Indirect method, defined

Using an alternative method, generally referred to as an indirect method, Eg may also be estimated following i.d. dosing alone and sampling portal blood and the systemic circulation concurrently. The mass of drug appearing in the portal vein (Ma) is defined as follows ... 

Using the well-defined system of polyoxoanion/Bu4N -stabilized iridium nanoparticles [9, 29] as a model for the studies, Finke and coworkers [30] proposed a method that attempted to explain the formation and growth of transition-metal nanoparticles. This indirect method is based on an autocatalytic mechanism that considers a nudcation step in which a precursor A is converted to a zero-valent nuclei B with a rate constant fej, and a second step that considers the autocatalytic surface growth of the metal nanoparticles where species B catalyzes its own formation with a rate constant tc2 (Scheme 15.5). 

Hence, two methods are available that can be applied to follow nanoparticles formation and growth (i) an indirect method that utilizes the consumption of molecular hydrogen pressure versus time and (ii) a direct method that follows the loss of precursor by the 1 1 conversion of its cyclo-octadiene ligand to cyclo-octane by GLC measurements. The mechanism developed by Watzky and Finke suggests that the nanoparticles act as Hving-metal polymers -a concept that could be used to obtain particles with defined sizes simply by adding the appropriate amounts of catalyst precursors [32]. 

It should be noted that there has been some confusion In the literature with respect to the apparent oxidation state of the T3 site In different T2D laccase preps. This derives from the use of Indirect methods to define oxidation state. We have run x-ray edge spectra of T2D laccase prepared by four of the research groups strongly Involved In this field, and In all cases the Type 3 site Is found to be fully reduced. 

Phosphorus itself is not directly accessible to atomic absorption spectrometry, as its most characteristic atomic lines appear in the vicinity of 200 nm. Indirect methods are necessary if the technique is to be applied, and the procedures often require previous conversion of the phosphorus into phosphate. One possible approach is the formation of a well defined stoichiometric complex between phosphate and another ion, which may then be isolated and determined by atomic absorption spectrometry. 

Arsenic does not combine directly with molecular hydrogen,9 and the element may be purified by sublimation in that gas. Hydrides, however, may be obtained by indirect methods (see pp. 79-84). Arsenic may be displaced by the gas from solutions of its salts at high temperatures and pressures. Thus arsenic separates in large well-defined crystals when a solution of sodium arsenate is subjected to the action of hydrogen at 25 atm. pressure 10 the action commences at 300° C., 15 per cent, of the arsenic being precipitated at this temperature, but it increases rapidly with rising temperature and at 350° C. 77 per cent, of the arsenic is liberated. Arsine is not produced in the reaction. 

When using indirect methods, the exposure is determined by combining information about the time spent in specific locations, called microenvironments, and the pollutants concentrations at these same places. A microenvironment is defined as a three-dimensional space where the pollution concentration at some specified time is spatially uniform or has constant statistical properties [8]. The microenvironment can be interior of a car, inside a house, inside an office or school, outdoors, etc. Thus total exposure is the sum of the exposure in all microenvironments during the time of interest. 

These two types of molecular weight averages are representative of the type called absolute methods, in that well-established thermodynamic equations can be used to convert the experimental data directly into a value of the molecular weight. However, some other methods require calibration. The most important of these indirect methods involves a measurement of the intrinsic viscosity. This quantity is a measure of the extent to which a polymer molecule increases the viscosity of the solvent in which it is dissolved. The viscosity method can be calibrated to yield a viscosity-average molecular weight, defined by... 

If the reaction is complex, that is, if intermediates are formed during the reaction, an indirect method has to be used. Samples of the reaction mass are taken at defined stages of the reaction and analysed either chemically or thermally, for example, by DSC. This approach is also recommended when unstable intermediates are present in the reaction mixture the stability of the reaction mass may pass through a minimum. Another method is to stop the feed during an experimental mn in a reaction calorimeter and to measure the heat evolved after the interruption it is proportional to the accumulation (Figure 7.4). 

According to the International Union of Pure and Applied Chemistry (IUPAC O)) the turnover frequency of a catalytic reac tion is defined as the number of molecules reacting per active site in unit time. The term active sites is applied to those sites for adsorption which are effective sites for a particular heterogeneous catalytic reaction. Because it is often impossible to measure the amount of active sites, some indirect method is needed to express the rate data in terms of turnover frequencies In some cases a realistic measure of the number of active sites may be the number of molecules of some compound that can be adsorbed on the catalyst. This measure is frequently used in the literature of the Fischer-Tropsch synthesis, where the amount of adsorption sites is determined by carbon monoxide adsorption on the reduced catalyst. However, it is questionable whether the number of adsorption sites on the reduced catalyst is really an indication of the number of sites on the catalyst active during the synthesis, because the metallic phase of the Fischer-Tropsch catalysts is often carbided or oxidized during the process. 

In addition to X-ray studies aimed at defining directly the structures of the Mo enzymes and especially the active sites, efforts to study them by indirect methods such as epr and endor continue. These methods are useful only for elucidating the nature of Mov species (Molv and MoVI being esr silent) which may, or may not, be... 

Radical polymerizations are almost always considered as kinetically stationary. However, the stationarity conditions are not always fulfilled. Living polymerizations with rapid initiation are stationary, but the character of the medium should not significantly change during polymerization in order to prevent shifts in the equilibria between ion pairs and free ions. All other polymerizations are non-stationary even, to some extent, living polymerizations with slow initiation. It is usually very difficult to define initiation and termination rates so as to permit exact kinetic analysis. When the concentration of active centres cannot be directly determined, indirect methods must be applied, and sometimes even just a trial search for best agreement with experiment. 

Hospital databases may, however, be used for the establishment of reference values that are fuUy concordant with the IFCC recommendations." The requirement is that laboratory data be combined with information stored in clinical databases (i.e., to apply a direct sampling strategy instead of the distribution-based indirect method). Laboratory results are to be used as reference values only if stated clinical criteria are fulfilled. One may define criteria for selecting individuals who have a specified state of health or the disease for which reference data are necessary. Usually certain constraints are also imposed on the use of their laboratory results, such as allowing only one result of each analyte under study from each selected individual. Such reference values have one advantage over those based on direct sampling from other types of populations hospital-based reference values are ideal for the interpretation of results from hospitalized patients because they are produced under similar conditions. 

An example of an indirect method is the use of a steady-shear-rate sweep test, which examines the steady-shear viscosity rf) and shear stress a as functions of shear rate (/). The results, once obtained, may be plotted in terms of steady-shear viscosity (tj) versus shear stress (shear stress is indicative of a yield stress, and the asymptotic stress is defined as the yield stress (measurable yield stress. This is shown diagrammatically in Figure 4.3. 

Another, this time indirect, method of assessing flowability was proposed by Carr36. This was based on measuring four properties of the powder (angles of repose and spatula, compressibility and uniformity coefficient, all as defined by Carr36) and, by awarding points (out of 25) for each, the sum total was then a measure of flowability and called Carr s Index . A commercial piece of equipment is available (Hosokawa Powder Characteristics Tester) for measuring the properties necessary for Carr s Index. 

A lithographic approach to the molecular imprinting of bacterial cell surfaces has been reported [133]. This indirect method resulted in the formation of polyamide beads with spatially-defined, highly functional patches, of size and shape corresponding exactly to those of the bacteria . Although only limited evaluation of the bacterial recognition properties have been carried out, the initial results suggest that discrimination between bacteria can be observed. 

The indirect methods of assaying for superoxide dismutase are the most widely used routine assays because the reagents used are inexpensive, widely available, and usually very sensitive to detection. However, these types of assay are quite susceptible to interferences. Some of these interferences are unfortunately ignored, with the consequence that various discrepancies arise in the results obtained from the various laboratories. These assays can operate at a very low steady-state level of O2 and are considered to be indirect negative assays when superoxide dismutase inhibits the formation of products and indirect positive assays when the enzyme accelerates the formation of products. In the indirect assays a unit of enzyme activity is generally defined as the amount of the enzyme that inhibits the reaction by 50%. 

Hybrid methods are a combination of direct and indirect programming methods. The program sequence is stipulated by indirect methods. The motion part of the program can be defined by teach-in or play-back methods or by sensor guidance. 

We define the hydration number as the average number of water molecules in the first sphere about the metal ion. The residence time of these molecules is determined generally by the nature of the bonding to the metal ion. For the f-element cations, ion-dipole interactions result in fast exchange between the hydration layer and the bulk solvent. The techniques for studying the nature (number and/or structure) of the hydration shell can be classified as either direct or indirect methods. The direct methods include X-ray and neutron diffraction, luminescence and NMR (nuclear magnetic resonance) relaxation measurements. The indirect methods involve compressibility, NMR exchange and absorption spectroscopy measurements. 

---