Empirical Units

This is measured as the time (in seconds) required for a sample to flow through the orifice of a Saybolt universal viscometer, according to the conditions specified in ASTM D88. Viscosities measured are expressed as, for example, Saybolt universal seconds (SUS), Saybolt seconds universal (SSU), or Saybolt universal viscosity (SUV), and are usually measured at both 100°F and 210°F. This is an outdated method, but as mentioned earlier, its memory lingers in the industry terminology. 

This is very similar to the method above, but is applied to very high viscosity samples such as asphalts. Results are reported as Saybolt seconds furol (SSF). 

This empirical method is used in Europe but has little use in North America. Like the Saybolt method, this method measures the time for a fixed volume to flow out of a standard Redwood viscometer by the IP70 procedure and the result is reported in Redwood seconds. 

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Fig. 8. Variation of the skin wound half-life with degradation rate R (in collagenase) of collagen-GAG matrix. The half-life is the time required for a wound to contract to 50% of the original area. The degradation is in empirical units, which are defined in terms of an in vitro assay. A somewhat arbitrary broken vertical line is drawn near R = 140 enzyme units. This line shows the level of degradation rate above which the half-life of matrices rapidly drops to the level of the ungrafted wound. The horizontal scale is logarithmic [79]...

Viscosity measurements are expressed in either systematic or empirical units both are used, but the current trend is very much toward using systematic units. 

However, empirical units have left a lasting impression on terminology, and while still employed from time to time in providing names for base stocks (e.g., 100N, 250N), their actual viscosity measurements and their ranges on specification sheets are measured in systematic units and converted to empirical... 

A more common empirical unit for pressure, used with all systems of units, is the standard aUnosphere (atm), defined by... 

The unit for work and mechanical energy in the fps system is the foot-pound force (ft-lby ). Power is measured by an empirical unit, the horsepower (hp), defined by... 

The SI unit of heat, as well as of work and energy is the joule, J as summarized in Fig. 2.3. Its dimension is expressed in [kg m s" ]. Heat and work describe the energy exchanged between thermodynamic systems, as discussed in Sect. 2.1.5 with the equation 6q -i- 8w = dU. An earlier, empirical unit, the calorie, was based on the specific heat capacity of water (1 calthemochemicai = 4.184 J). Since the early 2(f century, however, energy, heat, and work are more precisely determined in joules, making the calorie a superfluous unit. The calorie is not part of the SI units and should be abandoned. AU modem calorimetry is ultimately based on a comparison with heat generated by electrical work. 

Although the molecule CF, does have a transient existence, there are stable compounds which have the same empirical formula but are very different in structure. The empirical unit CF, forms the compound CjF as a dimer. The dimer, tetrafluoroethene, is a stable molecule with the structure shown in Figure 7.3. This contains a C=C double bond, so that both carbon atoms have a share in an octet of valency electrons and are four-valent. 

The number of existing empirical units for hyaluronidase activity nearly equals the number of workers in the field. The correlation of units obtained by different physicochemical with biological assay methods is of great theoretical and practical interest and has been the subject of several studies. 

Here the empirical compositions of polymer and reacting monomers are dilTerent and the structural unit (mer) has no constitutional identity with the monomer components. 

The traditional definition of a zeolite refers to microporous, crystalline, hydrated aluminosilicates with a tliree-dimensional framework consisting of comer-linked SiO or AlO tetrahedra, although today the definition is used in a much broader sense, comprising microporous crystalline solids containing a variety of elements as tetrahedral building units. The aluminosilicate-based zeolites are represented by the empirical fonmila... 

In this project, we shall predict the wavelength of the absorption maxima of the same four polyenes using the calculated difference (in units of eV), between the LUMO and HOMO of these four molecules (Fig. 8-6). Bear in mind that this is not an ab initio calculation of wavelengths of maximum absorption, because empirically fitted parameters, Yio exist within the program or are... 

The structural unit associated with an electronic transition m UV VIS spectroscopy IS called a chromophore Chemists often refer to model compounds to help interpret UV VIS spectra An appropriate model is a simple compound of known structure that mcor porates the chromophore suspected of being present m the sample Because remote sub stituents do not affect Xmax of the chromophore a strong similarity between the spectrum of the model compound and that of the unknown can serve to identify the kind of rr electron system present m the sample There is a substantial body of data concerning the UV VIS spectra of a great many chromophores as well as empirical correlations of sub stituent effects on k Such data are helpful when using UV VIS spectroscopy as a tool for structure determination... 

Since the monomers are specified to be vinyl monomers, each contributes two carbon atoms to the polymer backbone, with the associated extended length of 0.252 nm per repeat unit. Therefore the total extended length of the empirical formula unit is... 

With copolymers, it is not sufficient merely to describe the empirical formula to characterize the molecule. Another question that can be asked concerns the distribution of the different kinds of repeat units in the molecule. Starting from monomers A and B, the following distribution patterns are obtained in linear polymers ... 

Rate of Mass Transfer in Bubble Plates. The Murphree vapor efficiency, much like the height of a transfer unit in packed absorbers, characterizes the rate of mass transfer in the equipment. The value of the efficiency depends on a large number of parameters not normally known, and its prediction is therefore difficult and involved. Correlations have led to widely used empirical relationships, which can be used for rough estimates (109,110). The most fundamental approach for tray efficiency estimation, however, summarizing intensive research on this topic, may be found in reference 111. 

To estimate the number of transfer units for design, the following empirical correlations which were derived from efficiency measurements employing a variety of trays and operating conditions under the aforementioned assumptions are recommended (111) ... 

Production of a metal is usually achieved by a sequence of chemical processes represented as a flow sheet. A limited number of unit processes are commonly used in extractive metallurgy. The combination of these steps and the precise conditions of operations vary significantly from metal to metal, and even for the same metal these steps vary with the type of ore or raw material. The technology of extraction processes was developed in an empirical way, and technical innovations often preceded scientific understanding of the processes. 

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