Specimen identity testing

The main issue in hair testing is the avoidance of exogenous interpretive false positives, i.e., positives caused by external contamination of hair by drugs present in the environment, e.g., smoke, powder. This type of false positive is not the major issue for urinalysis where endogenous interpretive false positives are the main concern. But, the effective avoidance by urinalysis of exogenous false positives due to specimen contamination in the laboratory depends critically on the exclusion of drugusing personnel, and this can best be achieved by evasion-proof hair analysis. However, when such false positives occur, or when urinalysis labs are unable to guarantee that they have taken effective measures to exclude such contamination, then very little can be done to remedy the problem. For, in contrast to hair, the collection of a new urine specimen identical to the first one is not possible. 

Schematic illustrations of the bending type specimen test set-up (main parts striker, fixture with anvils, specimen (instrumented for higher testing rates) are shown in Fig. 2. While an identical striker was used in all bending test set-ups, the anvil geometry and distance in the 2 test set-ups is different (anvil radius of 1 mm in the Charpy fixture anvil radius of 5 mm in tlie SENB fixture). For tensile type fracture specimens 2 test set-ups were realized, to accommodate either the pin-loaded C(T), SENT and DENT specimens (Fig. 3(a)) or the grip loaded CRB specimens (Fig. 3(b)). While conventional grips were used for testing rates up to 0.1 m/s, a modified C(T) or CRB fixture was used with a slack adapter at higher testing rates (for more details see reference [4]).

Samples for identity testing can be any specimen that contains DNA. Samples obtained from an individual for paternity testing or as a reference sample to be compared with DNA prepared from evidence are usually peripheral blood or buccal mucosa. Samples useful for forensic testing, engraftment assays, and the identification of clinical samples may range from plucked hairs to bone marrow aspirates to paraffin embedded tissue. While subject to degradation over time in the presence of enzymes, acidic or basic conditions, or high temperature, DNA is a remarkably stable molecule that can be recovered and successfully analyzed from solutions, surfaces, and cells. 

MtDNA is primarily useful in identity testing in three contexts. First, a sample maybe available that contains mitochondrial but not nuclear DNA. For example, shed hairs that do not have roots generally contain only mtDNA. Second, when the DNA within a specimen, such as skeletal remains, is substantially degraded, the high copy number of mtDNA makes it more likely to yield a result than nuclear DNA. Third, mtDNA analysis may become essential when only a distant relative is available for a reference specimen. In this example, nuclear DNA requires samples from multiple close kindred, but mtDNA matching would require only a distant maternal relative. 

In pathology practice, DNA-based tissue identity testing is typically used to detect tissue contaminants or floaters and for mislabeled specimens. It is particularly... 

Precision of FIT and SIT measurements is usually fair. ASTM D 1929-96 lists examples for several different plastics among them are PVC, polystyrene, nylon, polyurethane, and phenol-formaldehyde resin (see Tables 14.11 and 14.12), tested by seven laboratories, using three replicates of each material. Repeatability in this case is the difference (in°C) between two averages, each one determined from three specimens of identical test material, using the same apparatus by the same analyst within a short time interval. 

Reproducibility in this case is the difference (in°C) between two averages, each one determined from three specimens of identical test material, found by two operators working in different laboratories. 

After removing the protective mylar film, the Tel-Tak measured the maximum force in psi required to separate a inch wide rubber test specimen from another identical rubber specimen after these test pieces are touched together under a given load for a given dwell time that is defined as between 0,1 and 6,0 minutes and a. selected contact pressure that is defined a.s between 16 and 32 psi. The rate of separation is 1 in. min. The tack (autoadhesion) is reported as the force required to separate the two identical rubber specimens. This test can be performed again where a stainless steel strip replaces the lower rubber specimen in order to measure the stickiness" of the upper rubber specimen on contact with this polished stainless steel surface. Lastly the so called true tack is calculated by subtracting the stickiness value (rubber-to-metal) from the original rubber-to-rubber tack value. 

Tests for the J R curve and the determination of can be conducted by employing multiple specimens or a single specimen. With the first method, identical multiple specimens arc tested to different load levels and then unloaded. The extent of stable crack growth is marked by staining or fatigue cracking after the test to facilitate the crack extension measurements. Multiple measurements enable the construction of a load vs. crack-extension curve. The single-specimen test technique relics on the determination of... 

An identical test procedure is prescribed by ASTM D 2859-1976 supplemented by the requirement the specimen has passed the test if the charred portion does not extend to within 25.4 mm of the edge of the hole in the steel frame at any point. 

Some variability in a toughness parameter like is expected when measured using nominally identical specimens and test procedures. Variability can be caused by variations in the flaw population and by variations in material and interface properties. Variations in fabrication and test procedures could also contribute. Many steps are required to make a butt-joint specimen. For example, the alkaline aqueous cleaning procedure involves ten separate steps, and many of these steps are carefully timed. Furthermore, some processes, such as sandblasting, are not fully controlled. The operator of the sandblaster manually directs the grit stream... 

Variability in Afac when measured using nominally identical specimens and test procedures... 

Usually a minimum of six identical testing specimens are made for testing. A specimen is tested first at the highest stress or strain amphtude. It is tested until it fails (breaks). The stress/strain amplitude is recorded along with the cycles it took to fail. Because of the variahility in the test, measurements are usually replicated a second or third time at the same stress/ strain amplitude. Next the stress/strain is reduced and the test is run till failure, which of course takes longer. The reduction in stress or strain continues until failure does not occur in lO -lO cycles. 

The disparities in the nature, size, geometry, location and orientation of flaws between nominally identical test specimens explain the great variations in the stress frequently observed. 

The radiation and temperature dependent mechanical properties of viscoelastic materials (modulus and loss) are of great interest throughout the plastics, polymer, and rubber from initial design to routine production. There are a number of laboratory research instruments are available to determine these properties. All these hardness tests conducted on polymeric materials involve the penetration of the sample under consideration by loaded spheres or other geometric shapes [1]. Most of these tests are to some extent arbitrary because the penetration of an indenter into viscoelastic material increases with time. For example, standard durometer test (the "Shore A") is widely used to measure the static "hardness" or resistance to indentation. However, it does not measure basic material properties, and its results depend on the specimen geometry (it is difficult to make available the identity of the initial position of the devices on cylinder or spherical surfaces while measuring) and test conditions, and some arbitrary time must be selected to compare different materials. 

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