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61.
K. M. Nowak T. Ohta T. Suganuma J. Fujimoto H. Mizoguchi A. Sumitani A. Endo 《Opto-Electronics Review》2013,21(4):345-354
It was shown both theoretically and experimentally that nanosecond order laser pulses at 10.6 micron wavelength were superior for driving the Sn plasma extreme ultraviolet (EUV) source for nano-lithography for the reasons of higher conversion efficiency, lower production of debris and higher average power levels obtainable in CO2 media without serious problems of beam distortions and nonlinear effects occurring in competing solid-state lasers at high intensities. The renewed interest in such pulse format, wavelength, repetition rates in excess of 50 kHz and average power levels in excess of 18 kiloWatt has sparked new opportunities for a matured multi-kiloWatt CO2 laser technology. The power demand of EUV source could be only satisfied by a Master-Oscillator-Power-Amplifier system configuration, leading to a development of a new type of hybrid pulsed CO2 laser employing a whole spectrum of CO2 technology, such as fast flow systems and diffusion-cooled planar waveguide lasers, and relatively recent quantum cascade lasers. In this paper we review briefly the history of relevant pulsed CO2 laser technology and the requirements for multi-kiloWatt CO2 laser, intended for the laser-produced plasma EUV source, and present our recent advances, such as novel solid-state seeded master oscillator and efficient multi-pass amplifiers built on planar waveguide CO2 lasers. 相似文献
62.
Abstract Ribozymes that distinguish a single base change in RNA were synthesized and used to specifically cleave c-Ha-ras messenger RNA. Using phosphorothioate containing oligonucleotide substrates, we have shown that Mg2+ binds to the pro-R oxygen of the phosphate and that the RNA cleavage reaction occurs via an in-line mechanism. Oligoribonucleotides containing a modified nucleoside are described. 相似文献
63.
Seiichi Ohta Susumu Inasawa Yukio Yamaguchi 《Journal of Polymer Science.Polymer Physics》2012,50(12):863-869
When a mixture of liquid crystal (LC) and photo reactive monomer is irradiated by UV light, polymerization occurs and LC droplets form through phase separation, producing polymer dispersed LCs (PDLCs). Although size control of LC droplets and reduced amounts of LC in PDLC films are important in applications, precise size control of LC droplets at a low LC fraction has not yet been accomplished. In this study, the phase diagrams of the LC/initial monomer and the LC/polymer during polymerization were used to control LC droplet size at various LC fractions. Both the relative position of the sample in the initial phase diagram and the shift of the phase separation line during polymerization were shown to be important in determining the size of LC droplets. Our results are expected to provide a new strategy for precise size control of LC droplets especially at a low LC fraction range, which would be a great help for PDLC applications. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012 相似文献
64.
Mechanistic Investigation of Catalyst‐Transfer Suzuki–Miyaura Condensation Polymerization of Thiophene–Pyridine Biaryl Monomers with the Aid of Model Reactions 下载免费PDF全文
Yu Tokita Masaru Katoh Dr. Yoshihiro Ohta Prof. Tsutomu Yokozawa 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(48):17436-17444
We have investigated the requirements for efficient Pd‐catalyzed Suzuki–Miyaura catalyst‐transfer condensation polymerization (Pd‐CTCP) reactions of 2‐alkoxypropyl‐6‐(5‐bromothiophen‐2‐yl)‐3‐(4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolan‐2‐yl)pyridine ( 12 ) as a donor–acceptor (D –A) biaryl monomer. As model reactions, we first carried out the Suzuki–Miyaura coupling reaction of X–Py–Th–X′ (Th=thiophene, Py=pyridine, X, X′=Br or I) 1 with phenylboronic acid ester 2 by using tBu3PPd0 as the catalyst. Monosubstitution with a phenyl group at Th‐I mainly took place in the reaction of Br–Py–Th–I ( 1 b ) with 2 , whereas disubstitution selectively occurred in the reaction of I–Py–Th–Br ( 1 c ) with 2 , indicating that the Pd catalyst is intramolecularly transferred from acceptor Py to donor Th. Therefore, we synthesized monomer 12 by introduction of a boronate moiety and bromine into Py and Th, respectively. However, examination of the relationship between monomer conversion and the Mn of the obtained polymer, as well as the matrix‐assisted laser desorption ionization time‐of‐flight (MALDI‐TOF) mass spectra, indicated that Suzuki–Miyaura coupling polymerization of 12 with (o‐tolyl)tBu3PPdBr initiator 13 proceeded in a step‐growth polymerization manner through intermolecular transfer of the Pd catalyst. To understand the discrepancy between the model reactions and polymerization reaction, Suzuki–Miyaura coupling reactions of 1 c with thiopheneboronic acid ester instead of 2 were carried out. This resulted in a decrease of the disubstitution product. Therefore, step‐growth polymerization appears to be due to intermolecular transfer of the Pd catalyst from Th after reductive elimination of the Th‐Pd‐Py complex formed by transmetalation of polymer Th–Br with (Pin)B–Py–Th–Br monomer 12 (Pin=pinacol). Catalysts with similar stabilization energies of metal–arene η2‐coordination for D and A monomers may be needed for CTCP reactions of biaryl D–A monomers. 相似文献
65.
Yoshihiro Ohta Makoto Karasawa Tetsurou Niiyama Akihiro Yokoyama Tsutomu Yokozawa 《Journal of polymer science. Part A, Polymer chemistry》2014,52(3):360-365
Well‐defined poly(3‐alkyl‐4‐benzamide) was synthesized by means of chain‐growth condensation polymerization of phenyl 3‐octyl‐4‐(4‐octyloxybenzyl(OOB)amino)benzoate ( 1c ) from initiator 2 , followed by removal of the OOB groups on amide nitrogen of poly 1c . Polymerization of 1c with phenyl 4‐(trifluoromethyl)benzoate ( 2b ) in the presence of 1,1,1,3,3,3‐hexamethyldisilazide (LiHMDS) and LiCl in THF at ?10 °C gave poly 1c with a narrow molecular weight distribution (Mw/Mn ≤ 1.08) and a well‐defined molecular weight (Mn = 4480–12,700) determined by the feed ratio of monomer to initiator (from 10 to 30). The OOB groups of poly 1c were removed with H2SO4 to give the corresponding N‐unsubstituted poly(p‐benzamide) (poly 1c′ ) with low polydispersity. The solublity of poly 1c′ in polar organic solvents was dramatically higher than that of poly(p‐benzamide), demonstrating that introduction of an alkyl group on the aromatic ring is very effective for improving the solubility of poly(p‐benzamide). © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 360–365 相似文献
66.
Yasuhito Tanaka 《Operations Research Letters》2019,47(5):406-409
We study a dynamic free-entry oligopoly with sluggish entry and exit of firms under general demand and cost functions. We show that the number of firms in a steady-state open-loop solution for a dynamic free-entry oligopoly is smaller than that at static equilibrium and that the number of firms in a steady-state memoryless closed-loop solution is larger than that in an open-loop solution. 相似文献
67.
68.
Abstract Oligomerization of butadiene with the catalyst system of nickel(II)chloride, electron donor, and lithium aluminum hydride or sodium borohydride has been studied. Most oligomers obtained with this catalyst were linear, and dihydrogenated dimers, trimers, and tetramers. They were n-octa-1,6-diene, n-octa-1,7-diene, n-dodeca-1,6,10-triene, and n-hexadeca-1,6,10,14-tetraene, which were identified by means of infrared, nuclear magnetic resonance, and mass spectrometry. Yields of each oligomer were strongly affected by the nature of the electron donors used. The hydrogen required for the formation of the hydrooligomers was assumed to originate from the lithium aluminum hydride or sodium borohydride used as a reducing agent. A proposed mechanism for the hydrooligomerization is that butadiene is oligomerized on the nickel atom, and the produced oligoolefins, bonded to the nickel by two terminal π-allylic bonds, are dihydrogenated to linear hydrooligomers. 相似文献
69.
Reductive dehalogenation of aryl halides was achieved using hydrogen and a palladium catalyst. By using deuterium gas, the deuterated arenes were readily prepared. 相似文献
70.
Kiyofumi Katagiri Keiko Ohta Kunihito Koumoto Kei Kurosu Yoshihiro Sasaki Kazunari Akiyoshi 《Colloid and polymer science》2013,291(6):1375-1380
Novel organic–inorganic hybrid nanoparticles consisting of polymer–hydrogel nanoparticles (nanogels) and iron oxide were developed for potential biomedical applications. Hybrid nanoparticles were prepared by a simple procedure using polysaccharide nanogels as a reactive site for iron oxide formation. The hybrid nanoparticles have a narrow size distribution with a diameter of approximately 30 nm and show high colloidal stability. These nanohybrid particles could be used as a contrast medium for magnetic resonance imaging or for magnetic hyperthermia therapy. 相似文献