizes so small it is not noticed when it is transferred

hair, paint, glass

Justification for collecting, IDing, and comparing evidence

Locard's Exchange Principle

Transfers Create

proxy data

Essentially all evidence is

transfer evidence

Starch

glucose polymer

maltese cross

hilum at center

Walter McCrone

most famous US microscopist

could ID 20,000 things on sight

Hair

at every scene where there is person to person or person to object contact

Hair DNA no root

mitochondrial

Medulla

center of hair that contains pigment granules

Scales/Cuticles

surround medulla

Human vs Animal Hair

animal hair has thicker medulla and more pigment/pattern

Human hair most similar animal

Monkey

Glass

Burglaries, break-ins

Breaks at scene

found in footwear, pant cuffs, etc

Paint

hit and runs

several layers- clear coat, color base coat, primer coat

Detection

using different light and magnification to find the sample

Isolation

separate sample from rest of group in order to analyze

Identification

Methods vary based on perceived identity and quantity of substance

Comparison

The identification tells you what to use to compare

Evaluation

significance, ubiquity, utility

Law of Reflection

Angle of incidence=angle of reflection with respect to the normal

Law of Reflection for Rough Material

normal is individual to each microfacet

Collection Methods Minimum Set

Handpicking

Tape lift

vacuum

wash scraping

Hand Picking

Use of forceps, W-needle, magnet

Parking Slides

Spots to place sample

Write 9 so it is a P when flipped over

W-needle particle size

10-90um

Required for particle size smaller than 10um

Embedding

Mini Coverslip

Scored from carbite scribe on coverslip

Adhesive Tape

know properties so it is known what is transferred

When not to use Polyethylene

thermosensitive

Refraction is not

the bending of light

Near Point

closest point at which an eye can focus

Higher amplitude=_______ brightness

increased

Slow light travel= _______ RI

increased

Physically distanced

greater than 2f apart

Total Magnification=

objective magnification x ocular magnification

Analyzer

Changes the privileged direction of light

Coverslip Thickness

thickness needed to correct spherical aberration

Angular Aperture

most extreme angle of light the objective can capture

Shorter wavelength=______ RI

higher

Vernier Scale Steps

First number is at zero rounded down

Decimal is what lines up on the ruler

Condenser creates

cone of light

Constructive Interference

Waves add to each other

Destructive Interference

Waves subtract from each other

d>r=

Resolved

d

Not resolved

d=r=

Rayleigh criteria met

Chance for resolution

White Becke Line into liquid

high contrast

liquid greater n

White Becke Line in Glass

high contrast

glass greater

Pumpkin orange BL into glass

Light blue BL into liquid

match range

Operating W-needle

need low grazing angle

Collection Technique Order

Hand pick- tape lift- vacuum

Greenough stereomicroscope suffers from

keystone magnification variation

Fume hood under _____ pressure

negative

Clean room under _____ pressure

positive

Transparent/lucent yellow with transmitted light appears

yellow

Light traveling from low RI to high RI bends

toward the normal

Light traveling from high RI to low RI bends

away from the normal

BL moves toward ______ RI when focus is raised

higher

Proxy data

physical remnants of events and transactions

DNA from hair with root

nuclear

Examination of Trace Steps

Detection

Isolation

Identification

Comparison

Evaluation

Stereomicroscope

1 objective used to feed light

Inverted prism so directions don't change

Abberations

deviations from ideal performance of a lens

Average adult near point

25 cm

1:1 photography

Everything is 2f away from eachother

Rapidly cooling glass causes

Strain birefringence

Diaphragm controls

Angularity and flux

Refractive Index (RI)

Relative measure of the speed of light between two materials

Lens

Translucent material that bends light

K+ positive

yellow octahedra

Whitish-yellow BL into glass

Dark blue-violet BL into liquid

Medium contrast

Glass is greater n

Lemon yellow BL into glass

Violet-blue BL into liquid

low contrast

glass is greater n

Red-orange BL into glass

White-blue BL into liquid

low contrast

liquid is greater n

Dark brown BL into glass

Blue white BL into liquid

medium contrast

liquid is greater

Birefringence=

R/t x 1,000

Olympus Thickness Conversion

2.5 um/os

Steps to Determine RI

Maximize contrast by closing aperture diaphragm

Focus on edge of glass

Raise focus by lowering stage

Temperature Correction for RI

Subtract 25 from temp in celcius

Multiply by dn/dt value

Range +/- 0.005

Isotropic vs Anisotropic

Extinction at NS and EW means Anisotropic

Positive SOE means n// _____ nperpendicular

greater than

Negative SOE means n//_____ nperpendicular

less than

Positive SOE change

more dull top right to bottom left

Negative SOE change

More vibrant top right to bottom left

Berek Average Angle Equation

theta1-theta2/2

Speed decreased = RI

increased

Glass slowly cooled allows for

no tension/compression

If NA=0.75, open AD to

0.75

If A is 22 cm to the left of the lens and B is 12 cm to the left of the lens and the lens is symmetrical with a focal length of 9 cm, which is closer and where do they appear

On the right

A is closer

Diffraction is more problematic at ____ wavelengths

longer

Chromatic Abberation

Variation in focal length with wavelength

Can't adjust

infinity corrected lenses

If RI at 25 celcius is 1.555, the RI at 650nm is ____ than 1.555

less

If an object is 140 cm left of an asymmetrical lens and propogating light 12 cm to the right of the lens, how does the object appear

Real, inverted, minified

Light color and AA to maximize resolution

blue and high AA

Light is traveling from glass with RI 1.652 to oil with RI 1.455 at an angle of incidence of 50 degrees. Which way does the light bend and at what angle?

Away from the normal at 60.4 degrees

A fiber in the leaves of the field diaphragm will appear

superimposed on the specimen

Color temperature does not equal

physical temperature

High blue under polychromatic light source means the field of view will appear ____ under a polarizing light source

blue

Dispersion lines don't cross =

high contrast

Birefringent

more than one principle RI