Two-color

A selected list of redox indicators will be found in Table 8.26. A redox indicator should be selected so that its if" is approximately equal to the electrode potential at the equivalent point, or so that the color change will occur at an appropriate part of the titration curve. If n is the number of electrons involved in the transition from the reduced to the oxidized form of the indicator, the range in which the color change occurs is approximately given by if" 0.06/n volt (V) for a two-color indicator whose forms are equally intensely colored. Since hydrogen ions are involved in the redox equilibria of many indicators, it must be recognized that the color change interval of such an indicator will vary with pH. 

The two forms of the indicator, HIn and In, have different colors. The color of a solution containing an indicator, therefore, continuously changes as the concentration of HIn decreases and the concentration of In increases. If we assume that both HIn and In can be detected with equal ease, then the transition between the two colors reaches its midpoint when their concentrations are identical or when the pH is equal to the indicator s piQ. The equivalence point and the end point coincide, therefore, if an indicator is selected whose piQ is equal to the pH at the equivalence point, and the titration is continued until the indicator s color is exactly halfway between that for HIn and In. Unfortunately, the exact pH at the equivalence point is rarely known. In addition, detecting the point where the concentrations of HIn and In are equal maybe difficult if the change in color is subtle. 

The problem of emissivity from real materials has stimulated the study of pyrometers that measure radiation at two different wavelengths. The principle of the two-color pyrometer is that the energy radiated from a source of one wavelength increases with temperature at a rate different from that radiated at another wavelength. Thus temperature can be deduced from the ratio of the intensities at the two wavelengths, regardless of emissivity. Two-color pyrometers are not widely used. 

In color technology and measurement, both types of approaches are used. Color printing, for example, generally employs three colors (usually plus black), and the ever useful CIE system was founded on experiments in which colors were matched by mixtures of three primary colors, often blue, green, and red. Yet transmitted television signals are based on the opponent system, with one intensity and two color-balance signals, as are the modern representations of color, such as the CIELAB and related color spaces based on red-green and yeUow-blue opponent axes. 

Finally, it cannot be overemphasized that despite instmmental measurements and data manipulations, it is the perception of the eye that still is the final arbiter as to whether or to what degree two colors match. Instmmental methods do serve well for the typical industrial task of maintaining consistency under sufficiently weU-standardized conditions however, a specific technique may not serve in extreme or unusual conditions for which it was not designed. 

Color Difference Evaluation. Shade evaluation is comparable in importance to relative strength evaluation for dyes. This is of interest to both dye manufacturer and dye user for purposes of quaUty control. Objective evaluation of color differences is desirable because of the well-known variabihty of observers. A considerable number of color difference formulas that intend to transform the visually nonuniform International Commission on Illumination (CIE) tristimulus color space into a visually uniform space have been proposed over the years. Although many of them have proven to be of considerable practical value (Hunter Lab formula, Friele-MacAdam-Chickering (FMC) formula, Adams-Nickerson formula, etc), none has been found to be satisfactorily accurate for small color difference evaluation. Correlation coefficients for the correlation between average visually determined color difference values and those based on measurement and calculation with a formula are typically of a magnitude of approximately 0.7 or below. In the interest of uniformity of international usage, the CIE has proposed two color difference formulas (CIELAB and CIELUV) one of which (CIELAB) is particularly suitable for appHcation on textiles (see Color). 

Ratio Pyrometers The ratio pyrometer is also called the two-color pyrometer. Two different wavelengths are utilized for detecting the radiated signal. If one uses Wien s law for small values of XT, the detected signals from spectral radiant energy flux emitted at the wavelengths and 2 with emissivities and are... 

D Shalon, SJ Smith, PO Brown. A DNA microairay system for analyzing complex DNA samples using two-color fluorescent probe hybridization. Genome Res 6 639-645, 1996. MB Eisen, PT Spellman, PO Brown, D Botstem. Cluster analysis and display of genomewide expression patterns. Proc Natl Acad Sci USA 95 14863-14868, 1998. 

The intense blue color which is obtained when tryptophan, in the presence of an aldehyde, is treated with concentrated sulfuric acid containing an oxidizing agent (Adamkiewicz-Hopkins-Cole reaction) was beheved to involve formation of a tetrahydro-j8-carboline intermediate, since most l,2,3,4-tetrahydro-j8-carbohne derivatives yield a similar color with concentrated sulfuric acid containing an oxidizing agent. The two colors have now been shown to have different absorption spectra. The nature of the carboline-blue color is still obscure. 

Table 3-2. Enantiodiscrimination of selected library members using the two-color assay with proline derivatives.

Let us consider again, and now solve, the necklace problem that was mentioned in the discussion of De Bruijn s Theorem, namely, to enumerate necklaces of six beads of two colors, red and green, where the two colors can be interchanged. We shall ask only for the total number, and can therefore use a simpler (unweighted) form of the power group enumeration theorem which gives as the required number the expression... 

This method can be used more generally to find what can be called the "unlabelled chromatic polynomial" of a graph — giving the number of ways of coloring in x colors the vertices of a graph when two colorings are equivalent if one is converted to the other by an automorphism of the graph. 

Over-molding Over-molding is also called in-mold assembly, two-color rotary, or two-color shuttle. Two materials are molded so that the first molded shot is over-molded by the second molded shot first molded part is positioned so the second material can be molded around, over, sections, or through it. The two materials can be the same or different and they can be molded to bond together or not bond together. If materials... 

Schoemaecker Moreau, C. et al.. Two-color laser-induced incandescence and cavity ring-down spectroscopy for sensitive and quantitative imaging of soot and PAHs in flames, Appl. Phys. B, 78,485,2004. 

Variations of flame temperatures with exhaust-gas recirculation. Flame temperature maps are obtained by processing images obtained from a combustion chamber of a heavy-duty diesel engine using two-color pyrometry. Images are taken at 2° after the TDC at 1200rpm low-load condition. 

Matsui, Y., Kamimoto, T., and Matsuoka, S., A Study on the Time and Space Resolved Measurement of Flame Temperature and Soot Concentration in a D.I. Diesel Engine by the Two-Color Method, SAE, 790491,1974. 

Ladommatos, N. and Zhao, H., A Guide to Measurement of Elame Temperature and Soot Concentration in Diesel Engines Using Two-Color Method—Part 1 Principles, SAE, 941956,1994. 

Colors in a laboratory should be coordinated, just as in a home. If pre-finished work benches are to be installed, they might set the color scheme. While they are available in several colors or combination of colors, the choice is not unlimited. In one case, the laboratory operator was color blind, so his wife took over the job as decorator. First, she selected a two-color scheme for the work benches. Color chips in hand, she then chose a floor covering from a number of samples submitted. For the wall paint, she found a standard color of the recommended quality that harmonized with the cabinets. A few appropriate charts and a colorful cloth wall-hanging of pipes and valves completed the decor. The result received many favorable comments from visitors to the facility. 

The laboratory operator had a preference for steel furniture, which the engineering firm shared. Rather than accept their recommendation for a manufacturer, however, the laboratory operator accumulated a stack of catalogs and studied them carefully. There was a substantial price difference between brands and their features varied. One maker seemed to offer the right combination between price and desired features. The sales representative arranged for the laboratory operator s visit to where this furniture had been in service for about two years. It was carefully inspected with slamming of doors and opening of drawers. Although the finish had at times been exposed to chemicals, it had held up well. Best of all, the work benches were available on short notice. After much deliberation, a cheerful two-color scheme of... 

The visible spectnun extends from about 4000 A to 7000 A. We find that the eye acts as an integrating instrument. Thus, two colors may appear equal to the eye even though one is monochromatic light and the other has a bcuid of wavelengths. This is shown in the following diagram ... 

When Munsell devised his color space, he did so on the basis of minimum observable color perception steps. But the problem with the Munsell System was one of reproducibility, which the CIE Standard Observer cured. In formulating a color match, one wants to be able to predict the correct concentration of colorants required, whose scattering and absorption properties are known, i.e.- the lightness, so as to match the sample submitted, starting with their spectrophotometric curves. In practice, this is not so simple, since two colors must have identical spectrophotometric curves to be exactly equal. It turns out that the human eye will identify the two colors to be equal if their spectrophotometric reflectances are reasonably close. Two colors may appear to be equal under Daylight illumination, but quite different under incandescent lamp illumination. These colors are known zus "metamers" and the phenomenon "metamerism". 

Given the color coordinates of x= 0.34 y = 0.51. Identify the color having this property. If x = 0.34 y = 0.61, identify the difference between these two colors. Identify the amounts of red, green and blue in each of these. 

An active matrix of two-color a-Si H photodetectors has been reported [645], where a n-i-p-i-n switching device is stacked on a two-color p-i-n-i-p structure. 

As the plastic liners are removed from the probe, they are capped on both ends, the appropriate labels affixed, and promptly placed in a freezer (an in-field sectioning technique used for further partitioning of the 0-15-cm core is described later in this section). By convention, red plastic caps are placed on top of the core (i.e., the end that was closest to the soil surface) and black caps are placed on the bottom. Use of the two-color capping system is important when the cores are sectioned at a later time. This approach is referred to as zero-contamination sampling and is the industry standard in field soil dissipation. 

Figure 3.24 Resonance Raman Stokes and anti-Stokes difference spectra of the photochemical ring opening of 1,3-cyclohexadiene. Anti-Stokes spectra were obtained with 284-nm pump and probe wavelengths, while the two-color Stokes spectra were generated with a 284-nm probe and a 275-nm pump. The line at 801 cm is due to the cyclohexane solvent. (Reprinted with permission from reference [122]. Copyright (1994) American Chemical Society.)...

Schmalzing, D., Koutny, L., Chisholm, D., Adourian, A., Matsudaira, P, and Ehrlich, D., Two-color multiplexed analysis of eight short tandem repeat loci with an electrophoretic microdevice, Anal. Biochem., 270, 148, 1999. 

Consider, by contrast, a two-color experiment where the continuum is accessed by two laser fields with a well defined relative phase, a and , . A schematic illustration of the experiment envisioned is provided in Fig. 1 a, where we consider the specific case of excitation with one- and three-photon fields of... 

---