Dynamic Transitions of Generalized Burgers Equation

In this article, we study the dynamic transition for the one dimensional generalized Burgers equation with periodic boundary condition. The types of transition are dictated by the sign of an explicitly given parameter b, which is derived using the dynamic transition theory developed by Ma and Wang (Phase transition dynamics. Springer, New York, 2014). The rigorous result demonstrates clearly the types of dynamics transition in terms of length scale l, dispersive parameter δ and viscosity ν.     

Dynamical force and imaging characterization of superhydrophobic surfaces

We devised a dangling cantilever optical lever setup with imaging that permits dynamical studies of superhydrophobic surfaces without the effects of gravitational acceleration for better insight into the mechanics. The setup enabled us to ascertain liquid loss and ascribe it to the interaction of liquid that just touched the superhydrophobic surface as it translated at various constant lateral speeds. At lower speeds (20-60 μm/s), the interactions were characterized by a strong initial liquid pin (at up to 0.6 nN force) and depin followed by a series of smaller force pin and depins before sufficient liquid loss led to total liquid detachment from the surface. At higher translation speeds (80-100 μm/s), the interactions were characterized by liquid pinning and depinning processes at a sustained force (around 0.7 nN) in which liquid loss was low enough to engender a much later liquid detachment (beyond 100 s). A linear reduction of the receding contact angle with time, but not with the advancing contact angle, was found up to the point of first liquid depinning. This suggested a stronger role played by the receding contact line in establishing liquid adherence to the superhydrophobic surface. The detachment process from the surface was also characterized by a liquid bridge driven to rupture by way of liquid being conveyed away from the bridge.     

Simultaneous determination of inorganic cations by capillary ion chromatography with a non-suppressed contactless conductivity detector

A non-suppressed capillary ion chromatographic method with a laboratory-made packed cation-exchange column (100 mm × 0.32 mm i.d.) was developed for the separation and simultaneous determination of five common inorganic cations (sodium, ammonium, potassium, magnesium and calcium). Cation exchangers were prepared by the reaction of the hydroxyl group on the surface of diol-group bonded silica gel with 1,3-propanesultone in methanol. Simultaneous separation of these five common inorganic cations were achieved within 17 min using 1 mM methanesulfonic acid and 0.1 mM 15-crown-5 ether in methanol-water (8:2, v/v) as the eluent. The effects of organic solvents and crown ethers in the eluent on the retention of analytes were investigated. The limits of detection (S/N = 3) of the cations were in the range of 18-124 μg/l, the linear correlation coefficients were 0.9991-0.9998, and the RSD values of retention time and peak height were all smaller than 2.1%. The present analytical method was successfully applied to the rapid and direct determination of inorganic cations in samples of river water and commercial drinks, with satisfactory results.     

Integrated optical devices based on broadband epsilon-near-zero meta-atoms

We verify the feasibility of the proposed theoretical strategy for designing the broadband near-zero permittivity (ENZ) metamaterial at optical frequency range with numerical simulations. In addition, the designed broadband ENZ stack is used as meta-atoms to build functional nanophotonic devices with extraordinary properties, including an ultranarrow electromagnetic energy tunneling channel and an ENZ concave focusing lens.     

Polyoxyethylene as the stationary phase in ion chromatography

The present article reviews the use of polyethylene glycol (PEG) or polyoxyethylene (POE) as the stationary phase for the separation of inorganic anions in ion chromatography and discusses about the retention mechanisms involved in the separation of anions on the novel stationary phases. PEG permanently coated on a hydrophobic stationary phase retained anions in the partition mode and allowed us to use high-concentration eluents because the retention of anions increased with increasing eluent concentration for most of the eluents. This situation was convenient to determine trace anions contained in seawater samples without any disturbance due to matrices. Chemically bonded POE stationary phases retained not only anions but also cations. Anions were retained in the ion-exchange mode, although POE chains possess no ion exchange sites. The retention behavior suggested that eluent cations could be trapped among multiple POE chains via ion-dipole interaction, and that the trapped cations worked as the anion-exchange sites. Anions could be separated using crown ether, i.e., cyclic POE, as the eluent additive with a hydrophobic stationary phase, where analyte anions were retained via electrostatic interaction with the eluent cation trapped on the crown ether.     

povel isomers of hexasulfur: Prediction of a stable prism isomer and implications for the thermal reactivity of elemental sulfur

High-level ab initio molecular orbital calculations were employed to explore the potential energy hypersurface of hexasulfur, S(6). Twelve isomeric structures of S(6) have been identified: two unbranched rings (chair and boat), one trigonal prism of D(3h) symmetry, two singly branched rings (S(5)double bondS), three triplet chains, one singlet chain, and three doubly branched rings (Sdouble bondS(4)double bondS). The prism structure is essentially a cluster of three S(2) molecules connected via a six-center pi(*)-pi(*)-pi(*) interaction. It is by 51 kJ mol(-1) less stable than the lowest-energy chair form. The reactions to generate the boat, the prism, and the singly branched isomers from the chair form are predicted to have lower barriers than the ring opening reaction of cyclo-S(6), which requires an activation energy of 149 kJ mol(-1). The prism and singly branched isomers are found to be more reactive species than the chair form and they are potential sources of S(2) in chemical reactions involving elemental sulfur.     

Thermoanalytical studies of rubber oxidation catalyzed by metallic ions

The effects of several metallic ions on the oxidation of natural rubber were studied by differential scanning calorimetry (DSC). The activation energy of oxidation was evaluated from DSC curves. Cobalt, manganese, iron and copper ions decreased the activation energy of oxidation. Nickel, zinc and tin ions did not affect the activation energy. The effective ions are those which are able to undergo one-electron transfer redox reaction with hydroperoxide. Based on the activation energy values, the catalytic activities of metallic ions are: Co > Mn > Cu ? Fe > Ni ? Zn ? Sn.     

Regio- and enantioselective intermolecular rhodium-catalyzed [2+2+2] carbocyclization reactions of 1,6-enynes with methyl arylpropiolates

Transition metal-catalyzed [m+n+o] carbocyclization reactions provide powerful methods for the construction of complex polycyclic systems that are generally not accessible through classical pericyclic reactions. We have developed the first regio- and enantioselective crossed intermolecular rhodium-catalyzed [2+2+2] carbocyclization of carbon- and heteroatom-tethered 1,6-enynes with unsymmetrical 1,2-disubstituted alkynes. This study clearly delineates the ligand requirements for obtaining excellent regio- and enantioselectivity. Furthermore, the ability to utilize various electron-withdrawing groups, and to introduce quaternary carbon stereogenic centers, provides the level of versatility necessary for its application to target-directed synthesis. Additional studies on the development and application of this novel methodology to the total synthesis of natural products are currently underway.