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Geometric-Arithmetic Index
Published in Mihai V. Putz, New Frontiers in Nanochemistry, 2020
A chemical reaction can be represented as the transformation of the chemical (molecular) graph representing the reaction’s substrate into another chemical graph representing the product. The type of chemical reaction where two substrates combine to form a single product (combination reaction) motivated Ramakrishnan et al. (2013) to study the effect of topological indices, particularly GA, when a bridge is introduced between the respective vertices (of degree i, i = 1,2,3) of two copies of the same graph. The authors claimed that the graph obtained in this manner may or may not represent a stable chemical compound in reality, but it is the interest of the chemist to check the stability of the so obtained structure of the resulting graph. Ramakrishnan et al. (2013) also presented an algorithm to compute the distance matrix of the resultant graph obtained after each iteration and thereby tabulated various topological indices including GA.
Overview
Published in James F. Pankow, Aquatic Chemistry Concepts, 2019
There are two major problems with applying kinetic models to natural water systems. First, relevant rate constants are usually not known very well at all, and trace species can sometimes act as catalysts that greatly affect rate constants. Second, rate expressions are often not as simple as in the example of Eq.(1.37) given below. For example, there is no guarantee that the rate of a given combination reaction for two species will be given simply by the product of a rate constant and the two concentrations. Overall, kinetic solutions to aquatic chemistry problems are usually sought only for highly specialized problems when the timeframe of interest is relatively short (minutes to days/weeks/months), and an equilibrium calculation would give a hopelessly unrealistic answer.
Experimental and numerical analyses of the combustion characteristics of Mg/PTFE/Viton fuel-rich pyrolants in the atmospheric environment
Published in Numerical Heat Transfer, Part A: Applications, 2020
Kangkang Zhang, Yuge Han, Dengfeng Ren, Chenguang Zhu
Figure 15 shows the mass fractions distribution curves of main components in Z direction for anaerobic combustion and aerobic combustion, respectively. Because fuel-rich ratio (Mg/PTFE > 33/67) is generally used in infrared decoy flares, the oxidant carried by the pyrolants alone is not enough to completely consume Mg. As shown in Figure 15(a), the mass fraction of Mg drops rapidly in anaerobic combustion core zone. When only the anaerobic combustion reaction occurs, there is excess Mg distribute downstream of the combustion core zone. On the contrary, the mass fractions of products MgF2 and C2 both increase rapidly and reach a maximum at Z = 47mm. It means that Mg has consumed the decomposition product of C2F4 in this region and produces MgF2 and C. It corresponds to the fast heating section, which further illustrates that the fast heating section near the burning surface is the core zone of the anaerobic combustion reaction. Subsequently, the components continue to diffuse downstream under the effect of the turbulent flow,and the mass distribution curve decreases gently. After considering the aerobic combustion reaction, the C,: CF2 and excess Mg will continue to undergo afterburning reactions with O2, resulting in changes in the mass fraction distribution of each component. The main combustion products of Mg are MgF2 and MgO. MgF2 is mainly produced in the anaerobic core zone (15 <Z < 47 mm), which is almost the same as anaerobic combustion, and then diffuses with the combustion jet. MgO is produced in the aerobic combustion diffusion zone (47 < Z < 100 mm), the mass fraction peaks at Z = 100 mm, and at the same time, Mg is completely consumed at the same location. It can be seen that the net consumption rate of the initial reactant Mg has increased in the aerobic environment, as shown in Table 4. The anaerobic combustion product C is easily oxidized by O2, which leads to an increase in the reverse reaction rate of the combination reaction of C (C + C=C2), so the net production rate C2 decreases. According to the reaction mechanism, the oxidation reaction of C with O2 firstly produces CO, then continues to generate CO2 in an atmosphere with O or O2, and finally diffuses into the environment. It is consistent with the distribution trend of the CO and CO2 mass fractions in the Z direction. It can also be seen that the formation of MgO also lags behind CO.