1,721,531 research outputs found
Interrelationship of apoptosis, mutation, and cell proliferation in N-methyl-N '-nitro-N-nitrosoguanidine (MNNG)-induced medaka carcinogenesis model
No full textThe present study examined the interrelationship of GSH depletion, apoptosis, mutation. and cell proliferation following carcinogen exposure. Medaka (Oryzias latipes) were investigated following a 28 day, three times/week pulse exposure to N-methyl-N'-nitro-N'-nitrosoguanidine (MNNG). Fish (5 weeks old) were exposed to MNNG at concentrations of 0, 0.5, and 1 mg l(-1) and reared for 3, 5 and 7 more months after the last day of exposure. GSH levels were decreased in the higher concentration groups and longer-reared groups. Flow cytometric analysis revealed that fish from the groups reared 3 and 5 months showed active apoptotic changes in the dose- and time-dependent manner, but the group reared 7 months had fewer apoptotic, rather showed more necrotic and carcinogenic alterations. Mutational responses were detected by an arbitrarily primed polymerase chain reaction (AP-PCR) fingerprinting method using whole body DNA samples as templates and pBR primer. A mutational change was expressed by a loss or gain of a band. There was a time-dependent mutational change. but no distinctive concentration-dependent one. A band from normal fish sample that disappeared after treatment of MNNG was excised and sequenced. The band had an 869 base pair-long sequence, however, there was no putative protein-coding region based on an analysis by DNAsis. Spindle cell sarcomas invading muscle were detected on the whole body sections from three of ten fish examined, and immunohistochemical analysis with PCNA showed that tumor cells were actively proliferating. However, terminal deoxynucleotidyl transferase (TdT) assay showed that tumored fish still had active apoptotic cell changes in the tissues without tumor. This study shows not only the interrelationship of GSH depletion, apoptosis, mutation and cell proliferation, but also indicates that medaka is appropriate as a fish model for research on the passage of carcinogenesis, (C) 2000 Elsevier Science B.V. All rights reserved.N
Biphenylene-bridged dinuclear group 4 metal complexes: Enhanced polymerization properties in olefin polymerization
No full textThe well-defined, novel dinuclear group 4 metal complexes [4,4'-(C6H4)(2)(C5Me4)(2)][CpZrX2](2) (X = Cl (2a), Me (2b)), [4,4'-(C6H4)(2)(C5Me4)(2)][TiCl3](2) (3), and [4,4'-(C6H4)(2)(C5Me4)(2)][Ti(O-2,6-(Pr2Ph)-Pr-i)Cl-2](2) (4) exhibit an increase of molecular weight as well as comparable or even higher catalytic activity in ethylene (2 and 4) and styrene (3 and 4) polymerization than their mononuclear counterparts.Financial support from the Korea
Science and Engineering Foundation (Grant No.
R02-2002-000-00057-0), the CMDS, and the BK 21
project are gratefully acknowledged
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Novel synthetic strategy for developing an isospeciric unbridged metallocene system for propylene polymerization
No full textNew unbridged zirconocenes functionalized with a Lewis base, [{1(E-C6H4)-3,4-Me(2)C(5)H2}(2)ZrCl2] (E = pNMe(2) (3); p-OMe (4); p-SMe (5)) were prepared and their propylene polymerization behavior was examined. Under methylaluminoxane (MAO) activation at atmospheric monomer pressure, these complexes afford mixtures of polymers exhibiting multimelting transition temperatures and broad molecular weight distribution, whereas they produce completely atactic polypropylenes under [Ph3C][B(C6F5)(4)] activation. Stepwise solvent extraction of the polymer mixtures reveals that the polymers consist of amorphous, moderately isotactic, as well as, highly isotactic portions and the weight ratio of each portion is dependent upon reaction temperature. The generation of rigid rac-like cationic active species in situ by the interaction between basic sites of catalysts and acidic sites of the [Me-MAO](-) counter anion is considered to be the origin of the observed isospecificity. Further investigation of bulk polymerization in liquid propylene shows not only a considerable increase of the isotactic portion of the obtained polypropylenes but also apparent isospecificity of 4 and 5/MAO systems even at high temperature. Variation of the Lewis basic center leads to a dramatic change in stereoselectivity of the catalyst in the decreasing order of 3 > 4 >> 5, in spite of their structural similarity.CMDSACHTUNGTRENUNG(KOSEF), POMRC, and the BK-21 projec
Endowing aspecific, unbridged-metallocene propylene-polymerization catalysts with isospecificity: The unprecedented role of MAO
No full textCMDS
POMRC
BK-21 project
Honam Petrochemical C
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