Computational study of the dissociation reactions of secondary ozonide

This contribution presents a comprehensive computational study on the reactions of secondary ozonide (SOZ) with ammonia and water molecules. The mechanisms were studied in both a vacuum and the aqueous medium. All the molecular geometries were optimized using the B3LYP functional in conjunction with several basis sets. M06-2X, APFD, and ωB97XD functionals with the full basis set were also used. In addition, single-point energy calculations were performed with the G4MP2 and G3MP2 methods. Five different mechanistic pathways were studied for the reaction of SOZ with ammonia and water molecules. The most plausible mechanism for the reaction of SOZ with ammonia yields HC(O)OH, NH3, and HCHO as products, with ammonia herein acting as a mediator. This pathway is exothermic and exergonic, with an overall barrier height of only 157 kJ mol−1 using the G3MP2 method. All the reaction pathways between SOZ and water molecules are endothermic and endergonic reactions. The most likely reaction pathway for the reaction of SOZ with water involves a water dimer, in which the second water molecule acts as a mediator, with an overall barrier height of only 135 kJ mol−1 using the G3MP2 method. Solvent effects were found to incur a significant reduction in activation energies. When the second H2O molecule acts as a mediator in the reaction of SOZ with water, the barrier height of the rate-determining step state decreases significantly

Influence of firm size on the competencies required to management engineers in the Jordanian telecommunications sector

This is an Accepted Manuscript of an article published by Taylor & Francis in European Journal of Engineering Education on [13 jun 2016], available online:http://www.tandfonline.com/ doi/abs/10.1080/03043797.2016.1197890.[EN] The objective of this study is to identify the competencies required to achieve success in the transition from higher education to the labour market based on the perceptions of employers. This paper analyses the assessments made by a group of engineering company employers. An item-battery of 20 competencies was grouped into 3 dimensions by using factor analysis. Subsequently, respondents scores were also clustered into three groups and characterised through contingency tables. The competencies demanded by employers were grouped into business and finance, problem-solving and strategic planning. Significant differences were found between responses from employers working in medium and small companies, who placed more importance on competencies related to problem-solving and strategic planning, and employers in big companies, who were more concerned about the difficulties of finding well-trained graduates. The findings from this paper have important implications for research in the areas of higher education and organisations that usually employ graduate engineers.The authors would like to thank the Education, Audiovisual and Culture Executive Agency (EACEA) [Tempus program. Project number 511074] of the European Commission for providing funding for conducting this study. This publication reflects the views only of the authors, and the Commission cannot be held responsible for any use which may be made of the information contained therein.Conchado Peiró, A.; Bas Cerdá, MDC.; Gharaibeh, KM.; Kaylani, H. (2016). 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Analytical Evaluation of the Performance of Proportional Fair Scheduling in OFDMA-Based Wireless Systems

This paper provides an analytical evaluation of the performance of proportional fair (PF) scheduling in Orthogonal Frequency- Division Multiple Access (OFDMA) wireless systems. OFDMA represents a promising multiple access scheme for transmission over wireless channels, as it combines the orthogonal frequency division multiplexing (OFDM) modulation and subcarrier allocation. On the other hand, the PF scheduling is an efficient resource allocation scheme with good fairness characteristics. Consequently, OFDMA with PF scheduling represents an attractive solution to deliver high data rate services to multiple users simultaneously with a high degree of fairness. We investigate a two-dimensional (time slot and frequency subcarrier) PF scheduling algorithm for OFDMA systems and evaluate its performance analytically and by simulations. We derive approximate closedform expressions for the average throughput, throughput fairness index, and packet delay. Computer simulations are used for verification. The analytical results agree well with the results from simulations, which show the good accuracy of the analytical expressions

Computational study on the deamination reaction of adenine with OH⁻/<i>n</i>H₂O (<i>n</i> = 0, 1, 2, 3) and 3H₂O

Deamination of adenine is one of several forms of premutagenic lesions occurring in DNA. In the present study, mechanisms for the deamination reaction of adenine with OH−/nH2O (n = 0, 1, 2, 3) and 3H2O were investigated. HF/6-31G(d), B3LYP/6-31G(d), MP2/6-31G(d), and B3LYP/6-31+G(d) levels of theory were employed to search for and optimize all geometries. Energies were calculated at the G3MP2B3 and CBS-QB3 levels of theory. The effect of solvent (water) was computed using the polarizable continuum model (PCM). Intrinsic reaction coordinate (IRC) calculations were performed for all transition states. Five pathways were investigated for the deamination reaction of adenine with OH−/nH2O and 3H2O. The first four pathways (A–D) are initiated by deprotonation at the amino group of adenine by OH−, while pathway E is initiated by tautomerization of adenine. For all pathways the next two steps involve formation of a tetrahedral intermediate followed by dissociation to products via a 1,3-proton shift. Deamination with a single OH− has a high activation barrier (190 kJ mol−1 using the G3MP2B3 level) for the rate-determining step. The addition of one water molecule reduces this barrier by 68 kJ mol−1 at the G3MP2B3 level. Adding additional water molecules decreases the overall activation energy of the reaction, but the effect becomes smaller with each additional water molecule. The most plausible mechanism is pathway E, the deamination reaction of adenine with 3H2O, with an overall G3MP2B3 activation energy of 139 and 137 kJ mol−1 for the gas phase and PCM, respectively. This barrier is lower than that for the deamination with OH−/3H2O by 6 and 2 kJ mol−1 for the gas phase and PCM, respectively. </jats:p

Decomposition of ethylamine through bimolecular reactions

Ethylamine (EA) often serves as a surrogate species to represent aliphatic amines that occur in biofuels. This contribution reports, for the first time, the thermochemical and kinetic parameters for bimolecular reactions of EA with three prominent radicals that form in the initial stages of biomass decomposition; namely, H, CH3 and NH2. Abstraction of a methylene H atom from the EA molecule largely dominates H loss from the two other sites (i.e., methyl and amine hydrogens) for the three considered radicals. We demonstrate that, differences in bond dissociation enthalpies of methylene C–H bonds among EA, ethanol and propane reflect their corresponding HOMO/LUMO energy gaps. At low and intermediate temperatures, the rate of H abstraction from the methylene site in EA exceeds the corresponding values for propane and ethanol. As the temperature rises, matching entropic factors induce comparable rate constants for the three molecules