Search

We demonstrate that centered likelihood ratio estimators for the sensitivity indices of complex stochastic dynamics are highly efficient with low, constant in time variance and consequently they are suitable for sensitivity analysis in long-time and steady-state regimes. These estimators rely on a new covariance formulation of the likelihood ratio that includes as a submatrix a Fisher information matrix for stochastic dynamics and can also be used for fast screening of insensitive parameters and parameter combinations. The proposed methods are applicable to broad classes of stochastic dynamics such as chemical reaction networks, Langevin-type equations and stochastic models in finance, including systems with a high dimensional parameter space and/or disparate decorrelation times between different observables. Furthermore, they are simple to implement as a standard observable in any existing simulation algorithm without additional modifications. [ABSTRACT FROM AUTHOR]

Mott proposed that impurity bands in corundum-symmetry Ti2O3 at high temperatures caused a collapse in the bandgap. However, the origin of the impurity bands has not yet been clarified. We examine the local structural properties of metal-to-insulator-transition Ti2O3 using in-situ x-ray absorption fine structure (XAFS) measurements at the Ti K edge in the temperature range from 288 to 739 K. The Ti2O3 powder is synthesized by using a chemical reaction method. X-ray diffraction (XRD) measurements from Ti2O3 with a Rietveld refinement demonstrate a single-phased R-3c symmetry without additional distortion. Extended-XAFS combined with XRD reveals a zigzag patterned Ti position and an anomalous structural disorder in Ti-Ti pairs, accompanied by a bond length expansion of the Ti-Ti pairs along the c-axis for T>450 K. The local structural distortion and disorder of the Ti atoms would induce impurity levels in the band gap between the Ti 3d a1g and eg p bands, resulting in a collapse of the band gap for T>450 K. [ABSTRACT FROM AUTHOR]

Mott proposed that impurity bands in corundum-symmetry Ti2O3 at high temperatures caused a collapse in the bandgap. However, the origin of the impurity bands has not yet been clarified. We examine the local structural properties of metal-to-insulator-transition Ti2O3 using in-situ x-ray absorption fine structure (XAFS) measurements at the Ti K edge in the temperature range from 288 to 739 K. The Ti2O3 powder is synthesized by using a chemical reaction method. X-ray diffraction (XRD) measurements from Ti2O3 with a Rietveld refinement demonstrate a single-phased R-3c symmetry without additional distortion. Extended-XAFS combined with XRD reveals a zigzag patterned Ti position and an anomalous structural disorder in Ti-Ti pairs, accompanied by a bond length expansion of the Ti-Ti pairs along the c-axis for T>450 K. The local structural distortion and disorder of the Ti atoms would induce impurity levels in the band gap between the Ti 3d a1g and eg p bands, resulting in a collapse of the band gap for T>450 K. [ABSTRACT FROM AUTHOR]

This paper investigates a three-patch Rift Valley fever virus transmission model with periodic coefficients. The basic reproduction number Ri0i=1,2,3 is calculated for the model by using the next infection operator method. The threshold conditions on the extinction and permanence in the mean of the disease with probability one. The Rift Valley fever disease will be permanent in the j-th j=1,2,3 patch if j≥i,Ri0>1 and dies out in the j-th patch if j

Highlights • Role of the common-ion effect on pit solution chemistry of pure Zn and Fe was investigated. • D.Δ C S decreased with increasing bulk Cl− concentration for both Zn and Fe. • Zn and Fe showed different dissolution behaviors due to different complexation tendencies. • Dissolution of Zn was related to a lowered diffusion rather than the common-ion effect. • Dissolution of Fe was affected by both the common-ion effect and a decreased diffusivity. Abstract The lead-in pencil electrode technique was used to study the pit solution chemistry of pure Zn and Fe in the presence and absence of a common cation. It was found that during 1-D pitting the relative importance of the common-ion effect on the dissolution kinetics, vis-à-vis that of the diffusion coefficient, is strongly related to the tendency of the dissolving metal to form chloro-complexes. The dissolution kinetics were characterized in terms of the limiting current density, salt film dissolution potential, supersaturation of the pit solution and pit growth rate. The dissolution kinetics decreased with increasing bulk Cl− concentration for both metals, irrespective of the presence of a common cation. The reduced dissolution kinetics of Zn with increasing bulk Cl− concentration was found to be associated with a lowered diffusion coefficient rather than the common-ion effect (which would reduce metal salt solubility). On the other hand, Fe dissolution was affected by both the common-ion effect and reduced diffusivity. These differing observations appear to be due to the different tendencies for Zn and Fe to form chloro-complexes, as well as their different chloride salt solubilities. [ABSTRACT FROM AUTHOR]

In many Ni-based superalloys, dynamic strain aging (DSA) generates an inhomogeneous plastic deformation resulting in jerky flow known as the Portevin-Le Chatelier (PLC) effect. This phenomenon has a deleterious effect on the mechanical properties and, at high temperature, is related to the diffusion of substitutional solute atoms toward the core of dislocations. However, the question about the nature of the atomic species responsible for the PLC effect at high temperature still remains open. The goal of the present work is to answer this important question; to this purpose, three different 718-type and a 625 superalloy were studied through a nonconventional approach by mechanical spectroscopy. The internal friction (IF) spectra of all the studied alloys show a relaxation peak P718 (at 885 K for 0.1 Hz) in the same temperature range, 700 K to 950 K, as the observed PLC effect. The activation parameters of this relaxation peak have been measured, Ea(P718) = 2.68 ± 0.05 eV, τ0 = 2·10−15 ± 1 s as well as its broadening factor β = 1.1. Experiments on different alloys and the dependence of the relaxation strength on the amount of Mo attribute this relaxation to the stress-induced reorientation of Mo-Mo dipoles due to the short distance diffusion of one Mo atom by exchange with a vacancy. Then, it is concluded that Mo is the atomic species responsible for the high-temperature PLC effect in 718 superalloy. [ABSTRACT FROM AUTHOR]

In the present investigations, the excess molar volumes, VijkE VijkE, excess isentropic compressibilities, (κSE)ijk (SE)ijk, and excess heat capacities, (CpE)ijk (CpE)ijk, for ternary 1-butyl-2,3-dimethylimidazolium tetrafluoroborate (i) + 1-butyl-3-methylimidazolium tetrafluoroborate (j) + 1-ethyl-3-methylimidazolium tetrafluoroborate (k) mixture at (293.15, 298.15, 303.15 and 308.15) K and excess molar enthalpies, (H E) ijk (HE)ijk, of the same mixture at 298.15 K have been determined over entire composition range of x i and x j. Satisfactorily corrections for the excess properties V E ijk VijkE κSE)ijk (κSE)ijk, (H E)ijk (HE)ijk and (Cp E)ijk (CpE)ijk have been obtained by fitting with the Redlich-Kister equation, and ternary adjustable parameters along with standard errors have also been estimated. The V E ijk VijkE, (κSE)ijk (κES)ijk, (H E ) ijk (HE)ijk and (C pE) ijk (CpE)ijk data have been further analyzed in terms of Graph Theory that deals with the topology of the molecules. It has also been observed that Graph Theory describes well V E ijk VijkE (κSE)ijk (κES)ijk, (H E)ijk (HE)ijk and (CpE)ijk (CpE)ijk values of the ternary mixture comprised of ionic liquids. [ABSTRACT FROM AUTHOR]

Highly efficient reactions of 4-hydroxycoumarin with hypervalent iodine reagents under mild conditions are described, which give rise to 4-aryloxycoumarins in good to excellent yields. [ABSTRACT FROM AUTHOR]

Radiofrequency-driven hydrodeoxygenation of sawdust pyrolysis vapor and the coking performance of the catalysts were investigated using Pt/Al 2 O 3 commercial pellets mixed with steel balls inside an alumina tube. The radio-frequency induction heating of the catalyst bed was compared with a conventional method of heating using electric tape engulfing the catalyst bed reactor. Partial deoxygenation of the oil was successfully achieved in the catalytic upgrading of pyrolysis oil at 234 °C, with the use of the induction heater. The molar O/C ratio of the oil decreased from 1.36 to 0.51. No deoxygenation of the oil was observed using the electric tape control under identical conditions as both carbon and oxygen appeared to be removed at approximately equal rates, with the carbon being deposited in the form of coke onto the catalyst instead of being recovered in the liquid. [ABSTRACT FROM AUTHOR]

For the simulation of atmospheric entry maneuvers at Mars and Saturn's Titan, the chemistry modeling of polyatomic molecules is implemented in the direct simulation Monte Carlo method within the reactive plasma flow solver PICLas. An additional reaction condition as well as the consideration of the vibrational degrees of freedom is described in the context of the total collision energy model. The treatment of reverse exchange and recombination reactions is discussed, where the low temperature exponent of the Arrhenius fit for methane dissociation limited the calculation of the reaction probability at relevant temperatures. An alternative method based on the equilibrium constant is devised. The post-reaction energy redistribution is performed under the assumption of equipartition of the remaining collisional energy. The implementation is verified for several reaction paths with simple reservoir simulations. Finally, the feasibility of the new chemistry model is demonstrated by a simulation of a trajectory point of Huygens probe at Titan. [ABSTRACT FROM AUTHOR]

In this review we survey the contributions that molecular beam experiments have provided to our understanding of the dynamics and kinetics of chemical interactions of gas molecules with solid surfaces. First, we describe the experimental details of the different instrumental setups and approaches available for the study of these systems under the ultrahigh vacuum conditions and with the model planar surfaces often used in modern surface-science experiments. Next, a discussion is provided of the most important fundamental aspects of the dynamics of chemical adsorption that have been elucidated with the help of molecular beam experiments, which include the development of potential energy surfaces, the determination of the different channels for energy exchange between the incoming molecules and the surface, the identification of adsorption precursor states, the understanding of dissociative chemisorption, the determination of the contributions of corrugation, steps, and other structural details of the surface to the adsorption process, the effect to molecular steering, the identification of avenues for assisting adsorption, and the molecular details associated with the kinetics of the uptake of adsorbates as a function of coverage. We follow with a summary of the work directed at the determination of kinetic parameters and mechanistic details of surface reactions associated with catalysis, mostly those promoted by late transition metals. This discussion we initiate with an overview of what has been learned about simple bimolecular reactions such as the oxidation of CO and H 2 with O 2 and the reaction of CO with NO, and continue with the review of the studies of more complex systems such as the oxidation of alcohols, the conversion of organic acids, the hydrogenation and isomerization of olefins, and the oxidative activation of alkanes under conditions of short contact times. Sections 6 and 7 of this review deal with the advances made in the use of molecular beams with more realistic models for catalysis, using surfaces comprised of metal nanoparticles dispersed on the oxide surfaces used as catalyst support and high-flux beams to approach the pressures used in catalysis. The next section deals with the study of systems associated with fields other than catalysis, mainly with the etching and oxidation of semiconductor surfaces and with the chemistry used to grow thin solid films by chemical means (chemical vapor deposition, CVD, or atomic layer deposition, ALD). We end with a personal assessment of the past accomplishments, present state, and future promise of the use of molecular beams for the study of the kinetics of surface reactions relevant to practical applications. [ABSTRACT FROM AUTHOR]

We implemented a numerical model to simulate transport of multiple species and geochemical reactions occurring during electrokinetic remediation of metal-contaminated porous media. The main phenomena described by the model were: (1) species transport by diffusion, electromigration and electroosmosis, (2) pH-dependent buffering of H + , (3) adsorption of metals onto particle surfaces, (4) aqueous speciation, (5) formation and dissolution of solid precipitates. The model was applied to simulate the electrokinetic extraction of heavy metals (Pb, Zn and Ni) from marine harbour sediments, characterized by a heterogeneous solid matrix, high buffering capacity and aged pollution. A good agreement was found between simulations of pH, electroosmotic flow and experimental results. The predicted residual metal concentrations in the sediment were also close to experimental profiles for all of the investigated metals. Some removal overestimation was observed in the regions close to the anode, possibly due to the significant metal content bound to residual fraction. [ABSTRACT FROM AUTHOR]

The purpose of this work was to investigate the influence of the common ion effect and varying NaOH molar concentrations on morphology, particle size and magnetism of iron oxide (Fe 3 O 4 ) magnetic particles (IOMPs) synthesized by co-precipitation. The IOMPs were characterized by SEM, XRD, FT-IR, TGA-DTA, EDX-SEM, SQUID and Raman Spectroscopy. SEM revealed cuboidal morphology (10–250 µm) with SQUID demonstrating saturation magnetization between 4.75–20 emu/g. The IOMPs synthesized in the presence of common ions was smaller in size with less magnetization and showed circular and creep crack fractures within an optimal pH zone. All other characterization studies supported these findings. Overall, results revealed that the morphology, particle size and magnetism of the IOMPs were influenced by common ions from two salt systems at varying concentrations of NaOH. [ABSTRACT FROM AUTHOR]

Key points Phosphatidylinositol-4,5-bisphosphate (PIP2) is a key regulator of many membrane proteins, including voltage-gated Kv7.2 channels., In this study, we identified the residues in five phosphorylation sites and their corresponding protein kinases, the former being clustered within one of four putative PIP2-binding domains in Kv7.2., Dephosphorylation of these residues reduced the sensitivity of Kv7.2 channels towards PIP2., Dephosphorylation of Kv7.2 affected channel inhibition via M1 muscarinic receptors, but not via bradykinin receptors., Our data indicated that phosphorylation of the Kv7.2 channel was necessary to maintain its low affinity for PIP2, thereby ensuring the tight regulation of the channel via G protein-coupled receptors., Abstract The function of numerous ion channels is tightly controlled by G protein-coupled receptors (GPCRs). The underlying signalling mechanisms may involve phosphorylation of channel proteins and participation of phosphatidylinositol-4,5-bisphosphate (PIP2). Although the roles of both mechanisms have been investigated extensively, thus far only little has been reported on their interaction in channel modulation. GPCRs govern Kv7 channels, the latter playing a major role in the regulation of neuronal excitability by determining the levels of PIP2 and through phosphorylation. Using liquid chromatography-coupled mass spectrometry for Kv7.2 immunoprecipitates of rat brain membranes and transfected cells, we mapped a cluster of five phosphorylation sites in one of the PIP2-binding domains. To evaluate the effect of phosphorylation on PIP2-mediated Kv7.2 channel regulation, a quintuple alanine mutant of these serines (S427/S436/S438/S446/S455; A5 mutant) was generated to mimic the dephosphorylated state. Currents passing through these mutated channels were less sensitive towards PIP2 depletion via the voltage-sensitive phosphatase Dr-VSP than were wild-type channels. In vitro phosphorylation assays with the purified C-terminus of Kv7.2 revealed that CDK5, p38 MAPK, CaMKIIα and PKA were able to phosphorylate the five serines. Inhibition of these protein kinases reduced the sensitivity of wild-type but not mutant Kv7.2 channels towards PIP2 depletion via Dr-VSP. In superior cervical ganglion neurons, the protein kinase inhibitors attenuated Kv7 current regulation via M1 receptors, but left unaltered the control by B2 receptors. Our results revealed that the phosphorylation status of serines located within a putative PIP2-binding domain determined the phospholipid sensitivity of Kv7.2 channels and supported GPCR-mediated channel regulation. [ABSTRACT FROM AUTHOR]

The densities, ρ , speeds of sound, u , and molar heat capacities, C P , of 1-butyl-2,3-dimethylimidazolium tetrafluoroborate (i) + 1-butyl-3-methylimidazolium tetrafluoroborate (j); 1-butyl-3-methylimidazolium tetrafluoroborate (i) + 1-ethyl-3-methylimidazolium tetrafluoroborate (j) and 1-butyl-2,3-dimethylimidazolium tetrafluoroborate (i) + 1-ethyl-3-methylimidazolium tetrafluoroborate (j) mixtures at temperatures (293.15, 298.15, 303.15, 308.15) K and excess molar enthalpies, H E , for the same mixtures at temperature (298.15) K have been measured over entire range of mole fraction under atmospheric pressure. Using experimental data, excess molar volumes, V E , excess isentropic compressiblities, κ S E , excess molar enthalpies, H E and excess molar heat capacities, C P E have been determined. The V E , κ S E , H E and C P E data have been fitted to Redlich-Kister equation to estimate the binary adjustable parameters and standard deviations between experimental and calculated values. The topology of the constituent molecules (Graph theory) has been utilized to predict V E , κ S E , H E and C P E data of the studied mixtures. The comparison of V E , κ S E , H E and C P E values determined by Graph theory with their corresponding experimental values lends additional support to the proposed molecular entities existing in mixtures along with various processes involved in the (i + j) mixtures formation. Further, IR studies and quantum mechanical calculations support the presence of proposed molecular entities in the studied mixtures. [ABSTRACT FROM AUTHOR]

A three-step reaction for the complete extraction of H 2 from H 2 O molecule using a small Al 6 Si cluster is determined based on first-principle calculations. All reactants, products, and transition states are found through optimization calculation and confirmed frequency analysis. The intrinsic reaction coordinate is also calculated to validate the reaction process. Charge distribution is used to analyze the novel reaction. The present results show that the entire reaction can be actively started when the H 2 O molecule is adsorbed on Al 6 Si cluster because the barrier of the first transition state only 0.1448 eV and the whole process is an exothermic reaction when zero-point energy is included. It is found that Al 6 Si cluster can strongly capture H 2 O molecule, as well as extract and store the H 2 molecule, at a favorable temperature. This result may serve as a basis for the development of a more efficient method of generating and storing H 2 from H 2 O molecule. [ABSTRACT FROM AUTHOR]

We have investigated a very interesting side-pathway leading to 1,3-dibromo-2-aryl-1H-indenes as opposed to isoquinoline N-oxides during the NBS mediated synthesis of isoquinoline N-oxide from 2-alkynylbenzaldoximes. [ABSTRACT FROM AUTHOR]

Chemical functionalization is a promising approach to controllably manipulate the characteristics of graphene. Here, we designed ris-dienes, featuring two dihydronaphthalene backbones, to decorate a graphene surface via Diels--Alder (DA) click reaction. The installation of a diene moiety into a nonplanar molecular structure to form cis-conformation enables a rapid (~5 min) DA reaction between graphene and diene groups. Patterned graphene of sub-micrometer resolution can be obtained by easily soaking poly(methyl methacrylate)- masked graphene in solution of hydroxyl-substituted cisdiene at room temperature. The functionalization degree can be further controlled by carrying out the reaction at higher temperature. The present result gives important insight into the effect of molecular conformation on the graphene functionalization process, and provides an effective and facile method for graphene functionalization. [ABSTRACT FROM AUTHOR]

Polymerization reactions with organic electron donors (OED) as initiators are presented herein. The metal-free polymerization of various activated alkene and cyclic ester monomers was performed in short reaction times, under mild conditions, with small amounts of organic reducing agents, and without the need for co-initiators or activation by photochemical, electrochemical, or other methods. Hence, OED initiators enabled the development of an efficient, rapid, room-temperature process that meets the technical standards expected for industrial processes, such as energy savings, cost-effectiveness and safety. Mechanistic investigations support an electron-transfer initiation pathway that leads to the reduction of the monomer. [ABSTRACT FROM AUTHOR]

The structural stability of electrode materials and their compatibility with electrolytes are the important properties for ion-intercalative electrochemical energy-storage devices. In the present work, we employed zinc hexacyanoferrates (ZnHCFs), which occurs as cubic or rhombic phases, as the probe to tailor the mechanism of capacity decay upon electrochemical cycling and the corresponding mitigating strategy. Capacity fading results from the loss of active materials, which is highly correlated to the phase states; this has been identified for both phases, where the cubic phase is demonstrated to be the dominant source of ZnHCF dissolution. In 1 m KNO3 electrolyte, rhombic ZnHCF behaves evidently more stable than the cubic phase for long-term galvanostatic charge/discharge cycling. Even when simply immersed in an aqueous environment, the rhombic-cubic phase transition can spontaneously occur, which, in particular, can be accelerated considerably by electrochemical redox processes in the potential window of 0.8-1.1 V. Utilizing the common-ion effect, specifically by incorporating ZnII into aqueous electrolytes, could considerably enhance the capacity retention of ZnHCF. Our results suggest that, if electrode materials are soluble at certain electrochemical stages, introducing electrochemically inert common ions into the electrolyte should be an efficient approach to improve the electrode-electrolyte compatibility for pursuing enhanced cycling performances. [ABSTRACT FROM AUTHOR]

An unprecedented multicomponent cascade asymmetric inverse-electron-demand Diels-Alder/nucleophilic addition/ring-opening reaction involving 2-methoxyfurans as efficient dienophiles was successfully developed with Cu(I)/tBu-Box complex as the catalyst. A diverse array of tetrahydropyridazines containing unexpectedly stable γ-hydroxyl ester moiety was obtained in generally good yield with exclusive regioselectivity and excellent stereoselectivity. [ABSTRACT FROM AUTHOR]

Deliquescence points (RH 0 , RH 0mix ) of ionic crystalline food ingredients and blends thereof were determined using water activity and moisture sorption techniques. Measured RH 0mix values of ingredient blends with and without a common ion were compared to Ross equation predictions of deliquescence lowering. In binary blends with no common ion, measured RH 0mix values ranged from 5% RH lower to 6% RH higher than predicted; however, when a common ion was present, the measured RH 0mix was consistently 6–8% RH higher than predicted. In tertiary blends with a common ion, RH 0mix values were 15–18% RH higher than predicted. The higher RH 0mix in blends with a common ion is caused by counterion dissociation competition from the common ion. At equilibrium, these solutions will have fewer solutes and a greater vapor pressure than assumed by the Ross equation. A modified Ross equation was developed to compensate for the common-ion effect and improve RH 0mix predictions. [ABSTRACT FROM AUTHOR]

Enhanced mode selective fragmentation of oriented ClCHO+ → Cl + HCO+, H + ClCO+, HCl+ + CO with linear polarized intense mid-IR pulses was demonstrated in our previous computational study ( J. Phys. Chem. Lett. 2012, 3, 2541). Simulations of angle-dependent strong field ionization of ClCHO indicate the ionization rate in the molecular plane is nearly twice as large as perpendicular to the plane, suggesting a degree of planar alignment can be obtained experimentally for ClCHO+, starting from neutral molecules. Classical trajectory calculations with a 4 cycle 7 μm laser pulse (peak intensity of 1.26 × 1014 W/cm2) show that circularly polarized light with the electric field in the plane of the molecule deposits more energy and yields larger branching ratios for higher energy fragmentation channels than linearly polarized light with the same maximum field strength. These results suggest circularly polarized mid-IR pulses can not only achieve control on reactions but also provide an experimentally accessible implementation. [ABSTRACT FROM AUTHOR]

Pharmaceutical process design and engineering increasingly recognizes the role of chemical engineering in optimizing the productivity of active pharmaceutical ingredient (API) as well as their scale-up. In the present study, this concept is outlined through the kinetic model of numerous parallel and serial reactions that proceed via a two-step benzazepine heterocyclic compound synthesis, introducing 1-(2-bromoethyl)-4-chlorobenzene (4CEBr) and allylamine (AA) as first step reactants, N -(4-chlorophenethyl)prop-2-en-1-aminium chloride (4CPAL) as intermediate (second step reactant), and (1 R )-8-chloro-1-methyl-2,3,4,5-tetrahydro-1 H -3-benzazepine (lorcaserin) as the desired product, with the second step heterogeneously/homogeneously (negligible mass transfer resistance) catalysed by AlCl 3 as Lewis acid. In addition to these, a plethora of by-products, formed through various mechanisms ranging from eliminations, nucleophilic and electrophilic substitutions and additions, Friedel–Crafts reactions and others, was identified and quantified by nuclear magnetic resonance (NMR), high-performance liquid chromatography coupled with mass spectroscopy (HPLC–MS) and gas chromatography. A large set of experiments was executed for both the first and second step, varying temperature (20–60 °C for the first and 100–120 °C for the second step), reactant and catalyst concentrations, as well as the presence of the first-step reactant (4CEBr and AA) in the second, whereas the stepwise multi-regression modelling with consequent sensitivity analysis ensued. Model optimization indicated that conversions as high as 91% may be achieved in the second step; nonetheless, that a trade-off between yield and productivity has to be considered. An efficient optimization of synthesis steps facilitates further downstream separation, as well as streamlines process intensification when proceeding to the crystallization of API polymorph. [ABSTRACT FROM AUTHOR]

In this paper, the dispersion of solute matter in a Jeffrey fluid flow through a porous medium in a peristaltic channel has been investigated under the influence of slip boundary conditions. Long wavelength approximation and Taylor's limiting condition are used to obtain the average effective dispersion coefficient in both the cases of homogeneous and heterogeneous chemical reactions. The effects of various pertinent parameters on the effective dispersion coefficient are discussed. Average effective dispersion coefficient increases with amplitude ratio. That is, more dispersion in the presence of peristalsis. Further, the average effective dispersion coefficient increases with the permeability parameter and the slip parameter; but decreases with the Jeffrey number, homogeneous / heterogeneous chemical reaction rate parameter. [ABSTRACT FROM AUTHOR]

Scrap Cu-modified cast iron (CMCI) is a potent material for the reduction of 2,4-dinitrotoluene (2,4-DNT) by a surface-mediated reaction. However, the effects of operational parameters and common ions on its reduction and final rate are unknown. Results show that the 2,4-DNT reduction was significantly affected by Cu:Fe mass ratio and the optimum m(Cu:Fe) was 0.25 %. The slight pH-dependent trend of 2,4-DNT reduction by CMCI was observed at pH 3 to 11, and the maximum end product, 2,4-diaminotoluene (2,4-DAT), was generated at pH 7. Dissolved oxygen (DO) in the water reduced the 2,4-DNT degradation and the formation of 2,4-DAT. CMCI effectively treated high concentrations of 2,4-DNT (60 to 150 mg L). In addition, varying the concentration of (NH)SO from 0.001 to 0.1 mol L improved the efficiency of the reduction process. The green rust-like corrosion products (GR-SO) were also effective for 2,4-DNT reduction, in which NaCO (0.01 to 0.2 mol L) significantly inhibited this reduction. The repeated-use efficiency of CMCI was also inhibited. Moreover, 2,4-DNT and its products, such as 4A2NT, 2A4NT, and 2,4-DAT, produced mass imbalance (<35 %). Hydrolysis of Fe and CO leading to the generation of Fe(OH) and conversion to FeOOH that precipitated on the surface and strongly adsorbed the products of reduction caused the inhibition of CO. The 2,4-DNT reduction by CMCI could be described by pseudo-first-order kinetics. The operational conditions and common ions affected the 2,4-DNT reduction and its products by enhancing the corrosion of iron or accumulating a passive oxide film on the reactivity sites. [ABSTRACT FROM AUTHOR]

This paper answers an open question of Chen et al. (DNA 2012: proceedings of the 18th international meeting on DNA computing and molecular programming, vol 7433 of lecture notes in computer science. Springer, Berlin, pp 25-42, ), who showed that a function $$f:\mathbb {N}^k\rightarrow \mathbb {N}^l$$ is deterministically computable by a stochastic chemical reaction network (CRN) if and only if the graph of $$f$$ is a semilinear subset of $$\mathbb {N}^{k+l}$$ . That construction crucially used 'leaders': the ability to start in an initial configuration with constant but non-zero counts of species other than the $$k$$ species $$X_1,\ldots ,X_k$$ representing the input to the function $$f$$ . The authors asked whether deterministic CRNs without a leader retain the same power. We answer this question affirmatively, showing that every semilinear function is deterministically computable by a CRN whose initial configuration contains only the input species $$X_1,\ldots ,X_k$$ , and zero counts of every other species, so long as $$f({\bf 0})={\bf 0}$$ . We show that this CRN completes in expected time $$O(n)$$ , where $$n$$ is the total number of input molecules. This time bound is slower than the $$O(\log ^5 n)$$ achieved in Chen et al. (), but faster than the $$O(n \log n)$$ achieved by the direct construction of Chen et al. (). [ABSTRACT FROM AUTHOR]

In this paper, hydromagnetic convection of a visco-elastic fluid over a continuously moving vertical surface with uniform suction and heat flux in presence of first-order chemical reaction through porous medium has been investigated. A uniform magnetic field is assumed to be applied perpendicular to the wall. The induced magnetic field assumed to be negligible. The solutions are obtained for velocity, temperature and concentration profiles. The profiles of velocity and skin friction are presented graphically for different combinations of the parameters involved in the flow problem. [ABSTRACT FROM AUTHOR]

We report a manganese-catalyzed aliphatic C-H azidation reaction that can efficiently convert secondary, tertiary, and benzylic C-H bonds to the corresponding azides. The method utilizes aqueous sodium azide solution as the azide source and can be performed under air. Besides its operational simplicity, the potential of this method for late-stage functionalization has been demonstrated by successful azidation of various bioactive molecules with yields up to 74%, including the important drugs pregabalin, memantine, and the antimalarial artemisinin. Azidation of celestolide with a chiral manganese salen catalyst afforded the azide product in 70% ee, representing a Mn-catalyzed enantioselective aliphatic C-H azidation reaction. Considering the versatile roles of organic azides in modern chemistry and the ubiquity of aliphatic C-H bonds in organic molecules, we envision that this Mn-azidation method will find wide application in organic synthesis, drug discovery, and chemical biology. [ABSTRACT FROM AUTHOR]

Three single-sided, triol-functionalized Anderson POM hybrids were successfully synthesized. With suitable solvents and the effect driven by common-ion synergy, enantiopure crystals were obtained when the spontaneous resolution of enantiomers occurred upon crystallization. The chirality of POM-organic hybrids was confirmed by single-crystal X-ray diffraction and solid-state CD spectrum. A reversible, spontaneous resolution process for POM-based inorganic-organic hybrids was observed in this work. [ABSTRACT FROM AUTHOR]

Human Bocaviruses (HBoV) were associated with respiratory diseases. Here, we assessed a TaqMan ® -based PCR for the detection of all four HBoV subtype infections with a sensitivity up to 15 copies/reaction. To evaluate this assay on clinical samples, 178 nasopharyngeal aspirate specimens from pediatric cases were analyzed and HBoV genome was detected in 13 out of 178 patients with a viral load range between 1.6 × 10 3 and 9.4 × 10 7 copies/ml. These results indicated that this method could be used as an alternative technique for the diagnosis of HBoV infection. [ABSTRACT FROM AUTHOR]

Mathematical modeling of a bimolecular chemical reaction in the liquid phase was carried out taking account of association of both reactants. The formally simple chemical reaction is thus transformed into a multistage process, which results in the formation of temporal dissipative structures. It was found that, apart from the usual dynamic modes, there appear oscillations of the concentrations of intermediates, characterized by two considerably differing periods. [ABSTRACT FROM AUTHOR]