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RISS 인기검색어
- 검색키워드
- 저자 : John J. Myers (검색결과 5 건)
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Tobin, John J.,Bergin, Edwin A.,Hartmann, Lee,Lee, Jeong-Eun,Maret, Sé,bastien,Myers, Phillip C.,Looney, Leslie W.,Chiang, Hsin-Fang,Friesen, Rachel IOP Publishing 2013 The Astrophysical journal Vol.765 No.1
<P>We present a study on the spatial distribution of N2D+ and N2H+ in 13 protostellar systems. Eight of thirteen objects observed with the IRAM 30 m telescope show relative offsets between the peak N2D+ (J = 2 -> 1) and N2H+ (J = 1 -> 0) emission. We highlight the case of L1157 using interferometric observations from the Submillimeter Array and Plateau de Bure Interferometer of the N2D+ (J = 3 -> 2) and N2H+ (J = 1 -> 0) transitions, respectively. Depletion of N2D+ in L1157 is clearly observed inside a radius of similar to 2000 AU (7 '') and the N2H+ emission is resolved into two peaks at radii of similar to 1000 AU (3 ''.5), inside the depletion region of N2D+. Chemical models predict a depletion zone in N2D+ and N2H+ due to destruction of H2D+ at T similar to 20 K and the evaporation of CO off dust grains at the same temperature. However, the abundance offsets of 1000 AU between the two species are not reproduced by chemical models, including a model that follows the infall of the protostellar envelope. The average abundance ratios of N2D+ to N2H+ have been shown to decrease as protostars evolve by Emprechtinger et al., but this is the first time depletion zones of N2D+ have been spatially resolved. We suggest that the difference in depletion zone radii for N2H+ and N2D+ is caused by either the CO evaporation temperature being above 20 K or an H-2 ortho-to-para ratio gradient in the inner envelope.</P>
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An Experimental Study on Bond Strength of Reinforcing Steel in Self-Consolidating Concrete
Trevor J. Looney,Mahdi Arezoumandi,Jeffery S. Volz,John J. Myers 한국콘크리트학회 2012 International Journal of Concrete Structures and M Vol.6 No.3
An experimental investigation was conducted to compare the bond strength of reinforcing steel in self-consolidating concrete (SCC) with conventional concrete (CC). This study investigated two different compressive strengths of SCC as well as CC. The experimental program consisted of 24 pull-out specimens as well as 12 full-scale beams (three for each concrete type and strength). The pull-out specimens were based on RILEM recommendations, and the beam specimens were tested under a simply supported four-point loading condition. The CC test results served as a control and were used to evaluate the results from the SCC pull-out and beam specimen tests. Furthermore, a comparison was performed between results of this study and a bond database of CC specimens. These comparisons indicate that SCC beams possess comparable or slightly greater bond strength than CC beams.
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An Experimental Study on Bond Strength of Reinforcing Steel in Self-Consolidating Concrete
Looney, Trevor J.,Arezoumandi, Mahdi,Volz, Jeffery S.,Myers, John J. Korea Concrete Institute 2012 International Journal of Concrete Structures and M Vol.6 No.3
An experimental investigation was conducted to compare the bond strength of reinforcing steel in self-consolidating concrete (SCC) with conventional concrete (CC). This study investigated two different compressive strengths of SCC as well as CC. The experimental program consisted of 24 pull-out specimens as well as 12 full-scale beams (three for each concrete type and strength). The pull-out specimens were based on RILEM recommendations, and the beam specimens were tested under a simply supported four-point loading condition. The CC test results served as a control and were used to evaluate the results from the SCC pull-out and beam specimen tests. Furthermore, a comparison was performed between results of this study and a bond database of CC specimens. These comparisons indicate that SCC beams possess comparable or slightly greater bond strength than CC beams.
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Research on the Compression Behavior of Steel Reinforced Concrete Columns With Built-in Steel Tubes
Cun Hui,Fan Zhang,Zhizeng Zhang,Xiaoli Liu,Ran Hai,John J. Myers 한국강구조학회 2020 International Journal of Steel Structures Vol.20 No.4
In order to study the compression behavior of rectangular steel reinforced concrete columns with built-in steel tubes under diff erent eccentric loads, three 1/10 scale specimens were designed and monotonic loading tests were carried out on them. The dimensions, steel bars and steel tube of the three specimens were the same except for the location of the loading point. The eccentricity ratios of the three specimens were 0, 0.25 and 0.5, respectively. The failure modes, load-bearing capacity and displacement characteristics of the test specimens were analyzed. According to the Chinese code, the load-bearing capacity calculation principles and methods of steel reinforced concrete columns with built-in steel tube were investigated for the comparison. The study shows that the peak vertical loads of specimens decrease and the corresponding vertical and horizontal peak displacement increase as the eccentricity increases. The load-bearing capacity calculation results from Chinese code are slightly smaller than the test result because of the unconsidered sleeve eff ect of the internal steel tube. The errors between them are small, and the calculation methods are benefi cial to ensure the structural safety.
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Evidence for lithium superoxide-like species in the discharge product of a Li–O<sub>2</sub> battery
Yang, Junbing,Zhai, Dengyun,Wang, Hsien-Hau,Lau, Kah Chun,Schlueter, John A.,Du, Peng,Myers, Deborah J.,Sun, Yang-Kook,Curtiss, Larry A.,Amine, Khalil The Royal Society of Chemistry 2013 Physical chemistry chemical physics Vol.15 No.11
<P>We report on the use of a petroleum coke-based activated carbon (AC) with very high surface area for a Li–O<SUB>2</SUB> battery cathode without the use of any additional metal catalysts. Electrochemical measurement in a tetra(ethylene) glycol dimethyl ether–lithium triflate (TEGDME–LiCF<SUB>3</SUB>SO<SUB>3</SUB>) electrolyte results in two voltage plateaus during charging at 3.2–3.5 and 4.2–4.3 V <I>versus</I> Li<SUP>+</SUP>/Li. Herein we present evidence from Raman and magnetic measurements that the lower plateau corresponds to a form of lithium peroxide with superoxide-like properties characterized by a low temperature magnetic phase transition and a high O–O stretching frequency (1125 cm<SUP>−1</SUP>). The magnetic phase transition and the high O–O stretching frequency disappear when charged to above 3.7 V. Theoretical calculations indicate that a surface superoxide structure on lithium peroxide clusters and some lithium peroxide surfaces have an unpaired electron and a high O–O stretching frequency that help explain the observations. These results provide evidence that the form of the lithium peroxide discharge product is important to obtaining a low charge overpotential, and thus improving the round-trip efficiency between discharge and charge.</P> <P>Graphic Abstract</P><P>We report on the use of a petroleum coke-based activated carbon in a Li–O<SUB>2</SUB> battery that gives two voltage plateaus during charging and evidence for a superoxide-like species. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c3cp00069a'> </P>
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