Effect of holding time on microstructure and mechanical properties of SiC/SiC joints brazed by Ag-Cu-Ti + B4C composite filler

The composite fillers have a number of advantages comparing with the traditional filler metals, and have been widely used for brazing ceramics. However, previous researches mainly focus on the strengthening mechanism of either whiskers or particles. It is still of great interest to investigate the reinforcement effect with the presence of both whiskers and particles. In this study, Ag-Cu-Ti + B4C composite filler was developed to braze SiC ceramics, and effects of holding time on the microstructure evolution and mechanical properties of the joints were investigated in detail. With the prolongation of holding time, the overall thickness of Ti3SiC2 + Ti5Si3 layers adjacent to SiC ceramic was increased correspondingly and the reaction between active Ti and B4C particles was promoted more extensively. The bending strength of the joints increased with holding time until the maximum bending strength of 140 MPa was reached and then decreased dramatically. The hardness and Young's modulus of the joints were characterized by nano-indentation to reveal the strengthening of the brazing seam. In addition, the strengthening mechanism of the joints brazed by the Ag-Cu-Ti + B4C composite filler was proposed on the basis of experimental observation and theoretical analysis

Predictors of failure of early neurological improvement in early time window following endovascular thrombectomy: a multi-center study

Background and objectiveEndovascular thrombectomy (EVT) has become the gold standard in the treatment of acute stroke patients. However, not all patients respond well to this treatment despite successful attempts. In this study, we aimed to identify variables associated with the failure of improvements following EVT.MethodsWe retrospectively analyzed prospectively collected data of 292 ischemic stroke patients with large vessel occlusion who underwent EVT at three academic stroke centers in China from January 2019 to February 2022. All patients were above 18 years old and had symptoms onset ≤6 h. A decrease of more than 4 points on the National Institute of Health Stroke Scale (NIHSS) after 24 h compared with admission or an NIHSS of 0 or 1 after 24 h was defined as early neurological improvement (ENI), whereas a lack of such improvement in the NIHSS was defined as a failure of early neurological improvement (FENI). A favorable outcome was defined as a modified Rankin scale (mRS) score of 0–2 after 90 days.ResultsA total of 183 patients were included in the final analyses, 126 of whom had FENI, while 57 had ENI. Favorable outcomes occurred in 80.7% of patients in the ENI group, in contrast to only 22.2% in the FENI group (p < 0.001). Mortality was 7.0% in the ENI group in comparison to 42.1% in the FENI group (p < 0.001). The multiple logistic regression model showed that diabetes mellitus [OR (95% CI), 2.985 (1.070–8.324), p = 0.037], pre-stroke mRS [OR (95% CI), 6.221 (1.421–27.248), p = 0.015], last known well to puncture time [OR (95% CI), 1.010 (1.003–1.016), p = 0.002], modified thrombolysis in cerebral infarction = 3 [OR (95% CI), 0.291 (0.122–0.692), p = 0.005], and number of mechanical thrombectomy passes [OR (95% CI), 1.582 (1.087–2.302), p = 0.017] were the predictors of FENI.ConclusionDiabetes mellitus history, pre-stroke mRS, longer last known well-to-puncture time, lack of modified thrombolysis in cerebral infarction = 3, and the number of mechanical thrombectomy passes are the predictors of FENI. Future large-scale studies are required to validate these findings