• International Journal of Aeronautical and Space Sciences
• /
• v.10 no.2
• /
• pp.43-51
• /
• 2009

In the flight of air vehicles, accurate air data information is required to control them effectively. Especially, helicopters are often put in drastic motion involved with high angle of attacks in order to perform difficult missions. Among various sensors, the multi function probe (MFP) has been used in the present study mainly owing to its advantages in structural simplicity and capability of providing various information such as static and total pressure, speed, and pitch and yaw angles. In this study, a five-hole multi-function probe (FHMFP) is developed and its calibration is conducted using multiple regressions. In this work a calibration study on the FHMFP, an air data sensor for helicopters, is reported. It is shown that the pitch and yaw angles' accuracy of calibration is ${\pm}0.91^{\circ}$ at a cone angle of $0^{\circ}{\sim}30^{\circ}$ and ${\pm}2.0^{\circ}$ at $30^{\circ}{\sim}43^{\circ}$, respectively, which is summarized in table 3.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.36 no.6
• /
• pp.550-557
• /
• 2008

Delamination damage at a bolt hole in a composite stiffened panel was detected using a built-in piezoelectric active sensor array. Various signal processing techniques were used to detect an invisible small scale delamination around a fastener hole due to localized transverse loading. A built-in piezoelectric sensor array was used to generate diagnostic signals and to measure response signals. Then, the response signals were processed to extract damage-sensitive features. Damage indexes were calculated to estimate the severity and location of the damage from the features.

• Journal of the Korean Society for Railway
• /
• v.2 no.2
• /
• pp.21-30
• /
• 1999

This study proposes the analysis and evaluation method of time series ultrasonic signal using the phase space-frequency domain. Features extracted from time series signal analyze quantitatively characteristics of weld defects. For this purpose, analysis objectives in this study are features of time domain and frequency domain. Trajectory changes in the attractor indicated a substantial difference in fractal characteristics resulting from distance shifts such as parts of head and flange even though the types of defects are identified. These differences in characteristics of weld defects enables the evaluation of unique characteristics of defects in the weld zone. In quantitative fractal feature extraction, feature values of 3.848 in the case of part of head(crack) and 4.102 in the case of part of web(side hole) and 3.711 in the case of part of flange(crack) were proposed on the basis of fractal dimension. Proposed phase space-frequency domain method in this study can integrity evaluation for defect signals of rail weld zone such as side hole and crack.

• The Bulletin of The Korean Astronomical Society
• /
• v.42 no.2
• /
• pp.52.1-52.1
• /
• 2017

The discovery of GW150914, black hole - black hole merger via gravitational waves (GWs) opened a new window to observe the Universe. GW frequencies from heavenly bodies and early Universe are expected to span between sub-nHz up to kHz. At present, GW detectors on Earth (LIGO, Virgo, KAGRA, LIGO-India) aims frequency ranges between 10-2000 Hz. The space-borne GW detector and Pulsar Timing Array targets mHz and nHz sources. Starting in March 2017, the KKN (KASI-KISTI-NIMS) collaboration launched a pilot study of SLGT (Superconducting Low-frequency Gravitational-wave Telescope). This project is funded by NST (Korea Institute of Science and Technology). The main detection bands expected for SLGT ranges between 0.1-10Hz, which is complementary of LIGO-type detectors and LISA for multi-band GW observation. We will present an overview of the SLGT project and report the status of the NST pilot study. We will also present prospective of GW astronomy with SLGT.

• Journal of Astronomy and Space Sciences
• /
• v.19 no.1
• /
• pp.25-30
• /
• 2002

Black hole binary candidates are known to be composed of a black hole with 10 $M_{\odot}$ and a K or M type companion. Because the companion is believed to fill the Roche lobe that is very aspherical, the light curves of black hole binaries are characterized by an ellipsoidal variation. It has been known that the ellipsoidal light curves exhibit asymmetric maximum brightness at the orbital phases 0.25 and 0.75, which has been attributed to star spots or the hot impact points of the accretion flow on to the accretion disk around the black hole. In this paper, it is pointed out that the special relativistic beaming effect contributes to the asymmetry of several percent often observed in the light curves. The typical orbital velocity 400 km $s^{-1}$ observed in black hole binaries may induce the temperature difference $\DeltaT/T$ ~ 1/400 of the late type companion star in the observer`s rest frame, because of the special relativistic Doppler beaming effect. This difference in temperature can result in several per cent of brightness sensitively dependent on the wavelength band, which is comparable to what has been observed in most black hole binary candidates. Considering the significant contribution of the special relativistic Doppler beaming effect, we conclude that the estimation of the sizes and temperatures of the star spots or the hot impact point needs serious revision.

• Tunnel and Underground Space
• /
• v.7 no.2
• /
• pp.108-115
• /
• 1997

Uniaxial and biaxial compressive tests were conducted on limestone specimens containing artificial joints and a circular hole to investigate the influence of inclination and number of joints on compressive strength and deformation behavior of rock with a circular hole. Under uniaxial and biaxial compressive condition, the inclination of joints showing the maximum and minimum strength were 0$^{\circ}$ and 30$^{\circ}$ respectively, which was independent of the number of joints. Under uniaxial compressive condition, relative maximum strength of rock with n=1 and 3 to intact rock with a circular hole were 12.5%~82.8% and 11.4~62.5% respectively, and under biaxial compressive condition, 18.2~91.0% and 17.0~87.5% respectively. The influence of the number of joints on the decrease of compressive strength was greater under uniaxial than under biaxial compressive condition. Under uniaxial and biaxial compressive condition, axial and lateral deformations of rock showed the least values where $\alpha$=30$^{\circ}$. Under uniaxial compressive condition, axial and lateral deformation at maximum strength of rock have the increasing tendency with increase the number of joints. But they have the decreasing tendency under biaxial compressive condition. Under uniaxial and biaxial compressive conditions, axial deformation of circular hole was greater than lateral deformation without respect to the number of joints and the inclination of joints.

• The Bulletin of The Korean Astronomical Society
• /
• v.38 no.2
• /
• pp.99-99
• /
• 2013

If the magnetic field is extremely strong, as in pulsar/black hole magnetospheres, the Alfven speed approaches to the speed of light and we need relativity to describe interactions of Alfvenic waves. In this poster, we discuss physics of Alfvenic turbulence in this limit. We first discuss interaction of Alfvenic wave packets and scaling relations of resulting turbulence. Then we show results of numerical simulations. Finally we compare relativistic Alfvenic turbulence and its Newtonian counterpart.

• The Bulletin of The Korean Astronomical Society
• /
• v.44 no.1
• /
• pp.50.4-50.4
• /
• 2019

We detect a new population of chromospheric jets in a polar coronal hole observed by Hinode/SOT. The propagating speed of the jets ranges in 30 - 490 km/s whose duration time is 3 - 52 s. The recurrent rate is approximately 3/min for a give segment of 1 arc-second horizontal interval. These jets are seemed to be more transient and faster than type II spicules at chromosphere, while the properties are compatible with the network jets seen in emission lines of transition region. We will discuss the implication of these jets for a coronal heating.

• Journal of Astronomy and Space Sciences
• /
• v.26 no.4
• /
• pp.439-450
• /
• 2009

Recurrent enhancements of relativistic electron events at geosynchronous orbit (GREEs) were observed in 2006. These GREE enhancements were associated with high-speed solar wind streams coming from the same coronal hole. For the first six months of 2006, the occurrence of GREEs has 27 day periodicity and the GREEs were enhanced with various flux levels. Several factors have been studied to be related to GREEs: (1) High speed stream, (2) Pc5 ULF wave activity, (3) Southward IMF Bz, (4) substorm occurrence, (5) Whistler mode chorus wave, and (6) Dynamic pressure. In this paper, we have examined the effectiveness about those parameters in selected periods.

• Journal of Korean Neurosurgical Society
• /
• v.45 no.6
• /
• pp.397-400
• /
• 2009

This article presents the case of a bilateral chronic subdural hematoma which was contaminated with Klebsiella pneumoniae and resulted in a life-threatening central nervous system infection. After repeated of bilateral burr-hole drainage, the patient became hyperpyrexic and drowsy. Suppuration within the subdural space was suspected and then the patient underwent bilateral fronto-temporo-parietal craniotomies, and pus was evacuated. Its cultures revealed Klebsiella pneumoniae. Intravenous meropenem was given for 6 weeks. He recovered completely. Microorganisms like Klebsiella pneumoniae may directly infect the subdural space with iatrogenic contamination.