2,010 research outputs found
Measurement of mechanical properties of multilayer thin-films by bulge test
No full text학위논문(석사) - 한국과학기술원 : 기계공학전공, 2004.2, [ vi, 54 p ]근래 MEMS 미소구조물의 기계적 물성 측정 연구가 많이 행해져 왔다. 잘 알려진 영계수를 구하는 시험법으로 Tensile Test, Bending Test, Bulge Test 등이 있다. 이 중 Bulge Test는 시편 제작의 용이성과 잔류 응력을 측정 할 수 있는 장점으로 박막 구조물에 특히 많이 이용되고 있다.
본 연구에서는 개발 중인 MEMS PZT inkjet의 박막에 대해 구동형상과 가장 비슷한 bulge test를 이용하였다. 이를 통해 PZT 박막 구조물의 설계 최적화와 동적 모델링을 위한 변형형상과 물성데이터를 확보 할 수 있다. 이제까지 행해져 왔던 Bulge test의 경우 크고 얇은 박막에 수 백 마이크로 대의 큰 변형이 일어나도록 해서 압력과 변형을 측정하였다. 그러나 본 연구에 사용된 PZT inkjet 박막의 경우 기존의 시험용 시편에 비해 작고 두꺼워 수백 나노 대 작은 변형이 일어난다. 그러므로 더 정밀한 변형 측정 방법으로 측정하였다. PZT inkjet 박막은 잉크를 담는 챔버 위에 크게 두 가지 Si (10m), PZT (22m) 가 적층 된 구조를 가지고 있다. Si 와 PZT의 물성을 각각 측정하기 위해서 layer by layer 로 시편을 준비하여 bulge test 하였다. Si 의 경우 반사면을 가지므로 Twyman-Green 레이저 간섭계로, PZT의 경우 비반사면을 가지므로 ESPI와 AFM으로 각각 측정방법을 달리하여 가압 시 full field 면 외 변위를 측정하였다. 그리고 영계수 Si 107㎬, PZT 47㎬ 을 구하였다. 또한 Bulge test를 통해 얻은 물성의 신뢰성을 확인 하기 위해 nanoindenter CSM을 이용하여 영계수를 측정하였고, 미소 박막 구조물의 물성 측정의 경우 bulge test가 geometry 영향을 nanoindenter보다 덜 받음을 확인하였다.한국과학기술원 : 기계공학전공
Effects of sintering conditions on mechanical properties of mechanically alloyed tungsten heavy alloys
No full textThe effects of sintering conditions on the microstructural evolution and mechanical properties of mechanically alloyed tungsten heavy alloys were investigated. W, Ni and Fe powders were mechanically alloyed in a tumbler ball mill at a milling speed of 75 rpm, ball-to-powder ratio of 20:1 and ball filling ratio of 15%. The mechanically alloyed powders were compacted and solid-state sintered at a temperature of 1300 degreesC for 1 hour in a hydrogen atmosphere. The solid-state sintered tungsten heavy alloy was subsequently liquid-phase sintered at 1470 degreesC with varying sintering times from 4 min to 90 min. The solid-state sintered tungsten heavy alloy showed fine tungsten particles of 3 mum in diameter and high relative density above 99%. The volume fraction of the W-Ni-Fe matrix phase was measured, as 11% and tungsten/tungsten contiguity was 0.74 in solid-state sintered tungsten heavy alloys. Mechanically alloyed and two-step sintered tungsten heavy alloys showed tungsten particles of 6-15 mum and a volume fraction of the W-Ni-Fe matrix phase of 16% and tungsten/ tungsten contiguity of 0.40. The solid-state sintered tungsten heavy alloy exhibited a yield strength of about 1100 MPa due to its finer tungsten particles, while it showed low elongation and impact energy due to its large tungsten/tungsten contiguity. The yield strength of two-step sintered tungsten heavy alloys increased with the decreasing of tungsten particle size and volume fraction of the W-Ni-Fe matrix
Simple and Sensitive Point‐of‐Care Bioassay System Based on Hierarchically Structured Enzyme‐Mimetic Nanoparticles
No full textAn enzyme-mimetic nanoparticle-based point of care bioassay device is developed for rapid and sensitive detection of analytes. Digital images acquired by smart cellular phones allow quantifying the amounts of analytes. Using this new device, quantitative analysis of liquid sample is performed within 15 min with an order of magnitude enhancement of sensitivity compared with conventional Au nanoparticle-based devices.N
Fabrication and properties of mechanically alloyed oxide-dispersed tungsten heavy alloys
No full textThe microstructures and mechanical properties of mechanically alloyed oxide-dispersed tungsten heavy alloys were investigated. Elemental powders of tungsten, nickel, and iron of a composition corresponding to 93W-5.6Ni-1.4Fe (wt.%) were mechanically alloyed with additional Y2O3 powders in a tumbler ball mill for 72 h. Mechanically alloyed powders were solid-state sintered at 1300degreesC for I h followed by secondary liquid-phase sintering at 1470degreesC for a sintering time ranging from 4 to 90 min. Liquid-phase sintering of oxide-dispersed tungsten heavy alloys at 1485degreesC for I h was also carried out. Oxide-dispersed tungsten heavy alloys containing 0.1-5 wt.% Y2O3 can be obtained and oxide dispersoids effectively inhibit the coarsening of tungsten particles during sintering. A high temperature compression test of tungsten heavy alloys at 800degreesC showed that the strength of mechanically alloyed oxide-dispersed tungsten heavy alloys increased with the oxide content. In split-Hopkinson bar tests at a strain rate of 10(4) s(-1), the oxide-dispersed tungsten heavy alloy showed a tendency for premature failure during localized shear deformation due to debonding at the oxide/matrix interfaces. (C) 2003 Elsevier B.V. All rights reserved.
Learning Curve for Lumbar Decompressive Laminectomy in Biportal Endoscopic Spinal Surgery Using the Cumulative Summation Test for Learning Curve
No full textOBJECTIVE: The purpose of the present study was to determine the learning curve for biportal endoscopic spinal surgery (BESS) for decompressive laminectomy in lumbar spinal stenosis using a learning curve cumulative summation test (LC-CUSUM). METHODS: The surgeon was proficient in open and microscopic decompressive laminectomy in lumbar spinal stenosis but did not have any experience with BESS or other endoscopic surgery techniques. The learning curve of BESS was investigated using LC-CUSUM analysis. Procedure success was defined as an operative time <75 minutes, the mean operative time with microscopic decompression laminectomy. RESULTS: The present study included the first 60 patients who had undergone single-level decompressive laminectomy using BESS by a single orthopedic surgeon. The mean operative time for decompressive laminectomy by BESS was 83.8 +/- 37.9 minutes. The mean operative time in the early learning period (<= 30 cases) and late learning period (second 30 cases) was 105.3 +/- 39.7 minutes and 62.4 +/- 19.9 minutes, respectively. The overall complication rate was similar to 10%. The LC-CUSUM signaled competency for surgery at the 58th operation, indicating that sufficient evidence had accumulated to prove that the surgeon was competent. Thus, a trainee with no experience with BESS had reached adequate performance at 58 cases. CONCLUSIONS: The results of the present study have demonstrated that a substantial learning period could be needed before adequate performance can be achieved with lumbar decompressive laminectomy using BESS.OAIID:RECH_ACHV_DSTSH_NO:T201903844RECH_ACHV_FG:RR00200001ADJUST_YN:EMP_ID:A079510CITE_RATE:1.924FILENAME:2019-World Neurosurg_Park_Learning curve for lumbar decompressive laminectomy.pdfDEPT_NM:의학과EMAIL:[email protected]_YN:YFILEURL:https://srnd.snu.ac.kr/eXrepEIR/fws/file/5fee23eb-0d3e-4d3f-ac81-b3acbde10930/linkN
Combination of mechanical alloying and two-stage sintering of a 93W-5.6Ni-1.4Fe tungsten heavy alloy
No full textThe microstructural evolution and mechanical properties of a mechanically alloyed and two-stage sintered tungsten heavy alloy were investigated. Elemental powders of tungsten, nickel and iron of a composition corresponding to 93W-5.6Ni-1.4Fe were mechanically alloyed in a tumbler ball mill for 72 h. Mechanically alloyed powders were solid-state sintered at 1300 degreesC for 1 hr in a hydrogen atmosphere followed by secondary sintering at 1445-1485 degreesC for a sintering time ranging from 4 to 90 min. Solid-state sintered tungsten heavy alloys exhibited full densification (above 99% in relative density) due to the enhanced sintering resulting from mechanical alloying. Secondary sintering with a rapid heating rate changed the microstructures of the solid-state sintered alloy with contiguous tungsten phases into a dispersion alloy with spherical tungsten particles embedded in the W-Ni-Fe matrix, maintaining fine tungsten particle due to the combination of a mechanical alloying and a short sintering time. The two-stage sintered tungsten heavy alloy from mechanically alloyed powders showed finer tungsten particle (about 6 mum in diameter) than in conventional liquid-phase sintered tungsten heavy alloys. The mechanical properties of a tungsten heavy alloy were found to be dependent on the microstructural parameters such as tungsten particle size, matrix volume fraction and tungsten/tungsten contiguity which are controllable through the two-stage sintering process. (C) 2002 Elsevier Science B.V. All rights reserved
Pt-Decorated Magnetic Nanozymes for Facile and Sensitive Point-ofCare Bioassay
No full textDevelopment of facile and sensitive bioassays is important for many point-of-care applications. In this study, we fulfilled such demand by synthesizing Pt-decorated magnetic nanozymes and developing a bioassay based on unique properties of the newly synthesized nanozymes. Fe3O4–Pt/core–shell nanoparticles (MPt/CS NPs) with various compositions were synthesized and characterized. Fe3O4 NP itself is a good nanozyme with catalytic activity superior to that of natural enzymes, but catalytic activity can be further improved by incorporating Pt to the outer layers of the Fe3O4 NPs and building heterogeneous nanostructures. Magnetic properties of MPt/CS NPs enable magnetic enrichment of liquid samples, whereas catalytic properties of MPt/CS NPs allow signal amplification by enzyme-like reactions. By integrating MPt/CS NPs in lateral flow immunoassay strips, one of the widely used point-of-care bioassay devices, and harnessing magnetic and enzyme-like properties of MPt/CS NPs, an increase in sensitivity of two orders of magnitude was achieved compared to the sensitivity of conventional lateral flow immunoassay based on Au nanoparticles.1
Effect of reductive cyclic carbonate additives and linear carbonate cosolvents on fast chargeability of LiNi0.6Co0.2Mn0.2O2/graphite cells
No full textFor application to electric vehicles, the fast charging of lithium-ion batteries is required. However, lithium-ion batteries are faced with undesirable Li plating causing the capacity fading with low Coulombic efficiency at high charge rates. Here, we present the effects of solid electrolyte interphase structures of the graphite anode and linear carbonate solvents on fast charging capability of LiNi0.6Co0.2Mn0.2O2/graphite full cells. To control the nature of the interfacial layer on the graphite anode affecting the Li plating behavior, we exploit three kinds of additives, ethylene carbonate, fluoroethylene carbonate and vinylene carbonate, as anode solid electrolyte interphase formers. In addition, the effect of ethyl methyl carbonate and dimethyl carbonate on the solvation and transport of high concentrations of Li ions de-intercalated from the LiNi0.6Co0.2Mn0.2O2 cathode in a full cell at high charge rates is explored in fluoroethylene carbonate-based electrolytes. Our investigation reveals that the combination of fluoroethylene carbonate and dimethyl carbonate in the electrolyte enables fast-charging LiNi0.6Co0.2Mn0.2O2/graphite full cells showing the excellent capacity retention of 79% after 1000 cycles at a high charging current density of 6&#8239;mA&#8239;cm&#8722;2, corresponding to 2C, and a discharge rate of 1C without Li plating on the graphite anode
Inhibitory effect of carbon dioxide on the fed-batch culture of Ralstonia eutropha: Evaluation by CO2 pulse injection and autogenous CO2 methods
No full textIn order to see the effect of CO2 inhibition resulting from the use of pure oxygen, we carried out a comparative fed-batch culture study of polyhydroxybutyric acid (PHB) production by Ralstonia eutropha using air and pure oxygen in 5-L, 30-L, and 300-L fermentors. The final PHB concentrations obtained with pure O-2 were 138.7 g/L in the 5-L fermentor and 131.3 g/L in the 30-L fermentor, which increased 2.9 and 6.2 times, respectively, as compared to those obtained with air. In the 300-L fermentor, the fed-batch culture with air yielded only 8.4 g/L PHB. However, the maximal CO2 concentrations in the 5-L fermentor increased significantly from 4.1% (air) to 15.0% (pure O-2), while it was only 1.6% in the 30-L fermentor with air, but reached 14.2% in the case of pure O-2. We used two different experimental methods for evaluating CO2 inhibition: CO2 pulse injection and autogenous CO2 methods. A 10 or 22% (V/V) CO2 pulse with a duration of 3 or 6 h was introduced in a pure-oxygen culture of R. eutropha to investigate how CO2 affects the synthesis of biomass and PHB. CO2 inhibited the cell growth and PHB synthesis significantly. The inhibitory effect became stronger with the increase of the CO2 concentration and pulse duration. The new proposed autogenous CO2 method makes it possible to place microbial cells under different CO2 level environments by varying the gas flow rate. Introduction Of O-2 gas at a low flow rate of 0.42 vvm resulted in an increase of CO2 concentration to 30.2% in the exit gas. The final PHB of 97.2 g/L was obtained, which corresponded to 70% of the PHB production at 1.0 vvm O-2 flow rate. This new method measures the inhibitory effect of CO2 produced autogenously by cells through the entire fermentation process and can avoid the overestimation of CO2 inhibition without introducing artificial CO2 into the fermentor. (C) 2003 Wiley Periodicals, Inc
Full three-dimensional subwavelength high-Q surface-plasmon-polariton cavity
No full textWe propose a full three-dimensional subwavelength surface-plasmon-polariton cavity based on a metal-coated dielectric nanowire with an axial heterostructure. Surface plasmon-polaritons are strongly confined at the nanowire-metal interface sandwiched by an effective plasmonic mirror that consists of lower-index nanowire core and metal shelf. Numerical simulations show for a cavity <50 x 50 x 40 nm(3) (mode volume, V 10(-5) mu m(3)) that a quality factor, Q(,) >36000 is achieved at 20 K. This ultrasmall plasmonic cavity can be used as a plasmonic emitter or laser device coupled to a plasmonic waveguide with a high coupling efficiency in deep-subwavelength photonic systems
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