The oil-pressboard insulation is a typical composite insulation system widely used in the design and manufactory of large power apparatus. The implement of oil-pressboard insulation may lead to surface electrification...The oil-pressboard insulation is a typical composite insulation system widely used in the design and manufactory of large power apparatus. The implement of oil-pressboard insulation may lead to surface electrification and discharge at the interface under certain condition. It is of significant importance to take an insight into the phenomenon occurring at the interface. Through experiment, the pressboard is found as a porous material. The interface changes abruptly from bulk pressboard to the bulk oil as a result of the porous structure. A new model is proposed which divides the interface into bulk oil region, transition region, and bulk pressboard region. The width of the transition region is decided according to the microtome figure. The effective permittivity of the transition region is calculated using a new model based on fractal theory. The model is validated and compared with previous calculation model. The effect of the existence of transition region on the electric field distribution is discussed.展开更多
This paper studies the problem of deriving an interface automata model from UML statechart, in which, interface automata is a formaliged model for describing component behavior in an open system, but there is no unive...This paper studies the problem of deriving an interface automata model from UML statechart, in which, interface automata is a formaliged model for describing component behavior in an open system, but there is no universal criterion for deriving behavior from component to construct the model. UML is a widely used modeling standard, yet it is very difficult to apply it to system verification and testing directly for its imprecise semantics. After analyzing the expression ability of the two models, several transforma- tion rules are defined and each step of transformation is described in detail, after that, the approach is illustrated with an example. The paper provides a method for acquiring interface automata and lays the foundation for related research.展开更多
This paper introduces an isolated reversible DC-DC converter with a particular topology, which benefits from both the NPC （neutral point clamped） structure and the series-parallel connection of converters. The key p...This paper introduces an isolated reversible DC-DC converter with a particular topology, which benefits from both the NPC （neutral point clamped） structure and the series-parallel connection of converters. The key property of the proposed topology is the output voltage elevation above the blocking capabilities of each switch, without taking to a delicate synchronization of series-connected semiconductors. The converter is composed by two identical cells, each containing a full bridge, a medium frequency transformer and an NPC converter, connected in parallel at the input and in series at the output. The operation principle of each cell, into which a trapezoidal modulation was implemented, is similar to a DAB （dual active bridge）. A new model improves the dynamic performance of the controller. Simulation and experimental results verify the proposed topology, its control and start-up strategy.展开更多
A novel two-phase approach towards the corrosion of PtNil0 nanoctahedra has been developed. In this strategy, the active component of Ni in oil-soluble PtNil0 nanoctahedra which resided in the upper toluene phase, suf...A novel two-phase approach towards the corrosion of PtNil0 nanoctahedra has been developed. In this strategy, the active component of Ni in oil-soluble PtNil0 nanoctahedra which resided in the upper toluene phase, suffered from etching and was then transferred into a lower aqueous phase with coordination by ethylenediaminetetraacetate （EDTA）. Due to the existence of the phase-transfer interface promoted by EDTA, the corrosion reaction proceeded at an accelerated rate under the mild conditions. Specifically, the resultant products of octahedral Pt4Ni nanoframes were successfully fabricated for the first time, and PtNi4 porous octahedra could be obtained when the dosage of EDTA-2Na was reduced. After a systematic study of this two-phase system, a ＂synergetic corrosion＂ mechanism is proposed to account for the formation of octahedral Pt4Ni nanoframes, involving contributions from many species （i.e., O2, H2O, H＋, OAm, and EDTA^4-）. As a result of the fascinating three-dimensional geometry of Pt4Ni nanoframes and PtNi4 porous octahedra, both of the corroded nanocrystals showed superior activity over the pristine PtNi^o nanoctahedra for ethanol electrooxidation in alkaline media and hydrogenation of nitrobenzene.展开更多
The heat transfer analysis of variable conductance heat pipe air preheater was carried out. The temperature trans-fer matrix was obtained for the air preheater that comprises several discrete heat transfer units with ...The heat transfer analysis of variable conductance heat pipe air preheater was carried out. The temperature trans-fer matrix was obtained for the air preheater that comprises several discrete heat transfer units with same or different heat transfer surface area in a parallel or counter flow mode. By using the temperature transfer matrix, the outlet fluid temperatures could be easily calculated for a given air preheater and inlet fluid temperatures. The active length of condenser in a variable conductance heat pipe is determined according to the flat interface model. With the same initial conditions, the comparisons between variable conductance heat-pipe air preheater and regular heat pipe air preheater has been analyzed and tested in terms of heat pipe wall temperature, heat transfer surface area and outlet fluid temperatures. Based on the real industrial applications, it has been confirmed that the variable conductance heat pipe air preheater has excellent performance of anti-corrosion and anti-ash-deposition especially at the variable working condition and the sulfur coal (5%-6% mass fraction of sulfur) condition.展开更多
Problems of thermodynamic phase transition originate inherently in solidification, combustion and various other significant fields. If the transition region among two locally stable phases is adequately narrow, the dy...Problems of thermodynamic phase transition originate inherently in solidification, combustion and various other significant fields. If the transition region among two locally stable phases is adequately narrow, the dynamics can be modeled by an interface motion. This paper is devoted to exhaustive analysis of the invariant solutions for a modified Kuramoto-Sivashinsky equation in two spatial and one temporal dimensions is presented. This nonlinear partial differential equation asymptotically characterizes near planar interfaces, which are marginally long-wave unstable. For this purpose, by applying the classical symmetry method for this model the classical symmetry operators are attained.Moreover, the structure of the Lie algebra of symmetries is discussed and the optimal system of subalgebras, which yields the preliminary classification of group invariant solutions is constructed. Mainly, the Lie invariants corresponding to the infinitesimal symmetry generators as well as associated similarity reduced equations are also pointed out. Furthermore,the nonclassical symmetries of this nonlinear PDE are also comprehensively investigated.展开更多
基金Project(2009CB724504)supported by the National Basic Research Program of China
文摘The oil-pressboard insulation is a typical composite insulation system widely used in the design and manufactory of large power apparatus. The implement of oil-pressboard insulation may lead to surface electrification and discharge at the interface under certain condition. It is of significant importance to take an insight into the phenomenon occurring at the interface. Through experiment, the pressboard is found as a porous material. The interface changes abruptly from bulk pressboard to the bulk oil as a result of the porous structure. A new model is proposed which divides the interface into bulk oil region, transition region, and bulk pressboard region. The width of the transition region is decided according to the microtome figure. The effective permittivity of the transition region is calculated using a new model based on fractal theory. The model is validated and compared with previous calculation model. The effect of the existence of transition region on the electric field distribution is discussed.
文摘This paper studies the problem of deriving an interface automata model from UML statechart, in which, interface automata is a formaliged model for describing component behavior in an open system, but there is no universal criterion for deriving behavior from component to construct the model. UML is a widely used modeling standard, yet it is very difficult to apply it to system verification and testing directly for its imprecise semantics. After analyzing the expression ability of the two models, several transforma- tion rules are defined and each step of transformation is described in detail, after that, the approach is illustrated with an example. The paper provides a method for acquiring interface automata and lays the foundation for related research.
文摘This paper introduces an isolated reversible DC-DC converter with a particular topology, which benefits from both the NPC （neutral point clamped） structure and the series-parallel connection of converters. The key property of the proposed topology is the output voltage elevation above the blocking capabilities of each switch, without taking to a delicate synchronization of series-connected semiconductors. The converter is composed by two identical cells, each containing a full bridge, a medium frequency transformer and an NPC converter, connected in parallel at the input and in series at the output. The operation principle of each cell, into which a trapezoidal modulation was implemented, is similar to a DAB （dual active bridge）. A new model improves the dynamic performance of the controller. Simulation and experimental results verify the proposed topology, its control and start-up strategy.
文摘A novel two-phase approach towards the corrosion of PtNil0 nanoctahedra has been developed. In this strategy, the active component of Ni in oil-soluble PtNil0 nanoctahedra which resided in the upper toluene phase, suffered from etching and was then transferred into a lower aqueous phase with coordination by ethylenediaminetetraacetate （EDTA）. Due to the existence of the phase-transfer interface promoted by EDTA, the corrosion reaction proceeded at an accelerated rate under the mild conditions. Specifically, the resultant products of octahedral Pt4Ni nanoframes were successfully fabricated for the first time, and PtNi4 porous octahedra could be obtained when the dosage of EDTA-2Na was reduced. After a systematic study of this two-phase system, a ＂synergetic corrosion＂ mechanism is proposed to account for the formation of octahedral Pt4Ni nanoframes, involving contributions from many species （i.e., O2, H2O, H＋, OAm, and EDTA^4-）. As a result of the fascinating three-dimensional geometry of Pt4Ni nanoframes and PtNi4 porous octahedra, both of the corroded nanocrystals showed superior activity over the pristine PtNi^o nanoctahedra for ethanol electrooxidation in alkaline media and hydrogenation of nitrobenzene.
文摘The heat transfer analysis of variable conductance heat pipe air preheater was carried out. The temperature trans-fer matrix was obtained for the air preheater that comprises several discrete heat transfer units with same or different heat transfer surface area in a parallel or counter flow mode. By using the temperature transfer matrix, the outlet fluid temperatures could be easily calculated for a given air preheater and inlet fluid temperatures. The active length of condenser in a variable conductance heat pipe is determined according to the flat interface model. With the same initial conditions, the comparisons between variable conductance heat-pipe air preheater and regular heat pipe air preheater has been analyzed and tested in terms of heat pipe wall temperature, heat transfer surface area and outlet fluid temperatures. Based on the real industrial applications, it has been confirmed that the variable conductance heat pipe air preheater has excellent performance of anti-corrosion and anti-ash-deposition especially at the variable working condition and the sulfur coal (5%-6% mass fraction of sulfur) condition.
文摘Problems of thermodynamic phase transition originate inherently in solidification, combustion and various other significant fields. If the transition region among two locally stable phases is adequately narrow, the dynamics can be modeled by an interface motion. This paper is devoted to exhaustive analysis of the invariant solutions for a modified Kuramoto-Sivashinsky equation in two spatial and one temporal dimensions is presented. This nonlinear partial differential equation asymptotically characterizes near planar interfaces, which are marginally long-wave unstable. For this purpose, by applying the classical symmetry method for this model the classical symmetry operators are attained.Moreover, the structure of the Lie algebra of symmetries is discussed and the optimal system of subalgebras, which yields the preliminary classification of group invariant solutions is constructed. Mainly, the Lie invariants corresponding to the infinitesimal symmetry generators as well as associated similarity reduced equations are also pointed out. Furthermore,the nonclassical symmetries of this nonlinear PDE are also comprehensively investigated.
