Competitiveness Measures

For shippers and transportation providers, an important metric is the total supply chain cost of transportation transactions. This total supply chain cost includes the effect on both transport costs and associated inventory costs. In addition, measures of performance include delivery lead time, percent on-time delivery or delivery within time windows, and schedule flexibility to accommodate shipment reschedules. Given the large volume of shipments that occur on dedicated contract trucking, there is scope for use of information, coordination agreements, and associated capadty commitments to improve performance across a supply chain. Competing carriers sell bundled routes to minimize shipper costs. 

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Related to competitiveness measures - improved quality, compressed lead time, reduced life-cycle costs, increased flexibility, improved productivity, more satisfied customers... 

In spite of the limitations of direct non-competitive measurements of KIE, their use is sometimes unavoidable. For example, when information on the KIE of the VmaX parameter for an enzymatic reaction is required, non-competitive kinetic runs using... 

Fig. 7.1 Spectrophotometric simultaneous non-competitive measurement of KIE. In this technique the reaction mixture containing the reference isotopomer is placed in the reference cell and the mixture with the other isotopomer in the sample cell (at identical concentrations). The two cells are placed in a common thermostat (www.chemguide.co.uk)...

Table 7.1 Isotopic differences in reaction progress as a function of fi, (simultaneous non-competitive measurement of isotope effects)...

The protocol described in Section 7.1.2 involves isotopic competition, but with the different isotopomers held in separate containers. Equations 7.10 to 7.13 apply equally well to a type of competition experiment known in biochemistry as the perturbation method for determining KIE s of reversible enzyme catalyzed reactions. The perturbation method differs from simultaneous non-competitive measurements in several important ways. One begins by mixing equilibrium concentrations of substrate and product but with one component (substrate or product) at a different isotopic composition than the other. Thus, the mixture is in chemical, but not isotopic equilibrium. At this stage no enzyme is present and the interconversion is... 

All correlations require reliable kinetic data, which may be obtained either from individual or competitive measurements. In the case of experimentation with individual compounds separately, great care should be taken... 

A key feature of the competitive isotope fractionation measurements is the use of natural abundance O2. Isotope effects are, therefore, determined for the reactions of the most abundant isotopologues 160-160 and 180-160. It is the intermolecular competition of these species that is reflected in the isotope effect. Aside from the obvious advantage of not requiring costly enriched materials, the competitive measurements also avoid the error that could arise from small leaks in the vacuum manifold and dilution due to ambient air. 

Information regarding ihe structure of very unstable carbenoids (copper) is evidently a result of speculation based on indirect observations, such as the effect of ligands on the selectivity of the reactions and kinetics measurements. Direct kinetics are generally not significant, because of the complexity of the reaction (several by-products arc often formed) so (hat kinetic data arc obtained from competition measurements. The studied carbenoidis formed in the presence of two different substrates, one of which is used as a probe. The relative reactivities of various substrates and carbenoids have been evaluated by this method 11,21. 

In the competitive technique, the enzyme reacts with a mixture of labeled and unlabeled substrate, yielding isotope effects on k t/Ku [29]. Competitive measurements, while limited to kcat/KM isotope effects, are substantially more precise than noncompetitive measurements. In addition, they allow the use of tracer-level radioactive labels, permitting tritium isotope effects at the primary and secondary positions (kH/kj or ko/kj) to be determined. General methods for determining competitive isotope effects have been published [17b]. One drawback is that multiple isotopic labels must often be used, leading to extensive synthetic efforts. 

In summary, competitive measurements yield the kinetic isotope effect on kcat/KM, and often rely upon tracer-level radioactivity, though recent developments also allow these values to be obtained using natural abundance NMR techniques [123]. Noncompetitive measurements can reveal the kinetic isotope effects on k t or kcat/KM, but suffer from larger propagated errors. 

For the competitive measurements 0.1 mg/mL BChE (270 nM) is mixed with various concentrations of DFP (ranging from 0.1 to 10 pM) and incubated for 30 min at room temperature (results shown in (14)). 

It is generally necessary to measure competitive KIEs to achieve the conhdence intervals of 0.002 to 0.005 needed to accurately describe a transihon state. In competitive measurements, labeled and unlabeled reactants are combined in a single reaction mixture and allowed to react as competitive substrates in the enzymatic reactions (or as competitive reactants in non-enzymatic reactions). If there is an isotope effect at the labeled position, the faster reacting isotope will become depleted in the reactant and enriched in the product and the isotope ratio (unlabeled labeled) will change. It is this change in isotopic composition that is measured to determine KIEs. 

Plate layout for measuring mouse Ig from samples. The gray box indicates no coating with IgG made. The standard dilution of Ig was make as a duplicate two-fold dilution range. Zero percent control competition measures the reaction between coated wells and conjugate, and 100% competition is the reaction between conugate and uncoated wells. 

In these equations, Nj is the molar rate of Nj produced, NOi is the molar feed rate of NO, reductant consumed is the molar rate of consumption of propene, and n is the number of O atoms required to completely convert the reductant (propene) into CO2 and HjO, which is 9 for the case of propene. The % NO competitiveness measures the effectiveness (selectivity) of the hydrocarbon reductant to convert NO to N2 versus reacting with O2. With this definition, reactions leading to the formation of N2O would not contribute to the % NO competitiveness. The term "% selectivity" is not used to avoid confusion with the term "selective reduction" of NO to N2. 

Selective gas adsorption and separation in flexible MOFs is considerably more complicated than that in their rigid counterparts. Due to the high degree of cooperativity in these systems (e.g. in inducing framework deformation, the uptake of one guest can dramatically alter the uptake of another), comparison of adsorption isotherms of pure gases is of limited use and competitive measurements are essential if separation capabilities are to be determined. Due to the fact that such measurements remain very rare, and that structural information is often unavailable for the mixed-sorbed phases, only limited understandings of gas separations in flexible MOFs currently exist. 

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