• 한국항공우주학회지
• /
• 제35권5호
• /
• pp.426-437
• /
• 2007

초음속 흡입구는 설계점에서 안정된 작동을 보이지만 탈설계점에서는 흔히 버즈라고 불리는 공력 불안정성에 직면하게 되고, 결과적으로 현저한 엔진 성능의 저하를 초래하게 된다. 버즈의 일반적인 특성을 파악하기 위해 1단 꺽임각을 갖는 외부 압축식 축대칭 흡입구를 이용하여 실험적, 수치적 연구를 수행하였다. 본 연구를 통해, 흡입구 목에서 박리에 의한 흡입구 질식이 버즈의 주요 원인임을 밝힘으로써 버즈 현상의 메커니즘을 파악하였다. 여러 면적비율에 따라 간헐적 버즈와 연속적 버즈가 관찰되었고 그 천이과정이 파악되었다. 면적비율이 감소할수록 버즈 주파수가 증가하였으나, 각 면적비율에서 흡입구 내 모든 위치의 압력 진동 주파수는 동일한 특성을 갖는다.

• 한국광물학회지
• /
• 제27권4호
• /
• pp.283-291
• /
• 2014

층상규산염광물 중 하나인 활석($Mg_3Si_4O_{10}(OH)_2$)은 경도가 매우 낮고, 산업분야에서 매우 다양하게 이용되는 재료물질이다. 실험에 이용한 활석은 외부가열열수고압기기를 이용하여 압력 200 MPa, 온도 $600^{\circ}C$인 조건하에서 합성한 분말시료이다. 포항가속기연구소에서 대칭다이아몬드 앤빌 기기와 방사광 및 각분산 X-선회절방법을 이용하여 상온에서 11.06 GPa까지 압축실험을 시행하였다. 본 실험의 압력 범위 내에서 상변이는 관찰하지 못하였다. 체적탄성률은 버치-머내한 상태방정식을 이용하여 72.4 GPa로 결정되었으며, 이 값은 천연산활석에 비해 낮은 것으로 나타났다.

• 한국초전도ㆍ저온공학회논문지
• /
• 제15권3호
• /
• pp.5-8
• /
• 2013

We have studied Hall effect for potassium (K)-doped $BaFe_2As_2$ superconducting thin films by analyzing the relation between the longitudinal resistivity (${\rho}_{xx}$) and the Hall resistivity (${\rho}_{xy}$). The thin films used in this study were fabricated on $Al_2O_3$ (000l) substrates by using an ex-situ pulsed laser deposition (PLD) technique under a high-vacuum condition of ~$10^{-6}$ Torr. The samples showed the high superconducting transition temperatures ($T_c$) of ~ 40 K. The ${\rho}_{xx}$ and the ${\rho}_{xy}$ for K-doped $BaFe_2As_2$ thin films were measured by using a physical property measurement system (PPMS) with a temperature sweep (T-sweep) mode at an applied current density of $100A/cm^2$ and at magnetic fields from 0 up to 9 T. We report the T-sweep results of the ${\rho}_{xx}$and the ${\rho}_{xy}$ to investigate Hall scaling behavior on the basis of the relation of ${\rho}_{xy}={A{\rho}_{xx}}^{\beta}$. The ${\beta}$ values are $3.0{\pm}0.2$ in the c-axis-oriented K-doped $BaFe_2As_2$ thin films, whereas the thin films with various oriented-directions like a polycrystal showed slightly lower ${\beta}$ than that of c-axis-oriented thin films. Interestingly, the ${\beta}$ value is decreased with increasing magnetic fields.

• 문화기술의 융합
• /
• 제3권2호
• /
• pp.55-59
• /
• 2017

본 연구는 무선통신 방식에 따른 통신 코드를 통해 생체신호를 전달하는 과정을 확인하였다. 생체 시스템은 ECG, PPG, Bluetooth으로 구성하여 신호를 받았고, 통신방식은 국제표준으로 IEEE802.15.1에 따라 진행하였으며, 주파수이동에 필요한 대역통신방식으로 신호를 산출하여 전송하였다. 무선통신으로 받은 신호를 표현하기 위해 사용된 프로그램은 Serial Chart, Processing, App Inventor를 구성하여 신호가 원활하게 전송됨을 확인하였다. 따라서 신호처리에 따른 실시간 그래프를 위한 코드와 프로세싱을 활용한 Serial Chart 그래프의 정량적 유추가 진행되면 원활한 무선통신 방식의 개선효과가 있을 것으로 예상된다.

• 한국세라믹학회지
• /
• 제47권4호
• /
• pp.343-352
• /
• 2010

A zirconia gel/polymer hybrid nanofiber was produced in a nonwoven fabric mode by electrospinning a sol derived from hydrolysis of zirconium butoxide with a polyvinyl butyral. Results indicated that the hydroxyl groups on the vinyl alcohol units in the backbone of the polymer were involved in the hydrolysis as well as grafting the hydrolyzed zirconium butoxide. In addition, use of acetic acid as a catalyst resulted in further hydrolysis and condensation in the sol, which led to the growth of -Zr-O-Zr- networks among the polymer chains. These networks gradually transformed into a crystalline zirconia structure upon heating. The as-spun fiber was smooth but partially wrinkled on the surface. The average fiber diameter was $690{\pm}110\;nm$. The fiber exhibited a strong but broad blue photoluminescence with its maximum intensity at a wavelength of ~410 nm at room temperature. When the fiber was heat-treated at $400^{\circ}C$, the fiber diameter shrunk to $250{\pm}60\;nm$. Nanocrystals which belonged to a tetragonal zirconia phase and were ~5 nm in size appeared. A strong white photoluminescence was observed in this fiber. This suggests that oxygen or carbon defects associated with the formation of the nanocrystals play a role in generating the photoluminescence. Further heating to $800^{\circ}C$ resulted in a monoclinic phase beginning to form In the heat-treated fibers, coloring occurred but varied depending on the heating temperature. Crystallization, coloring, and phase transition to the monoclinic structure influenced the photoluminescence. At $600^{\circ}C$, the fiber appeared to be fully crystallized to a tetragonal zirconia phase.

• 한국지반환경공학회 논문집
• /
• 제13권9호
• /
• pp.75-82
• /
• 2012

본 논문은 2006년 태풍 에위니아와 빌리스의 영향으로 강원 영서지역에서 발생한 집중호우에 의한 산사태 발생 원인과 특성에 대하여 분석한 결과이다. 강원 영서지역은 편마암, 화강암이 풍화된 화강풍화토가 주를 이루는 지역으로 집중호우 시 산사태 및 토석류의 피해에 취약한 것으로 나타났으며 강우특성 분석결과, 산사태 발생은 3일 이내의 누적강우량과 밀접한 관계가 있었고 지역별 발생빈도의 차이는 최대시우량의 영향으로 나타났다. 영서지역에서 발생한 산사태 860개소에 대한 자료의 분석 결과, 파괴 형태는 전이형 슬라이드로 시작되어 유동성 슬라이드로 변화되는 양상을 보였으며, 사면 경사는 $20{\sim}30^{\circ}$ 사면 길이는 11~20m 범위, 사면 폭은 6~10m 범위에서 발생빈도가 높은 것으로 나타났고, 영서지역의 산사태는 사면 폭이 좁은 소규모 형태로 편마암, 화강암 지대의 산사태 전형으로 분석되었다.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
• /
• pp.288.1-288.1
• /
• 2014

We investigated the optical properties of Ge1-xSex and Ge1-x-ySexAsy amorphous semiconductor films using spectroscopic ellipsometry and Raman spectroscopy. The dielectric functions and absorption coefficients of the amorphous films were determined from the measured ellipsometric angles. We obtained the optical gap energies and Urbach energies from the absorption coefficients, and found a strong bowing effect in the optical gap energy of Ge1-x-ySexAsy where the endpoint binaries were Ge0.50Se0.50 and Ge0.31As0.69. Based on the correlation between optical gap energies and Urbach energies, the large bowing parameter was attributed to the electronic disorder. We found the composition dependence of several phonon modes using Raman spectroscopy. For Ge1-x-ySexAsy, the D mode (232-267 cm-1) changed from As-As (or As3 pyramid), to As(Se1/2)3 pyramid, and finally to Se clusters, as the Se composition increased. Resonant Raman phenomenon was observed in Ge0.38Se0.62 at a laser excitation of 514 nm (2.41 eV). We verified that this laser energy corresponds to the transition energy of Ge0.38Se0.62 using the second derivative of the dielectric function of Ge0.38Se0.62.

• 정보처리학회논문지:소프트웨어 및 데이터공학
• /
• 제6권3호
• /
• pp.141-148
• /
• 2017

인간의 위치 이동 데이터를 모바일 기기에서 수집한 위치 정보를 이용해 얻을 수 있게 되면서, 위치 정보를 어떻게 이용할 수 있는지 그 활용 방안이 중요시 되고 있다. 이 연구에 앞서 위치 정보에 포함된 위치 정보와 시간 정보를 이용한 개인 이동성 모델 도출 연구가 선행되었다. 이동성 모델의 개념을 집단으로 확장하여 특정 집단에 속한 사람들의 개인 이동성 모델을 이용한 집단 이동성 모델을 도출하는 방법에 대해서 연구했고, 두 명의 개인 이동성 모델을 이용한 집단 이동성 모델과 그 모델을 표현하는 Markov 모델을 생성할 수 있었다. 본 논문에서는 세명 이상의 개별 이동 모델을 포함하는 사람의 이동성 모델을 생성하고 집단 모델 내 군집간의 확률 기반 Markov 모델을 도출하는 방법에 대해 소개한다. 또한 GPGPU 기법을 통해 생성 시간을 줄이는 기법을 이용하여 실용화를 고려하였다.

• The Korean Journal of Physiology and Pharmacology
• /
• 제22권5호
• /
• pp.585-595
• /
• 2018

Amitriptyline, a tricyclic antidepressant, is commonly used to treat depression and neuropathic pain, but its mechanism is still unclear. We tested the effect of amitriptyline on 5-hydroxytryptamine 3 ($5-HT_3$) receptor currents and studied its blocking mechanism because the clinical applications of amitriptyline overlapped with $5-HT_3$ receptor therapeutic potentials. Using a whole-cell voltage clamp method, we recorded the currents of the $5-HT_3$ receptor when 5-HT was applied alone or co-applied with amitriptyline in cultured NCB-20 neuroblastoma cells known to express $5-HT_3$ receptors. To elucidate the mechanism of amitriptyline, we simulated the $5-HT_3$ receptor currents using Berkeley $Madonna^{(R)}$ software and calculated the rate constants of the agonist binding and receptor transition steps. The $5-HT_3$ receptor currents were inhibited by amitriptyline in a concentration-dependent, voltage-independent manner, and a competitive mode. Amitriptyline accelerated the desensitization of the $5-HT_3$ receptor. When amitriptyline was applied before 5-HT treatment, the currents rose slowly until the end of 5-HT treatment. When amitriptyline was co-applied with 5-HT, currents rose and decayed rapidly. Peak current amplitudes were decreased in both applications. All macroscopic currents recorded in whole cell voltage clamping experiments were reproduced by simulation and the changes of rate constants by amitriptyline were correlated with macroscopic current recording data. These results suggest that amitriptyline blocks the $5-HT_3$ receptor by close and open state blocking mechanisms, in a competitive manner. We could expand an understanding of pharmacological mechanisms of amitriptyline related to the modulation of a $5-HT_3$ receptor, a potential target of neurologic and psychiatric diseases through this study.

• Korea-Australia Rheology Journal
• /
• 제13권1호
• /
• pp.29-35
• /
• 2001

The development of filament stretching extensional rheometers over the past decade has enabled the systematic measurement of the transient extensional stress growth in dilute and semi-dilute polymer solutions. The strain-hardening in the extensional viscosity of dilute solutions overwhelms the perturbative effects of capillarity, inertia & gravity and the kinematics of the extensional deformation become increasingly homogeneous at large strains. This permits the development of a robust open-loop control algorithm for rapidly realizing a deformation with constant stretch history that is desired for extensional rheometry. For entangled fluids such as concentrated solutions and melts the situation is less well defined since the material functions are governed by the molecular weight between entanglements, and the fluids therefore show much less pronounced strain-hardening in transient elongation. We use experiments with semi-dilute/entangled and concentrated/entangled monodisperse polystyrene solutions coupled with time-dependent numerical computations using nonlinear viscoelastic constitutive equations such as the Giesekus model in order to show that an open-loop control strategy is still viable for such fluids. Multiple iterations using a successive substitution may be necessary, however, in order to obtain the true transient extensional viscosity material function. At large strains and high extension rates the extension of fluid filaments in both dilute and concentrated polymer solutions is limited by the onset of purely elastic instabilities which result in necking or peeling of the elongating column. The mode of instability is demonstrated to be a sensitive function of the magnitude of the strain-hardening in the fluid sample. In entangled solutions of linear polymers the observed transition from necking instability to peeling instability observed at high strain rates (of order of the reciprocal of the Rouse time for the fluid) is directly connected to the cross-over from a reptative mechanism of tube orientation to one of chain extension.