Maximum optical density

Table XI presents the results of tests on the same materials in the NBS smoke chamber. It is immediately clear that these results do not correlate well with those measured on the RHR apparatuses. Furthermore, an attempt at a linear correlation between the flaming mode specific maximum optical density and the Cone calorimeter SmkPar at 20 kW/m2 yielded a correlation coefficient of ca. 1%, a coefficient of variation of 217% and statistically invalid correlations. A comparison between a Cone and OSU calorimeter correlation and one with the NBS smoke chamber is shown in Figure 4. This suggests that unrelated properties are being measured.

Table XI. Maximum Optical Density in the NBS Smoke Chamber...

In nominally identical experiments the differences between rates, maximum optical densities and conductivities were never greater than could be accounted for by instrument errors or by errors arising from computation of concentrations. No inexplicable irreproducibilities were found. 

Fig. 2. Parameters affecting the efficiency of energy transfer. (A) Overlay of FITC emission spectrum and PE absorbance spectrum normalized to maximum fluorescence intensity and maximum optical density, respectively. FITC fluorescence intensity was measured as a function of emissions wavelength using a fluorimeter with an excitation wavelength of 488 nm. PE optical density was measured as a function of wavelength using a spectrophotometer. (B) Schematic representation of energy absorption and the possible pathways for the subsequent energy release (abbreviations as in the text).

Treu (1976) measured transmission spectra (optical density) for indium films of the type used for immunological slides. His calculations based on Mie theory led him to the conclusion that this theory was not compatible with observations. In particular, calculations for spheres of diameter 1390 A showed a feature that was not observed in experiments. Although calculations for spheres half this size did not show this feature, the wavelength of maximum optical density was much shorter than that observed. 

Equation 7.33 given l y Wonacott (19) is incorrect. At present, spots used for inter-film scaling by AXIS may not have a maximum optical density, including background, greater than 1.7 (see section 1.2). 

The plates are read A405 nm at 30 min, or when the maximum optical density exceeds 1. 

The surface area of the powder is derivable from the initial concentration of the suspension and the maximum optical density... 

This behavior obtains when photodegradation is not occurring. However, it is experimentally observed that the maximum optical density at the end of the flash depends strongly on the number of flashes i.e., Dr =f(n). Clearly, the simplistic A B scheme does not correctly describe the behavior of the system as photodegradation processes slowly deplete the concentration of the A and B species. A more complete scheme was then adopted in which degradation products D were introduced ... 

A typical oscilloscope trace is shown in Figure 5. (The decay rate did not change when the argon pressure was varied from 58 to 95 atm., or when the benzene pressure was changed from 2 to 8 cm.). The absorption did not decay to zero, but seemed to reach a plateau of about half of the maximum optical density. Because of noise and the difficulty of establishing the plateau, first and second order tests on such decay... 

The decay of the transients was also followed at 330 n.m. The transients formed either from Au(CN)2" + N20 or from AuCIf -f CH3OH decay according to a second order rate law (see Figure 4) up to about 70% of the maximum optical density. The slopes of a number of such decay curves pertaining to both the two systems average around (2.1 0.4) X 104 sec."1, and they are the same at 25/xM and 50/xM gold concentrations which are much in excess of the free radicals or hydrated electrons produced per pulse. The second order decay indicates a disproportionation reaction... 

Figure 1 shows the principles of the ELISA used. The basis of the test is the prevention of pretitrated monoclonal antibody (mAb) from binding to rinderpest antigen on the wells of a microtiter plate hy polyclonal antibodies in samples (serum). The degree of prevention is measured with reference to controls with no sample added (Cm) in which maximum optical density (OD) values are observed, and to wells in which is only conjugate is added (Cc) where low color is observed. Percentage inhibition (PI%) values are calculated with reference to these values. 

The deposition was considered complete when the maximum optical density (absorbance or, in the case of opaque substrates, spectral absorption) allowed for... 

The time for attaining the maximum optical density is also noted. 

The mean smoke density, is also calculated as the arithmetic mean of all five values of the maximum optical density at one irradiance level. 

The optical density is plotted against time during the test procedure. The maximum optical density (i>niax) is read and the area under the curve (5) is calculated in conventional units (corresponding to a rectangle of area 1 min by unit value of the optical density). Smoke formation is expressed by the following indices ... 

Various parameters can be obtained from the NBS test. Those usually quoted are maximum optical density, time to maximum density, the time to reach an optical density of 16 (the critical observation time) and the optical density after 4 minutes. The critical observation time is an indication of how long before visibility would become too bad to allow one to find a way out of a room, while the density at four minutes is relevant to whether smoke would affect escape from, say an aircraft, before other life threatening aspects of a fire became important. 

Within a resin category, the location of the spectral bands were constant. However, offsets, slopes, and the maximum optical density (OD) varied considerably due to the variability in each sample s color, shape, thickness, and orientation in the spectrometer. Figure 36.5 shows several spectra of polystyrene, collected from various samples. Baseline offsets are present with typical variations on the order of 0.25 OD and a maximum deviation of 1.7 OD for a black-pigmented polystyrene sample. Sloping offsets are also apparent in several of the spectra. While preprocessing can eliminate some of the deviations, others must be incorporated into the model. 

After 25 to 30 min fill a spectrophotometer cell with the test solution. Record the optical density at 5 min intervals until the maximum reading is obtained. The maximum optical density is usually obtained between 40 min and 120 min after addition of the hydrogen peroxide reagent depending on the concentration of Nonox in the test solution. 

From the calibration graph read off the number of micrograms of Nonox corresponding to the maximum optical density reading obtained. The concentration of Nonox in the polyethylene is given by ... 

D is the maximum optical density and K is the average optical density over the size range under examination. If Km is assumed equal to unity, equation (5.9) gives the mass specific surface by photoextinction with no correction for the breakdown in the laws of geometric optics. 

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