Atomically resolved images of I(h) ice single crystals in the solid phase

The morphology and crystal structure of nanoparticles of ice were examined by high-resolution transmission electron microscopy. Two different crystal structures were found and unambiguously assigned to hexagonal (I(h)) and cubic (I(c)) ice crystals. Direct observation of oxygen columns clearly revealed the hexagonal packing of water molecules. Electron energy-loss spectroscopy was used to monitor the electronic excitation in ice, suggesting possible dissociation of water molecules. Dynamic process of phase transition between I(h) and I(c) phases of individual ice nanoparticles under electron beam irradiation was also monitored by in situ transmission electron diffractometry.     

Cyclic Voltammetry Study of the Mn‐Substituted Polyoxoanions [MnII4(H2O)2(H4AsW15O56)2]18− and [((MnIIOH2)MnII2PW9O34)2(PW6O26)]17−: Electrodeposition of Manganese Oxides Electrocatalysts for Dioxygen Reduction

The electrochemical behavior of two manganese (Mn)‐substituted polyoxoanions, the dissymmetrical Dawson sandwich‐type [Mn^II₄(H₂O)₂(H₄AsW₁₅O₅₆)₂]^18? and the Keggin sandwich banana‐shaped [((Mn^IIOH₂)Mn^II₂PW₉O₃₄)₂(PW₆O₂₆)]^17? is investigated. At pH 5, the oxidation of the Mn^II‐centers results in one oxidation wave for [Mn^II₄(H₂O)₂(H₄AsW₁₅O₅₆)₂]^18? and two oxidation waves for [((Mn^IIOH₂)Mn^II₂PW₉O₃₄)₂(PW₆O₂₆)]^17?. To the best of our knowledge, presence of the second Mn‐based wave is rarely observed in the electrochemistry of Mn‐containing polyoxometalates. Deposition of Mn‐oxides electrocatalysts for dioxygen reduction is noticed by cyclic voltammetry, which can be distinguished by the significant positive shift in potentials of the dioxygen reduction reaction.     

Surface X-ray scattering of stepped surfaces of platinum in an electrochemical environment: Pt(331) = 3(111)-(111) and Pt(511) = 3(100)-(111)

Real surface structures of the high-index planes of Pt with three atomic rows of terraces (Pt(331) = 3(111)-(111) and Pt(511) = 3(100)-(111)) have been determined in 0.1 M HClO(4) at 0.1 and 0.5 V(RHE) with the use of surface X-ray scattering (SXS). The surfaces with two atomic rows of terraces, Pt(110) = 2(111)-(111) and Pt(311) = 2(100)-(111) = 2(111)-(100), are reconstructed to a (1 × 2) structure according to previous studies. However, the surfaces with three atomic rows of terraces have pseudo-(1 × 1) structures. The interlayer spacing between the first and the second layers, d(12), is expanded 13% on Pt(331) compared to that of the bulk, whereas it is contracted 37% on Pt(511). The surface structures do not depend on the applied potential on either surface.     

Theoretical studies on [2 + 2 + 2] reaction mechanisms of three ethynes. More accurate estimation of activation energy

The mechanisms of the [2 + 2 + 2] cycloaddition reaction of three ethyne molecules were studied by ab initio molecular orbital and density functional methods. The transition states range from that of the concerted mechanism with D_3h symmetry to that of the stepwise mechanism with C₂ symmetry. The transition state structure and the activation energy depend on the basis set and computational method employed in the analysis. The activation energy barrier was determined to be in the range of 36–44 kcal/mol. The activation energy determined by various methods corresponds to the interaction energy, which is related to the electron correlation energy. The best estimation of the activation energy barrier is 41.6 kcal/mol, achieved from the relation between the interaction energy and the activation energy. Copyright © 2013 John Wiley & Sons, Ltd.     

Ignition in a supersonic flow by a plasma jet of mixed feedstock including CH4

Ignition tests of hydrocarbon fuels in a supersonic airflow by plasma jet (PJ) torches of mixed feedstock, including methane (CH₄), such as N₂/CH₄ and N₂/CH₄/O₂ mixtures, were conducted. The Mach number of the airflow was 2.0, and the total temperature and total pressure of the main flow were those of room conditions. The wall pressure increase due to combustion of hydrocarbon fuels for the N₂/CH₄ PJ exceeded those of pure O₂ and N₂ PJs at high electric power input. Equilibrium calculations showed that the main species in high-temperature PJ, aside from N₂, were H₂, H, and HCN. Considering the slight impact of the HCN species on ignition delay time, the combustion enhancement by the N₂/CH₄ PJ was caused primarily by the existence of a large amount of H and H₂ dissociated from CH₄ molecules in the PJ. Moreover, the addition of O₂ to the N₂/CH₄ feedstock further enhanced the combustion and stability of the N₂/CH₄ PJ. The existence of O₂ increased the temperature and the number of H radicals in the PJ exhaust.     

Efficient identity-based encryption with Hierarchical key-insulation from HIBE

Hierarchical key-insulated identity-based encryption (HKIBE) is identity-based encryption (IBE) that allows users to update their secret keys to achieve (hierarchical) key-exposure resilience, which is an important notion in practice. However, existing HKIBE constructions have limitations in efficiency: sizes of ciphertexts and secret keys depend on the hierarchical depth. In this paper, we first triumph over the barrier by proposing simple but effective design methodologies to construct efficient HKIBE schemes. First, we show a generic construction from any hierarchical IBE (HIBE) scheme that satisfies a special requirement, called MSK evaluatability introduced by Emura et al. (Des. Codes Cryptography 89(7):1535–1574, 2021). It provides several new and efficient instantiations since most pairing-based HIBE schemes satisfy the requirement. It is worth noting that it preserves all parameters’ sizes of the underlying HIBE scheme, and hence we obtain several efficient HKIBE schemes under the k-linear assumption in the standard model. Since MSK evaluatability is dedicated to pairing-based HIBE schemes, the first construction restricts pairing-based instantiations. To realize efficient instantiation from various assumptions, we next propose a generic construction of an HKIBE scheme from any plain HIBE scheme. It is based on Hanaoka et al.’s HKIBE scheme (Asiacrypt 2005), and does not need any special properties. Therefore, we obtain new efficient instantiations from various assumptions other than pairing-oriented ones. Though the sizes of secret keys and ciphertexts are larger than those of the first construction, it is more efficient than Hanaoka et al.’s scheme in the sense of the sizes of master public/secret keys.

     

Synthesis of syndiotactic‐rich star‐shaped poly(methyl methacrylate) by core‐first group transfer polymerization using N‐(trimethylsilyl)bis(trifluoromethanesulfonyl)imide

The N‐(trimethylsilyl)bis(trifluoromethanesulfonyl)imide‐catalyzed (Me₃SiNTf₂‐catalyzed) group transfer polymerization (GTP) of methyl methacrylate (MMA) has been studied for synthesizing stereospecific star‐shaped poly(methyl methacrylate)s (PMMAs). The catalytic property of Me₃SiNTf₂ for the GTP of MMA using 1‐methoxy‐1‐trimethylsilyloxy‐2‐methyl‐propene as the initiator was confirmed by a kinetic investigation and matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry measurement. The initiating efficiency (f) of Me₃SiNTf₂ was 0.94–1.00, which was estimated by the value of M_n(calcd)/M_n(SEC). The Me₃SiNTf₂‐catalyzed GTP of MMA was carried out using initiators possessing three, four, and six MTS groups (MTS₃, MTS₄, and MTS₆, respectively) under the condition of [MMA]₀/[MTS₃, MTS₄, or MTS₆]₀ = 120 at ?55 °C. All the obtained PMMAs exhibited unimodal and narrow molecular weight distributions as M_w/M_ns = 1.03–1.04 and the M_w(MALS)s of the 3‐, 4‐, and 6‐armed star‐shaped PMMAs (PMMA₃, PMMA₄, and PMMA₆, respectively) were 12.9, 12.9, and 13.4 kgmol^?1, respectively, which fairly agreed with the calculated M_w(calcd) values. The syndiotacticities, rrs, of PMMA₃, PMMA₄, and PMMA₆ were in the range of 87–89%. The stereoblock synthesis of PMMA₃, PMMA₄, and PMMA₆ was performed by the first and second polymerizations at ?55 and 45 °C; the rrs of the first and second PMMA blocks were 87.0, 87.0, and 86.0% and 65.0, 65.0, and 64.0%, respectively. The glass transition temperatures (T_gs) were 118.1, 115.8, and 111.5 °C for the respective syndiotactic‐rich PMMA₃, PMMA₄, and PMMA₆ and 111.5, 109.7, and 107.6 °C for the respective stereoblock ones. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Statistical theory applied to a vortex street generated from meander of a jet

Statistic features of a vortex street formed by instability of a jet are investigated by numerical calculation and statistic theory. A formation process of a vortex street is numerically calculated using a simple barotropic quasi-geostrophic system: a jet in the initial state begins to meander owing to its instability and vortices are formed in both flanks of the jet and become a steady vortex street. Statistic theory of vorticity mixing for two-dimensional fluid, which describes the statistically steady equilibrium state based on the maximum entropy assumption, is applied to the numerically obtained features of the steady vortex street. The theoretically derived relation between stream function and potential vorticity explains the results in the numerical calculation very well. However, in the numerical calculation, there remain regions where the fluid is not mixed well. By calculating mixing process of another scalar, the unmixed region is clearly shown on the physical plane.