The designs of sealing device have prominent influence on the performance of aero-engine. The high temperature environment during the working process of aero-engine also has important influence on the performance of s...
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The designs of sealing device have prominent influence on the performance of aero-engine. The high temperature environment during the working process of aero-engine also has important influence on the performance of sealing device which is located in the aero-engine. Finger seal has a flexible characteristic and high price performance compared with the other seal devices, thus it gets more attention, and lots of researchers have studied about finger seal's performance recently. But so far the dynamic performance of finger seal considering temperature effect is not yet analyzed and discussed. Based on this, an equivalent dynamic model based on distributed mass considering temperature effect is proposed in the paper. The effects of environment temperature and heat through friction on the equivalent structural stiffness of finger stick and contact pressure between finger stick and rotor are discussed. Moreover, the data exchange between the dynamic and thermal analysis is confirmed based on the movement relationship between the rotor excitation and finger stick response. Therefore, the dynamic performance analysis of finger seal including thermal-structure coupling is obtained based on an equivalent dynamic method. The effect of temperature on the dynamic performance of finger seal using this model is analyzed, and the effect of c/ccomposite structural parameters on the finger seal performance is investigated considering the temperature effect. The above results show that the temperature effect has important influence on the performance of finger seal, so it is necessary to consider the temperature effect when the performance of finger seal is analyzed. The current work further improves the theoretical system about finger seal equivalent dynamic research, and has higher academic significance and engineering value.
Functionally graded materials (FGMs) are increasingly being used in high-temperature structural components. The time-dependent c-integral, c(t), is a significant parameter in characterizing the crack tip stress field ...
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Functionally graded materials (FGMs) are increasingly being used in high-temperature structural components. The time-dependent c-integral, c(t), is a significant parameter in characterizing the crack tip stress field from the small-scale to the extensive steady-state creep stages. In this paper, the creep crack behavior of FGMs with a crack parallel to the material property gradients was studied by using the finite element method. It was proven that c(t) remained valid for FGMs. An engineering method was proposed to estimate c(t) in the small scale and transition creep stages and estimate the crack tip stress field. Finite element results verified that the method could estimate c(t) in the small scale and transition creep stages and estimate the crack tip stress field. For cases with creep properties that increased in the crack growth direction, the effect of constraint on the estimated crack tip stress field had to be considered. The constraint parameter of Q was significantly affected by the creep property gradients. The method was independent of the gradient variation law of material properties. (c) 2016 Elsevier Ltd. All rights reserved.
Backtrack programming is such a powerful technique for problem solving that a number of languages, especially in the area of artificial intelligence, have built-in facilities for backtrack programming. This paper desc...
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Backtrack programming is such a powerful technique for problem solving that a number of languages, especially in the area of artificial intelligence, have built-in facilities for backtrack programming. This paper describes cBack, a simple, but general tool for backtrack programming in the programming language c. The use of the tool is illustrated through examples of a tutorial nature. In addition to the usual depth-first search strategy, cBack provides for the more general heuristic best-first search strategy. The implementation of cBack is described in detail. The source code, shown in its full length, is entirely written in ANSI c and highly portable across diverse computer architectures and ccompilers.
The physical properties and device electrical properties of superlattice-like c/Sb phase change films are investigated. compared with Sb monolayer films, the superlattice-like c/Sb films have preferable thermal stabil...
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The physical properties and device electrical properties of superlattice-like c/Sb phase change films are investigated. compared with Sb monolayer films, the superlattice-like c/Sb films have preferable thermal stability, including higher crystallization temperature, longer data life, and larger crystallization activation energy. As the thickness of the carbon layer increases, the band gap gradually increases. X-ray photoelectron spectroscopy results show that c-Sb bonds exist in the c/Sb superlattice-like films. X-ray diffraction and atomic force microscope results show that the addition of carbon inhibits the grain growth, making the grain size smaller and inhibiting the crystallization of Sb materials. Phase-change memory devices based on [c(6nm)/Sb(4nm)](8) superlattice-like films have smaller threshold voltages and lower power consumption compared to Sb films. In conclusion, c/Sb superlattice-like films have high thermal stability and low power consumption.
y Recently, approaches based on tree-decompositions (TDs) of control-flow graphs (cFGs) have been introduced for many classical problems in compiler construction. Some found practical use in SDcc, a mainstream ccompi...
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y Recently, approaches based on tree-decompositions (TDs) of control-flow graphs (cFGs) have been introduced for many classical problems in compiler construction. Some found practical use in SDcc, a mainstream ccompiler for embedded systems. Using TD-based algorithms, SDcc generates faster and often smaller code for its target architectures than other compilers. The width of the TD crucially influences runtime, hence good algorithms computing TDs of small width are essential. The current standard approach to obtain TDs of cFGs is Thorup's heuristic, which was also used in SDcc. Thorup claims that his heuristic will give TDs of width at most 6 for cFGs from ccode that contains no goto statements. We present a counter example resulting in a tree-width of 7. We show how to construct ccode without goto statements for which the cFG has tree-width 3, but Thorup's heuristic will yield TDs of arbitrary width. We demonstrate how this flaw adversely affects the compilation of real-world code. We present a constructive proof giving a tight bound on the tree-width of cFGs of c programs. This corrects Thorup and shows the effect that goto has on the tree-width. We empirically evaluate various approaches to finding TDs of cFGs and their impact on compiler runtime and code quality in SDcc. Our research resulted in the replacement of the unconditional use of Thorup's heuristic by a better approach in SDcc 3.7.0, drastically reducing compiler runtime. (c) 2019 Elsevier B.V. All rights reserved.
Monodispersed c, Ag co-modified TiO2 microspheres were successfully synthesized through a two-step method. Firstly, monodisperse spherical TiO2 particles were obtained via controlled hydrolysis of TBOT (tetrabutyltita...
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Monodispersed c, Ag co-modified TiO2 microspheres were successfully synthesized through a two-step method. Firstly, monodisperse spherical TiO2 particles were obtained via controlled hydrolysis of TBOT (tetrabutyltitanate) in ethanol. Secondly, the c, Ag co-modified TiO2 microspheres were prepared through a simple calcination process, in which the AgNO3 and citric acid was used as Ag and c source, respectively. The physical and chemical properties of c, Ag co-modified TiO2 microspheres were carefully studied by using XRD, SEM, TEM, Raman, PL spectra and UV-vis diffuse reflectance spectra (DRS), while the chemical states of c and Ag were discussed via EDS (energy dispersive spectrometer) and XPS. The photocatalytic activity of the as-prepared products was evaluated by photocatalytic decolorization of Rhodamine B (Rh B) aqueous solution at ambient temperature under UV and visible-light irradiation. The photocatalytic activity research shows that, with the cooperation of two modified materials, c, Ag co-modified TiO2 microspheres exhibit enhanced photocatalytic activity both in ultraviolet and visible-light region compared with that of pure TiO2 and single Ag modified TiO2 microspheres. (c) 2013 Elsevier B.V. All rights reserved.
Lignin and ash are the main factors to limit integrated utilization of Si-rich biomass. In this study, core-shell structured lignin-SiO2 composites are prepared from rice husks (RHs) by alkali extraction and acid prec...
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Lignin and ash are the main factors to limit integrated utilization of Si-rich biomass. In this study, core-shell structured lignin-SiO2 composites are prepared from rice husks (RHs) by alkali extraction and acid precipitation and applied as the precursors of anode materials to achieve efficient application. Alkaline lignin is employed to supplement carbon to improve electrochemical performance of c/SiO2 composites. The optimal sample c/SiO2-6 possesses integrated coating shells and appropriate carbon content (38.27%), resulting in stable cycling performance and high capacity retention of 534 mA h g(-1) at 1 A g(-1) after 1000 cycles, close to 574 mA h g(-1) of the c/SiO2 composite synthesized by commercial raw materials. Meanwhile, c/SiO2-6 has superior rate performance and lower impedance, because the carbon coating improves conductivity and kinetic performance. The method provides a strategy for integrated utilization of Si-rich biomass and preparation of c/SiO2 anode materials with desirable electrochemical properties.
MXenes are a large class of materials that are chemically exfoliated from metal-aluminum-carbon (MAX) bulk crystals into low-dimensional sheets. While many MXenes have been theoretically predicted, the careful balance...
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MXenes are a large class of materials that are chemically exfoliated from metal-aluminum-carbon (MAX) bulk crystals into low-dimensional sheets. While many MXenes have been theoretically predicted, the careful balance required in the exfoliation between breaking the inter-layer bonds without damaging the intra-layer bonds of the sheets has limited synthesis and experimental study. Here, we developed the synthesis of cr2c from its parent cr2Alc MAX phase and showed the etching is optimized using sodium fluoride and hydrogen chloride with a modified minimally intensive layer delamination (mMILD) method in a cold environment of 9 celcius. We further optimized the intercalation and delamination using sonication and washing methods. The resulting cr2ccrystal structure was characterized. These results open up cr2c to experimental study, including of its predicted emergent magnetic properties, and develop guidelines for synthesizing new MXene materials.
coimplantation of equal concentrations of c and Al in 6H- and 4H-Sic has been investigated comparatively with implantation of Al alone in the Al concentration range of N-AI = 8x10(19) to 2 x 10(21) cm(-3). c-Al coimpl...
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coimplantation of equal concentrations of c and Al in 6H- and 4H-Sic has been investigated comparatively with implantation of Al alone in the Al concentration range of N-AI = 8x10(19) to 2 x 10(21) cm(-3). c-Al coimplantation at either room temperature (RT) or 600 degrees c, when implanted with N-Al > 1 x 10(20) cm(-3), gives improvements over Al alone implantation in the specificcontact resistance pc of Al ohmiccontacts on the implanted surfaces. The lowest median values of pc obtained are 3 x and 6 x 10(-5) Omega cm(2) for 6H- and JH-S1c. respectively. Ln the mid to high 1020 cm(-3) N-AI range, sheet resistivity. of the p-type implanted layers are also reduced by the coimplantation at RT, Temperature-dependent Hall-effect measurements reveal the correlated trends in increased impurity-band conduction and high-temperature (>400 K) hole concentration. implantation at 600 degrees c, by either coimplantation or Al atone implantation, degrades the electrical characteristics in the mid 10(20) cm(-3) N-AI range, which implies that amorphization of as-implanted Layers is necessary for effective activation of Al acceptors, It will be shown that c-AI coimplantation at RT can produce p(+)-n diodes with low reverse leakage currents and high forward current capability as evidenced by the 110 A/cm(2) forward current density at 2.8 V and 19 nA/cm(2) Leakage current density at -100 V for 4H-Sic p(+)-n diodes created by c-AI coimplantation at RT.
Herein, we report the effects of the catalyst support surface chemical/physical state of commercially available high -surface-area carbons on the electrochemical performance of Pt/c electrocatalysts synthesized using ...
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Herein, we report the effects of the catalyst support surface chemical/physical state of commercially available high -surface-area carbons on the electrochemical performance of Pt/c electrocatalysts synthesized using carbons as the support for platinum nanoparticles (Pt-NPs). A series of Pt/c electrocatalysts were synthesized through a microwave-assisted polyol process. The support carbons and the Pt/ccatalysts were characterized for their structural characteristics including crystallinity, microstructure (morphology and particle size distribution), physical surface area, porosity, thermal behavior, and surface chemical state. Evaluation of the electrocatalytic performances and durability parameters of the Pt/ccatalysts was performed through cyclic voltammetry and an accelerated stress test (AST). The results showed that the support carbons have similar physical properties except for the amounts and types of oxygen-containing surface functional groups. The Pt/ccatalysts supported on the carbon with a higher surface oxygen content were found more durable during the AST, as compared to their corresponding counterparts supported on the carbon with a lower surface oxygen content. This was attributed to the presence of oxygen functional groups that may function as the active sites for the nucleation of new Pt-NPs, hence inhibiting Ostwald ripening to some extent. This study provides valuable catalyst support selection criteria and synthesis parameters at different pressures.
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