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Quantum Chemical Analysis of Polyamic Acids and Polyimides
Published in Michael I. Bessonov, Vladimir A. Zubkov, Polyamic Acids and Polyimides, 2020
It has been suggested that in media containing trifluoroacetic anhydride the isoimide is formed via neutral mixed anhydride (29a), () cyclization of 29a being facilitated by the high activity of its electrophilic group.65,66 The suggestion means that the reaction proceeds via the stable bipolar intermediate (29b). However, the calculated energy profile of this cyclization with RC’O as a reaction coordinate has no minimums corresponding to stable intermediates and is the same as for neutral amic acid cyclization (Figure 7), i.e., in the case of neutral mixed anhydrides of amic acid and trifluoroacetic acid, the probability of cyclization proceeding via a bipolar intermediate is also negligible.
A Decision Support for Prioritizing Process Sustainability Tools Using Fuzzy Analytic Hierarchy Process
Published in Ali Emrouznejad, William Ho, Fuzzy Analytic Hierarchy Process, 2017
In the context of the metal removal process, 90% of the environmental impact is due to electrical energy consumed (Vimal et al., 2015b). As far as manufacturing processes are concerned, electrical energy consumption has been studied extensively in the past. Newman et al. (2012) identified possible ways to improve the energy efficiency of manufacturing process through energy consumption mathematical modeling and energy-conscious metal cutting. Gutowski et al. (2006) further studied various electrical energy requirements for manufacturing processes through analysis of specific energy requirements. The energy studies are viewed from four levels, namely, process, machine, line, and factory. Many researchers adopted different methods to study energy consumption and the efficiency of manufacturing processes such as energy efficiency of discrete manufacturing, energy-based modeling, energy profile creation, thermodynamic analysis, power study, energy optimization, modeling embodied product energy, and axiomatic modeling.
The Food-Energy Problem
Published in Maurice Lévy, John L. Robinson, Energy and Agriculture: Their Interacting Futures, 2017
Maurice Lévy, John L. Robinson
Whatever the future evolution of real energy prices, the highest priority should be attached to the design and implementation of energy efficient food systems, encompassing all stages i.e. crop and livestock production, storage and conservation, transport and distribution, processing and preserving as well as kitchen practices. In other words, the energy profile of the food systems, defined along the same lines as in the joint UNDP/UNRISD/ IFPRI project, should be analysed with a view at identifying all the energy inputs as well as energy outputs and opening up the range of alternatives in terms of product mix, agricultural techniques (including the search for alternative sources of plant nutrient), product and process technologies (with particular reference to dehydration technologies), scale and location of production (with reference to the degree of local self-sufficiency in food and the consequent reduction of transportation flows), scope for energy conservation and use of wastes, methods of cooking and kitchen technology as well as changes in food habits. (See Figure III).
Competition of quantum effects in H 2/D 2 sieving in narrow single-wall carbon nanotubes
Published in Molecular Physics, 2021
Manel Mondelo-Martell, Fermín Huarte-Larrañaga
Previous theoretical works [33–37] on the diffusion of hydrogen in nanoporous carbon, regardless of the specific potential energy surface employed, show that the interaction between the molecule and the nanostructure generates a potential energy profile that consists of collection of minima (adsorption sites) separated by maxima (diffusion barriers). In the particular case of narrow carbon nanotubes as the (8,0) one studied here (0.6 nm diameter), the minima and maxima are located along the nanotube axis, and this structure forces single-file diffusion of the confined molecules. This limits the influence of interactions among adsorbed molecules, which will therefore be neglected hereafter. Given these features of the potential energy surface, and following previous studies [38] on similar systems, we have modelled the molecular diffusion process a set of uncorrelated jumps between neighbouring adsorptions sites separated by a distance l [39,40]. Using this model and in the low-pressure limit the diffusion coefficient is obtained through: where is the hopping probability between adjacent sites, and d is the dimensionality of the system (1 in this case). The problem of calculating the diffusion coefficient is then reduced to the calculation of . Following Zhang and Light [38], this probability will be calculated through the flux-correlation function approach in a quantum dynamics formalism, which is summarised below.
Theoretical investigations of the hydrogen bond in a tetraamido/diamino quaternized macrocycle
Published in Molecular Physics, 2019
Phillip Johannes Taenzler, Keyarash Sadeghian, Christian Ochsenfeld
We next computed the energy profile along the reaction coordinate which defines the proton exchange between the two oxygen atoms (O and O). The energy profile, depicted in Figure 2, shows that the encircled proton is trapped in a shallow potential with a very small barrier of 0.4 kcal mol−1 which becomes negative (−0.6 kcal mol−1) after the inclusion of zero-point energy corrections via numerical frequency analysis. The energetic asymmetry of the proton transfer path is the result of the positional constraint placed on the system. The corresponding computed 1H-NMR shieldings vary in the 15–24 ppm range (relative to TMS) for the low energy region of the proton-exchange profile.
Hamilton–Jacobi equation, reaction action surface and the emergence of the force concept in chemical reaction dynamics
Published in Molecular Physics, 2018
Chemical reactions involve nuclear displacements (structural reordering) and electronic rearrangements so as to transform reacting species into product species. The energetic description of a chemical reaction, which relies on an energy profile providing thermodynamic and kinetic information of the reaction, is an age old concept. Thus, computational methods for calculating minimum energy path (MEP) are widely used in the field of theoretical chemistry [1]. The MEP describes the mechanism of reaction and the energy barrier along the path which can be used to calculate the reaction rate. Reactions where the reactant and product states are connected by a single transition state (TS) are called elementary reactions. Traditional approach for the mechanism of a reaction and consequently, the calculation of the rate parameters have relied on identifying and analysing the properties of the TSs. Intrinsic reaction path [2–4], introduced by Fukui, is a special type of MEP which is defined as the steepest descent from theTS in mass-weighted Cartesian coordinate. Such a TS invariably occurs in the reaction rate theory such as, TS theory [5] or variational TS theory [6]. The predominant occurrence of a TS barrier [7] is based on the simple fact that the MEP, at least in the vicinity of the energy barrier, represents a local minimum of the potential energy surface (PES) in all directions except for one, which is the reaction path coordinate. Indeed a detail on the reaction mechanism can be obtained from the MEP by adhering to the reaction path hamiltonian approach.