Self-resonant Coil for Contactless Electrical Conductivity Measurement under Pulsed Ultra-high Magnetic Fields

In this study, we develop experimental apparatus for contactless electrical conductivity measurements under pulsed high magnetic fields over 100 T using a self-resonant-type high-frequency circuit. The resonant power spectra were numerically analyzed, and the conducted simulations showed that the apparatus is optimal for electrical conductivity measurements of materials with high electrical conductivity. The newly developed instruments were applied to a high-temperature cuprate superconductor La$_{2-x}$Sr$_x$CuO$_4$ to show conductivity changes in magnetic fields up to 102 T with a good signal-to-noise ratio. The upper critical field was determined with high accuracy.Comment: 11 pages, 5 figure

Reactions of HO2 with n-propylbenzene and its phenylpropyl radicals

Abstraction of an H atom from the propyl side chain by hydroperoxyl radicals (HO2) constitutes a central reaction in the low-temperature oxidation of n-propylbenzene (nPB). Herein, we calculate reaction rate constants for H abstraction from primary, secondary and benzylic sites in nPB. Rate of abstraction of a benzylic H atom dominates that of a secondary H atom with negligible abstraction of the primary H atom at T ⩾ 600 K. We present the reaction enthalpies for 1-phenyl-1-propyl (R1), 1-phenyl-2-propyl (R2) and 1-phenyl-3-propyl (R3) radicals, and compare the computed reaction rate constants and bond dissociation enthalpies with analogous scarce literature values. Addition of HO2 radicals to radical sites in R1, R2 and R3 proceeds in a highly exothermic process and results in the formation of HO2–phenylpropyl adducts. Mapped potential energy surfaces illustrate all plausible exit channels of the three HO2–phenylpropyl adducts. Master equation calculations for the three phenylpropyl + HO2 reactions indicate that direct O–OH bond fission and water elimination control the fate of the adducts leading to the formation of ketonic-type structures. Results from this study should be useful to update kinetic models for the low-temperature oxidation of alkylbenzenes in general

Factors Affecting the Adoption of E-Learning: Jordanian Universities Case Study

Innovation in learning is always the main interest of any educational institute to develop their learning models. E-learning is one of the most innovative models in education. This paper investigates and analysis the factors that influence the adoption of e-learning systems in Jordan as one of the third developing countries. The investigation has been done in the high universities, public and private. A new model has been presented in this research. The results of this research has been shown that the legislations issues, human factors, infrastructure, economics and web content had a significant impact on learning goals and objectives. Therefore it is difficult to have a complete e-learning system in Jordanian universities. The novel contribution of this research is achieved by using the results of investigations and analysis to assist in building of a theory that will be tested through quantitative methods in the future.   Keywords: E-learning; Jordanian Universities; Quality; integration

Formation of polybrominated dibenzofurans from polybrominated biphenyls

Decades after phasing out their production and use, especially in the formulations of brominated flame retardants (BFRs), polybrominated biphenyls (PBBs) still pose serious environmental and health problems. The oxidation of PBB has been hypothesised as a pathway for the formation of the notorious polybrominated dibenzofurans (PBDFs) and their dispersion in the environment. However, the exact reaction corridor remains misunderstood, with the existing mechanisms predicting the reaction to proceed via a high energy process that involves the breakage of C-C linkage (~118.0kcalmol-1) and the subsequent formation of bromophenols molecules, where the latter are supposed to act as precursors for the formation of PBDFs (~40.0-60.0kcalmol-1). Herein, we show that PBBs produce PBDFs in a facile mechanism through a series of highly exothermic reactions (i.e., overall barriers reside 8.2-10.0kcalmol-1 below the entrance channel). Whilst the fate of the ROO-type intermediates in oxidation of all aromatics is to emit CO or CO2, PBDFs constitute the dominant products from the oxidation of PBBs. Initially formed R-OO adduct evolves in a very exoergic mechanism to yield PBDFs. In view of the facile oxidative transformation of PBBs into PBDFs, we conclude that, it is unsafe to dispose BFRs in oxidation processes, as this practice generates high yields of toxic PBDFs

Catalytic de-halogenation of halogen-containing solid wastes by transition metal oxides

Catalytic co-pyrolysis of halogenated compounds with electric arc furnace dust (EAFD) constitutes an effective disposal strategy regarding energy recovery and environmental safeguard. However, despite many detailed experimental investigations over the last few years; the specific underlying mechanism of the reactions between the halogen laden materials with EAFD remain largely poorly understood. In this contribution, systematic theoretical thermo-kinetic investigations were performed using the accurate density functional theory calculations to understand, on a precise atomic scale, the reaction mechanisms of major products from thermal decomposition of polyvinyl chloride (PVC) and brominated flame retardants (BFRs) with nanostructures (clusters and surfaces) of hematite (α-Fe2O3), zincite (ZnO) and magnetite (Fe3O4). The detailed kinetic analysis indicates that the dissociative adsorption of hydrogen halides molecules, the major halogen fragments from thermal degradation of halogen laden materials, over those metal oxide structures affords oxyhalides structures via modest activation barriers. Transformation of oxyhalides into metal halides occurs through two subsequent steps, further dissociative adsorption of hydrogen halides over the same structures followed by the release of H2O molecule. In the course of the interaction of halogenated alkanes and alkenes with the selected metal oxide structures, the opening channel in the dissociative addition route requires lower activation barriers in reference to the direct HCl/Br elimination pathways. However, sizable activation barriers are encountered in the subsequent β C-H bond elimination step. The obtained accessible reaction barriers for reactions of halogenated alkanes and alkenes with the title metal oxides demonstrate that the latter serve as active catalysts in producing clean olefins streams from halogenated alkanes

Anisotropic Hc2 of K0.8Fe1.76Se2 determined up to 60 T

The anisotropic upper critical field, Hc2(T), curves for K0.8Fe1.76Se2 are determined over a wide range of temperatures down to 1.5 K and magnetic fields up to 60 T. Anisotropic initial slopes of Hc2 ~ -1.4 T/K and -4.6 T/K for magnetic field applied along c-axis and ab-plane, respectively, were observed. Whereas the c-axis Hc2|c(T) increases quasi-linearly with decreasing temperature, the ab-plane Hc2|ab(T) shows a flattening, starting near 25 K above 30 T. This leads to a non-monotonic temperature dependence of the anisotropy parameter \gamma= Hc2|ab/Hc2|c. The anisotropy parameter is ~ 2 near Tc ~ 32 K and rises to a maximum \gamma ~ 3.6 around 27 K. For lower temperatures, \gamma decreases with T in a linear fashion, dropping to \gamma ~ 2.5 by T ~ 18 K. Despite the apparent differences between the K0.8Fe1.76Se2 and (Ba0.55K0.45)Fe2As2 or Ba(Fe0.926Co0.074)2As2, in terms of the magnetic state and proximity to an insulating state, the Hc2(T) curves are remarkably similar.Comment: slightly modified version, accepted to PRB, Rapid Communication

Products of incomplete combustion from biomass reburning

Fuel reburning usually serves in mitigating NOx formation in stationary combustion sources. However, the use of biomass as reburning fuel could facilitate the production of relatively more nitrogen-containing aromatic products of incomplete combustion. This study investigates the heterogeneous reaction between biomass and mixtures of NO/O2 gases, employing isothermal high-temperature experiments in a vertically-entrained reactor, and in situ diffuse reflective infrared Fourier transform spectroscopy (DRIFTS) under a non-isothermal heating condition ranging from ambient temperature to 700 °C. The method enables sensitive evaluation of the surface species ensuing during the thermal reaction. Results from this study elucidate the formation of nitrated structures as active intermediate species of the heterogeneous reaction. The nitrogenated signatures persist on the surface of the residual ash, suggesting the production of N-aromatics such as nitro-PAH. Considering the severe toxicity and bioaccumulative properties of these by-products, further research should focus on the relative contribution of various reburning fuels, while favouring sustainable fuels such as non-charring plastics

Combustion chemistry of COS and occurrence of intersystem crossing

This contribution combines results of experiments with kinetic modelling to probe the unusual behaviour of carbonyl sulfide (COS), a sulfur species that frequently arises in fuel systems. The experiments identified CO and SO2 as the primary oxidation products, with no formation of CO2. The low ignition temperature (<600 K) of COS observed in prior experiments conflicts with the high activation barrier for the reaction COS + O2 → CO2 + SO of 211.3 kJ mol−1 on the traditional triplet reaction surface. We proposed that, this kinetic barrier prompts the reaction to transfer onto the singlet surface through intersystem crossing that allows the process to surmount lower-energy hurdles. By considering the oxidation of COS as a single step reaction, we fitted the Arrhenius parameter for the reaction COS + O2 → CO + SO2 directly from our experimental measurements. The fitted activation energy of 70.1 kJ∙mol−1 agrees with that of 85.4 ± 20.0 kJ∙mol−1 as calculated in literature at the Hartree-Fock level of theory, indicating the appearance of the intersystem crossing process in the oxidation of COS. The reaction mechanism based on this comportment leads to excellent agreement between the kinetic model and the experimentally measured quantities, such as the onset temperature and the conversion profiles of detected species. The proposed kinetic model for the oxidation of COS provides a tool to design both the SOx mitigation processes and industrial systems for safe handling of sulfur impurities in fossil fuels

Thermodynamic parameters including acid dissociation constants for bromochlorophenols (BCPs)

This contribution reports standard gas-phase enthalpies of formation (ΔfH°298), entropies (S°298), and heat capacities (Cp°(T)) for all plausible 64 bromochlorophenols (BCPs) at the M062X meta hybrid level using a polarized basis set of 6-311+G(d,p). Isodesmic work reactions served to calculate the standard enthalpies of formation for all bromochlorophenol molecules and several bromochlorophenoxy radicals. Standard entropies and heat capacities comprise correction terms due to the treatment of O-H bonds as hindered rotors. Values of the bond dissociation enthalpies (BDHs) of O-H bonds, calculated for a selected series of bromochlorophenols, vary slightly with the change in the pattern and degree of halogenation of the phenyl ring. A thermodynamic cycle facilitated the estimation of pKa values, based on the calculated solvation and gas-phase deprotonation energies. We estimated the solvation energies of 19 out of 64 BCPs and their respective anions based on the integral equation formalism polarizable continuum model using optimized structures in the aqueous phase. Values of pKa decrease significantly from around 9 for monohalogenated to around 3 for pentahalogenated phenols