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Background and Purpose. The vascular morphology in crowd with family history of stroke remains unclear. The present study clarified the characteristics of the intracranial vascular CoW and prevalence of intracranial aneurysms in subjects with family history of stroke. Methods. A stratified cluster, random sampling method was used for subjects with family history of stroke among rural residents in Jixian, Tianjin, China. All the subjects underwent a physical examination, head computed tomography (CT) scan, and cephalic and cervical computed tomography angiography (CTA) scan. Anatomic variations in the Circle of Willis and cerebrovascular disease in this population were analyzed. Results. In the crowd with similar living environment, stable genetic background, and family history of stroke and without obvious nerve function impairment (1) hypoplasia or absence of A1 segment was significantly different in gender (male versus female: 9.8% versus 18.8%, p=0.031), especially the right-side A1 (male versus female: 5.9% versus 16.4%, p=0.004). (2) Hypoplasia or absence of bilateral posterior communicating arteries was more common in men than women (58.2% versus 45.3%, p=0.032). Unilateral fetal posterior cerebral artery was observed more often in women than men (17.2% versus 8.5%, p=0.028). (3) The percentage of subjects with incomplete CoW did not increase significantly with age. Compared to healthy Chinese people, the crowd had a higher percentage of incomplete CoW (p<0.001). (4) No obvious correlation between risk factors and CoW was found. (5) The prevalence of aneurysm was 10.3% in the special crowd. Conclusions. The certain variations of CoW showed significant relation to gender, but not to age in people with family history of stroke. The incomplete circle may be a dangerous factor that is independent of common risk factors for stroke and tend to lead to cerebral ischemia in the crowd with family history of stroke. The prevalence of intracranial aneurysm is comparatively high in the present subjects compared to other people. [ABSTRACT FROM AUTHOR]

Viscous flow behavior of silica melts on an uncooled carbon/silicon carbide composite nozzle was investigated in the combustion environment of a liquid-fueled rocket engine simulated by an ethanol/oxygen combustion gas generator. The results showed that severe ablation of the nozzle throat were attributed to flow downstream and blow-off of the silica scales derived from vigorous oxidation of the silicon carbide matrix. The viscous flow behavior of the silica was determined by both the intrinsic viscosity of silica melts and the external aerodynamic forces of the combustion gas. [ABSTRACT FROM AUTHOR]

Structural, electronic and mechanical properties of the nH-SiC (n = 2, 4, 6, 8 and 10) polytypes are calculated by using the first-principles calculations based on the density-functional theory approach. The optimized lattice parameters of nH-SiC are in good agreement with the experimental data. The mechanical properties, including elastic constants, bulk modulus, Young's modulus, shear modulus and Poisson's ratio, are calculated. The analysis of elastic properties indicates that the effects of n on the mechanical properties of the five nH-SiC structures have no difference. The indirect band gap relationship for the five polytypes is Ebg2H > Ebg4H > Ebg6H > Ebg10H > Ebg8H. [ABSTRACT FROM AUTHOR]

In situ synthesis technology was adopted to fabricate SiC reinforced Ti3SiC2 composite by displacement reaction of Si and TiC powders. The formation of SiC particles as reinforcements with elongated or equiaxed shape distributed in Ti3SiC2 matrix. The average size of SiC equiaxed particles was about 2 μm and that of elongated ones was in the range of 5–8 μm in length and 2 μm in width. TiC with about 1 μm in size was also found in the composite. The particles of SiC or TiC inhibited the grain-boundary migration of Ti3SiC2 resulting in a fine Ti3SiC2 matrix with a grain size of 10 μm. Differential scanning calorimetry showed that Si reacted drastically with TiC at 1340 °C with release of heat. The presence of TiC in the Ti3SiC2/SiC composite should be attributed to decomposition of Ti3SiC2 at 1500 °C rather than the loss of Si during reaction process that resulted in unreacted TiC left. Reaction paths in the present experiment were postulated on the basis of Ti–Si–C system and reaction model of Mo2C–Si to understand the mechanism of the formation of Ti3SiC2 and SiC. [Copyright &y& Elsevier]

Ti3SiC2/SiC composite has been synthesized by in situ displacement reaction of Si and TiC powders. Its relative density is >98%. Its Vickers hardness was measured to be 8.7 GPa. Its flexural strength and the fracture toughness were 505 MPa and 5.3 MPa·m1/2, respectively. Scanning electron micrograph (SEM) and transmission electron micrograph (TEM) were used to observe the microstructure of the composite. Mechanisms for its high flexural strength and fracture toughness were discussed, respectively. The composite shows a better oxidation resistance than monolithic Ti3SiC2 at high temperatures. The oxidation layers were comprised of an outer layer with coarse TiO2 grains and an inner layer with a mixture of fine-grained SiO2 and TiO2. Its weight gain is only about 7.9 mg/cm2 at 1200 °C in air for 21 h. However, that of Ti3SiC2 is 30 mg/cm2. The results suggested that the in situ formation of SiC improved its oxidation resistance. [Copyright &y& Elsevier]

The oxidation behavior of Ti3SiC2 with additive-Al2O3 was studied over the temperature range of 1000–1500 °C in air. Ti3SiC2 based composite has a good oxidation resistance at below 1100 °C. The oxidation kinetics followed a parabolic and a linear law respectively at different oxidation stages. Morphology of oxidation products was observed from the oxidized surface by scanning electron microscope (SEM). Oxides were identified by X-ray diffraction (XRD) and energy-dispersive spectroscopy (EDS). The existence of additive-Al2O3 influenced the morphology of oxides and the oxidation behavior of Ti3SiC2. The formation of pores or cavities at high temperature provided the channels for diffusion of oxygen and accelerated the oxidation behavior of Ti3SiC2 based composite. The effects related to the morphology and microstructure features on the oxidation kinetics are discussed. [Copyright &y& Elsevier]