Synthesis of nano-polycrystalline diamond from glassy carbon at pressures up to 25 GPa

ABSTRACT

Nano-polycrystalline diamond (NPD) with various grain sizes has been synthesized from glassy carbon at pressures 15–25?GPa and temperatures 1700–2300°C using multianvil apparatus. The minimum temperature for the synthesis of pure NPD, below which a small amount of compressed graphite was formed, significantly increased with pressure from ～1700°C at 15?GPa to ～1900°C at 25?GPa. The NPD having grain sizes less than ～50?nm was synthesized at temperatures below ～2000°C at 15?GPa and ～2300°C at 25?GPa, above which significant grain growth was observed. The grain size of NPD decreases with increasing pressure and decreasing temperature, and the pure NPD with grain sizes less than 10?nm is obtained in a limited temperature range around 1800–2000°C, depending on pressure. The pure NPD from glassy carbon is highly transparent and exhibits a granular nano-texture, whose grain size is tunable by selecting adequate pressure and temperature conditions.     

Organic–Inorganic Hybrid Gold Halide Perovskites: Structural Diversity through Cation Size

Crystal structures of a series of organic–inorganic hybrid gold iodide perovskites, formulated as A₂[Au^II₂][Au^IIII₄] [A=methylammonium (MA) ( 1 ) and formamidinium (FA) ( 2 )], A′₂[I₃]_1−x[Au^II₂]_x[Au^IIII₄] [A′=imidazolium (IMD) ( 3 ), guanidinium (GUA) ( 4 ), dimethylammonium (DMA) ( 5 ), pyridinium (PY) ( 6 ), and piperizinium (PIP) ( 7 )], systematically changed depending on the cation size. In addition, triiodide (I₃⁻) ions were partly incorporated into the AuI₂⁻ sites of 3 – 7 , whereas they were not incorporated into those of 1 and 2 . Such a difference comes from the size of the organic cation. Optical absorption spectra showed characteristic intervalence charge-transfer bands from Au^I to Au^III species, and the optical band gap increased as the size of the cation became larger.     

An ASE Reduction Filter Using Cascaded Optical Fiber Grating Couplers in EDFA Repeater

A new configuration for an ASE reduction filter in EDFA repeaters for WDM optical transmission systems using optical fiber grating couplers (FGCs) was proposed and first demonstrated. The filtering characteristics of the proposed filter for amplified single wavelength signal and 2-channel WDM signals using EDFA were identified. It was found that the filter was effective to improve SNR in optical domain by reducing ASE noise. The required FGC characteristics for the filter were theoretically predicted under the condition that the total filter loss did not exceed 3 dB. More than 70% of drop efficiency was required in each FGC for the application of the proposed filter to an 8-channel WDM system using EDFA repeaters.     

Alternating copolymerization of carbon dioxide and epoxide by manganese porphyrin: The first example of polycarbonate synthesis from 1-atm carbon dioxide

The first successful example of the formation of polycarbonate from 1-atm carbon dioxide and epoxide was demonstrated by the alternating copolymerization of carbon dioxide and epoxide with manganese porphyrin as a catalyst. The copolymerization of carbon dioxide and cyclohexene oxide with (porphinato)manganese acetate proceeded under the 1-atm pressure of carbon dioxide to give a copolymer with an alternating sequence. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3549–3555, 2003     

Size distribution of fractured areas in one-dimensional systems

We study a one-dimensional model for fracture, identifying fractured areas with intervals on which a stress field exceeds a threshold value. When is a diffusion process, the cumulative numberN(l) of fractured areas whose length is greater thanl obeys a power lawCl ^–p asl0 with probability one. The exponentp and the constantC are determined. The exponentp agrees with the Hausdorff dimension of the end points of fractured areas, i.e., ^–1(). Even if is self-similar with parameterH>0, i.e.,(cx)– is equivalent toc ^H {(x)–} for anyc>0, the exponentp does not depend solely onH;p=H, where(0, 1/H) is another parameter characterizing. Non-diffusion processes are given whereN(l) does not follow a power law.     

Photopolymerization of methyl methacrylate in the presence of tertiary amines

The sensitization effect of tertiary amines on the photopolymerization of methyl methacrylate was studied. N,N-Dimethylbenzylamine, triethylamine, and N,N-dimethylaniline increased the rate of polymerization in this order, but pyridine did not show any effect. A free-radical mechanism was confirmed by the tacticity of polymer, the retarding effect of hydroquinone, and the copolymer composition with styrene. On the basis of the detailed kinetics of the sensitized polymerization and the ultraviolet spectra of the reaction mixtures, a sensitization mechanism is proposed, in which the excited monomer and the amine form a complex and generate an initiating radical.     

Alternative copolymerization of aziridines and carbon monoxide by γ-ray irradiation

The copolymerization of carbon monoxide and aziridines such as ethylenimine and propylenimine was carried out by γ-ray irradiation. Aziridines and carbon monoxide were allowed to copolymerize under γ-ray irradiation from a Co⁶⁰ source and gave a crystalline solid copolymer. The yield of the copolymer increased with reaction temperature. The composition of copolymers obtained did not depend on the feed ratio of monomers and was found to be almost equimolar. The copolymer of ethylenimine and carbon monoxide melted at about 322–335°C. with decomposition and has an infrared spectrum identical with that of poly-β-alanine obtained by the hydrogen-migration polymerization of acrylamide. The hydrolyzed product of the ethylenimine–carbon monoxide copolymer was confirmed to be β-alanine by paper chromatography. These results lead to the conclusion that the copolymerization of aziridines and carbon monoxide took place alternatively by γ-ray irradiation, and produced crystalline poly-β-alanines.     

Hybrid Ia antigens: genetic, serologic, and biochemical analyses

Ia specificities 22 and 23 were found to be determinants on hybrid Ia molecules, formed by the noncovalent binding of a 26,000--28,000 dalton beta polypeptide chain (Ae) coded by the I-A subregion and a 32,000--35,000 dalton alpha chain (E alpha) coded by the I-E subregion. For expression of Ia.23 the Ae chain, coded by the I-A subregion, must be derived from the H-2d haplotype, while Ab, As, or Ak can provide the complementing beta chain for the expression of Ia.22. For expression of Ia.22 and Ia.23, most Ia.7 positive strains can provide the complementing alpha chain (E alpha), with the one exception of B10.PL (Eu), which is Ia.7 positive but will not complement with Ad to express Ia.23. Antisera were also produced against hybrid Ia antigens by immunizing with F1 cells expressing Ia.22 or Ia.23 generated by generated by trans-complementation. These antisera detect the same specificities as conventional anti-Ia.22 and anti-Ia.23 sera produced against cis-complementing Ia antigens. It is postulated that hybrid Ia determinants are involved in recognition and generation of immune response to antigens under dual Ir gene control. It is also suggested that there are 2 types of Ia specificities: 1) allotypic Ia specificities expressed on the alpha or beta chains (for example, Ia.7 on the E alpha chain) and 2) hybrid Ia specificities, which are unique interaction determinants formed by the association of alpha and beta chains (for example, Ia.22 and Ia.23). These interaction gene products may be involved in antigen recognition and presentation.