Reflectance function measurement

Thermal Fixation Properties of Disperse Dyes on Polyester—Gotton. This method assesses the fixation properties of disperse dyes as a function of the time, temperature, dyestuff concentration, or presence and amount of auxiUary agents. The polyester—cotton fabric is padded and dried, the cotton dissolved in sulfuric acid and washed out of the blend, and the amount of dye on the polyester component assessed by either reflectance or measuring the optical density of a solution of dye obtained by extracting the dye with boiling chloroben2ene solvent. 

The parameter n reflects the measure of deviation of the system from the behavior of the monomeric acid where n = 1, i.e., it characterizes the degree of interaction between the neighboring functional groups of the macroion. The value of n depends on the structure of the polyelectrolyte and the nature of the counterion pK = pK0 — log (1 — a)/a is the negative decadic logarithm of the effective dissociation constant of the carboxylic CP depending on a. 

By measuring V z), which includes examining the reflectance function of solid material, measuring the phase velocity and attenuation of leaky surface acoustic waves at the liquid-specimen boundary, the SAM can be used indetermining the elastic constants of the material. 

In addition to the indirect experimental evidence coming from work function measurements, information about water orientation at metal surfaces is beginning to emerge from recent applications of a number of in situ vibrational spectroscopic techniques. Infrared reflection-absorption spectroscopy, surface-enhanced Raman scattering, and second harmonic generation have been used to investigate the structure of water at different metal surfaces, but the pictures emerging from all these studies are not always consistent, partially because of surface modification and chemical adsorption, which complicate the analysis. 

The number of reflection intensities measured in a crystallographic experiment is large, and commonly exceeds the number of parameters to be determined. It was first realized by Hughes (1941) that such an overdetermination is ideally suited for the application of the least-squares methods of Gauss (see, e.g., Whittaker and Robinson 1967), in which an error function S, defined as the sum of the squares of discrepancies between observation and calculation, is minimized by adjustment of the parameters of the observational equations. As least-squares methods are computationally convenient, they have largely replaced Fourier techniques in crystal structure refinement. 

Neuroimaging techniques assessing cerebral blood flow (CBF] and cerebral metabolic rate provide powerful windows onto the effects of ECT. Nobler et al. [1994] assessed cortical CBE using the planar xenon-133 inhalation technique in 54 patients. The patients were studied just before and 50 minutes after the sixth ECT treatment. At this acute time point, unilateral ECT led to postictal reductions of CBF in the stimulated hemisphere, whereas bilateral ECT led to symmetric anterior frontal CBE reductions. Regardless of electrode placement and stimulus intensity, patients who went on to respond to a course of ECT manifested anterior frontal CBE reductions in this acute postictal period, whereas nonresponders failed to show CBF reductions. Such frontal CBF reductions may reflect functional neural inhibition and may index anticonvulsant properties of ECT. A predictive discriminant function analysis revealed that the CBF changes were sufficiently robust to correctly classify both responders (68% accuracy] and nonresponders (85% accuracy]. More powerful measures of CBF and/or cerebral metabolic rate, as can be obtained with positron-emission tomography, may provide even more sensitive markers of optimal ECT administration. 

Anyone who has successfully used a microscope to image properties to which it is sensitive will sooner or later find himself wanting to be able to measure those properties with the spatial resolution which that microscope affords. Since an acoustic microscope images the elastic properties of a specimen, it must be possible to use it to measure elastic properties both as a measurement technique in its own right and also in order to interpret quantitatively the contrast in images. It emerged from contrast theory that the form of V(z) could be calculated from the reflectance function of a specimen, and also that the periodicity and decay of oscillations in V(z) can be directly related to the velocity and attenuation of Rayleigh waves. Both of these observations can be inverted in order to deduce elastic properties from measured V(z). 

Thus, by measuring V(u) and inverse Fourier transforming it, the reflectance function may be deduced. Four practical constraints are immediately apparent from the theoretical formation. 

Fig. 8.3. Reconstruction of the reflectance function of duraluminium from magnitude only V(z) data, measured at 320 MHz. (a) Steps in the reconstruction of P(9)R(9) after (i) 1 (ii) 3 (iii) 10 and (iv) 30 iterations of the phase retrieval algorithm, (b) Reconstructed R 8) (Fright etal. 1989).

The integration could be performed by calculating V(z) for each 0, corresponding to V(z) curves such as the measured one in Fig. 11.7(a), and then integrating over 0. Alternatively, a complex mean reflectance function (denoted by prime) may be calculated as... 

Reflects a fundamental aspect of waking neurocognitive functions Measures the ability to use attention or working memory over time Capitalizes on brain structures subserving basic cognitive functions... 

When the reaction compartment of an element is illuminated at a suitable wavelength, the amount of diffuse light recovered with the aid of the reflective function is a measure of the progress of the reaction, where a chromophore is either generated or degraded. The commonly used expression for reflectance... 

As several researchers have shown empirically, the use of —log(reflectance) can provide, analogous to a transmittance measurement, a linear relationship between the transformed reflectance and concentration, if the matrix is not strongly absorbing as can be found for many samples studied by near-infrared spectroscopy. This issue is presented in detail below. A different approach based on a physical model was considered for UV/VIS measurements and later also applied within the mid-infrared. A theory was derived by Kubelka and Munk for a simple, onedimensional, two-flux model, although it must be noted that Arthur Schuster (1905) had already come up with a reflectance function for isotropic scattering. A detailed description of theoretical and practical aspects was given by Korttim. The optical absorption... 

Foraminifera from the sediments of the Cariaco Trench (Fig. 7.6) (Hughen et al, 2004). Since the sediments of this anoxic basin are varved, the age filter applied to most sediment cores by bioturbation is not an issue. Calendar ages of the varves in the sediments of this basin were determined by matching the percent reflectance (a measure of the color of the sediments) with 5 0 variations in the ice of a Greenland ice core (described later in Fig. 7.19). Since the latter record is precisely dated back to 40 000 years by actual counting of annual ice layers, and the two records are undeniably correlated, it was possible to determine an accurate calendar age for the Cariaco Trench sediment core by using variations in the percent reflectance record. The results in Fig. 7.6 indicate offsets of up to 5 ky between C age and calendar age at about 30 ky BP and an abrupt shift at 40 calendar kiloyears (cal. ky) BP in which 7000 C years elapsed in only 2000 y. The results have been explained as variations in the source function and the ventilation of the deep sea and are now used to correct C dates back to more than 40 cal. ky BP. 

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