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The hydrogen-donor solvent (H-donor) used in direct coal liquefaction (DCL) plays a critical role in both the oil yield and distribution of the products. However, the mechanism of the reaction between H-donor and coal in the DCL is unclear. In this study, the reaction of H-donor and coal in the DCL was investigated using the model compounds tetralin (H-donor) and diphenylmethane (DPM, coal). Density functional theory calculations were employed to examine both pyrolytic radical and solvent-mediated hydrogenolysis mechanisms. Based on the computed results, a modified solvent-mediated hydrogenolysis mechanism was proposed, namely the synergistic double-hydrogen-transfer mechanism, in which the β- and α-hydrogen atoms simultaneously transfer from tetralin to the ipso- and meta-carbon atoms of DPM. The calculated energy barriers of hydrogen transfer were lower than most of the bond dissociation enthalpies for coal. The energy barriers range of the synergistic double-hydrogen-transfer reaction did not correlate with the dissociation enthalpies of Caryl−Calkyl bond, although they were consistent with the order of the hydrogen-donating abilities of different solvents. This study may provide a theoretical guidance to improve the efficiency of H-donor in the DCL.

Catalytic hydrodeoxygenation is an efficient method to upgrade the quality of low-temperature coal tar and coal liquefied oil. However, only limited researches are performed on the mechanism of hydrodeoxygenation and, therefore, innovation of more efficient and stable catalysts is less progressed and still remains a challenging subject. In this study, density functional theory calculations are carried out to get a deeper insight in the mechanism of dibenzofuran hydrodeoxygenation on the Pt(111) surface. Calculated energies and activation barriers indicate that five-membered-ring opening of tetrahydrodibenzofuran is easier than that of hexahydrodibenzofuran. Then, the generated intermediate can be preferentially hydrogenated through a non-consecutive pathway to 2-cyclohexylphenol, and would result in multiple radical species. The dehydroxylation of that intermediate formed by adding five hydrogen atoms to the phenyl ring of 2-cyclohexylphenol shows a moderate reaction barrier of 1.07 eV; whereas, dehydroxylation of cyclohexylcyclohexanol needs a higher energy barrier of 2.04 eV. For the hydrodeoxygenation of dibenzofuran on the Pt(111) surface, the target product bicyclohexane is most likely to be formed through a radical intermediate. This investigation may provide a potent theoretical guidance to design new catalyst for hydrodeoxygenation of coal to liquid.

The structure of transition state is very significant to further understand the related reaction system auxiliary N N bond cleavage process. Here, in order to sort out some DFT functionals in searching the transition states in a N N bond cleavage reaction mediated by the diiron complexes, we compared 49 density functionals with benchmark data of MP2 and DLPNO-CCSD(T) methods. By analyzing the structures and relative energies, we have found two HGGA functionals (B1B95, mPW1PBE) that are more consistently reliable ones. Among them, the B1B95 functional provides the most reliable energetic properties within 8.6 kcal/mol compared with the data of DLPNO-CCSD(T) method. And six HGGA functionals (B1B95, PBE0, mPW1PBE, mPW1PW91, HSEh1PBE, HSE1PBE) and two functionals (B2PLYP-D3, PBE0-D3) with D3 empirical dispersion well optimize the structure of Fe2S2 clusters and evaluate the reaction thermodynamic energy of N N bond cleave process. The functionals with long range correction and D3 empirical dispersion underestimate easily the energy barrier of N N bond cleavage of Fe2S2 clusters.

To induce double-proton transfer (DPT) with guanine in a biological environment, 12 cytosine analogues (Ca) were formed by atomic substitution. The DPT reactions in the Watson–Crick cytosine–guanine model complex (Ca0G) and 12 modified cytosine–guanine complexes (Ca1-12G) were investigated using density functional theory methods at the M06-2X/def2svp level. The intramolecular proton transfers within the analogues are not facile due to high energy barriers. The hydrogen bond lengths of the Ca1-12G complexes are shorter than those in the Ca0G complex, which are conducive to DPT reactions. The DPT energy barriers of Ca1-12G complexes are also lower than that of the Ca0G complex, in particular, the barriers in the Ca7G and Ca11G complexes were reduced to −1.33 and −2.02 kcal/mol, respectively, indicating they are significantly more prone to DPT reactions. The DPT equilibrium constants of Ca1-12G complexes range from 1.60 × 100 to 1.28 × 107, among which the equilibrium constants of Ca7G and Ca11G are over 1.0 × 105, so their DPT reactions may be adequate. The results demonstrate that those cytosine analogues, especially Ca7 and Ca11, are capable of inducing DPT with guanine, and then the guanine tautomer will form mismatches with thymine during DNA replication, which may provide new strategies for gene therapy.

The flow and heat transfer characteristics in slip flow regime at low pressure state are numerically investigated by using CFD solver. The complete boundary conditions of first-order velocity slip are considered by User Defined Functions (UDFs), which include effects of thermal creep and wall curvature, as well as temperature jump. Based on the dimensionless continuity, momentum and energy equations along with these boundary conditions, the numerical simulation for flow and heat transfer behaviors over a circular cylinder is conducted in a wide range of Re = 0.001 to 20 and Kn = 0.01 to 0.1. It is found that the prediction results without considering the slip boundary conditions obviously deviate from the experimental values with the increase of Knudsen number, while the one by the developed model is in good agreement with the experimental results. Meanwhile, the variation of physical fields under different Reynolds and Knudsen numbers is discussed in detail. The empirical correlations in the slip flow regime for predicting average drag coefficient and average Nusselt number are proposed on the basis of simulation data, which makes the traditional method used for continuous flow regime be successfully applied into the prediction of flow and heat transfer performances in the slip flow regime.

The presence of inorganic ions and organic matter in natural water would cause unpredictable consequence on the oxidation efficiency and pathways of sulfate radical (SO4 −) based advanced oxidation process (SR-AOPs). In this study, the impacts of water constituents, namely, halides (including chloride (Cl−) and bromide (Br−)), bicarbonate (HCO3−) and natural organic matter (NOM) on SO4 − induced degradation of salbutamol (SAL) and terbutaline (TBL) were evaluated systematically. Our results indicated that chloride exhibited no effect on oxidation efficiencies of SAL and TBL, while Br−, HCO3− and NOM all showed inhibitory effects. Specifically, the detrimental effect of bromide was mainly attributed to the scavenging of SO4 − to form the less reactive species, Br2 −. By using laser flash photolysis (LFP), the second-order rate constants of Br2 − with SAL and TBL were estimated to be 2.1 and 3.9 × 108 M−1 s−1, respectively, much smaller than those with SO4 − (3.7 × 109 M−1 s−1 for SAL and 4.2 × 109 M−1 s−1 for TBL). Moreover, bromine addition products of SAL and TBL were detected in the presence of Br−, which were believed to be more toxic than the parent compounds. Similar to bromide, HCO3− could also quench SO4 − to generate carbonate radical (CO3 −), also less reactive than sulfate radical with SAL (4.8 × 107 M−1 s−1) and TBL (3.2 × 108 M−1 s−1). In the case of NOM, a light screening effect was regarded as the major factor responsible to the decrease of reaction rates, while sulfate radical scavenging played a very limited role. The present work would increase the awareness of secondary reactions during SR-AOPs, as more toxic products were generated in the case of bromide.

Biochar-supported nickel (Ni/BC) catalysts have potential applications in steam reforming of tar during biomass gasification. However, the industrial application of Ni/BC catalysts is restricted by their rapid deactivation caused by the gasification of biochar support and deposition of carbon on the active Ni metal. In this study, the effect of boron doping was explored on the performance of Ni/BC catalysts in steam reforming of toluene as a tar model compound. A series of Ni/BC and boron-doped Ni/BC catalysts were prepared by impregnating Ni salts on raw and acid-washed biomass as the starting materials and used in steam reforming of toluene as the tar model compound. It was found that boron doping significantly prolonged the lifetime of Ni/BC catalysts by interacting with Ni and the biochar support simultaneously. It is believed that boron doping lowered the gasification consumption rate of the biochar support in three ways: transforming the inherent K into more stable borates, inhibiting the desorption of CO and CO2, and forming B2O3 as the active site blocker. Furthermore, boron doping also reduced coke deposition on the Ni particles.

This study provides a quantitative forecast method for predicting the potential maximum wind gust at certain automatic weather stations (AWSs) in South China through the investigation of the relationship between the wind gusts observed at the stations and tropical cyclones’ (TCs) main characteristics: TC intensity, TC distance to the station, TC azimuth relative to the station, and TC size. Historical TC data from 1968 to June 2014 within a distance of 700 km to several AWSs in South China are analyzed. The wind gust data available for the same period taken from six coastal AWSs: Yantian International Container Terminal (YICT), Mawan Port (MWP), and Shekou Ferry Terminal (SFT) in Shenzhen, and Hong Kong Observatory (HKO), Cheung Chau Island (CCH), and Waglan Island (WGL) in Hong Kong, are used to build the statistical relationship. The probability of gust gale occurrence (wind gust ≥ 17 m s−1) at these six stations is also computed. Results show that the wind induced by offshore TCs is strongly affected by the surrounding terrain conditions of the stations. Coastal stations open to the wind direction suffer a greater wind influence than do stations with obstructions located in the wind direction. When TCs are approaching the coast in South China, the most dangerous area is the northeast quadrant of TCs. In this quadrant, typhoons might incur gust gales at coastal stations in South China even at a distance of more than 400 km from the stations.

International audience; Application of activated peroxymonosulfate (PMS) to generate sulfate radical or hydroxyl radical is a promising strategy for wastewater treatment, while our knowledge on the background reaction, namely, the direct interaction between PMS and target contaminants is quite limited. In this contribution, the degradation kinetics, stoichiometry, products and mechanism of the reaction between unactivated PMS and trimethoprim (TMP), one of the most commonly detected micro-pollutants in the aquatic system were investigated systematically. The results indicated that TMP was susceptible to degradation by direct PMS oxidation via a non-radical process. By recording the decay of two reactants simultaneously, the stoichiometric ratio between PMS and TMP was estimated to be approximately 1. Higher PMS levels exhibited a promotion effect on PMS decay. And the degradation was pH-dependent, basic conditions were favorable for TMP degradation, which could be well modeled based on the species-specific reactions. The two amine groups on the pyrimidine ring were identified as the reactive sites. After direct attacks by PMS, they would be oxidized to form hydroxylamine-products, namely, N8–OH-TMP and N9–OH-TMP. These two hydroxylamine-products were quite stable and resistant to further oxidation by PMS, preventing the formation of more toxic nitroso- and nitro-products. The new findings in the present work would provide beneficial information on the strategy choice for the elimination of specific pollutants, like TMP, as PMS also exhibits relatively high reactivity towards them.

DFT calculations have been conducted for investigating the relation between the electronic states and catalytic properties of iminopyridine-ligated cationic iron complexes in the stereoselective polymerization of isoprene. Iminopyridine ligand is found to be redox-inert in this catalytic system. The neutral pre-catalyst and active cationic species present as a high spin quintet and the open-shell unpaired 3d-electrons reside on Fe center. The trans and cis polymerization of isoprene catalyzed by the complexes [(octyl-iminopyridine)FeII(Me)]+ (A1) and [(supermesityl-iminopyridine)FeII(Me)]+ (A2) could be attributed to the electronic and steric effects in the transition states, respectively.

Recent in vivo and in vitro experiments indicated that methoxylated polybrominated diphenyl ethers (MeO-PBDEs) can be biotransformed into hydroxylated PBDEs (HO-PBDEs) that are more toxic than PBDEs and MeO-PBDEs. Nevertheless, the enzymatic transformation mechanism is not clear. We hypothesized that cytochrome P450 enzymes (CYPs) play a key role in the transformation and employed the density functional theory calculations to unveil the mechanism. The transformation of a model compound, 6-MeO-BDE-47, catalyzed by the active center of CYPs (Compound I), was computed. For the first time, our results show that the energy barriers for the addition of Compound I to the C atoms on the phenyl of 6-MeO-BDE-47 are much higher than that for hydroxylation of the methoxyl, indicating that O-demethylation is a dominating metabolic pathway. This is in line with experimental observations performed by others. The pathways for the transformation of 6-MeO-BDE-47 catalyzed by Compound I were clarified. A C-H bond of the methoxyl is activated by Compound I, followed by radical rebound to form carbinol intermediates, then the carbinols decompose to form 6-HO-BDE-47 with the assistance of water molecules. The computational method can be potentially employed to develop models that predict biotransformation of xenobiotics catalyzed by CYPs.

Multiple secondary eyewall formations (SEFs) and eyewall replacement cycles (ERCs) are simulated with the fifth-generation Pennsylvania State University (PSU)–National Center for Atmospheric Research (NCAR) Mesoscale Model (MM5) at horizontal grid spacing of 0.67 km. The simulated hurricane is initialized from a weak, synthetic vortex in a quiescent environment on an f plane. After spinup and rapid intensification, the hurricane enters a mature phase during which the intensity change is relatively slow. Convective clouds then organize into a ring with a secondary tangential wind maximum at radii beyond the hurricane’s primary eyewall. This secondary eyewall (SE) then contracts and strengthens. The primary eyewall weakens and is eventually replaced by the SE. The hurricane grows in size and the radius of maximum wind (RMW) increases as similar ERCs repeat 5 times during the simulation. Two existing hypotheses on SEF are evaluated using the simulation output. Then, model diagnostics are used to reveal that crucial linked components of SEF are (i) a broadening of the swirling flow, (ii) the structure of the evolving secondary circulation, and (iii) the structure of the net radial force (NRF) in the boundary layer (with largest contributions from the agradient and frictional forces). During SEF, there exists strong positive NRF in the region of the primary eyewall, a secondary positive maximum over the SEF region, and a minimum between the two. As a response of the boundary layer depth–integrated radial flow to the NRF, a secondary maximum convergence zone (SMCZ) in the boundary layer develops at the SEF radii. Eventually moist convection in the SMCZ becomes active as the SEF develops.

Flower-like tellurium (Te) nanocrystals with uniform branches were successfully prepared in large quantities by a surfactant-assisted method. The product was characterised with X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electronic diffraction (SAED) and energy dispersive X-ray spectroscopy (EDS). The characterisation results revealed that the branch of flower-like Te was grown along [001] direction. Furthermore, the Raman spectrum of the flower-like Te with uniform branches was studied. The result shows that the flower-like Te exhibits three typical vibration peaks. This study provides a simple method to prepare three-dimensional Te nanostructures in large scale, which broadens their practical applications.

Rainfall prediction remains one of the most challenging problems in weather forecasting. In order to improve high-resolution quantitative precipitation forecasts (QPF), a new procedure for assimilating rainfall rate derived from radar composite reflectivity has been proposed and tested in a numerical simulation of the Chicago floods of 17–18 July 1996. The methodology is based on the one-dimensional variation scheme (1DVAR) assimilation approach introduced by Fillion and Errico but applied here using the Kain-Fritsch convective parameterization scheme (KF CPS). The novel feature of this work is the continuous assimilation of radar estimated rain rate over a three hour period, rather than a single assimilation at the initial (analysis) time. Most of the characteristics of this precipitation event, including the propagation, regeneration of mesoscale convective systems, the frontal boundary across the Midwest and the evolution of the low-level jet are better captured in the simulation as the radar-estimated precipitation rate is assimilated. The results indicate that precipitation assimilation during the early stage can improve the simulated mesoscale feature of the convection system and shorten the spin-up time significantly. Comparison of precipitation forecasts between the experiments with and without the 1DVAR indicates that the 1DVAR scheme has a positive impact on the QPF up to 36 hours in terms of the bias and bias equalized threat scores.

Because of the lack of three-dimensional (3D) high-resolution data and the existence of highly nonelliptic flows, few studies have been conducted to investigate the inner-core quasi-balanced characteristics of hurricanes. In this study, a potential vorticity (PV) inversion system is developed, which includes the nonconservative processes of friction, diabatic heating, and water loading. It requires hurricane flows to be statically and inertially stable but allows for the presence of small negative PV. To facilitate the PV inversion with the nonlinear balance (NLB) equation, hurricane flows are decomposed into an axisymmetric, gradient-balanced reference state and asymmetric perturbations. Meanwhile, the nonellipticity of the NLB equation is circumvented by multiplying a small parameter ɛ and combining it with the PV equation, which effectively reduces the influence of anticyclonic vorticity. A quasi-balanced ω equation in pseudoheight coordinates is derived, which includes the effects of friction and diabatic heating as well as differential vorticity advection and the Laplacians of thermal advection by both nondivergent and divergent winds.This quasi-balanced PV–ω inversion system is tested with an explicit simulation of Hurricane Andrew (1992) with the finest grid size of 6 km. It is shown that (a) the PV–ω inversion system could recover almost all typical features in a hurricane, and (b) a sizeable portion of the 3D hurricane flows are quasi-balanced, such as the intense rotational winds, organized eyewall updrafts and subsidence in the eye, cyclonic inflow in the boundary layer, and upper-level anticyclonic outflow. It is found, however, that the boundary layer cyclonic inflow and upper-level anticyclonic outflow also contain significant unbalanced components. In particular, a low-level outflow jet near the top of the boundary layer is found to be highly unbalanced (and supergradient). These findings are supported by both locally calculated momentum budgets and globally inverted winds. The results indicate that this PV inversion system could be utilized as a tool to separate the unbalanced from quasi-balanced flows for studies of balanced dynamics and propagating inertial gravity waves in hurricane vortices.

By the use of the WKBJ method combined with the characteristic line method, the asymptotic solution of a gravity wave envelope in the atmosphere of horizontal heterogeneous stratification and time-varying stratification is obtained. The solution shows that not only the variation of amplitude of the gravity wave but also the variation of wavelength and the width of the envelope are affected by the horizontal heterogeneity. As the wave envelope moves from a region, of strong stratification to a weak one, the horizontal wavelength will become shorter, the width of the envelope will narrow and its amplitude will increase. The variation of stratification with time cannot lead to the variation of wavelength and envelope width, but the amplitude of the wave envelope will increase while the amplitude of the wave decreases in time.