Single-point quality

Mechanical properties of plastics can be determined by short, single-point quality control tests and longer, generally multipoint or multiple condition procedures that relate to fundamental polymer properties. Single-point tests include tensile, compressive, flexural, shear, and impact properties of plastics creep, heat aging, creep rupture, and environmental stress-cracking tests usually result in multipoint curves or tables for comparison of the original response to post-exposure response. 

The melt flow index is more than just a single-point quality control parameter and this fact has been reemphasized in Chapter 9. It outlines various correlations among parameters involved in polymer manu cture, product fabrication, and property evaluation with MFl. 

There are a variety of ways to express absolute QRA results. Absolute frequency results are estimates of the statistical likelihood of an accident occurring. Table 3 contains examples of typical statements of absolute frequency estimates. These estimates for complex system failures are usually synthesized using basic equipment failure and operator error data. Depending upon the availability, specificity, and quality of failure data, the estimates may have considerable statistical uncertainty (e.g., factors of 10 or more because of uncertainties in the input data alone). When reporting single-point estimates or best estimates of the expected frequency of rare events (i.e., events not expected to occur within the operating life of a plant), analysts sometimes provide a measure of the sensitivity of the results arising from data uncertainties. 

A completely different type of property is for example spin-spin coupling constants, which contain interactions of electronic and nuclear spins. One of the operators is a delta function (Fermi-Contact, eq. (10.78)), which measures the quality of the wave function at a single point, the nuclear position. Since Gaussian functions have an incorrect behaviour at the nucleus (zero derivative compared with the cusp displayed by an exponential function), this requires addition of a number of very tight functions (large exponents) in order to predict coupling constants accurately. ... 

The Ml test equipment is easy to operate, provides repeatable results, and low cost to operate. It is widely used for quality control and for distinguishing between members of a single family of plastics. Specifically, this MI makes a single-point test that provides information on resistance to flow at only a single shear rate. Because variations in branching or MWD can alter the shape of the viscosity curve, the MI may give a false ranking of plastics in terms of their shear rate resistance to flow. To overcome this problem, extrusion rates are sometimes measured for two loads, or other modifications are made. 

Risk assessment pertains to characterization of the probability of adverse health effects occurring as a result of human exposure. Recent trends in risk assessment have encouraged the use of realistic exposure scenarios, the totality of available data, and the uncertainty in the data, as well as their quality, in arriving at a best estimate of the risk to exposed populations. The use of "worst case" and even other single point values is an extremely conservative approach and does not offer realistic characterization of risk. Even the use of arithmetic mean values obtained under maximum use conditions may be considered to be conservative and not descriptive of the range of exposures experienced by workers. Use of the entirety of data is more scientific and statistically defensible and would provide a distribution of plausible values. 

Several in vitro tests are currently employed to assure drug product quality. These include purity, potency, assay, content uniformity, and dissolution specifications. For a pharmaceutical product to be consistently effective, it must meet all of its quality test criteria. When used as a QC test, the in vitro dissolution test provides information for marketing authorization. The dissolution test forms the basis for setting specifications (test, methodology, acceptance criteria) to allow batch release into the market place. Dissolution tests also provides a useful check on a number of physical characteristics, including particle size distribution, crystal form, etc., which may be influenced by the manufacturing procedure. In vitro dissolution tests and QC specifications should be based on the in vitro performance of the test batches used in in vivo studies or on suitable compendial specifications. For conventional-release products, a single-point dissolution... 

In many cases a Cusum plot will not show the expected horizontal line but rather a line with a small but constant slope owing to the value attributed to the mean of means being incorrect. The plot is still acceptable and in such cases a change in the slope will indicate a change from the expected value and the possibility of error. Some of the difficulties with the Cusum plot is that variations are most obvious retrospectively, little information can be gained from a single point and errors are only apparent from several consecutive points. Thus it is debatable whether this type of plot can be classed as true quality control. 

It is immediately noticed that this factor does not depend on the length of the considered chain. [On the other hand, it depends on the chemical nature of the chain as a consequence of the appearance of fa — Oj), cf. Section 5.1.2]. Of particular importance is the elimination of the influence of distribution function ip, as in this way the influence of the state of flow (or strain in a permanent network) is eliminated. In this way, the validity of the stress-optical law, as described by eq. (1.4), seems fairly secured. As will be shown in Section 5.1.3, for flowing systems of uncross-linked chain molecules this result is due to the fact that the interaction of chains with their surroundings is thought to be concentrated in single points like their end-points. A discussion of the quality of this approximation will also be tried in that section. This approximation, however, has tacitly been made by all theories for Gaussain chains known at present. 

Single-point specificationsAs a routine quality control test. (For highly soluble and rapidly dissolving drug products.)... 

Incorporating these procedures and the resulting documents into the quality management system will afford a single point of control and archive for all validation procedures. 

The melt flow indexer. The melt flow indexer is often used in industry to characterize a polymer melt and as a simple and quick means of quality control. It takes a single point measurement using standard testing conditions specific to each polymer class on a ram type extruder or extrusion plastometer as shown in Fig. 2.45. 

An MP2(full)/6-31G geometry optimization, wanted to get a high-quality geometry for all the subsequent calculations (which are thus single-point jobs)... 

Ab initio MP2 calculations with DZ quality basis sets were performed on the reactions of C2H4 with GeH (n = 0-3)389. Single-point calculations at the QCISD(T)/6-31 lG(3df,2p) level were performed. The results were used to speculate on the mechanisms of reactions occurring during radiolysis of germane/ethylene mixtures. 

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