688 research outputs found
Platinum(II) complexes of 3,3'-disubstituted-2,2'-bipyridines. Synthesis, structures, cytotoxic effect and unusual solvolysis in DMSO
No full textThe reaction of 3,3'-disubstituted-2,2'-bipyridines, 2,2'-bipyridyl-3,3'-dicarboxylic acid (H2BDC) and 3,3'-dimethylol-2,2'-bipyridine (DMB) with potassium tetrachloroplatinate(II) in water gives Pt(H2BDC)Cl-2 (1) and Pt(DMB)CI, (2), respectively. Both complexes were characterized by elemental analysis and various spectroscopic techniques. The molecular structures of 1 and 2 have been determined by single-crystal X-ray diffraction. 1.2DMF: triclinic system, space groupP1,alpha=8.089(9) Angstrom,b=9.707(8) Angstrom,c= 15.541(4) Angstrom,alpha = 106.88(6)degrees, beta=100.41(3)degrees: gamma=94.39(8)degrees, V=1137.8(2) Angstrom(3), Z=2. 2: monoclinic system, space group P2(1)/c, alpha=7.849(5) Angstrom, b=16.125(3) Angstrom, c=21.613(5) Angstrom, beta=94.10(2)degrees, V= 2728.5(9) Angstrom(3), Z=8. X-ray structures indicate that two pyridine rings of the bipyridyl ligand in both compounds cannot attain the coplanar state owing to the steric bulkiness of the substituents in the 3,3'-positions. The solvolysis of 1 in DMSO, characterized by H-1, C-13 and Pt-195 NMR spectra, leads to the unprecedented example for the complete release of the free amine ligand H2BDC, yielding the formation of cis-[Pt(Me2SO)(2)Cl-2]. No antitumor activity was observed for 1 and 2 against the leukemia L1210 cell line. (C) 1997 Elsevier Science S.A.no sponsor
Sequential multiple functions of the conserved sequence in sequence-specific termination by T7 RNA polymerase
No full texthttp://www.pnas.org/cgi/content/abstract/102/1/75?ctEscherichia coli rrnB terminator t1 contains an RNA hairpin-dependent (class I) and a sequence-specific (class II) termination signal. The latter consists of an 8-bp conserved sequence (CS), TATCTGTT, immediately followed by an 8-bp T rich sequence. In this study, elongation complexes of T7 RNA polymerase at various positions of the class II signal and several mutant signals were obtained by stepwise walking on immobilized DNA templates free of the class I signal. Multiple CS-associated conformational changes were observed, starting at the beginning of the signal and occurring sequentially. When the complexes reach the first base pair of the CS-DNA duplex, which is downstream of the RNA-DNA heteroduplex, their stability, as measured by time-course retention of radiolabeled transcripts, markedly decreases. Further elongation leads to an abrupt change in polymerase-RNA interaction. Crosslinking of the polymerase to a 4-thio-UMP incorporated into RNA 8 nucleotides upstream of the 3' end and just upstream of the heteroduplex is initially strong but diminishes when the polymerase reaches the fourth base pair of the CS. After a further 7-nt elongation, the exposed single-stranded region of nontemplate strand is contracted; RNA in the upstream half of the heteroduplex becomes dissociated, and the CS-DNA duplex is reformed. During the next 5-nt elongation before termination, the CS duplex is prevented from translocation, and the contracted transcription bubble expands only downstream. These findings suggest that the CS duplex plays essential roles by successively binding to polymerase both downstream and upstream of the heteroduplex.the Korea Science and Engineering Foundation (R01-1999-00111) and the 21C Frontier Project (M1-03KB010006). Y.S. is a recipient of a postdoctoral fellowship (M02-2004-000-11191-0
Analysis of Single Buffer Random Polling System With State-Dependent Input Process and Server/Station Breakdowns
No full textModels and analytical techniques are developed to evaluate the performance of two variations of single buffers (conventional and buffer relaxation system) multiple queues system. In the conventional system, each queue can have at most one customer at any time and newly arriving customers find the buffer full are lost. In the buffer relaxation system, the queue being served may have two customers, while each of the other queues may have at most one customer. Thomas Y.S. Lee developed a state-dependent non-linear model of uncertainty for analyzing a random polling system with server breakdown/repair, multi-phase service, correlated input processes, and single buffers. The state-dependent non-linear model of uncertainty introduced in this paper allows us to incorporate correlated arrival processes where the customer arrival rate depends on the location of the server and/or the server's mode of operation into the polling model. The author allows the possibility that the server is unreliable. Specifically, when the server visits a queue, Lee assumes that the system is subject to two types of failures: queue-dependent, and general. General failures are observed upon server arrival at a queue. But there are two possibilities that a queue-dependent breakdown (if occurs) can be observed; (i) is observed immediately when it occurs and (ii) is observed only at the end of the current service. In both cases, a repair process is initiated immediately after the queue-dependent breakdown is observed. The author's model allows the possibility of the server breakdowns/repair process to be non-stationary in the number of breakdowns/repairs to reflect that breakdowns/repairs or customer processing may be progressively easier or harder, or that they follow a more general learning curve. Thomas Y.S. Lee will show that his model encompasses a variety of examples. He was able to perform both transient and steady state analysis. The steady state analysis allows us to compute several performance measures including the average customer waiting time, loss probability, throughput and mean cycle time.</jats:p
Underwater spark discharge with long transmission line for cleaning horizontal wells
No full textA transmission line is discussed for application in an underwater spark-discharge technique in the cleaning of a horizontal well by incorporating a power-transmission model into the simulation. The pulsed-spark-discharge technique has been proposed for clogged-well rehabilitation, because it removes incrustations that are attached to well screens by using strong pressure waves that are generated by the rapid expansion of a spark channel. To apply the pulsed-spark-discharge technique to the cleaning of horizontal wells, the coaxial cable between the pulsed power supply and the spark gap as a load needs to be extended to a few hundred meters. Prior to field application, pulsed-spark-discharge experiments were conducted and the role of the transmission line was examined using an improved simulation model. In the model, a non-linear interaction of the spark channel and the capacitor bank is described by the pulse-forming action of the coaxial cable. Based on the accurate physical properties of the water plasma, such as the equation of state and electrical conductivity within the region of interest, the amount of energy contributed to the development of a shock wave was evaluated. The simulation shows that if the initial conditions of the spark channel are the same, no further reduction in strength of the pressure wave occurs, even if the cable length is increased above 50 m. Hence, the degraded peak pressure that was observed in the experiments using the longer cable is attributed to a change in the initial condition of the spark channel. The parametric study suggests that the low initial charging voltage, the high ambient water pressure, and the long cable length yield the low initial spark-channel density, which results in a reduced peak pressure. The simulation of line charging is presented to discuss the principle of disturbing the pre-breakdown process by an extended cable. © 2017 Author(s).OAIID:RECH_ACHV_DSTSH_NO:T201719639RECH_ACHV_FG:RR00200001ADJUST_YN:EMP_ID:A080568CITE_RATE:0DEPT_NM:에너지시스템공학부EMAIL:[email protected]_YN:NN
A Study of Zeolite Membrane Material Balance and Commercialization Potential
No full textabstract: The United States and most of the world is pushing to significantly reduce carbon emissions, with many countries intent on fostering carbon negative energy processes to offset ozone depletion and climate changes. 30% of the U.S. greenhouse gas emissions are generated from the combustion of fossil fuels to generate electricity1. Current commercial IGCC carbon capture processes employ a capital and operating cost intensive water-gas shift reaction facilitated by a high temperature reactor followed by a low temperature reactor and an amine absorber to separate the hydrogen and carbon dioxide streams to capture the carbon. Dr. Jerry Y.S. and his laboratory at Arizona State have developed a hydrogen permselective MFI type ZSM-5 zeolite membrane reactor that effectively facilities the water gas shift reaction with high conversion and separates the CO2 and H2 streams during reaction to generate ultrapure retentate and permeate streams. The membrane, formed by secondary free growth, is synthesized on an ultrapure a-alumina membrane support currently purchased from an outside vendor. The purpose of this study was to design an α-alumina support processing plant with capability to supply one full-scale commercial reactor annually with membranes. The design yielded a DCFRoR of 71% for a 20-year project life. A zeolite membrane processing material balance was conducted using alumina support as the raw material. The study showed very low material costs and consumption rates for all materials except a gas used to refine the membrane after processing. The results of both studies were favorable enough to suggest further study
Democratization and Institutionalization-- A Reflection of Latin American Experience
No full text本文適過解放、自由化、民主化的名詞解析，以比較眼光分析拉丁美洲的民主化困局。作者以此一分析架構，初步檢討拉丁美洲「民主─威權」循環模式的成因及轉型的關鍵因素，可做為分析拉丁美洲政局的一項參考架構。This essay compares and analyses the concepts of liberation, liberalization, democratizations and their interactions in Latin American politics. According to this analytical framework, the author makes a preliminary analysis of the “democracy-authoritarianism-democracy” cycle in the Latin political history. This essay also discusses the causes and consequences of liberalization and democratization during the 1970’s and 1980’s
An Experimental Study on the Effect of Adoption of Special Rudders on Course Stability of a Ship
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