Density Techniques

General schemes for the identification of natural and synthetic fibers have been estabhshed by the Textile Institute and by the American Association of Textile Chemists and Colorists (8). A comprehensive treatment of burning, solvent, staining, microscopy, and density techniques has been given (9) and a general discussion of procedures for identifyiag synthetic fibers has been presented (10). 

Density Techniques. Many methods are in use, with the selection depending on... 

For their current density technique at the dme, Kies and Van Dam82c reported a standard deviation for a single solution (8 10 5 AfTlN03), based on 11 recordings, of 0.5% and rectilinear calibration graphs in the range 20-1000 nM. 

The bulk density, A, is measured by a widely used tap-density technique by weighing of a convenient known macroscopic volume (e.g., a barrel) of PS [55], A void between granules can be generally considered as macroscopic pores, and its specific volume can be determined as Ua=A 1-(5 1=(1-A/(5)/A. 

Tuovinen, O.H. Button, K.S. Vuorinen, A. Carlson, L. Mair, M. Yut, L.A. (1980) Bacterial, chemical, and mineralogical characteristics of tubercles in distribution pipelines. Am. Water Works Assoc. J. 72 626-635 Turchenek, L.W. Oades, J.M. (1979) Fractionation of organo-mineral complexes by sedimentation and density techniques. Geoderma 21 311-343... 

The classical constant current density experiments were not run as continuous processes, and the concentration of the reducible material diminished gradually. When the limiting current ld becomes smaller (Id ) than the applied current 70. the potential is forced to a more negative value, when the next electrode reaction takes place. Figure 4b illustrates this I0 > Id and the potential drops to about — 0.94 volt where the reduction of 8 also is possible. The two processes thus compete for the electrons and the reduction of 7 is no longer selective. Evidently one of the most advantageous features of the electrolytic process disappears when the classical constant current density technique is used. 

Rodriguez R, Haberly LB. 1989. Analysis of synaptic events in the opossum piriform cortex with improved current source-density techniques. J Neurophysiol 61 702-718. 

This is a thorough study of the vapour pressures of Zn(g) and Se2(g) in equilibrium with a-ZnSe using optical density techniques. The Gibbs energy for the reaction... 

An approach somewhat related to the broken-path method, but more accurate, has been employed by Johnson (1972). It also makes use of curvilinear coordinates (s, p) chosen with constant curvature, and divides the intermediate region into several sectors. In each of these the variables s, p are separable. Calculations were done with the amplitude density technique, matching functions and derivatives at each sector s boundary. The potential was that of Porter and Karplus, and the local vibrational motion was assumed to be harmonic. Good agreement was found with Diestler s at low energies. 

Turchenek, L. W. and Oades, J. M. (1979). Fractionation of organo-min-eral complexes by sedimentation and density techniques. Geoderma 21, 311-343. 

X-Ray, birefringence, and density techniques used to obtain crystalline and amorphous contents and Hermans-Steln orientation functions have also been defined In detail previously. (1-2) The orientation function Is directly related to the angle (if) that the average chain segment makes relative to the fiber axis and Is defined as follows. (3)... 

Thus, using one eminently reasonable partitioning scheme between polarization and donor-acceptor effects, we find that the latter disappears at the complete basis set Hmit. This is exactly the behavior we would expect because polarization and donor-acceptor interactions are the same phenomenon. As the calculations become better and better, the picture of the effect being pure polarization becomes clearer. In this respect, we can consider donor-acceptor interactions found in difference-density techniques to be an artifact of the incomplete basis sets used. 

The body of information on the criticality of sub-critical components of fissile materials arranged in reflected critical arrays has grown sufficiently in the past ten years to warrant examination of. density techniques and understanding of concepts employed. in nuclear criticality safety. Monte Carlo calculations of experimental data have permitted valid extensions of these limited data. Correlations of the data have been effected and have resulted in an analytic expression relating the total number of units, N, in an array, the edge dimension,... 

A few general conclusions are that the interaction methods are more practical and reliable for arrays consisting Of a small number (say <64) of units, while the semiemplrlcal techniques are most applicable to arrays with a large number of low-reactivity units. The albedo method, with suitable input parameters, was found to be the preferred interaction method. The s/v surface density technique, used in areas where it has been developed, was the most useful semiempirical model. 

There are several surface density techniques, > some of which meet the criteria for a model with appropriately defined areas of applicability. One of interest parallels the solid-angle method in its proposed application by specifying conservative but unknown subcriticality. Only two criticality data points appear necessary that for the geometries of the infinite slab and of the unit considered for storage. The situation is aptly presented in Fig. 1 where the ratio of surface densities, that of the storage array to the infinite slab for the same reflector condition, is shown as a function of the ratio of storage-unit mass to. the critical mass in the same geometry, expressed as a fraction. The systems presented are described in the... 

All analytical HPLC columns with particles < 20 pm (usually 5 or 10 pm) are packed by the slurry technique [19], which can be further classified into the high-viscosity technique and the balanced-density technique. In the latter, the particles are suspended in a fluid that has a density similar to theirs, so particle segregation by sedimentation decreases. In both techniques, the suspending fluid must be chosen in such a way that particle dispersion is maintained without aggregation and particle agglomeration is avoided by proper selection of the polarity of the sluiTy [19], [24]. 

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