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고온자전반응합성과 확산 열처리를 이용한 FeAl계 금속간화합물 복합판재의 제조
김연욱,윤영목,Kim, Yeon-Wook,Yun, Young-Mok 한국재료학회 2008 한국재료학회지 Vol.18 No.3
Fe-aluminides have the potential to replace many types of stainless steels that are currently used in structural applications. Once commercialized, it is expected that they will be twice as strong as stainless steels with higher corrosion resistance at high temperatures, while their average production cost will be approximately 10% of that of stainless steels. Self-propagating, high-temperature Synthesis (SHS) has been used to produce intermetallic and ceramic compounds from reactions between elemental constituents. The driving force for the SHS is the high thermodynamic stability during the formation of the intermetallic compound. Therefore, the advantages of the SHS method include a higher purity of the products, low energy requirements and the relative simplicity of the process. In this work, a Fe-aluminide intermetallic compound was formed from high-purity elemental Fe and Al foils via a SHS reaction in a hot press. The formation of iron aluminides at the interface between the Fe and Al foil was observed to be controlled by the temperature, pressure and heating rate. Particularly, the heating rate plays the most important role in the formation of the intermetallic compound during the SHS reaction. According to a DSC analysis, a SHS reaction appeared at two different temperatures below and above the metaling point of Al. It was also observed that the SHS reaction temperatures increased as the heating rate increased. A fully dense, well-bonded intermetallic composite sheet with a thickness of $700\;{\mu}m$ was formed by a heat treatment at $665^{\circ}C$ for 15 hours after a SHS reaction of alternatively layered 10 Fe and 9 Al foils. The phases and microstructures of the intermetallic composite sheets were confirmed by EPMA and XRD analyses.
등척성 악력운동이 교감신경 활성화에 대한 경동맥 혈관과 심혈관 재반응에 미치는 영향
김연욱 ( Yun Wook Kim ),성준엽 ( Joon Youp Seong ),민호정 ( Ho Jeong Min ),최태구 ( Tae Gu Choi ),정용준 ( Yong Joon Jung ),조민정 ( Min Jeong Cho ),김현정 ( Hyun Jeong Kim ),제세영 ( Sae Young Jae ) 대한스포츠의학회 2024 대한스포츠의학회지 Vol.42 No.1
Purpose: Isometric handgrip exercise (IHE) has a favorable cardiovascular effect and improves hemodynamic responses. Whether IHE attenuates stress-related hemodynamic reactivity assessed during a sympathetic challenge remains unexplored. We tested the hypothesis that an acute bout of IHE would improve carotid arterial function and attenuate cardiovascular vasoreactivity response to sympathetic stress in healthy adults. Methods: In a randomized cross-over design, sixteen healthy adults (aged 21.8±3.1 years) were enrolled. Participants completed two testing sessions, separated by 1 week. Trials were either a control trial or performed IHE for two sets of 2 minutes at 30% of maximal voluntary contraction for each hand. The participant’s hand was immersed in an ice water bath (4℃) up to the wrist for 2 minutes. Carotid artery diameter, β-stiffness index, and compliance using ultrasound machine and brachial blood pressure (BP), heart rate (HR) were measured as indices of vasoreactivity at baseline, during, and recovery from cold pressor testing (CPT). Results: The BP, HR, carotid artery diameter, and β-stiffness index increased similarly during CPT in both trials (p< 0.001), without any interaction effect. Compared with the IHE trial, arterial compliance decreased in the control groups at 120 seconds during recovery with a significant interaction effect (p=0.02). Conclusion: These findings suggest that an acute IHE did not attenuate BP, HR, carotid artery diameter and β-stiffness index vasoreactivity, but improved carotid artery compliance to sympathetic activation in healthy young adults.
고지방식이 섭취 후 간헐적 저항성 신체활동을 통한 좌식 차단이 혈관 기능 및 식후 대사기능에 미치는 영향
조민정 ( Min Jeong Cho ),정용준 ( Yong Joon Jung ),김연욱 ( Yun Wook Kim ),최태구 ( Tae Gu Choi ),김재엽 ( Jae Yeop Kim ),김현정 ( Hyun Jeong Kim ),제세영 ( Sae Young Jae ) 대한스포츠의학회 2023 대한스포츠의학회지 Vol.41 No.2
Purpose: Numerous studies have reported the effects of interrupting prolonged sitting with aerobic exercise on vascular and postprandial function, but the effects of resistance exercise for interrupting prolonged sitting remain unclear. We tested the hypothesis that intermittent resistance activity breaks would attenuate prolonged sitting-induced vascular and postprandial metabolic dysfunction. Methods: Fourteen healthy adults (age, 24±2 years; body mass index, 22.0±2.4 kg/㎡) completed two trials in a randomized cross-over design. During a 4-hour sitting after a high-fat meal, the participants underwent either resistance activity (RA) with 10 repetitions of five exercises every hour or uninterrupted sitting as a control trial (SIT). Plasma glucose, triglycerides, and brachial artery blood pressure, along with blood flow and shear rate in the superficial femoral artery and carotid artery were measured at baseline and every hour during the 4-hour sitting period. Brachial artery flow-mediated dilation (FMD) was measured at baseline, 2 hours, and 4 hours after the start of the sitting. Results: Plasma glucose and triglycerides increased after a high-fat meal in both RA and SIT groups without a significant interaction effect. In addition, while SIT group decreased brachial artery FMD (7.2%±2.0% to 6.5%±2.7% to 5.1%±2.6%), RA did not attenuate a decrease in FMD (7.6%±3.4% to 7.3%±3.1% to 6.7%±2.7%, interaction p=0.581). Conclusion: Our findings indicate that interrupting prolonged sitting with intermittent RA did not attenuate the negative effects of sitting on vascular function and postprandial metabolism in young healthy adults.