Excess scattering

Occasionally, materials are tested in tension by applying the loads in increments. If this method is used for plastics then special caution is needed because during the delay between applying the load and recording the strain, the material creeps. Therefore if the delay is not uniform there may appear to be excessive scatter or non-linearity in the material. In addition, the way in which the loads are applied constitutes a loading history which can affect the performance of the material. A test in which the increments are large would quite probably give results which are different from those obtained from a test in which the increments were small or variable. 

Use hypochlorite solutions in excess scattered over spillage of cyanide solutions and wearing respirator and gloves, mop up and collect in buckets. Allow to stand for 24 hours before diluting greatly and running to waste... 

There are several common methods in geochronology to deal with excess scatter isochrons (that is, isochrons whose data points scatter significantly more than indicated by their analytical errors), none of which are particularly satisfactory. These are to ... 

Using the standard error from replicates or excess-scatter isochrons with small N (say <6 or so), instead of a confidence level ... 

Presenting excess-scatter isochrons without discussion of the cause and significance to the validity of the apparent age. 

The excess scattering from an ensemble of isolated chains (negligible intermolecular interactions in the scattering... 

For polymer solutions, scattering due to solvent molecules forms a finite but small amount and a difference between solution and solvent scattering should be considered. This is also known as excess scattering. If n0 is the refractive index of pure solvent n, that of solution, the relation (n2 n02) = 4pna... 

Fig. 55. Dependence of square root of excess LS for solutions of (a) polyethyleneglycol methacrylate and (b) polymethyl methacrylate in mixed solvents comprising 2,2,3,3-tetrafIuoropro-panol (volume fraction ) and benzyl alcohol. (T = 25 °C, 0 = 546 nm). Broken lines indicate composition of mixed solvent yielding no excess scattering from the polymer in each case1 S2 ...

Fig. 6.16 NSE relaxation curves obtained from a 16% volume fraction poly(fluorosilicone) gel in acetone using tbe bigb resolution NSE spectrometer INI5 at tbe ILL, Grenoble. Tbe existence of plateaus that represent tbe level of excess scattering from static inhomogenieties at low wave vector Q is clearly visible. Tbe decay rates times of tbe dynamic parts yield tbe collective diffusion coefficient of tbe gel. (Reprinted with permission from [291]. Copyright 2002 American Chemical Society)...

Note If the scattering intensity is not reduced to the Rayleigh ratio, the difference between the scattering intensities for a dilute solution and that for pure solvent is named excess scattering . 

Note Several modifications of the Zimm plot are in frequent use the most common one uses the excess scattering instead of the excess Rayleigh ratio. 

As discussed in Section II, measured excess scattering intensity, after a melt is cooled below its melting point, increases exponentially with time at all scattering wavevectors and the inverse of niax (at which intensity is a maximum) diverges as These observations are similar to those... 

Very recently, results from low angle neutron scattering with undiluted mixtures of deuterated and ordinary polymers have begun to appear. In these cases all units along the chain contribute to the excess scattering, and the radius of gyration is obtained. Cotton et al. (29) have measured the dimensions of a rather... 

Infrared Absorption. Attempts to determine the nature of carbon-hydrogen bonding by means of a Beckman IR-5 infrared spectrophotometer were not successful, probably because of the near opacity of the anthraxolite and excessive scatter caused by inadequate grinding. Highly graphitized carbons are commonly opaque to Infrared radiation because the absorption edge of electronic excitation occurs in the infrared range. 

There are a number of reasons for excessive scatter of results found between laboratories - wrong calibration, incorrect apparatus, misinterpretation of the standard, deviation from the procedure, operator mistakes etc. They reduce in the end to either the standard being too lax in its specification and tolerances or somebody is doing something wrong. An interlaboratory comparison tells you the magnitude of the scatter but not which of the possible causes is responsible. That requires further and probably very expensive investigation. 

The upward shift in the excess scattering at the discontinuity between ranges as the dilution goes from 40 to 20 ppb is an interesting effect and may arise from a redistribution of scattering material at a critical concentration. 

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