Direct and indirect methods

Ha.logena.tlon, One review provides detailed discussion of direct and indirect methods for both mono- and polyhalogenation (20). As with nitration, halogenation under acidic conditions favors reaction in the benzenoid ring, whereas reaction at the 3-position takes place in the neutral molecule. Radical reactions in the pyridine ring can be important under more vigorous conditions. 

Daley, M. A., Tandon, D., Economy, J. and Hippo, E. J., Elucidating the porous structure of activated carbon fibers using direct and indirect methods. Carbon, 1996,34(10), 1191 1200. 

Mathematical models of the reaction system were developed which enabled prediction of the molecular weight distribution (MWD). Direct and indirect methods were used, but only distributions obtained from moments are described here. Due to the stiffness of the model equations an improved numerical integrator was developed, in order to solve the equations in a reasonable time scale. 

For the calibration to absolute intensity several direct and indirect methods have been proposed (Feigin and Svergun [86], p. 73-76). 

A list of commonly used direct and indirect methods of gas detection methods is given in Table 1, listing their principal advantages and disadvantages. 

Kaye SA, Lim SG, Taylor M, Patel S, Gillespie S, Black CM Small bowel bacterial overgrowth in systemic sclerosis Detection using direct and indirect methods and treatment outcome. BrJ Rheumatol 1995 34 265-269. 

Both direct and indirect methods were tested in the Lisbon area. Direct methods include the assessment of hydrocarbon compositional signatures in surface soils, outcrop fracture-fill soils and mosses, and 6-ft (2 m) deep free-gas samples. Indirect methods pertain to the major and trace element chemistry of soils to look for alteration effects resulting from hydrocarbon microseepage. 

Both direct and indirect methods are used in studying soil chemistry. While in all cases direct methods are preferable, it is not always possible to make direct observations of all the chemical species, and physical and chemical changes of interest. Thus, it is often necessary to modify the soil before analysis. In many cases, it is essential to extract components before analysis can be carried out. It is also possible to obtain valuable information about the chemistry of soil by carrying out analyses that destroy all or a part of the soil matrix. A summary of analysis types and instruments commonly used in soil analysis is given in Table 8.1. 

In the direct method substrates are oxidized by electron transfer from the substrate to the anode, while in the indirect method they are oxidized in solution by the oxidized form of a mediator that is generated from the reduced form at the anode. Thus, efficiencies in direct and indirect methods are largely dependent on the oxidation potentials of substrates and mediators, respectively. 

The electrochemical oxidation of carbonyl compounds is achieved by direct and indirect methods. 

Later, a TAG CSP was included in the aforementioned investigation by direct and indirect methods, the chiral derivatizing agent being, in this case, the new reagent (S)-A-(4-nitrophenoxycarbonyl)phenylalanine methoxyethyl ester [149]. 

Peter, A. et al.. Comparison of column performances in direct high performance hquid chromatographic enantioseparation of 1- or 3-methyl-substituted tetrahy-droisoquinohne analogs. Application of direct and indirect methods, Biomed. Chromatogr, 19, 459, 2005. 

Compared with chiroptical methods and nuclear magnetic resonance spectroscopy (NMR), only chiral chromatography by direct and indirect methods is suitable for the accurate determination of enantiomeric impurities of less than 1% and for quantitative stereochemical analyses of small sample amounts (for example, in vivo studies of the metabolic pathway or pharmacokinetic effects of chiral pharmaceuticals.)... 

If we try to establish the major routes that have been used for the preparation of //-methylene complexes, we find that both direct and indirect methods can be employed. The first approach involves the use of reagents that have had a long history as useful carbene precursors in... 

Recently, Street and Schenk (13) reported a spectrofluo-rimetric analysis of salicylamide in the presence of acetylsalicylic acid and salicylic acid as impurities by direct and indirect methods. Salicylic acid is determined in the range of 10-Tm concentration after separation from salicylamide. The instrumental conditions for the spectrofluorimetric determination of salicylamide, acetylsalicylic acid and salicylic acid is shown in Table 1. 

Binding of NO occurs very rapidly, and the kon and kot t values of 105 dm3/(mol s) and 4 s-1, respectively, were reported for 14.7 °C. An improvement in precision of the /i ii values was secured by using the NO trapping method. While there is some concern for the lack of match of the rate constant from the direct and indirect methods, the kinetically derived value of KNO corresponds very well to that obtained from equilibrium measurements (ZfNO = 1.7 x 105mol/dm3 at 25 °C). Markedly positive entropies and volumes of activation for both on and off reactions were obtained A/Uon = + 138, AS off = + 161 J/(molK), AV on I 10.8, AV off = 16.9 cm3/mol. 

It is not straightforward to calculate phase equilibria or chemical potentials in a simulation, and special techniques must be used. This has been an active research area over the past few years [15]. Several methods have been proposed, and these can be divided into direct methods, in which the coexistence properties of the phases are calculated directly, and indirect methods, where the chemical potential is first calculated and then used to determine the phase equilibrium conditions (Table 4). 

In human health risk assessment, direct and indirect methods of exposure assessment are distinguished. The direct method involves measurements of exposure at the point of contact or uptake, for instance, by monitoring chemical concentrations in humans or the environments they are exposed to (food, air, water). The indirect methods use modeling and extrapolation techniques to estimate exposure levels (Fryer et al. 2006). Also in environmental exposure assessment, these 2 ways to assess exposure may be applied. 

For both direct and indirect methods of estimating the sulfonate content of lignin in pulp, the sulfonate content of the lignin is obtained by dividing the sulfonate content of the pulp by the sum of its Klason and acid-soluble lignin contents (Loras and Loschbrandt 1961). 

Measurements of body composition consist of direct and indirect methods. Direct methods include measures of body protein, water, fat, and ash (minerals). An alternative direct approach is measurement of individual tissue weights. While these methods are unambiguous and preferred, they are generally limited to studies with animals. In non-sacrificial beings, direct determinations of tissue weights are impossible, and determinations of body composition are restricted to use of indirect, noninvasive methods. 

Measurement of soil activity there are a number of laboratory methods which are suitable for measuring the biological activity of the soil. In principle, a distinction is made between direct and indirect methods for the determination of soil activity. The biomass in the soil, for example, can be estimated by counting the individual organisms in the soil, or the measurement of respiration after the addition of a nutrient in excess can provide an indication of active biomass. Moreover, in determinations of activity, a distinction is made between actual and potential activity. Actual activity values are values measured at the time that the sample was taken. Determinations of potential activity, on the other hand, show the level of performance that microorganisms are capable of under optimum experimental conditions, after the addition of a nutrient substrate and prolonged incubation. 

Forest biomass in the Amazon has been estimated through direct and indirect methods. Independent of the method used, one should take into consideration that all components of forest biomass must be quantified. Besides the trees that are the main component of the forest, other components to be included are vines Gianas), understory plants, litter, roots, palms, etc. 

Direct and indirect methods are used to make sequence specific assignments. The direct method is to use a number of larger than two-dimensional hetero NMR spectra to generate the heteronuclei-based interresidue backbone atom correlations. One of the schemes of the direct method is shown in Fig. 12. These three-dimensional NMR experiments need not only C- and N-enriched samples, but also very expen-... 

Taylor, B. Methodus Incrementorum Directa et Inversa. Proposition 7. [Direct and indirect methods of incrementation.] Peajsniansis Londini (1715) dusker, J. P., Orehowsky, W. Jr., Casciato, C. A., and Carrell, H. L. X-ray crystal analysis of the substrates of aconitase. X. The structure of dipotassium ds-aconitate. Acta Cryst. B28, 419-425 (1972). 

Taylor, B. Methodus Incrementorum Directa et Inversa. Proposition 7. [Direct and indirect methods of incrementation.] Pearsniansis Londini (1715)... 

Phenyl-substituted oxiranes may be reduced in DMF akin to benzyl ethers by direct and indirect methods the regioselectivity is slightly higher in the indirect reduction [76]. Benzoyloxiranes can be reduced in MeCN to aldoles addition of acetic acid prevents a retroaldol reaction catalyzed by the EGB [77]. The ring opening is analogous to the reduction of 2-alkoxyacetophenone to acetophenone. 

Various direct and indirect methods are generally used to determine the permeability of a sedimentary basin. The direct methods include laboratory measurements on core samples wire-line formation tests, single-well tests and interference tests. The data from the different types of well test and interference test can be analysed and interpreted by well-established procedures (Da Prat, 1990 Earlougher, 1977 Kruseman et al., 1990 Matthews and Russel, 1967). The conventional, indirect methods are theoretical, semi-empirical and empirical procedures which are based on the relation between permeability, grainsize characteristics and porosity (e.g. the Kozeny-Carman method, Domenico and Schwartz, 1990 Van Baaren method. Van Baaren, 1979). The laboratory methods and the conventional indirect methods provide permeability values which are representative of only a very small portion of the subsurface (cm-scale). The single-well test and interference test provide information representative of a larger volume of the subsurface (m - km scale). 

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