Composition spectra

Figure 2. Spectral Residual for Typical (Coal EH) and Worst (Coal SL) Least-Squares Fits. Spectra Shown are Original LTA, Least-Squares Composite, and Difference (Original Minus Composite). LTA and Composite Spectra are Displaced Along the Absorbance Axis for Clarity.

In the real world samples generally contain more than one constituent, and their spectra usually overlap. If we had a 2-component sample with individual and composite spectra like those in Figure 8, and if we wanted to determine the concentration of J, we would need to make measurements at two wavelengths, j and k. The tail (leading edge) of K overlaps the peak of J, giving rise to a composite absorbance (the solid line) which is higher than J s contribution. 

This nitroxide is more soluble in liquid regions of bilayers than it is in solid regions. As bilayers are warmed in the EPR spectrometer, the solubility of this spin-labeled compound in the lipid can be followed (see figure). The lower of the three spectra approximates that of the spin label in water alone, while the others are composite spectra for which part of the spin label has dissolved in the phospholipid bilayers. 

Abstract. A multi-wavelength, multi-sensor Look-Up-Table (LUT) algorithm has been developed to retrieve information about stratospheric aerosols from satellite-based observations of particulate extinction. Specifically, the LUT algorithm combines extinction measurements from SAGE n with similar measurements from the CLAES instrument, and uses the composite spectra in month-latitude-altitude bins to retrieve values and uncertainties of particle effective radius, surface area, volume and size distribution width. 

The surface characteristics of reworked substrates and several rework processes are described later in several tables and the discussion. The substrate condition following the rework process is characterized by the results of three tests ESCA or XPS [19] surface chemical composition spectra, actual lithographic resist pattern lift testing [2, 6], and water droplet contact angle measurement, 0HjO [3]. 

Figure 2. Simulated composite spectra consisting of 4% of the nitroxides undergoing motional narrowing (isotropic, homogeneous broadening of 1 G) with rotational correlation times as indicated...

The sharpness of the fast component in the composite spectra in Figures It and 5 is a good indication that there is not a wide distribution of correlation times, and by reference to Figure 1, that the mobile segment density of the adsorbed polymer extending into the solvent is dilute. The nature of the mobile units-loops, tails, or some of each-cannot be deduced from these data. 

Figure 7 illustrates the usefulness of this optical arrangement. Radiation from a multielement hollow cathode lamp containing Mn and Cr was allowed to fall on one fiber-optic strand. Radiation from a second hollow cathode lamp containing Li was incident on a second fiber optic strand. Individual and composite spectra are shown in the figure. With this optical system, lithium can be determined simultaneously with Cr and Mn by atomic emission, or lithium could be used as an internal standard for the analysis. To do this with a conventional one-dimensional dispersive system would require a wavelength window from 403 nm to 671 nm, resulting in poor resolution. 

The strengths of the spectral lines of the cobaltatom and ion are measurable in composite spectra from stars, where iron is also observable and is usually taken as a standard measure of the abundance of heavy elements within stars. Observations show that the abundance ratio Co/Fe has, through most of galactic history, remained constant, even while each has increased in its proportion to H. A puzzle exists only in the most metal-poor stars, where stunning recent observations reveal a Co/Fe ratio that is almost five times greater than solar when Fe/H is near 1/10 oooth of that in the Sun, and that ratio... 

In the forward search, all of die ions in both the library spectrum and the unknown specdiun are used in the calculation of the fit factor, while in the reverse search only the ions in the library specdiun are used in this calculation. Forward searches work well only for pure compounds, while die reverse search is admirably suited for dealing widi die composite spectra fiom mixtures. 

Infrared Spectroscopy. An inspection of the infrared spectra of dry or hydrated pure Nafion in the sulfonic add or various cationic salt forms reveals a multiplidty of bands (28, 30, 31) some of which are inconveniently located in close proximity to the aforementioned peaks characteristic of silicon oxide strudures. The Nafion contribution to the composite spectra was subtracted in each case using the 2860 cm band (combination 1140 + 1720 cm, both CF,CF,) as an internal thickness standard. While this band appears weak and may not be an ideal internal standard (Membranes were not available to test absorbance vs. thickness linearity.), it is backbone-related, lies in a region of peak noninterference and the resultant subtractions do appear effective. 

II. sdB stars with composite spectra (usually sdB+G) showing small or no velocity variations. Orbital periods are thought to range from tens of days to several years (15-20%),... 

A second conformation that is frequently encountered in chlorofluorocarbon matrices is the gauche-at-C2 conformation, which is obtained from the extended conformer by 120° rotation around C2-C3 (see Fig. 5.1). In this conformation, the unpaired electron and positive hole delocalize over the planar part of the C-C skeleton as well as over one in-plane chain-end and penultimate C-H bond (on opposite sides of the radical cation). Other more twisted conformations (such as obtained from the extended conformer by 120° rotation around the penultimate C-C bond as well as around C2-C3, either both clockwise or one clockwise and the other counterclockwise) have also been observed, but they are less common in chlorofluorocarbon matrices. In n-alkanes in the liquid state, many conformers are present and the paramagnetic absorption reflects this by the fact that an unresolved spectrum is observed for the radical cations, resulting from hyperfine coupling with many different protons [10]. As a result of increased delocalization, the line width of such composite spectra decreases with increasing chain length. 

Analysis of composite spectra, where the responses of the crystalline, amorphous and intermediate regions are superimposed. 

Figure 13.16. Example of sequencing of DNA using the Maxam-Gilbert method. MALDI spectra of the sequencing reactions are shown in (a) and b), and the composite spectra of the 30-mer DNA is shown in (c). (Reproduced from ref. 81 by permission of the American Chemical Society, Washington, DC, copyright 1999.)...

The chemical composition of the three minerals is also not very well-constrained since the natural species exhibit significant chemical substitutions with cations as Cu, Co, Ni and Mn that expand the chemical composition spectra. Since the asbolane crystallography is not yet clearly defined, this phase is usually not referenced in XRD databases. However, its crystallographic... 

Figure 6-23. UV-visible spectra of a) a silver hydrosol and b) a gold hydrosol as they agglomerate under the influence of added pyridine. The composite spectra show the splitting of the plasmon absorption peaks and the shift to longer wavelength of the lower energy component with time, (i) As prepared, (ii) etc. after addition of pyridine. (Reproduced by permission from ref. [209].)...

Dominant near-infrared spectral features include the measurement of the overtones and combination absorption bands from the following functional groups. The table and composite spectra further define the locations of these groups in typical NIR spectra. 

Plots of applied versus ln(Aj - Aj )/( Aq - Aj) are linear for reversible systems ° is determined from the intercept and n from the slope. Because the spectra are measured under equilibrium conditions, iR drop is nnimportant to the measurement. This description of determination assumes that the two redox forms of the analyte have discrete absorbance spectra which do not overlap. It is also possible to assess E° for more complex systems in which spectra are not well resolved throngh deconvolution of the contributions to the composite spectra. Spectropotentiostatic measurements of this type have been applied to multiredox steps in supramolecular systems containing several of the same chromophore units undergoing sequential redox steps. Distributions of redox species can be estimated using iterative algorithms based on the Nemst equation to obtain E° values for each step (23). 

The ESR spectrum corresponding to the F component was isolated by subtracting the spectrum of the slow component presented at the top of Fig. 4 from one of the composite spectra. After this step it was easy to superimpose the two components, and to reproduce all composite spectra the relative concentration of each spectral component was then obtained by double integration. After examination of numerous samples, we became convinced that the same F and S components are detected in different samples, and the corresponding composite spectra differ only in the relative intensity of the two components. The percentage of the fast component, %F, calculated as described above, is given for all spectra shown in Fig. 4. 

Laser spectroscopy has been extensively used in solids to suppress inhomogeneous contributions and to isolate features which are characteristic to a designated site or field distribution. In this, site selective excitation spectra (fig. 3) or FLN have been used to deconvolute the individual components of composite spectra. For example, when trivalent rare earths are doped into a divalent host such as... 

The overall kinetics represents an averaging over the reactivity and composition spectra. Such averaging should be different in reactors with... 

Direct fluorescence, phosphorescence and X-ray fluorescence spectroscopy for polymer/additive analysis have been reported [513]. In commercial polymers, additives having electronic absorption bands in the visible and near-UV wavelength regions may fluoresce and give rise to composite spectra. Some general applications of fluorescence spectroscopic analysis for polymeric materials relate to ... 

The above discussion has considered the spin-label or spin-probe to be in a homogeneous system with a single correlation time. In some cases, however, the observed ESR spectrum is of neither the fast- nor the slow-motion type but is a mixture of the two (Figure 9.3). Such composite spectra arise when the spin-labels or probes simultaneously occupy two motionally distinct environments, one of which is significandy more restricting than the other. This behaviour may occur in situations such as adsorption of a polymer onto a solid [9], phase separations of polymers or polymer blends [25], polymer networks [26] or any other system where more than one phase is present. 

Analysis of composite spectra can be achieved by computer simulation of the fast and slow components, yielding the relative proportions of the label or probe in the different environments. It must be noted that a few percent of fast motion in an otherwise slow-motion spectrum is readily detected, whereas this is not true of the reverse situation. This is because the peak-to-peak intensity of an ESR line is proportional to the inverse of the square of the linewidth (see Equation (2)) and fast-motion lines are much narrower than slow-motion lines. 

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