Grade meaning

The raw materials used are common and available from a variety of industrial sources and are always used as-received without further purification. All raw materials must be urethane grade, meaning mainly that the water content is less than about 0.05% by weight. If in doubt, water level should be measured.413,42 Bayer products are used where possible, but a detailed description of each compound is given so that substitutes from other manufacturers may be used. However, it cannot be overemphasized that extreme care must be taken when choosing substitutes because even small differences in these complex materials can cause marked discrepancies in results. Sources for common materials, such as 1,4-butanediol, are not specified as these are readily available... 

We now turn from the logical to the psychological analysis, which is complicated by the fact that causal and diagnostic contingencies are usually confounded in the real world. Suppose undergraduates know that students who attend a review session for the final examination get better grades than students who do not attend. Does the correlation between attendance and grade mean that the review session really helps Or does it mean that reviews are attended primarily by conscientious students who would do well, session or no Insofar as... 

Figure 7 Clinical disease grading. (A) Anterior chamber cell grade. (B) Anterior chamber flare grade. (C) Fundus opacity grade (mean SEM, P < 0.001, a Mann-Whitney U nonpara-metric test). Source From Ref. 22.

Grade Mean thermal expansion coefficient between 20 ° C Density Thermal Specific... 

The distillation of crudes chosen for their yield in heavy fractions is the most common means. Bitumen is extracted from the residue from a vacuum distillation column (a few dozen mm of mercury), the latter being fed by atmospheric distillation residue. Unlike the practice of a decade ago, it is now possible to obtain all categories of bitumen, including the hard grades. 

At strains over 300% the stress occurs mostiy in the amorphous regions up to the point where the sample breaks. AH of the grades exhibit permanent set, and the curves of grades with a Shore Hardness of 55 and higher exhibit a yield point. This means that parts have to be designed for low strains to stay within the area of elastic recovery. Special grades of elastomer are available to provide hydrolysis resistance (194), improved heat aging (195), and improved uv-stabihty (196). 

Pyridine is also sold as a 1° grade, which means that the boiling poiat range of 98% of the sample will fall ia a 1°C range which iacludes the normal boiling poiat of (1) (115.3 0.1°C). Niacia (27) and niacinamide (26), equivalent forms of vitamin B, are generally sold under a US. Pharmacopeia (USP) specification (78). They are also sold as a feed-grade supplement (see Vitamins). 

For commercial grades of unfractionated PVP prepared by similar means (presumed to exhibit similar molecular weight distribution (MWD) and degree of branching), the following regression formula can be employed (71) ... 

Asphalt (bitumen) also occurs in various oil sand (also called tar sand) deposits which occur widely scattered through the world (17) and the bitumen is available by means of various extraction technologies. A review of the properties and character of the bitumen (18) suggests that, when used as an asphaltic binder, the bitumen compares favorably with specification-grade petroleum asphalts and may have superior aging characteristics and produce more water-resistant paving mixtures than the typical petroleum asphalts. 

---