Methods subtractive

An alternative formulation of QM/MM is the energy subtraction method. In this method, calculations are done on various regions of the molecule with... 

Samples with Interfering Materials Differential and Subtractive Methods... 

The subtractive method was adapted from Horwitz [182], and is easiest in use. The principle is to measure the power delivered to the system, including the tuned matching network, in the case that the discharge is on (Ptot) and in the case that it is off, i.e. when the system is evacuated (Pvac)- with the constraint that in both cases Plot and Pvac are measured for the same electrode voltage Vpp. The matcher efficiency [181] or power transfer efficiency r]p [183] then is defined as... 

These methods, and the most simple one with K — 1, were comparatively analyzed in a series of iPPs with crystallinity levels ranging from 0.50 to 0.80. The results are shown in Table 1. For this system, the corrections proposed by Natta and the most simple subtraction method (K — 1) gave similar results. The values obtained by the Hermans-Weidinger method are only slightly lower however, the method developed by Mo and Zhang yield consistently higher values. From this comparison, it appears that the most used simple method with K — 1 gives reasonable crystallinity values. 

A standard cell potential depends only on the identities of the reactants and products in their standard states. As you will see in the next Sample Problem, you do not need to consider the amounts of reactants or products present, or the reaction stoichiometry, when calculating a standard cell potential. Since you have just completed a similar Sample Problem, only a brief solution using the subtraction method is given here. Check that you can solve this problem by adding a reduction potential and an oxidation potential. 

In addition techniques, the test substance concentration is determined from the difference in the ISE potentials obtained before and after a change in the sample solution concentration. The main advantage Ues in the fact that the whole measurement is carried out in the presence of the sample matrix, so that results with satisfactory accuracy and precision can be obtained even if a substantial portion of the test substance is complexed. Several addition techniques can be used, namely, single, double or multiple known addition methods, in which the sample concentration is increased by additions of a test substance standard solution single, double or multiple known subtraction methods, in which the sample concentration is decreased by additions of a standard solution of a substance that reacts stoichiometrically with the determinand and analyte addition and subtraction methods, in which the sample is added to a test substance solution or to a reagent solution. 

The simplest addition methods are the known addition method (KAM) and known subtraction method (KSM). Two potential values are obtained in the sample solution, before the addition (Ei) and after the addition (E2 ) of volume 1 of a standard solution to sample volume Vq. The sample concentration is Cx, the standard solution concentration is c. In KAM, the standard solution contains... 

The known addition method has an advantage in greater rapidity and somewhat improved precision compared with calibration with two standards. It is claimed that it requires about half the time necessary for two-standard calibration [17] and that the relative error is about 2% [22]. A disadvantage is the necessity of determining the value for most systems. The method should be used only for concentrations corresponding to the linear part of the calibration curve. To eliminate the effect of a change in the ionic strength, it has been recommended [19] that a mixture of a standard with the test solution be added to the sample. The known subtraction method is much less used in practice. 

The analyte addition method (AAM) involves adding the sample solution to a standard solution of the determinand, whereas in the analyte subtraction method (ASM) the sample is added to a standard solution of an ion that reacts stoichiometrically with the test substance and is sensed by an ISE. These methods are advantageous for determinations on small samples for which microelectrodes would otherwise have to be used. pH adjustment and masking of interferents in the sample is unnecessary because all these operations can be done beforehand on the standard solution. Furthermore, the analyte subtraction method widens... 

Potentiometric titration is actually a form of the multiple known subtraction method. The main advantage of titration procedures, similar to multiple addition techniques in general, is the improved precision, especially at high determinand concentrations. ISEs are suitable for end-point indication in all combination titrations (acid-base, precipitation, complexometric), provided that either the titrand or the titrant is sensed by an ISE. If both the titrant and the titrand are electro-inactive, an electrometric indicator must be added (for example Fe ion can be titrated with EDTA using the fluoride ISE when a small amount of fluoride is added to the sample solution [126]). 

Processing the data file to remove the artificial absorption signal is relatively easy in the event that the spectrum is not too densely populated with lines and 0% absorptance levels may be found across the range of the recorded spectrum. We find that a simple point-to-point base-line subtraction method is simplest and gives the best results. This requires some accurate method to display and measure data values in the file. In our case, we use a graphic display with light pen to acquire a base-line subtraction data set. Other, less direct methods should work also. Sensitivity tests are not difficult to design and execute. 

A variety of infrared methods have been available for the simple problems of verifying the purity of the initial resin components and mixtures of those components. The simplest possible test of the purity of a reactant is to compare its spectrum with a known standard. Subtractive methods may be employed to emphasize the most significant intensity changes 19). Composition analysis of the blended resins and hardeners becomes more difficult. In some cases, one may simply select characteristic isolated absorption bands for each component and estimate the composition by comparison to standard spectra of known composition 20,21). 

We have seen that full color perception can be achieved by subtraction methods using dyes in suitable combinations. We now have to consider how such dyes are formed on exposure and development of color film. First though, you should recognize that a photographic emulsion, whether for color or black-and-white film, is light-sensitive primarily because of the presence of silver halide. You will recall from previous discussions (Section 26-2C) that the sequence from exposure to development involves the following ... 

Subtractive methods (see Basic Protocol 2) are based on the use of bleaching agents that... 

Efforts to elucidate the genetic basis of biosynthetic pathways tend to result in the identification of structural genes, i.e. genes encoding enzymes that catalyze the conversion of intermediates in a specific pathway. This is in part due to the relatively high expression of the structural genes, which results in abundant representation in expressed sequence tag (EST) libraries, or high probability of identification when cDNA subtraction methods or other methods that rely on differential expression are used. 

Figure 8.2.6 H spectra of four different samples (500 mM in D2O) obtained by using the subtraction method. These represent the post-processed spectra of (a) methanol (4.7 and 3.2ppm), (b) f-butanol (4.7 and 1.1 ppm), (c) water (4.7ppm) and (d) acetonitrile (1.9ppm), and (e) the spectrum of the four different samples before data processing. Reprinted from MacNamara, E., Hou, T., Fisher, G., Williams, S. and Raftery, D., Multiplex Sample NMR an approach to high-throughput NMR using a parallel coil probe , Anal. Chim. Acta, 397, 9-16, copyright (1999), with permission of Elsevier Science...

In the subtractive method, clay is removed from a clay piece to form an object. 

The subtractive method involves removing portions of the material. (See Figure 4.2.) A sculptor working in stone, for instance, chisels away areas of marble or granite to create the three-dimensional image. A wood carver removes areas of the material to reveal a shape. Generally, in the subtractive method, once pieces of the material are removed, they cannot be replaced (clay is an exception). 

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