Centroid molecular dynamics approach to the transport properties of liquid para-hydrogen over the wide temperature range

Fundamental transport properties of liquid para-hydrogen (p-H(2)), i.e., diffusion coefficients, thermal conductivity, shear viscosity, and bulk viscosity, have been evaluated by means of the path integral centroid molecular dynamics (CMD) calculations. These transport properties have been obtained over the wide temperature range, 14-32 K. Calculated values of the diffusion coefficients and the shear viscosity are in good agreement with the experimental values at all the investigated temperatures. Although a relatively large deviation is found for the thermal conductivity, the calculated values are less than three times the amount of the experimental values at any temperature. On the other hand, the classical molecular dynamics has led all the transport properties to much larger deviation. For the bulk viscosity of liquid p-H(2), which was never known from experiments, the present CMD has given a clear temperature dependence. In addition, from the comparison based on the principle of corresponding states, it has been shown that the marked deviation of the transport properties of liquid p-H(2) from the feature which is expected from the molecular parameters is due to the quantum effect.     

Comparison of DNA hydration patterns obtained using two distinct computational methods, molecular dynamics simulation and three-dimensional reference interaction site model theory

Because proteins and DNA interact with each other and with various small molecules in the presence of water molecules, we cannot ignore their hydration when discussing their structural and energetic properties. Although high-resolution crystal structure analyses have given us a view of tightly bound water molecules on their surface, the structural data are still insufficient to capture the detailed configurations of water molecules around the surface of these biomolecules. Thanks to the invention of various computational algorithms, computer simulations can now provide an atomic view of hydration. Here, we describe the apparent patterns of DNA hydration calculated by using two different computational methods: Molecular dynamics (MD) simulation and three-dimensional reference interaction site model (3D-RISM) theory. Both methods are promising for obtaining hydration properties, but until now there have been no thorough comparisons of the calculated three-dimensional distributions of hydrating water. This rigorous comparison showed that MD and 3D-RISM provide essentially similar hydration patterns when there is sufficient sampling time for MD and a sufficient number of conformations to describe molecular flexibility for 3D-RISM. This suggests that these two computational methods can be used to complement one another when evaluating the reliability of the calculated hydration patterns.     

A radiochemical study on the existence of dineutron

A radiochemical study has been made to search for dineutron² n produced in the simultaneous two-neutron emission of the excited⁶He nuclei,⁶He^*, induced in the reaction of⁹Be+n→-⁶He^*+α with fast neutrons in a reactor. It was attempted to detect the radio-activity of²⁸Mg as a product of the reaction² n+²⁷Al→²⁸Mg+p. The²⁸Mg radioactivity observed in heterogeneous samples composed of the² n-producing target Be and the² n-detecting target Al separately was not found to be more than that of a side reaction,²⁷Al{(n, p)(n _th, γ)+(n _th, γ)(n, p)}²⁸Mg, whereas it clearly exceeded that of the side reaction in alloy samples made of Be and Al metals. The former experiment gives an upper limit of the production rate of the dineutron in the bound state 1×10^?7 per event of the simultaneous two-neutron emission. A tentative explanation for the excessive²⁸Mg radioactivity observed in the latter experiment is the following two-step process,⁹Be+n→⁶He+α and²⁷Al+⁶He→+²⁸Mg+α+p, rather than the process induced by the dineutron in a virtual state.     

Synthesis of a C3-symmetric tris-imine via dynamic covalent bond formation between a trialdehyde and a triamine

Dynamic covalent chemistry is an effective technique for the preparation of complex organic compounds. We succeeded in synthesizing a cage-shaped compound through the aggregation of two types of functional molecules. More specifically, a tris-imine 5 was quantitatively obtained by reacting a C₃-symmetric trialdehyde 1 with a triamine 4 in acetonitrile in the presence of a trifluoroacetic acid catalyst. We also achieved the synthesis of the corresponding triamine 9 and the acetylated derivative 10 through reduction of the tris-imine CN double bonds and subsequent acetylation.     

Ferromagnetism Induced by Substitution of the Iron(IV) Ion by an Unusual High‐Valence Nickel(IV) Ion in Antiferromagnetic SrFeO3

Novel cubic perovskites SrFe_1?xNi_xO₃ (0≤x≤0.5) with unusual high‐valence iron(IV) and nickel(IV) ions were obtained by high‐pressure and high‐temperature synthesis. Substantial magnetic moments of Ni^IV, which is intrinsically nonmagnetic with a nominal d⁶ electron configuration, were induced by the large magnetic moments of Fe^IV through orbital hybridization with oxygen. As a result, ferromagnetism with the transition temperature (T_c) above room temperature could be induced.     

High-resolution photoemission study of FeSr2YCu2O7+δ

We have performed high-resolution photoemission spectroscopy (PES) on FeSr₂YCu₂O_7+δ, of which superconductivity of T_c=49 K was recently reported. We clearly observed opening of a d-wave-like superconducting gap and estimated the maximum gap value (Δ_max) to be 10 meV at 15 K. This gap value gives 2Δ_max/k_BT_c∼5, suggesting a strong-coupling nature of superconductivity in FeSr₂YCu₂O_7+δ. Comparative PES study with superconducting and insulating samples shows that the valence band is rigidly shifted as a function of doping without evolution of additional states within the insulating gap.     

Synthesis and electrode performance of carbon coated Na2FePO4F for rechargeable Na batteries

Carbon-coated Na₂FePO₄F is synthesized by a simple solid-state method with ascorbic acid as carbon source. Structural characterization of Na₂FePO₄F by synchrotron X-ray diffraction, scanning/transmission electron microscopy, and Raman spectroscopy reveals that ascorbic acid effectively suppresses the particle growth of Na₂FePO₄F, forming the nano-sized carbon coated materials. Electrode performance of Na₂FePO₄F for rechargeable sodium batteries is also examined. The carbon-coated Na₂FePO₄F sample (1.3 wt% carbon) delivers initial discharge capacity of 110 mAh g^-1 at a rate of 1/20 C (6.2 mA g^-1) with well-defined voltage plateaus at 3.06 and 2.91 V vs. Na metal. The sample also shows acceptable capacity retention and rate capability as the positive electrode materials for rechargeable Na batteries, which is operable at room temperature.     

Explicit Solution to a Certain Non-ELQG Risk-sensitive Stochastic Control Problem

A risk-sensitive stochastic control problem with finite/infinite horizon is studied with a 1-dimensional controlled process defined by a linear SDE with a linear control-term in the drift. In the criterion function, a non-linear/quadratic term is introduced by using the solution to a Riccati differential equation, and hence, the problem is not ELQG (Exponential Linear Quadratic Gaussian) in general. For the problem, optimal value and control are calculated in explicit forms and the set of admissible risk-sensitive parameters is given in a concrete form. As applications, two types of large deviations control problems, i.e., maximizing an upside large deviations probability and minimizing a downside large deviations probability, are mentioned.