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FRNSC 411 > Fiber and Soil Analysis > Flashcards

Fiber and Soil Analysis Flashcards

1
Q

what is a textile?

A
  • flexible material consisting of network of natural or artificial fibers (yarn or thread)
  • formed by weaving, knitting, crocheting, knotting, or felting
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2
Q

what is a fiber?

A

threadlike strand used for spinning yarn (smallest unit)

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3
Q

what is yarn?

A

continuous length of interlocked fibers used for manufacturing textiles

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4
Q

what is a thread?

A

multiple yarns plied together producing a long, thin strand used in sewing or weaving

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5
Q

what are the warp and weft of weave patterns?

A
  • warp = threads strung over loom, holding tension while weaving
  • weft = threads woven between warp threads, creating pattern and structure
  • weave patterns can create very different qualities of fabric (plain, basket, satin, twill, etc.)
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6
Q

what do fiber-plastic fusions indicate?

A

forceful contact in vehicle accidents and other impacts

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7
Q

what does reconstruction indicate?

A

contact with limited suspects

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8
Q

what is active transfer?

A

copious amounts of fibers link transfer to specific, uncommon event (EX: damaged textile from tearing fabric to bind victim)

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9
Q

what is the difference between dyes and pigments?

A
  • dyes = soluble; permeate fiber
  • pigments = insoluble; physically and chemically unaffected
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10
Q

what can fiber evidence reveal?

A
  • identification and classification (natural vs manmade, generic type and sub-type)
  • manufacturing info (source textile type, manufacturer)
  • physical damage and surface characteristics (circumstances, fracture match)
  • comparison (color, diameter, inclusions, cross-section)
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11
Q

what are the categories for natural and synthetic fibers?

A
  • natural (animal, vegetable, mineral)
  • synthetic (regenerated, totally synthetic)
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12
Q

what are most animal fibers derived from?

A

proteins - hair (besides silk)

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13
Q

what are notable natural fibers?

A
  • cotton (seed fiber)
  • hemp (bast fibers/plant stems)
  • asbestos (mineral)
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14
Q

what are regenerated fibers?

A
  • type of synthetic fiber
  • natural polymers which are regenerated to form longer chains (most made from cellulose)
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15
Q

how is cellulose regenerated?

A

acetylated with acetic anhydride (remove OH to allow cellulose polymers to float free)

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16
Q

what can synthetic fibers be made into?

A

plastics (Nylon 6,6)

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17
Q

what is the only synthetic fiber that is less dense than water?

A

olefins (polyethylene)

18
Q

what are some of the analytical strategies for fibers?

A
  • morphology (for natural fibers and rayon)
  • color comparison (dyed fibers)
  • damage (FTIR tear, cut, melt)
  • surface debris (microspectrophotometry)
  • solubility testing
  • size
  • cross-section (round, trilobal, ribbon, bean)
  • delusterants (small particles to make less shiny)
  • indication of processing (crimp, weave)
  • birefringence
  • sign of elongation
19
Q

what is important when doing color comparison of fibers?

A
  • sufficient number and variety of known samples
  • should be conducted under several different lighting conditions
20
Q

what is metamerism?

A

when color perception is affected by background in which it appears

21
Q

are dyes unique between manufacturers?

A

no

22
Q

how are synthetic fibers manufactured?

A
  • spinnerets have multiple holes so that numerous fibers can be produced simultaneously to form continuous filaments of semi-solid polymer
  • at some point after spinning, drawing occurs (filaments are stretched, pulling the molecular chains together and orienting them along fiber axis - strengthens the fiber)
23
Q

what is microspectrophotometry (MSP) used for?

A

differentiating colors from dyes, inks, and other substances

24
Q

what is polarized light microscopy (PLM) used for?

A

determining sign of elongation and estimate birefringence

25
Q

what is Fourier transform infrared (FTIR) spectrophotometry used for?

A

confirmatory identification

26
Q

what is soil?

A
  • layer(s) of generally loose mineral and/or organic material that are affected by physical, chemical, and/or biological processes at or near the planetary surface
  • usually holds liquids, gases, biota, and supports plants
27
Q

what is the difference between soil and dirt?

A

soil can support life while dirt has lost the ability to support life (EX: tracked in dirt inside)

28
Q

what is the organic component of soil made of? what is soil that is only comprised of organic compounds?

A
  • humus (decayed plant and animal remains)
  • peat
29
Q

what is the inorganic component of soil made of? what is soil that is only comprised of inorganic compounds?

A
  • minerals
  • sand
30
Q

why is soil significant in investigations?

A
  • violent crimes often occur/end up on ground
  • criminals frequently bury bodies and other evidence
  • crimes involving a vehicle (especially if used to dispose of evidence in a remote location) often involve driving in soil
  • soil is everywhere and varies in composition within meters not miles
  • soil evidence is commonly transferred to shoes, clothing, carpets, shovels, tools, tires, wheel wells, floormats, and vehicle trunks
  • soil transfers often go unnoticed
  • soil varies horizontally and vertically
  • most transfers only involve topsoil but can interact with other layers
31
Q

how is soil used as class evidence?

A
  • not sufficient to individualize to single location
  • can refute false alibi
  • can profile unknown samples to provide leads (roadside, riverbank, industrial, etc.)
32
Q

how is soil evidence analyzed and compared?

A
  • color
  • texture (particle and density distribution)
  • stratification (layers)
  • percent organic content
  • pH
  • mineral identification (PLM or X-Ray Diffraction)
33
Q

what are the three components of soil color?

A
  • hue = dominant wavelength (blue, green, red, etc.)
  • value = brightness
  • chroma = saturation
34
Q

what are the size comparisons of soil texture components?

A

sand (largest) then silt then clay (smallest)

35
Q

how is particle size analysis of soil done?

A
  • after drying, soil is weighed and gently shaken through series of sieves (each with finer mesh)
  • contents of each sieve are weighed
36
Q

how is density distribution of soil done?

A
  • density gradient column with two immiscible liquids of different densities
  • high density layered on top of low density to form gradient
  • soil added to column; sink until reach neutral buoyancy
37
Q

how is percent organic of soil determined?

A

sample dried, ground up, weighed, and pyrolyzed to be weighed again

38
Q

natural soil pH reflects the combined effects of what?

A
  • climate
  • organic and mineral content
  • elevation and drainage
  • time of year
39
Q

what has lower pH and why? silt, sand, clay

A

sand because water is able to pass through it more quickly

40
Q

what elements have the greatest effect on pH?

A

Calcium, Magnesium, and Potassium (raise pH)

41
Q

are areas of forest or grass more acidic?

A

forest

FRNSC 411 (4 decks)

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