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- 검색키워드
- 저자 : J. Riedel (검색결과 4 건)
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J. Riedel,D. G. Holmes,B. P. McGrath 전력전자학회 2015 ICPE(ISPE)논문집 Vol.2015 No.6
Dual Active Bridge (DAB) converters offer an unmatched capability to transfer energy in either direction between two DC sources, while also providing galvanic isolation and high conversion efficiency. However, to operate at high efficiencies, the bridges must operate with Zero-Voltage-Switching (ZVS) over as wide an operating range as possible. The conventional approach to determine ZVS operation uses time domain analysis with ideal AC coupling inductances, which only approximately identifies the ZVS boundaries. This paper proposes a new approach using frequency domain analysis of the bridge switching patterns, which accurately predicts the ZVS boundaries over a full range of operating conditions while also accommodating more complex AC coupling structures and practical impedance non-idealities. An exact theoretical analysis is presented for two level modulation of the two bridges coupled through a general impedance structure. An analytical solution is then presented for a single coupling impedance, while boundaries for more complex coupling structures and practical impedances are solved by numerical integration. ZVS boundaries for selected systems are validated by matching simulation and experimental results.
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Riedel, M.,Brent, T.A.,Taylor, G.,Taylor, A.E.,Hong, J.-K.,Jin, Y.-K.,Dallimore, S.R. Elsevier 2017 Marine and petroleum geology Vol.81 No.-
<P><B>Abstract</B></P> <P>The presence of a wedge of offshore permafrost on the shelf of the Canadian Beaufort Sea has been previously recognized and the consequence of a prolonged occurrence of such permafrost is the possibility of an underlying gas hydrate regime. We present the first evidence for wide-spread occurrences of gas hydrates across the shelf in water depths of 60–100 m using 3D and 2D multichannel seismic (MCS) data. A reflection with a polarity opposite to the seafloor was identified ∼1000 m below the seafloor that mimics some of the bottom-simulating reflections (BSRs) in marine gas hydrate regimes. However, the reflection is not truly bottom-simulating, as its depth is controlled by offshore permafrost. The depth of the reflection decreases with increasing water depth, as predicted from thermal modeling of the late Wisconsin transgression. The reflection crosscuts strata and defines a zone of enhanced reflectivity beneath it, which originates from free gas accumulated at the phase boundary over time as permafrost and associated gas hydrate stability zones thin in response to the transgression. The wide-spread gas hydrate occurrence beneath permafrost has implications on the region including drilling hazards associated with the presence of free gas, possible overpressure, lateral migration of fluids and expulsion at the seafloor. In contrast to the permafrost-associated gas hydrates, a deep-water marine BSR was also identified on MCS profiles. The MCS data show a polarity-reversed seismic reflection associated with a low-velocity zone beneath it. The seismic data coverage in the southern Beaufort Sea shows that the deep-water marine BSR is not uniformly present across the entire region. The regional discrepancy of the BSR occurrence between the US Alaska portion and the Mackenzie Delta region may be a result of high sedimentation rates expected for the central Mackenzie delta and high abundance of mass-transport deposits that prohibit gas to accumulate within and beneath the gas hydrate stability zone.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Discovery of permafrost related gas hydrate regime in Beaufort shelf region. </LI> <LI> Base of gas hydrate stability zone follows trend predicted by thermal modelling. </LI> <LI> Permafrost-associated gas hydrate regime poses geo-hazards to drilling. </LI> <LI> Deep-water marine hydrate regime appears irregular across Beaufort margin. </LI> </UL> </P>
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High-temperature oxidation behavior of polymer-derived SiHfBCN ceramic nanocomposites
Yuan, J.,Galetz, M.,Luan, X.G.,Fasel, C.,Riedel, R.,Ionescu, E. Elsevier Science Publishers 2016 Journal of the European Ceramic Society Vol.36 No.12
Within this study, the oxidation behavior of SiHfBCN ceramic powders and monoliths was studied at temperatures from 1200 to 1400<SUP>o</SUP>C. Both powder and monolithic samples exhibited parabolic oxidation behavior characterized by very low rates (10<SUP>-9</SUP>-10<SUP>-8</SUP>mg<SUP>2</SUP>cm<SUP>-4</SUP>h<SUP>-1</SUP>). The activation energy of 112.9kJmol<SUP>-1</SUP>, which was determined for the SiHfBCN powder, is comparable to that of other silica formers such as silicon or SiC and relates to the diffusion of molecular oxygen through silica scale. Whereas, the values determined for the SiHfBCN ceramic monoliths (174 and 140kJmol<SUP>-1</SUP>, depending on the Hf content) indicate the complex nature of their oxidation process, leading at temperatures below 1300<SUP>o</SUP>C to a continuous oxide scale consisting of borosilicate, silica, m-and t-HfO<SUB>2</SUB>. At higher temperatures, the oxide scale consists of silica, HfSiO<SUB>4</SUB> as well as m-and t-HfO<SUB>2</SUB> and becomes discontinuous, probably due to the evaporation of boria.
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Daniela Krause,Verena B. Kirnich,Theresa M. Stapf,Anika Hennings,Sabine Riemer,Michael Riedel,Ralf Schmidmaier,Francisco Pedrosa Gil,Winfried Rief,Markus J. Schwarz 대한정신약물학회 2019 CLINICAL PSYCHOPHARMACOLOGY AND NEUROSCIENCE Vol.17 No.1
Objective: Previous studies have suggested alterations in the kynurenine pathway as a major link between cytokine and neurotransmitter abnormalities in psychiatric disorders. Most of these studies used a cross-sectional case-control study design. However, knowledge is still lacking regarding the stability over time of kynurenine pathway metabolites and the functionally related cytokines. Therefore, we studied the stability of cytokines and tryptophan (TRP) parameters over a period of 12 weeks. Methods: A total of 117 participants-39 with major depression, 27 with somatoform disorder, and 51 healthy controlswere enrolled. Four evaluations, including blood withdrawal and psychometric testing, were performed over a period of 12 weeks. We used ELISA to measure interleukin (IL)-6, IL-1 receptor antagonist (RA) and tumor necrosis factor (TNF ). High-performance liquid chromatography was used to analyze neurotransmitter variables, i.e. TRP, 5-hydroxyindoleacetic acid (5-HIAA), kynurenine (KYN), 3-OH-kynurenine (3-HK), and kynurenic acid (KYNA). Results: We found no significant fluctuations of TRP, its metabolites (5-HIAA, KYN, KYNA, and 3-HK), or the cytokines (IL-1RA, IL-6, and TNF ) in any of the groups over the 12 weeks. Conclusion: To our knowledge, this is the first longitudinal study performed in psychiatric patients to verify the stability and consequently the reliability of the biological parameters we investigated. Our data indicate that TRP metabolites and cytokines are reliable biological parameters in psychiatric research because they do not fluctuate significantly over time.
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