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기계연마에 기인한 Pd(100)의 표면 지형에 대한 AFM 분석
박현주,정경한,추명석,진원배 동아대학교 기초과학연구소 2001 基礎科學硏究論文集 Vol.18 No.1
기계 연마에 기인하는 Pd(100) 표면의 지형 및 연마과정 중에 행해지는 표면 세척방법에 따라 표면 거칠기에 미치는 영향을 AFM으로 조사하였다. 연마 입자의 크기별로 순차적으로 3, 1, 0.1, 0.04 ㎛의 입자로 연마를 수행하였다. 연마의 매 단계마다 시료 표면에 남아있는 연마제를 제거하기 위하여 시료 표면을 단순히 흐르는 물로 세척하는 경우와, 흐르는 물에서 솜으로 세척하는 경우의 표면 거칠기를 비교한 결과, 제곱평균 제곱근에 의한 표면 거칠기는 5×5 ㎛2의 주사영역에서 평균적으로 각각 1.61, 1.08, 0.82 nm 정도의 차이로, 후자의 경우가 훨씬 효과적임을 보여주었다. 이러한 사실로부터 단순히 흐르는 물에 의한 세척으로는 연마의 전 단계에서 사용된 연마 입자들이 표면상에서 완전히 제거되지 않고 다음 단계의 연마 결과에 영향을 미친다는 것을 알 수 있었다. 또한 연마과정 중 bulk로부터 빠져 나온 것으로 보이는 알갱이들이 연마입자에 의해서 발생하는 스크래치의 가장자리를 따라 흡착되어 있는 것이 관측되었다. The effect of surface cleaning performed at every step of mechanical polishing process on surface roughness was investigated with AFM surface topography. Diamond suspensions with grain sizes of 3, 1, 0.1 ㎛ and colloidal silica of 0.04 ㎛ for final polishing were used as abrasive in turn. When the specimen was cleaned with only flowing water at each polishing step, some part of particles remained on the specimen after cleaning. These remaining particles gave rise to relatively pronounced scratches on the surface during the subsequent polishing step, In the other hand, in the case cleaned with a soft wool in flowing water, it was showed that the remaining particles were removed almost all. The lower degree of rms-surface roughness in the latter case compared to that of the former case was obtained, as the differences of rms-surface roughness between both cases were on an average 1.6 nm,1.1 nm, and 0.8nm, respectively, for an area of 5×5 ㎛2 after polishing with 1, 0.1, and 0.04㎛ grain size. In addition, it was found that particles are deposited at the edges of the scratches, which are probably Pd particles removed by the mechanical polishing.
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이온 스퍼터링에 의해 Pd(100)상에 형성된 cone과 crater에 미치는 어닐링 효과
김남희,김홍식,정경한,진원배 동아대학교 기초과학연구소 2000 基礎科學硏究論文集 Vol.17 No.1
Pd(100) 표면을 Ar 이온으로 충돌시켰을 때 형성되는 표면 지형(surface topography)이 어닐링 온도에 따라 어떻게 변하는지를 AFM, SEM, 그리고 광학 현미경으로 조사하였다. Pd(100) 표면을 에너지가 500eV, 그리고 시료에서의 전류 밀도가 ~10nA인 Ar이온으로 5시간 충돌시켰을 때, 표면상에 주로 ㎛크기의 cone과 crater 모양의 구조들과 그외의 형태가 불규칙한 구조들이 형성되었음을 AFM과 SEM영상으로부터 확인할 수 있었다. 이러한 표면 구조물들이 열처리 과정에 의해 어떻게 변하는지를 어닐링 온도와 시간에 따라 조사하였다. 스퍼터링에 의한 시료 세정과정(cleaning process)에서는 Pd인 경우, 일반적으로 200℃의 어닐링 온도에서 거울 면으로 회복되는데 비하여, 어닐링 온도와 시간이 증가함에 따라 cone 과 crater의 분포밀도 및 크기가 감소함을 보여 주고는 있으나, 800℃까지의 온도에서도 이들 구조들이 완전히 소멸되지 않고 일부 남아 있음을 보여주었다. An effect of annealing temperature and time on the surface topography of Pd(100) produced by Ar ion bombardment was investigated using AFM, SEM, and optical microscope. When Pd(100) was bombarded for 5 h by Ar ions with the target current density of ~10 nA and 500 eV, the fact that cones, craters and the other diverse features are produced on the resulting surface was found from SEM image. The other diverse features except for cones and craters on the Ar ion bombarded surface were removed as the annealing temperature increases up to 600℃. But a part of cones and craters still remained at elevated temperature of 800℃, even though the dimensions of them decreased.
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Robust H∞ State Feedback Control of NCSs with Poisson Noise and Successive Packet Dropouts
Faiz Rasool,Sing Kiong Nguang 제어·로봇·시스템학회 2015 International Journal of Control, Automation, and Vol.13 No.1
This paper examines various constraints of networked control systems (NCSs) such as network- induced random delays, successive packet dropouts and Poisson noise. Time delays are represented as modes of Markov chain and successive packet dropouts are modeled using Poisson probability distribution. For each delay-mode, a separate Poisson distribution is used with the help of an indicator function. Poisson noise is incorporated in the design to cater sudden network link failures and power shutdowns. After modeling these constraints, a stability criterion is proposed by using Lyapunov- Krasovskii functional. On the basis of the stability criteria, sufficient conditions for the existence of a robust H∞ state feedback controller are given in terms of bilinear matrix inequalities (BMIs). Later, BMIs are converted into quasi-convex linear matrix inequalities (LMIs) and are solved by using a cone complementarity linearizing algorithm. The effectiveness of the proposed scheme is elaborated with the help of two simulation examples. Moreover, the effects of successive packet dropouts and Poisson noise on H∞ performance are analyzed.
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Graphene nanosheets encapsulated poorly soluble drugs with an enhanced dissolution rate
Shou-Cang Shen,Wai Kiong Ng,Kumaran Letchmanan,Ron Tau Yee Lim,Reginald Beng Hee Tan 한국탄소학회 2018 Carbon Letters Vol.27 No.-
In this study, graphene oxide(GO) was used as drug carriers to amorphize poorly watersoluble drugs via a co-spray drying process. Two poorly water-soluble drugs, fenofibrate and ibuprofen, were investigated. It was found that the drug molecules could be in the graphene nanosheets in amorphous or nano crystalline forms and thus have a significantly enhanced dissolution rate compared with the counterpart crystalline form. In addition, the dissolution of the amorphous drug enwrapped with the graphene oxide was higher than that of the amorphous drug in activated carbon (AC) even though the AC possessed a larger specific surface area than that of the graphene oxide. The amorphous formulations also remained stable under accelerated storage conditions (40°C and 75% relative humidity) for a study period of 14 months. Therefore, graphene oxide could be a potential drug carrier and amorphization agent for poorly water-soluble drugs to enhance their bioavailability.
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Damage detction and characterization using EMI technique under varying axial load
Yee Yan Lim,Chee Kiong Soh 국제구조공학회 2013 Smart Structures and Systems, An International Jou Vol.11 No.4
Recently, researchers in the field of structural health monitoring (SHM) have been rigorously striving to replace the conventional NDE techniques with the smart material based SHM techniques, employing smart materials such as piezoelectric materials. For instance, the electromechanical impedance (EMI) technique employing piezo-impedance (lead zirconate titanate, PZT) transducer is known for its sensitivity in detecting local damage. For practical applications, various external factors such as fluctuations of temperature and loading, affecting the effectiveness of the EMI technique ought to be understood and compensated. This paper aims at investigating the damage monitoring capability of EMI technique in the presence of axial stress with fixed boundary condition. A compensation technique using effective frequency shift (EFS) by cross-correlation analysis was incorporated to compensate the effect of loading and boundary stiffening. Experimental tests were conducted by inducing damages on lab-sized aluminium beams in the presence of tensile and compressive forces. Two types of damages, crack propagation and bolts loosening were simulated. With EFS for compensation, both cross-correlation coefficient (CC) index and reduction in peak frequency were found to be efficient in characterizing damages in the presence of varying axial loading.
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