Optical density Order separation

Rate constants for methanol and ethyl alcohol relative to those for benzoate ion, phenylacetate ion and p-nitrobenzoate ion are shown in Table III. Each value in the table consists of experiments at five separate concentration ratios. The random uncertainty in each value is less than 10%. In determining these rate constants from optical density ratios it was necessary to make a small correction for the contribution to the optical density by the H-adduct free radical. The molar extinction coefficients at 340-350 m/x for the H-adduct and OH-adduct are similar for benzoic acid (22) and were assumed to be comparable for the other two aromatic ions in the table. The correction is necessary since the rate constants for the reaction of hydrogen atoms with the alcohols used are two orders of magnitude lower than the rate constants for hydrogen atom addition to the aromatic ring, while the analogous hydroxyl rate constants are roughly comparable. 

Synthetic homopolymers poly(A) and poly(U), which separately are in random coil conformation in aqueous solution, associate together to form well-ordered double-stranded poly(A+U). This hybridization is detectable by a decrease in the optical density at 260 nm... 

A separate spectrophotometric determination of the E. coli growth rate was made. The doubling time was the same as determined by HTDSLS. There was a striking difference of nearly four orders of magnitude between the low particle densities that can be determined by HTDSLS and the lowest densities needed for optical density measurements. HTDSLS also gave the characterization of the coexisting polymer, to which optical density measurements are insensitive. 

An important specific feature of the present experiment is worth noting. The X-ray photons have energies that are several orders of magnitude larger than those of optical photons. The pump and probe processes thus evolve on different time scales and can be treated separately. It is convenient to start with the X-ray probing processes, and treat them by Maxwellian electrodynamics. The pumping processes are studied next using statistical mechanics of nonlinear optical processes. The electron number density n(r,t), supposed to be known in the first step, is actually calculated in this second step. 

Owing to their structure, crazes have a lower density and a lower refractive index than the bulk polymer. Thus it is possible to measure their sizes and shapes using optical interference, provided that the separations involved are comparable in order of magnitude to the wavelength of light, that the refractive index of the craze is significantly different from that of the bulk material, that the boundary between the two regions is sharp and last but not least that the material is transparent. 

The plates used were sli tly wedge-shaped in order to make the different reflection images more easily separable. The unevermesses on the optical flat surfaces were smaller than 400 A which is probably the limit obtainable. The area of the plates mainly used was 4 cm, their density at 15 C was = 2 556, their refractive index = 1 5209. Later on glass plates with area 1 cm, d 2 55, = 1 515 and quartz plates d s = 2 66 na (ord.)... 

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