Volume obscuration

Kusters et al. [22] analysed polystyrene latex particles of about 1 p,m diameter aggregated in salt solution in a stirred tank, with samples withdrawn from the tank by pipette for light-scattering measurements. They found mass fractal dimensions of around 2.5 using the volume obscuration method. 

Spicer et al. [21] analysed 0.87 p,m particles in a stirred tank system similar to that used by Kusters et. al. and found, using the volume obscuration method, mass fractal dimensions of 2.1 for small floes increasing to 2,5 for larger floes, consistent with the findings of Oles. The increase was attributed to shear-induced restructuring. 

Although the volume of commercial pyridine compounds is relatively large, economic aspects resemble those of specialty markets more than those of commodities. Commercial transactions occur withHtde pubHcity, trade secrets are carefully guarded, and patents proliferate, thus obscuring the industrial processes used for their manufacture. 

Economic summaries of the cosmetic industry, commonly documented by sales volume, are sometimes based on unit sales, sometimes on manufacturers sales in monetary units, and sometimes on consumer spending. Figures normally include contributions by private labeling operations but do not necessarily reflect the value of the industry service sector, which includes suppHers of raw materials, beauticians, testing laboratories, and other speciaHsts. Moreover, product categories caimot be rigidly defined. For example, the differentiation between a deodorant (a cosmetic) and an antiperspirant (an OTC dmg) is often obscured by its trade name. 

A second source of difficulty is caused by the unavoidable empty space in recycle reactors. This limits their usefulness in some studies. Homogeneous reactions in the empty gas volume may interfere with heterogeneous catalytic measurements. Transient experiments could reveal much more information on various steps in the reaction mechanism but material in the empty space can obscure sharp changes. 

Heterogeneity, nonuniformity and anisotropy are defined as follows. On a macroscopic basis, they imply averaging over elemental volumes of radius e about a point in the media, where e is sufficiently large that Darcy s law can be applied for appropriate Reynolds numbers. In other words, volumes are large relative to that of a single pore. Further, e is the minimum radius that satisfies such a condition. If e is too large, certain nonidealities may be obscured by burying their effects far within the elemental volume. 

The solid-flame model can be used to overcome the inaccuracy of the point-source model. This model assumes that the fire can be represented by a solid body of a simple geometrical shape, and that all thermal radiation is emitted from its surface. To ensure that fire volume is not neglected, the geometries of the fire and target, as well as their relative positions, must be taken into account because a portion of the fire may be obscured as seen from the target. 

Flow markers are often chosen to be chemically pure small molecules that can fully permeate the GPC packing and elute as a sharp peak at the total permeation volume (Vp) of the column. Examples of a few common flow markers reported in the literature for nonaqueous GPC include xylene, dioctyl phthalate, ethylbenzene, and sulfur. The flow marker must in no way perturb the chromatography of the analyte, either by coeluting with the analyte peak of interest or by influencing the retention of the analyte. In all cases it is essential that the flow marker experience no adsorption on the stationary phase of the column. The variability that occurs in a flow marker when it experiences differences in how it adsorbs to a column is more than sufficient to obscure the flow rate deviations that one is trying to monitor and correct for. 

The use of totally permeated flow markers in aqueous GPC offers similar advantages along with many of the same shortcomings that one finds in nonaqueous GPC. One problem commonly found in aqueous GPC is that salt peaks due to the on-column ion exchange of counter ions of a polyelectrolyte with dissimilar ions in the GPC mobile phase will occur at or near the total permeation volume of the column. These salt peaks will often obscure the flow marker used in the analysis. Short of preconditioning the sample to exchange... 

Recently efficient techniques were developed to simulate and analyze polymer mixtures with Nb/Na = k, k > I being an integer. Going beyond meanfield theory, an essential point of asymmetric systems is the coupling between fluctuations of the volume fraction (j) and the energy density u. This coupling may obscure the analysis of critical behavior in terms of the power laws, Eq. (7). However, it turns out that one can construct suitable linear combinations of ( ) and u that play the role of the order parameter i and energy density in the symmetrical mixture, ... 

Multi-fuel operation with coal-firing equipment is more difficult to achieve, partly because the grate obscures some of the boiler heating surfaces and partly due to the volume that it also occupies. Systems do exist for this requirement, but changeover is not as instant as oil and gas, as it is normally necessary to remove part of the coal-firing equipment. 

Obscuring Power of White Smokes. The total obscuring power, TOP, of a white smoke agent used for screening purposes, is obtained by multiplying the product of volume, in cubic ft or smoke produced per lb of material, and the reciprocal of the smoke layer, in ft, necessary to obscure the filament of a 40-watt Mazda lamp. The TOP for some white smoke agents, at low altitudes where atm constituents are plentiful, is given in Table 1... 

Figure 3.1 Four-step construction of the Bjerrum difference plot for a three-pi molecule, whose constants are obscured in the simple titration curve (see text) (a) titration curves (b) isohydric volume differences (c) rotated difference plot (d) Bjerrum plot. [Avdeef, A., Curr. Topics Med. Chem., 1, 277-351 (2001). Reproduced with permission from Bentham Science Publishers, Ltd.]...

Toxicity of Military Smokes and Obscurants, Volume 1 (1997), Volume 2 (1999), Volume 3 (1999)... 

Fig. 12.6. Observable baryons in the Universe as a function of time. The curves represent the total mass density in stars (in Af0Mpc-3) from Rudnick et al. (2003) based on a survey of near-infrared selected galaxies in the Hubble Deep Field South, assuming a Salpeter(O.l) IMF. (For a Kennicutt (1983) IMF, the numbers would be approximately halved.) The points with error bars show the cosmic density of H I from DLAs and sub-DLAs at various redshifts, uncorrected for obscuration, while the point at bottom right shows the present-day density of H i clouds determined by Zwaan et al. (2005). The typical H I co-moving volume density corresponds to S2Hi — 0.7 x 10-3 (taking h = 0.65). After Peroux, Dessauges-Zavatsky, D Odorico et al. (2005).

Poly(trimethylene terephthalate) (PTT) is a newly commercialized aromatic polyester. Although available in commercial quantities only as recently as 1998 [1], it was one of the three high-melting-point aromatic polyesters first synthesized by Whinfield and Dickson [2] nearly 60 years ago. Two of these polyesters, polyethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT), have become well-established high-volume polymers. PTT has remained an obscure polymer until recent times because one of its monomers, 1,3-propanediol (PDO), was not readily available. PDO was sold as a small-volume fine chemical at more than 10/lb., and was therefore not suitable as a raw material for commercial polymers. 

The basic features of equations of state are not complicated when they are expressed as PV/RT versus density. Figure 3 is a sample plot for methanol. These curves are characteristic of all fluids, and equations of state only differ in their ability to accurately predict these curves. The actual curves are relatively simple and they change only slightly from one material to another for this reason, simple equations of state such as the Redlich-Kwong equation have been about as successful as the BWR equation. The simplicity of the actual curves is often hidden because the data are not usually plotted as PV/RT versus density. More often the data are plotted as PV/RT versus pressure shown in Figure 4, or pressure versus volume shown in Figure 5. Both of these plots obscure the real simplicity shown in Figure 3. 

Least-altered metavolcanic samples have Na20 and MgO contents of 1.8-4.0 wt. % and 4-25 wt. %, respectively, whereas strongly altered samples (having greater than 30% hydrothermal minerals by volume, in dense net-textured veins, in places obscuring primary textures) contain less than 1.5 wt. % Na20 and 11-23 wt. % MgO. 

The structure-function relationship of the indole-indoline binary alkaloids was relegated to obscurity until the recent achievement of methodologies for their complete syntheses (see Chapter 2, this volume). Our work with C-20 congeners of VBL has established that the complex interactions between this molecule and tubulin or microtubules can be modified by structural alteration. The various, concentration-dependent reactions of VBL with the microtubule system in vitro are sensitive to subtle modifications at a single molecular locus. In addition, these reactions are distinctive on a mechanistic level as seen from the unique activity profiles of most of our C-20 alkyl congeners. At first light, we can look toward the future with secured optimism. 

The need for a Greek key fold remains obscure. The apoproteins are clearly stable without metals there are examples other than immunoglobulins of Greek key folds. So far copper seems to be found in a very limited subset of structures other chapters in this volume show that zinc, for example, has a much wider variety of environments in proteins, as does iron. It may be that the copper-containing Greek key proteins represent a very small evolutionary niche. Structures of other copper proteins will undoubtedly reveal new surprises and help to clarify the essential role of copper in biological systems. 

In retrospect, the reason for this is not all that obscure. Most of the soldiers were in hypo-volaemic shock with low blood pressure, low blood volume, and as part of the shock syndrome, systemic circulation was minimal with intense vasoconstriction - hence the poor therapeutic effect. The repeated doses of morphine were usually given intramuscularly into the buttock or thigh but their clearance into the systemic circulation was minimal until resuscitation occurred and the peripheral circulation was restored. Blood flow to the muscle increased and all the morphine injected became available - all at once. This was the reason for the morphine overdoses and the occasional death. Thereafter it has become standard practice to give morphine in emergency directly into the veins and not into poorly perfused muscles. 

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