• 한국재료학회지
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• 제13권9호
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• pp.613-618
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• 2003

The magnetic heating effect of $SiO_2$coated $ \Upsilon-Fe_2$$O_3$nanocomposite particle due to magnetic relaxational loss of superparamagnetic regime was investigated by measuring the generated heat from nanocomposite particles in alternative applied magnetic fields. The commercial $ \Upsilon-Fe_2$$O_3$nanoparticles were coated by SiO$_2$in water solution with TEOS and the synthesized nanocomposite powders and its magnetic properties were characterized and compared with the raw$ \Upsilon-Fe_2$$O_3$nanoparticles. The 10∼30 nm sized $ \Upsilon-Fe_2$$O_3$. nanoparticles were coated by 5 nm thickness of amorphous $SiO_2$film. The nanocomposite particle has very low Mr and Hc value showing superparamagnetic behavior The magnetic heating effect of nanocomposite particle on surface coating phase of $SiO_2$was discussed in terms of superparamagnetic behaviors of each particles, and their potential for hyperthermia application was evaluated.

• 한국재료학회지
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• 제16권4호
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• pp.218-224
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• 2006

RF sputtering process was applied to produce thin hydroxyapatite(HAp) films on Ti-6Al-4V alloy substrates. The effects of different heat treatment conditions on the hardness between HAp thin films and Ti-6Al-4V alloy substrates were studied. Before deposition, the Ti-6Al-4V alloy substrates were heat treated for 1h at $850^{\circ}C\;under\;3.0{\times}10^{-3}torr$, and after deposition, the HAp thin films were heat treated for 1h at $400^{\circ}C,\;600^{\circ}C\;and\;800^{\circ}C$ under the atmosphere, and analyzed FESEM-EDX, FTIR, XRD, nano-indentor, micro-vickers hardness, respectively. Experimental results represented that the surface defects of thin films decreased by relaxation of internal stress and control of substrate structure followed by heat treatment of substrates before the deposition, and the HAp thin films on the heat-treated substrates had higher hardness than none heattreated substrates before the deposition, and the hardness properties of HAp thin films and Ti-6Al-4V alloy substrates appeared independent behavior, and the hardness of HAp thin films decreased by formation of $VTiO_3(OH),\;{\theta}-Al_{0.32}V_2O_5,\;Al_{0.33}V_2O_5$.

• 한국자기학회지
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• 제23권2호
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• pp.43-48
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• 2013

Chalcogenide $Fe_{0.9}M_{0.1}Cr_2S_4$(M=Co, Ni, Zn)에 대하여 X-선 회절법, 자기저항측정, Mossbauer 분광법을 이용하여 CMR특성과 자기적 성질을 연구하였다. 10 at%의 M 치환에서는 상온에서 입방정으로 정상 spinel 구조를 갖는 것으로 나타났다. 자기저항 실험결과 $T_C$ 부근에서는 도체-반도체 전이의 특성을 보이며 최대자기저항 온도가 나타났다. M$\ddot{o}$ssbauer 분광 실험 결과에서 Fe에 대한 Ni 치환은 초교환 상호작용을 강화시키고 Jahn-Teller 효과에 의한 완화 현상의 심화를 보여준다. CMR 특성은 망간산화물의 $Mn^{3+}$와 $Mn^{4+}$ 사이의 이중교환상호작용과 다르게 동적 Jahn-Teller 효과와 관계된 polaron에 기인한 도체-반도체 전이 의한 것으로 해석된다.

• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1995년도 춘계학술대회
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• pp.27-33
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• 1995

A time-dependent large deformation fracture theory is developed for application to soft biological tissues. The theory uses the quasilinear viscoelastic theory of Fung, and particularizes it to constitutive assumptions on polyvinyl-chloride (PVC) (Part I) and cartilage (Part II). This constitutive theory is used in a general viscoelastic theory by Christensen and Naghdi and an energy balance to develop an expression for the fracture toughness of the materials. Experimental methods are developed for measuring the required constitutive parameters and fracture data for the materials. Elastic stress and reduced relaxation functions were determined using tensile and shear tests at high loading rates with rise times of 25-30 msec, and test times of 150 sec. The developed method was validated, using an engineering material, PVC to separate the error in the testing method from the inherent variation of the biological tissues. It was found that the the proposed constitutive modeling can predict the nonlinear stress-strain and the time-dependent behavior of the material. As an approximation method, a pseudo-elastic theory using the J-integral concept, assuming that the material is a time-independent large deformation elastic material, was also developed and compared with the time-dependent fracture theory. For PVC. the predicted fracture toughness is $1.2{\pm}0.41$ and $1.5{\pm}0.23\;kN/m$ for the time-dependent theory and the pseudo-elastic theory, respectively. The methods should be of value in quantifying fracture properties of soft biological tissues. In Part II, an application of the developed method to a biological soft tissue was made by using bovine humeral articular cartilage.

• Bulletin of the Korean Chemical Society
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• 제26권7호
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• pp.1065-1070
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• 2005

$[Mn_{12}O_{12}(O_2CPh-4-SMe)_{16}(H_2O)_4]{\cdot}7CH_2Cl_2$ (1), a new single-molecule magnet complex has been successfully synthesized by substitution of acetate ligand of Mn12ac with 4-(methylthio)benzoic acid. Complex 1 crystallizes into triclinic P$\overline{1}$ with a = 18.321(3) $\AA$, b = 19.011(3) $\AA$, c = 27.230(4) $\AA$, $\alpha$ = 86.973(3)$^{\circ}$, $\beta$ = 76.919(3)$^{\circ}$, $\gamma$ = 87.613(3)$^{\circ}$, and Z = 2. In complex 1, one Mn(III) ion has an abnormal Jahn-Teller elongation axis oriented at an oxide ion. Complex 1 has two out-of-phase ac susceptibility peaks in the 2-4 K and 4-7 K regions. Effective anisotropy energy barrier and pre-exponential factor are $U_{eff}$ = 45.95 K, 1/$\tau$0 = 8.6 ${\times}\;10^9s^{-1}\;for\;{\chi}_M$'' peaks in the lower temperature region and $U_{eff}$ = 59.45 K, 1/$\tau_0$ = 2.2 ${\times}\;10^8\;s^{-1}$ for $\chi_M$'' peaks in the higher temperature region. The parameters of S = 10, g = 1.87, D = -0.40 $cm^{-1}$, and E = 0.00034 $cm^{-1}$ were obtained from the M/N${\mu}_B$ vs. H/T plot of complex 1.

• 한국군사과학기술학회지
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• 제13권6호
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• pp.1121-1126
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• 2010

Borosilicate glass (81% $SiO_2$-2% $Al_2O_3$-13% $B_2O_3$-4% $Na_2O_3$) was prepared, and the glass was ion exchanged in $KNO_3$ powder containing different temperature and time. The $K^+-Na^+$ ion exchange takes place at the glass surface and creates compressed stress, which raise the mechanical strength of the glass. The depth profile of $Na^+$ and $K^+$ was observed by electron probe micro analyzer. With the increasing heat-treatment time from 0min to 20min, the depth profile was increased from 17.1um to 29.4um, but mechanical properties were decreased. It was also found out that excessive heat treatment brings stress relaxation. The Vickers hardness, Fracture Toughness and bending strength of ion exchanged samples at $570^{\circ}C$ for 10min were $821.8H_v$, $1.3404MPa{\cdot}m^{1/2}$, and 953MPa, which is about 120%, 180%, and 450% higher than parent borosilicate glass, respectively. Transmittance was analyzed by UV-VIS-NIR spectrophotometer. Transmittance of ion exchanged borosilicate glass was decreased slightly at visible-range. It can be expected that transparent bulletproof materials in more light-weight and thinner by ion exchanged borosilicate glass.

• The Korean Journal of Physiology
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• 제30권1호
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• pp.11-20
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• 1996

To investigate the properties of cromakalim-opened $K^{+}\;channels$ in aorta of spontaneously hypertensive rats (SHR), the effect of cromakalim on tension was compared in endothelium-rubbed aortic rings from SHR and normotensive Wistar-Kyoto rats (WKY). 1. Cromakalim relaxed the aortic ring contracted by $10^{-7}$ M norepinephrine (NE) dose-dependently, and this relaxant response to cromakalim was blocked by $10^{-5}$ M glybenclamide. 2. Cromakalim also relaxed the contraction induced by high $K^{+}$-solution or 10 mM tetraethylammonium dose-dependently. However, the relaxant response to cromakalim was decreased by raising the $K^{+}$ concentration. 3. SHR aorta exhibited myogenic tone in resting state which was inhibited by cromakalim, verapamil or $Ca^{2+}-free\;PSS.$ Whereas, WKY aorta did not exhibit any myogenic tone in resting state. 4. When aortic rings from both strains were contracted by $20\;mM\;K^{+}\;or\;NE$, relaxant responses to low concentration of cromakalim $(below\;10^{-7}\;M)$ were not different between WKY and SHR, but maximum relaxant response to cromakalim $(above\;3{\times}10^{-7} \;M)$ was greater in SHR than in WKY. 5. When the relaxant response to cromakalim was expressed as percent of maximum relaxation induced by $Ca^{2+}-free\;PSS$, relaxant response to cromakalim in 20 mM $K^{+}-induced$ contraction was not different between WKY and SHR. From the above result, it is suggested that relaxant responses to cromakalim are greater in SHR than WKY, and this may be due to the myogenic tone of aortic rings from SHR.

• 대한기계학회논문집A
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• 제40권12호
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• pp.1027-1035
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• 2016

내식성과 기계적 성능이 우수한 316L 스테인리스 강의 저주기 변형률제어 피로시험에서 3가지 변형률진폭과 3가지 변형률비의 조건이 피로수명에 미치는 효과를 분석하였다. 낮은 변형률범위에서 곡선이 거의 중첩되는 Masing 거동이 나타나고, 높은 변형률범위에서 비선형거동 응력범위가 서로 크게 벗어나는 non-Masing 거동과 함께 평균응력의 감소가 나타났다. 소성 변형률에너지를 이용하여 저주기 피로수명을 예측하고 non-Masing 거동을 고려한 수명예측 방법의 정확성 여부를 검토하였다. 각각의 변형률진폭과 변형률비의 조건에서 초기 수 사이클 동안 반복경화 현상 후 장시간동안 점진적으로 낮아져 연화하다가 파괴 되었다. 저사이클 피로수명을 정확히 예측하기 위해서는 변형률진폭에 따라 Masing 및 non-Masing 거동을 구분하고, 이를 반영한 수명예측식을 적용해야 함을 알았다.

• 한국재료학회지
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• 제11권2호
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• pp.151-154
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• 2001

상부전극, Pt, Ir, 그리고 $IrO_2$, 에 따라 수소 열처리전과 후, 그리고 회복열처리시 누설전류특성을 고찰하였다. Pt/PLZT/Pt 케페시터는 수소열처리 후에 다시 회복열처리를 수행하면 완전히 이력곡선의 회복을 보이며 또한 피로특성도 거의 회복 된다. Pt과 IrO$_2$ 상부전극의 경우의 진 누설전류 특성은 열처리조건에 관계없이 강한 시간 의존성을 갖는 space-charge influenced injection모델에 적합하다. 반면에 Ir 상부전극의 경우는 Ir과 PLZT 사이의 계면에 헝성된 전도성 상인 $IrO_2$로 인해 높은 누설전류 밀도를 보이면서 relaxation current 영역이 없이 steady state 영역을 보이는, 주로 Schottky barrier 모델에 의해 설명된다.

• Bulletin of the Korean Chemical Society
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• 제2권4호
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• pp.142-147
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• 1981

A blend polymeric system composed of poly(methyl methacrylate) (PMMA or PM) and polystyrene (PS) dissolved in chloroform was rheologically studied. The viscosities ${\eta}_{bl}$ of the blend system with various blending ratios ${\chi}$ changing from zero (pure PS solution) to unity (pure PMMA solution) were measured at $25{\circ}C$ as a function of shear rates ${\dot{s}}$ by using a Couette type viscometer. ${\eta}_{bl}$ at a given ${\dot{s}}$ decreased exponentially with ${\chi}$ reaching asymptotic constant value of ${\eta}_{bl}$ ; ${\eta}_{bl}$ at a given ${\chi}$ is greater at a smaller ${\dot{s}}$. These results are explained by using Ree-Erying's theory of viscosity, ${\eta}_{bl}=(x_1{\beta}_1/{\alpha}_1)_{b}_1＋ (x_2{\beta}_2/{\alpha}_2)_{bl}[sinh^{-1}{\beta}_2(bl) {\dot{s}}]/{\beta}_2(bl){\dot{s}}$. The Gibbs activation energy ${\Delta}G_i^\neq$(i = 2 for non-Newtonian units) entering into the intrinsic relaxation time ${\beta}$ is represented by a linear combination ${\Delta}G_i^\neq(bl) ={\chi}{\Delta}G_i^{\neq}_{iPM}+(1-{\chi}){\Delta}G_i^{\neq}_{iPS}$;the intrinsic shear modulus$[[\alpha}_i]^{-1}$ is also represented by $[{\alpha}_i(bl)]^{-1}={\chi}[{\alpha}_{iPM}]^{-1}+(1-{\chi})[{\alpha}_{iPS}]^{-1}$ and the fraction of area on a shear surface occupied by the ith flow units $x_i(bl)$ is similarly represented, i.e., $x_i(bl) = {\chi}x_{iPM}+(1-{\chi})x_{iPS}$. By using these ideas the Ree-Eyring equation was rewritten which explained the experimental results satisfactorily.