• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.11 no.12
• /
• pp.1128-1132
• /
• 1998

We have investigated the relationship between the polar anchoring energy and the surface order parameter in nematic liquid crystal (NLC), 4-n-pentyl-4-cyanobiphenyl (5CB), on the two kinds of the weakly rubbed polyimide (PI) surfaces. The observed polar anchoring energy of 5CB is approximately 2${\times}10^{-4}(J/m^2$) and then increases with increasing the rubbing strength (RS) on weakly rubbed surface (RS=57mm) with side chain at $30^{\circ}C$; same results are obtained on weakly rubbed PI surface without side chain. The surface order parameter of 5CB on rubbed PI surfaces increases with increasing the RS at a weak rubbing region. The surface order parameter of 5CB is strongly related to the characteristics of PI material. Consequently, we suggest that the polar anchoring energy of NLC is strongly attributed to the surface order parameter on rubbed PI surfaces.

• Publications of The Korean Astronomical Society
• /
• v.15 no.spc2
• /
• pp.1-13
• /
• 2000

Through the coupling between the near-earth space environment and the polar ionosphere via geomagnetic field lines, the variations occurred in the magnetosphere are transferred to the polar region. According to recent studies, however, the polar ionosphere reacts not only passively to such variations, but also plays active roles in modifying the near-earth space environment. So the study of the polar ionosphere in terms of geomagnetic disturbance becomes one of the major elements in space weather research. Although it is an indirect method, ground magnetic disturbance data can be used in estimating the ionospheric current distribution. By employing a realistic ionospheric conductivity model, it is further possible to obtain the distributions of electric potential, field-aligned current, Joule heating rate and energy injection rate associated with precipitating auroral particles and their energy spectra in a global scale with a high time resolution. Considering that the ground magnetic disturbances are recorded simultaneously over the entire polar region wherever magnetic station is located, we are able to separate temporal disturbances from spatial ones. On the other hand, satellite measurements are indispensible in the space weather research, since they provide us with in situ measurements. Unfortunately it is not easy to separate temporal variations from spatial ones specifically measured by a single satellite. To demonstrate the usefulness of ground magnetic disturbance data in space weather research, various ionospheric quantities are calculated through the KRM method, one of the magneto gram inversion methods. In particular, we attempt to show how these quantities depend on the ionospheric conductivity model employed.

• Journal of Advanced Marine Engineering and Technology
• /
• v.24 no.1
• /
• pp.127-133
• /
• 2000

A numerical study of the flow of incompressible fluid in a polar cavity is presented. Irregular grids is proposed by applying the interior division principle to the variables on polar coordinate grid formation. Stability analysis and the pressure correction method of SOLA algorithms were discussed in detail on cylindrical coordinates. The results present that unsteady flow behavior appears over $Re=3{\times}10^4$ on polar cavities but nearly steady state at $Re=10^4$. Furthermore, with increasing Reynolds numbers, vortices behaviors indicate more complicated flow phenomena and more severe temporal fluctuation of total kinetic energy and time variation of velocity components at arbitrary pick-up points are detected in case of $Re=5{\times}10^4$.

• Bulletin of the Korean Space Science Society
• /
• 2008.10a
• /
• pp.25.2-25.2
• /
• 2008

Polar rain is a spatially uniform precipitation of electrons with energies around 100eV that penetrate into the polar cap region where geomagnetic field lines are connected to the Interplanetary Magnetic Fields (IMF). Since their occurrences depend on the IMF sector polarity, they are believed to originate from the field aligned component of the solar wind. However, statistically direct correlation between polar rain and solar wind has not been shown. In this presentation, we examined specifically the IMF strength influence on the polar rain flux variation by classifying of IMF sector polarities. For this study, we employed the polar rain flux data measured by STSAT-1 and compared them with the solar wind parameters obtained from the WIND and ACE satellites. We found the direct mutuality between polar rain flux and IMF strength with correlation coefficient above 0.5. This proportional tendency appears stronger when the northern hemisphere is in the away sector of the IMF, which could be associated with a favorable geometry for magnetic reconnection. Simple particle trajectory simulation clearly shows why polar rain intensity depends on the IMF sector polarity. These results are consistent with the direct entry model of Fairfield et al.(1985), while low correlation coefficient with solar wind density, the similarity between slops of both energy spectra shows that transport process occur without acceleration.

• Journal of Astronomy and Space Sciences
• /
• v.30 no.3
• /
• pp.145-152
• /
• 2013

Rotation-powered pulsars are excellent laboratories for studying particle acceleration as well as fundamental physics of strong gravity, strong magnetic fields and relativity. Particle acceleration and high-energy emission from the polar caps is expected to occur in connection with electron-positron pair cascades. I will review acceleration and gamma-ray emission from the pulsar polar cap and associated slot gap. Predictions of these models can be tested with the data set on pulsars collected by the Large Area Telescope on the Fermi Gamma-Ray Telescope over the last four years, using both detailed light curve fitting, population synthesis and phase-resolved spectroscopy.

• Proceedings of the IEEK Conference
• /
• 2000.06c
• /
• pp.181-184
• /
• 2000

In this paper, we propose new features for describing texture images by using multi-channel Gabor filter and log-polar transform based on human visual system (HVS). Gabor features are extracted by the mean and standard deviation of energy in Gabor response, followed by Fourier series extension. Log-polar features are extracted by log-polar transform and projection. The proposed texture descriptor performs reasonably well with less number of features than other texture descriptors, which has been verified by experiments using some texture images of MPEG-7 data set.

• Journal of the Korean Solar Energy Society
• /
• v.25 no.3
• /
• pp.53-60
• /
• 2005

Energy resource is very important to the survival in the polar region. Wind energy, which is one of renewable energy, can guarantee the clean, inexhaustible, natural resource in the polar region. It is essential to assess the wind energy resource of the site where wind turbines will be installed. In the present study, the wind characteristics of the antarctic King Sejong station are analysed from its meteorological observation data. The wind resource of the Sejong station is also simulated and predicted using WAsP program. From the results, the Sejong station has very excellent wind resource and the site where small wind turbines will be installed is determined.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2003.07b
• /
• pp.1078-1081
• /
• 2003

The polar anchoring strength and surface ordering in a NLC, 4-n-pentyl-4'-cyanobiphenyl (5CB), on a rubbed polyimide (PI) surface containing trifluoromethyl moiety were studied. The large extrapolation length de of 5CB for washing process of water was measured at RS=114 mm. The polar anchoring energy of 5CB on the rubbed PI surface is decreased by the washing process. Also, the polar anchoring energy of 5CB increases with the rubbing strength on the PI surface. The surface ordering of 5CB for all washing processes is smaller than the non-washing process; it is attributed to the washing process.

• Bulletin of the Korean Chemical Society
• /
• v.20 no.9
• /
• pp.1010-1016
• /
• 1999

We synthesized the photoresponsive side chain polymers containing aminonitro azobenzene for studying the effect of temperature on photoinduced birefringence. Four different copolymers were prepared using methacrylate, α-methylstyrene, and itaconate monomer. Photoisomerization was observed under the exposure of UV light using UV-VIS absorption spectroscopy. Reorientation of polar azobenzene molecules induced optical anisotropy under a linearly polarized light at 532 nm. The change of the birefringence was observed with increasing the sample temperature under a continuous irradiation of excitation light. We could estimate the activation energy of molecular motion in thermal and photochemical mode. Besides the effect of glass transition temperature on the activation energy, we focused our interests on the effect of geometrical hindrance of polar azobenzene molecules and cooperative motion of environmental mesogenic molecules in the vicinity of polar azobenzene molecules.

• Transactions on Electrical and Electronic Materials
• /
• v.3 no.4
• /
• pp.36-40
• /
• 2002

The polar anchoring strength and surface ordering in a NLC,4-n-pentyl-4'-cyanobiphenyl (5CB), on a rubbed polyimide (PI) surface containing trifluoromethyl moiety were studied. The large extrapolation length de of 5CB for washing process of water was measured at RS=114 mm. The polar anchoring energy of 5CB on the rubbed PI surface is decreased by the washing process. Also, the polar anchoring energy of 5CB increases with the rubbing strength on the PI surface. The surface ordering of 5CB for all washing processes is smaller than the non-washing process; it is attributed to the washing process.