Epitaxial growth of boron-doped graphene by thermal decomposition of B4C

We grew graphene by thermal decomposition of B(4)C and investigated its features by high-resolution transmission electron microscope observations. At temperatures higher than 1600 °C in a vacuum, B(4)C decomposes and graphene forms epitaxially on its surface. The number and the morphology of the graphene layers depend on the surface orientation. An electron diffraction technique revealed the presence of a superstructure with a two-times larger unit cell, which is consistent with the structure of BC(3). We have directly confirmed boron in the graphene layers by electron energy loss spectroscopy measurements and boron-mapping experiments.     

cis-Tetrahydrofuran-3,4-diol structure as a key skeleton of new protecting groups removable by self-cyclization under oxidative conditions

A variety of carbonate-type acyl groups having a cis-tetrahydrofuran-3,4-diol (1,4-anhydroerythritol) backbone structure and a TrS or MMTrS group have been examined as new "protected" protecting groups of the 5'-hydroxyl group of nucleosides. These acyl groups were designed in a manner where they could be deprotected by I(2)-promoted removal of the TrS or MMTrS group followed by self-cyclization involving an intramolecular attack of the once-generated neighboring hydroxyl group on the acyl carbon. It turned out that these acyl groups could be introduced into the 5'-hydroxyl group of a 3'-O-protected thymidine derivative by use of the corresponding acyl imidazolides or 4-nitrophenyl esters as well as by reaction with carbonyldiimidazole or 4-nitrophenyl chloroformate. Among the acyl groups tested, it was found that the CTFOC group could be easily introduced into the 5'-hydroxyl group of 3'-masked deoxyribonucleoside derivatives and rapidly removed under mild conditions using iodine.     

Microscopic Fourier Transform Infrared Characterization on Two Types of Spherulite with Polymorphic Crystals in Poly(heptamethylene terephthalate)

FTIR microspectrometry with in situ temperature variation and IR‐peak‐mapping capability, and POM characterization were used to study the crystal distribution in dual spherulites in poly(heptamethylene terephthalate). By tracing the crystalline IR bands of the α‐crystal and β‐crystal to get the crystal distribution, the techniques resolve that the ringed and ringless spherulites comprise α‐ and β‐crystals, respectively. In addition, temperature‐dependent IR analyses on the spots related to the two crystals also reveal the α‐ and β‐crystals melt at 98 and 104 °C, respectively. The ringed and ringless spherulites were proven to be correlated with the α‐ and β‐crystal forms, respectively.

     

Time‐resolved wide‐angle X‐ray scattering measurements during the isothermal crystallization and ferroelectric phase‐transition processes of a vinylidene fluoride/trifluoroethylene copolymer

The time‐resolved measurement of wide‐angle X‐ray scattering was performed with a synchrotron radiation source during the processes of the isothermal crystallization and ferroelectric phase transition of a vinylidene fluoride/trifluoroethylene copolymer with 73 mol % vinylidene fluoride. When the sample was cooled rapidly from the melt to the temperature region of the paraelectric high‐temperature phase, the peak position of the 200/110 reflection shifted toward the higher angle side and the half‐width became narrower. This indicated an increase in the crystallite size with a more compact chain‐packing mode. Even when the temperature jump was made from the melt into the region of the ferroelectric or low‐temperature phase, the crystallization of the high‐temperature phase was first observed before the appearance of the low‐temperature phase. This was consistent with a prediction based on the so‐called Ostwald state rule: the thermodynamically unstable but kinetically preferable high‐temperature phase can appear first even when the thermodynamically more stable low‐temperature phase should be created. The time‐dependent intensity changes were analyzed with the Avrami kinetic equation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4175–4181, 2004     

The mixed joint universality for a class of zeta‐functions

A mixed joint limit theorem in the space of holomorphic functions, and a mixed joint universality theorem are proved for a rather general class of Euler products and periodic Hurwitz zeta‐functions.     

Behavior of polymer chains grafted from latex particles at soft interfaces

We have studied the behaviors of a poly(methyl methacrylate) (PMMA) chains anchored to polystyrene particles at air/water and oil/water interfaces to recognize the roles of oil molecules in the PMMA property at the interfaces. Through the comparison of π-A isotherms we found two aspects of unique structural and rheological characteristics observed in PMMA-grafted polystyrene latex (PSL-PMMA) monolayer system in common. (1) The π-A isotherms showed surface pressure increase at larger occupied area compared to the PSL-PMMA size in solution at three different types of interfaces in most cases. (2) Compressional modulus, C _s ^?1, obtained by π-A isotherm analysis for PSL-PMMA at interfaces, showed the tendency to decrease with molecular weight of PMMA. This is opposite to that of PMMA homopolymer at interfaces. The effect of oil molecules on PSL-PMMA system at interfaces are found both in the difference of occupied area and C _s ^?1. The occupied areas were larger for the isotherms at the oil/water interfaces than those at the air/water interface in most cases, which suggested the reduced attractive interactions between anchored polymers by oil molecules. On the other hand, C _s ^?1 of PMMA monolayers is strongly dependent on the constituents of the interface and the order of C _s ^?1 is air/water?>?decane/water?>?dibutyl ether/water interfaces. The difference between oil species was not explained only by PMMA/oil interaction in bulk, but we suggested that interfacial tension of oil/water interface affects the miscibility of oil molecules with PMMA to cause higher miscibility between PMMA and dibutyl ether at the oil/water interfaces.     

Rate Constant for Long-Chain Branch Formation in Free-Radical Polymerization of Ethylene

Quantitative measurements on the rate constant for long-chain branching in radical polymerization of ethylene have not yet been cited. This paper presents a convenient method of calculating the ratio of the rate constant for long-chain branching to that for propagation, by means of polymerization parameters, average degrees of polymerization (X_n and X_w), and amount of total unsaturation. The results of calculation based on our experimental data show that the activation energy E_trp -E_p, and the activation volume ΔV ^trp _?-ΔV ?_p were 3.6 kcal/mole and 24 cc/mole, respectively, in radical polymerization of ethylene. The validity of these values is discussed.     

Microwave-optical interactions

Optical and Quantum Electronics -