We identify a set of primitive operations supporting coroutines, and demonstrate their usefulness. We then address their implementation in c according to a set of criteria aimed at maintaining simplicity, and achieve ...
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We identify a set of primitive operations supporting coroutines, and demonstrate their usefulness. We then address their implementation in c according to a set of criteria aimed at maintaining simplicity, and achieve a satisfactory compromise between it and effectiveness. Our package for the PDP-11 under UNIX† allows users of coroutines in c programs to gain access to the primitives via an included definitions file and an object library; no penalty is imposed upon non-coroutine users.
An active Ag-based filler metal, containing trace alloy elements of Al, cu and Ti, was successfully applied to braze c/ccomposite and Nb. The microstructure and formation mechanism of the c/ccomposite and Nb brazed ...
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An active Ag-based filler metal, containing trace alloy elements of Al, cu and Ti, was successfully applied to braze c/ccomposite and Nb. The microstructure and formation mechanism of the c/ccomposite and Nb brazed joint were investigated in this study. Moreover, the influence of brazing parameters on microstructural evolution and mechanical properties of brazed joints was evaluated. The typical interfacial microstructure of the joint obtained at 950 degrees c for 600 s was c/c/Tic + Alcu2Ti/Ag(s, s) + Alcu2Ti + particle cu/Alcu2Ti + AlcuTi + (Ti, Nb)3Al + Nb(Ti)/Nb. The dispersive Alcu2Ti phase was uniformly distributed in the Ag matrix, which was a beneficial structure for the brazed joint. The shear strength of the brazed joint was sensitive to the brazing temperature and holding time, which was closely related to the Tic layer bordering the c/ccomposite. The thickness of the Tic layer first increased as temperature increased to 950 degrees c, and then decreased when temperature reached 970 degrees c. The carbon fiber eroded by the filler at 970 degrees c entered to the brazing seam and reacted with Ti, resulting the reduction of the thickness of Tic, thus damaging the strength of the joint. With extension of holding time from 300 s to 1200 s, the interface reaction became more sufficient. Therefore, the thickness of the Tic layer increased. However, at 1200 s, the over-thick Tic broke the c/c substrate because of the mismatch of coefficient of thermal expansions. The maximum shear strength of the joint (950 degrees c/600 s) reached 55 MPa at room temperature and 35 MPa tested at 550 degrees c.
carbon fiber-reinforced silicon carbide composites (c/Sic) are widely used in lightweight aerospace structures for thermal protection due to its excellent mechanical properties. The low interfacial shear strength of t...
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carbon fiber-reinforced silicon carbide composites (c/Sic) are widely used in lightweight aerospace structures for thermal protection due to its excellent mechanical properties. The low interfacial shear strength of the composites decreases its performance and limits its application. To investigate the shearing performance of c/Siccomposite, interlaminar shear and in-plane shear tests were conducted. Real-time X-ray micro-computed tomography (XcT) non-destructive testing technology is an effective method for damage analysis of composite materials. The damage mechanisms of 2D plain weave c/Siccomposites prepared by chemical vapor infiltration process under interlaminar shear loading are investigated using the combination of XcT and acoustic emission detection system. The in-situ XcT results reveal the damage visualization mechanisms of the composites and the damage evolution process including matrix damage, interfacial debonding and fiber fracture. The failure mechanisms and morphology of the shear effect for 2D plain weave c/Sic were analysed.
The a.c. impedance behaviour of a commercial sealed Li-ion cell is studied in the temperature range -10 to 40 degreesc at various state-of-charge (SOc) values. The data comprise an inductive part in the frequency regi...
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The a.c. impedance behaviour of a commercial sealed Li-ion cell is studied in the temperature range -10 to 40 degreesc at various state-of-charge (SOc) values. The data comprise an inductive part in the frequency region of 100 kHz-100 Hz, and two capacitive parts in the frequency region of 100 Hz-10 mHz. The data are analysed using an equivalent circuit and a nonlinear least square fitting procedure, and the impedance parameters are evaluated. The inductance is found to be independent of temperature and SOc of the cell. The resistance corresponding to the high frequency semicircle of the Nyquist impedance plot, which is attributed to the surface film on the electrodes, shows a weak dependence on the SOc of the cell. On the other hand, it exhibits Arrhenius dependence on temperature. A value of 0.4 +/- 0.05 eV is obtained for activation energy of charge-transport in the surface film. The resistance corresponding to the low frequency semicircle is due to the electron-transfer reactions, and exhibits a strong dependence on the SOc and also temperature. The data are analysed using the Butler-Volmer kinetic equation for activation controlled charge-transfer reaction, and the kinetic parameters, namely, the apparent exchange current, transfer coefficient and activation energy of the cell reaction are evaluated.
This high-level toolbox for the calculus with Taylor polynomials is named after L.F.A. Arbogast (1759-1803), a French mathematician from Strasbourg (Alsace), for his pioneering work in derivation calculus. Arbogast is...
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This high-level toolbox for the calculus with Taylor polynomials is named after L.F.A. Arbogast (1759-1803), a French mathematician from Strasbourg (Alsace), for his pioneering work in derivation calculus. Arbogast is based on a well-defined extension of the c programming language, Modular c, and places itself between tools that proceed by operator overloading on one side and by rewriting, on the other. The approach is best described as contextualization of ccode because it permits the programmer to place his code in different contexts-usual math or automatic differentiation (AD)-to reinterpret it as a usual c function or as a differential operator. Because of the type generic features of modern c, all specializations can be delegated to the compiler. The higher order AD with arbogast is exemplified on families of functions of mathematical physics and on models for complex dielectric functions used in optics.
c/c-Zrccomposites are promising thermal structural materials for aerospace applications. However, until now, the reported c/c-Zrccomposites exhibited a porous matrix and weaker mechanical properties. In this study, ...
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c/c-Zrccomposites are promising thermal structural materials for aerospace applications. However, until now, the reported c/c-Zrccomposites exhibited a porous matrix and weaker mechanical properties. In this study, the matrices of c/c-Zrccomposites were modified by slurry infiltration in order to improve density and properties. Different slurry powders such as Sic, Zrc, and ZrB2 were used to densify the c/c-Zrccomposites. After slurry infiltration, the loose c-Zrc matrix was connected to a dense matrix, and some ceramic powders settled on the surface of the composites. The density of the composites increased from 1.94 to 2.42 +/- 0.06 g cm-3, while the porosity decreased from 39.4 +/- 4.4% to 10.3 +/- 1.9% after infiltration with various slurries. The ablation and mechanical properties of the c/c-Zrccomposites improved significantly by matrix modification. The flexural strength of the composites increased from 116 to 269 +/- 21 MPa after slurry infiltration. Furthermore, the ablation properties of c/c-Zrccomposites infiltrated with the ZrB2 slurry showed the lowest linear rate (24.7 mu m s-1) and mass recession rate (7.5 mg s-1).
A rapid method was developed to fabricate c/c-Zrc-Sic-cuxSiy composites with low open porosity by precursor infiltration and pyrolysis combining with pressure assisted reactive melt infiltration. Dominant phases of Zr...
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A rapid method was developed to fabricate c/c-Zrc-Sic-cuxSiy composites with low open porosity by precursor infiltration and pyrolysis combining with pressure assisted reactive melt infiltration. Dominant phases of Zrc and Sic with scattered cuxSiy inclusions were present in continuous infiltrated matrix, in which the dimension of submicron Zrc particles displayed gradient change. At ablation test, the heat absorbing effect of cuxSiy-phase and formation of protective ZrO2-SiO2 cover enhanced the ablative property of composites for short-time ablation, causing ablation rates of 30 s ablation reached 1.7 +/- 0.1 mu m/s and 1.3 +/- 0.1 mg/s, respectively. As ablation time extends to 60 s, the massive consumption of Si-phase damaged the integrity of surface oxide cover, but the partial melted ZrO2 improved the viscosity and self-healing ability of ZrO2-SiO2 mixture, protecting substrate from further erosion. Thus, ablation rates were increased and decreased to 3.8 +/- 0.2 mu m/s and 1.2 +/- 0.1 mg/s, respectively.
c/ccomposite is widely used in aerospace due to excellent high temperature mechanical properties. Improving its ablation resistance has become the focus of attention. Due to anisotropy of composite materials, the dif...
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c/ccomposite is widely used in aerospace due to excellent high temperature mechanical properties. Improving its ablation resistance has become the focus of attention. Due to anisotropy of composite materials, the difference of thermal conductivity and thermal expansion coefficient between fiber and matrix, surface morphologies affect ablation performance greatly. In particular, fiber exposed length (FEL) and crack had a significant impact on its ablation resistance. Therefore, this paper constructed a FEL theoretical model based on machining damage, and verified that the error of the modified model was within 12 % through experiments. Meanwhile, improvement effect of rotary ultrasonic machining (RUM) was clarified. It is found that RUM reduced FEL by 15%~38% in all fiber angles and decreased the crack pores on machined surface. Then, oxyacetylene ablation experiments on c/ccomposite surface under conventional machining (cM) and RUM were carried out. The results showed that RUM surface had better ablation resistance, and interface ablation and porosity decreased significantly.
An implementation of the well-known LU decomposition method for solving systems of linear equations is presented. Operation counts typically stated for this method are derived from a theoretical analysis of the algori...
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An implementation of the well-known LU decomposition method for solving systems of linear equations is presented. Operation counts typically stated for this method are derived from a theoretical analysis of the algorithm and ignore the practical aspects of the implementation. The overhead associated with assessing elements of the two-dimensional coefficient array are explored herein, and seen to be substantial. This overhead is incorporated into the analysis of LU decomposition and new operation counts are developed. By exploiting the addressing capabilities of c the cost of array access is significantly reduced, resulting in an efficient implementation. The techniques employed here can be applied to a wide variety of c programs which utilize multi-dimensional arrays.
An environment-friendly oxidation-reduction method was used to prepare Pd/c hybrid nanocomposites (Ncs) using carbon as host and Pd nanoparticles (NPs) as surface loading, and sodium citrate was used as a reducing age...
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An environment-friendly oxidation-reduction method was used to prepare Pd/c hybrid nanocomposites (Ncs) using carbon as host and Pd nanoparticles (NPs) as surface loading, and sodium citrate was used as a reducing agent. The structures and morphologies of the Pd/c hybrid Ncs were characterized by X-ray diffraction, transmission (high-resolution) electron microscopy (TEM, HRTEM), X-ray photoelectron spectroscopy and so on. The results demonstrated that the Pd NPs were deposited on the surface of the c sphere beads, and the Pd NPs were homogeneous and monodispersed. The results also indicated that the diameter of the Pd NPs was 3 +/- 0.5 nm and the Pd/c Ncs were 197 +/- 6.5 nm. In addition, the Pd/c Ncs showed improved electrocatalytic activity for formic acid oxidation in comparison with commercial Pd NPs through controlling the surface structures. So, the environment-friendly preparation method provided developmental direction to fabricate all kinds of metal/c hybrid Ncs architectures.
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