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Bayer, Arnold S.,Mishra, Nagendra N.,Cheung, Ambrose L.,Rubio, Aileen,Yang, Soo-Jin Oxford University Press 2016 The Journal of antimicrobial chemotherapy Vol.71 No.8
<P>In small series or individual reports, SNPs within the mprF ORF and dysregulation of its expression in Staphylococcus aureus have been linked to daptomycin resistance (DAP-R) via a proposed gain-in-function mechanism. Similarly, dysregulation of dltABCD has also been associated with DAP-R. Using 22 well-characterized, isogenic daptomycin-susceptible (DAP-S)/DAP-R clinical MRSA strain pairs, we assessed potential relationships of the DAP-R phenotype with: (i) regulation of mprF transcription; (ii) regulation of dltABCD transcription; (iii) expression of the two-component regulatory system, graRS (upstream regulator for both mprF and dltABCD transcription); (iv) SNPs within the graRS promoter or its ORF; and (v) altered mprF transcription and lysyl-phosphatidylglycerol (L-PG) synthesis. Enhanced expression of mprF occurred with SNPs in highly distinct and well-chronicled MprF domain 'hot spots' and rarely occurred without such mutations. Increased expression and/or dysregulation of mprF and dltABCD were not uncommon in DAP-R strains, occurring in 27% of strains for each gene. In these latter strains, neither graRS expression profiles nor polymorphic sequences within the graRS promoter or ORF could be significantly linked to altered transcription of mprF or dlt. Although graRS can co-regulate mprF and dltABCD expression, loci outside of this regulon appear to be involved in dysregulation of these latter two genes and the DAP-R phenotype. Finally, DAP-R strains exhibiting significantly altered mprF transcription profiles produced significantly increased levels of L-PG.</P>
North Korea`s Nuclear Option: Observations and Reflections on the Recent NPT Crisis
( James Bayer ),( Robert E Bedeski ) 한국국방연구원 1993 The Korean Journal of Defense Analysis Vol.5 No.2
In March 1993 the North Korean government announced its intention to withdraw from the Nuclear Nonproliferation Treaty. Pyongyang`s motives have been the subject of much speculation, but could be explained by one of four possible interpretations. The "conspiracy thesis" argues that the North Koreans decided to withdraw from the NPT when International Atomic Energy Agency (IAEA) inspections threatened to expose their clandestine program of nuclear weapons development. The "frustration" theory says that the decision was in direct retaliation for international community`s failure to give the economic and political rewards promised North Korea when it agreed to give up its nuclear weapons option and accept IAEA inspec- tions of its nuclear facilities. The "Israeli approach" is predicated on the assumption that North`s withdrawal from the NPT is intended to prevent the international community from discovering that Pyongyang was not developing nuclear weapons, or alternatively, that they had encountered technical setbacks in their nuclear research and development program. Finally is the "embarrassment" interpretation, speculating that Pyongyang inadvertently provided the IAEA with incorrect data on its plutonium holdings and now wishes to avoid the dishonor and humili- ation of being publicly found out. If Pyongyang is absolutely intent on building nuclear weapons, the issue is unlikely to be resolved satisfactorily irrespective of what the international community offers in return. If, as seems more likely, the North Koreans are using the nuclear weapons issue in a last ditch attempt to achieve nonnuclear objectives, the issue will likely be resolved to everyone`s mutual satisfaction but only after long and difficult negotiations. The objective of the international community during these objectives ``must be: to ensure that North Korea remains a member of the NPT, to convince North Korea to open suspect nuclear waste sites to IAEA inspections, and to have North Korea satisfactorily explain the apparent inconsistencies between its declared plutonium holdings to the IAEA and the IAEA findings on the matter. In return the international community will have to satisfy legitimate concerns and expectations raised in Pyongyang. There is much to be gained and little to be lost from such a conciliatory approach at this time.
Microstructural characterization of mullite and anorthitebased Porcelain tile using regional clay
Zahide Bayer Ozturk 한양대학교 세라믹연구소 2016 Journal of Ceramic Processing Research Vol.17 No.6
The study focused on using of regional clay (Nevsehir/Turkey) instead of different clay and kaolin to prepare porcelain tilesalong with dolomite and albite. Considering the variation of regional clay with other clay and kaolin the physical properties,phase-microstructure analysis and the determination of sintering temperatures by means of optical dilatometer of sampleswere studied. Uni-axially pressed samples were exposed to firing regime at 1205 oC for 42 min and tested to comply with ISO10545 tile standards. The crystal phases were detected as quartz, anorthite and mullite. The mechanical strength was foundto increase as the mullite content. When the Nevsehir’s clay content in the starting composition added, glassy matrix becamericher in kaolinite glass and earth-alkaline oxide favorably affected the sintering temperatures. Almost all technologicalproperties and sintering behavior of new compositions demonstrated the suitability of Nevsehir clay as a potential raw materialfor ceramic tile industry. This regional clay is affect to microstructure and crystalline phases of tile bodies.
An investigation of the effect of alkaline oxides on porcelain tiles using factorial design
Zahide Bayer Ozturk 한양대학교 세라믹연구소 2012 Journal of Ceramic Processing Research Vol.13 No.5
In this study, the effect of alkaline oxides (MgO, CaO, Na2O and K2O) was investigated in porcelain tile compositions. Talc (MgO) and dolomitic clay (CaO, MgO) were added to porcelain tile compositions instead of feldspar (Na2O, K2O). In the experiments 21 × 32 mixed-level factorial design was used, the individual effects of three main factors and their interactions were determined. The effect of the amount of talc (0, 2, 4 wt. %), dolomitic clay (0, 2, 4 wt. %) and firing conditions (1, 2) on porcelain tile properties were examined. Firing shrinkage, water absorption and the strength of samples were studied by means of factorial design. The porosity and bulk density of samples, color measurement and SEM analyses of these samples were also investigated. It was found that the strength increased and water absorption decreased by means of alkaline oxides variation in the porcelain tile body. According to factorial design, it has been found that the amount of dolomitic clay and talc are the main factors affecting the strength, firing shrinkage and water absorption values. It appeared that the magnitude of these properties were dependent on the amount of alkaline-earth oxides (CaO, MgO).