Specimen Variation

In analyzing the spectrum of a polymer we do not, of course, limit ourselves to the study of a single specimen. We have already noted the significant information which can be obtained by studying oriented samples as well as deuterated polymers, when possible. In this section we will consider briefly how the study of other kinds of specimens adds to our knowledge of the origin of bands. 

In particular instances special kinds of experiments will be called for, but it should be clear that the study of varied specimens and analogous compounds is an important means by which we can obtain information which is directly relevant to the assignment of absorption bands to normal modes of the molecule. 

Polyethylene has been studied spectroscopically in greater detail than any other polymer. This is primarily a result of its (supposedly) simple structure and the hope that its simple spectrum could be understood in detail. Yet as simple as this structure and spectrum are, a satisfactory analysis had not been made until relatively recently, and even then significant problems of interpretation still remained. The main reason for this is that this polymer in fact generally contains structures other than the simple planar zig-zag implied by (CH2CH2) there are not only impurities of various kinds that differ chemically from the above, but the polymer always contains some amorphous material. In the latter portion of the material the chain no longer assumes an extended planar zig-zag conformation, and as we have noted earlier, such ro-tationally isomeric forms of a molecule usually have different spectra. Furthermore, the molecule has a center of symmetry, which as we have seen implies that some modes will be infrared inactive but Raman active, so that until Raman spectra became available recently it was difficult to be certain of the interpretation of some aspects of the spectrum. As a result of this work, and of detailed studies on the spectra of n-paraffins, it now seems possible to present a quite detailed assignment of bands in the vibrational spectrum of polyethylene. 

A polarized infrared spectrum of a stretched sample of polyethylene is shown in Fig. 4 [Krimm, Liang, and Sutherland (102)]. This specimen was of moderate crystallinity and had a fairly 

1 vs = very strong, m = medium, w = weak, b = broad, n = parallel, C = perpendicular [o0(w = polarization along a (6) crystal axis], A = amorphous, C = crystalline. 

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One of the most common explanations for unresponsiveness of apparently estrogen receptor positive tumors to hormonal therapy is tumor heterogeneity. We found that 38% of the results change when comparing the estrogen receptor proteins from the primary tissue with those from the metastatic tissue. Although there are extrinsic factors, as already mentioned, there could be intrinsic factors that alter the receptor measurement. These findings underscore the need to conduct biopsies and assay readily accessible recurrences rather than to rely on the results of prior specimens. Variation of results also occurred with metastatic tissue from some patients, obtained usually after a period of 19 months (R4). 

Of course, the scatter of data in both distributions is a result of the spedmen-to-specimen variation in the size of the critical flaw. Therefore, the time Weibull distribution can be deduced from the strength Weibull distribution [Eq. (12)] by taking SCCG into account. 

This situation is most likely to occur at the following test conditions at small strains (around 1 % and less) where levels of applied stress are close where the number of replicate tests are small. Common sources of experimental variation are test method reproducibility specimen-to-specimen variation due to fabrication and composition variables, reproducibility of temperature control and variation in loading rate and technique. For certain types of stresses, such as bending and compression, it is possible that variation in stress distribution within the specimens at different levels of applied stress also contribute. 

Adhesive Testing The bonded specimens were tested for lap shear strength on an Instron Universal Testing Instrument at a crosshead speed of 0.05"/min. (1200-1400 psi/min.) as detailed in ASTM D-1002. Lap shear strengths in the tables represent a minimum of four specimens. Variations among specimens were no more than 15 percent of the average values. 

The effect of cycle duration for FeCrAl(RE) alloys, (Fig. 17.7). The effect cannot be unequivocally identified on the basis of the submitted data because of large specimen-to-specimen variation. 

The experimental investigations are carried out in order to get an idea about the variations of the visibility of the indications during practical inspections. The specimen where a test piece with spare eroded artificial defects (Width 25 pm depth d = 30, 60, 120 pm) and other specimen with natural cracks, a forged steering lever and a weld. As an example, in Fig 4 the steering lever with 2 cracks can be seen and below the dependance on the visibilty of a weak indication and a part of the bright indications on the field strenght H. 

The schlieren microscope is able to detect refractive index variations to six decimal places. Any small difference in optical path (index difference, film thickness, etc) is very precisely detected by the schlieren microscope, especially in the Dodd modification. It is, in effect, a darkfield method. The specimen is illuminated with light in a portion of the illuminating cone and that direct light is masked in the conjugate back focal plane of the objective (Fig. 3). The only light to pass through this plane is refracted, reflected, or diffracted by the specimen. 

Coaxial (Concentric Cylinder) Viscometer, The eadiest and most common type of rotational viscometer is the coaxial or concentric cylinder instmment. It consists of two cylinders, one within the other (cup and bob), keeping the specimen between them, as shown in Figure 27. The first practical rotational viscometer consisted of a rotating cup with an inner cylinder supported by a torsion wire. In variations of this design the inner cylinder rotates. Instmments of both types ate useful for a variety of apphcations. 

The reproducibility of test results between labs using the neutral salt spray tests has not been consistent, but the repeatability, within one lab, is better, and the test has value in comparing variations in coating systems. Correlation of hours of exposure in the salt spray test to actual performance of the plated part in service, even in marine atmospheres, is not consistent and usually avoided. A classic example is that cadmium deposits outlast zinc deposits on steel in salt spray tests and clean marine atmospheres, yet zinc outlasts cadmium when exposed to real, industrial atmospheres, because of the presence of sulfur-bearing corrodents in industrial environments. An important variable in salt spray testing is the position of the surface to be tested. Whereas the surface of test panels is specified to be 15—30° from the vertical (40), when salt spray testing chromated zinc-plated specimens, this range has appeared excessive (41). 

More uniform results may be expected if a substantial layer of metal is removed from the specimens to ehminate variations in condition of the original metaUic surface. This can be done by chemical treatment (pickling), electrolytic removal, or grinding with a coarse abrasive paper or cloth, such as No. 50, using care not to work-harden the surface. At least 2.5 X 10 mm (0.0001 in) or 1.5 to 2.3 mg/cm (10 to 15 mg/iu") should be removed. If clad alloy specimens are to be used, specif attention must be given to ensure that excessive metal is not removed. After final preparation of the specimen surface, the speci-... 

Cleaning Specimens after Test Before specimens are cleaned, their appearance should be observed and recorded. Locations of deposits, variations in types of deposits, and variations in corrosion produces are extremely important in evaluating localized corrosion such as pitting and concentration-cell attack. 

At X-ray fluorescence analysis (XRF) of samples of the limited weight is perspective to prepare for specimens as polymeric films on a basis of methylcellulose [1]. By the example of definition of heavy metals in film specimens have studied dependence of intensity of X-ray radiation from their chemical compound, surface density (P ) and the size (D) particles of the powder introduced to polymer. Have theoretically established, that the basic source of an error of results XRF is dependence of intensity (F) analytical lines of determined elements from a specimen. Thus the best account of variations P provides a method of the internal standard at change P from 2 up to 6 mg/sm the coefficient of variation describing an error of definition Mo, Zn, Cu, Co, Fe and Mn in a method of the direct external standard, reaches 40 %, and at use of a method of the internal standard (an element of comparison Ga) value does not exceed 2,2 %. Experiment within the limits of a casual error (V changes from 2,9 up to 7,4 %) has confirmed theoretical conclusions. 

In neutron reflectivity, neutrons strike the surface of a specimen at small angles and the percentage of neutrons reflected at the corresponding angle are measured. The an jular dependence of the reflectivity is related to the variation in concentration of a labeled component as a function of distance from the surface. Typically the component of interest is labeled with deuterium to provide mass contrast against hydrogen. Use of polarized neutrons permits the determination of the variation in the magnetic moment as a function of depth. In all cases the optical transform of the concentration profiles is obtained experimentally. 

The major artifacts contributing to uncertainties in PDCE results stem from effects caused by bombardment of nonideal specimens, particularly thick specimens. The ideal thick specimen would be a homogeneous, smooth electrical conductor that does not change during bombardment. Except for rather simple, well-defined layered structures (e.g., surface oxide layers), specimens having compositional variations with depth yield spectra whose analyses can have large inaccuracies. 

For specimens where gradients in the ms etic moment are of interest, similar arguments apply. Here, however, two separate reflectivity experiments are performed in which the incident neutrons are polarized parallel and perpendicular to the surfiice of the specimen. Combining reflectivity measurements under these two polarization conditions in a manner similar to that for the unpolarized case permits the determination of the variation in the magnetic moments of components parallel and perpendicular to the film surface. This is discussed in detail by Felcher et al. and the interested reader is referred to the literature. 

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