• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.357-357
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• 2010

Using ab initio density functional theory, we study the structural and electronic properties of interface between Cu surface and highly electron withdrawing hexaazatriphenylene-hexanitrile (HAT-CN) known as an efficient hole injection layer for organic light emitting diodes (OLEDs). We calculate the equilibrium geometries of the interface with different HAT-CN coverages. Usually, some of C-N bonds located at the edge of the HAT-CN molecule are deformed toward Cu atoms resulting in the reconstruction of Cu surface. By analyzing the electron charge and the potential distributions over the interface, we observe the formation of surface dipoles, which modify the work function at the interface. Such dipole formation is attributed to two origins, one of which is a geometrical nature and the other is a bond dipole. The former is related to structural deformation mentioned above, whereas the latter is due to charge transfer between organic and metal surface.

• Geophysics and Geophysical Exploration
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• v.9 no.1
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• pp.121-128
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• 2006

Magnetic survey flights by helicopters are usually parallel to the topographic surface, with a nominal clearance, but especially in high-resolution surveys the altitudes at which observations are made may be too variable to be regarded as a smooth surface. We have developed a reduction procedure for such data using the method of equivalent sources, where surrounding sources are included to control edge effects, and data from points distributed randomly in three dimensions are directly modelled. Although the problem is generally underdetermined, the method of conjugate gradients can be used to find a minimum-norm solution. There is freedom to select the harmonic function that relates the magnetic anomaly with the source. When the upward continuation function operator is selected, the equivalent source is the magnetic anomaly itself. If we select as source a distribution of magnetic dipoles in the direction of the ambient magnetic field, we can easily derive reduction-to-pole anomalies by rotating the direction of the magnetic dipoles to vertical.

• Journal of the Society of Naval Architects of Korea
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• v.28 no.2
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• pp.159-173
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• 1991

This paper describes a potential-based panel method formulated for the analysis of a super-cavitating two-dimensional hydrofoil. The method employs normal dipoles and sources distributed on the foil and cavity surfaces to represent the potential flow around the cavitating hydrofoil. The kinematic boundary condition on the wetted portion of the foil surface is satisfied by requiring that the total potential vanish in the fictitious inner flow region of the foil, and the dynamic boundary condition on the cavity surface is satisfied by requiring thats the potential vary linearly, i.e., the tangential velocity be constant. Green's theorem then results in a potential-based integral equation rather than the usual velocity-based formulation of Hess & Smith type. With the singularities distributed on the exact hydrofoil surface, the pressure distributions are predicted with improved accuracy compared to those of the linearized lilting surface theory, especially near the leading edge. The theory then predicts the cavity shape and cavitation number for an assumed cavity length. To improve the accuracy, the sources and dipoles on the cavity surface are moved to the newly computed cavity surface, where the boundary conditions are satisfied again. This iteration process is repeated until the results are converged. Characteristics of iteration and discretization of the present numerical method are much faster and more stable than the existing nonlinear theories. The theory shows good correlations with the existing theories and experimental results for the super-cavitating flow. In the region of small angles of attack, the present prediction shows and excellent comparison with the Geurst's linear theory. For the long cavity, the method recovers the trends of the Wu's nonlinear theory. In the intermediate regions of the short super-cavitation, the method compares very well with the experimental results of Parkin and also those of Silberman.

• Selected Papers of The Society of Naval Architects of Korea
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• v.1 no.1
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• pp.15-25
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• 1993

A potential-based panel method is presented for the analysis of a partially-cavltatlng two-dimensional hydrofoil. The method employs normal dipoles and sources distributed on the foil and cavity surfaces. It is shown that the source plays an Important role in positioning the cavity surface through an iterative process. The cavity closure consition is found very effective in generating the cavity shape. Upon convergence, the method predicts the cavitation nurser, together with the lift, the drag and the surface pressure distribution, for a given cavity length. Systematic convergence tests shows that the present numerical method is fast and stable. The present computations show a good agreement with the previously computed and measured results.

• Bulletin of the Korean Chemical Society
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• v.32 no.1
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• pp.41-48
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• 2011

The wettabilities of the partially fluorinated polymers (ethylene-tetrafluoroethylene copolymer (ETFE), ethylenechlorotrifluoroethylene copolymer (ECTFE), and poly(vinylidene fluoride) (PVDF)) were investigated by contact angle measurements. Zisman plots for ETFE and ECTFE exhibited linear relationships, while the Zisman plot for PVDF showed a slight curvature, which was interpreted to indicate strong non-dispersive interactions between the surface and the contacting liquids. The Lifshitz-van der Waals forces of the fluoropolymers were estimated to increase in the order of ETFE < PVDF $\ll$ ECTFE. An evaluation of the polar or "acid-base" interaction energies showed that PVDF, which possesses the most acidic hydrogens among the examined fluoropolymers, has the strongest acid-base interactions.

• Advances in concrete construction
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• v.13 no.3
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• pp.255-264
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• 2022

Vibration is expected to occur in microtubules as tubular heterodimers. They oscillate like electric dipoles. Several research studies have estimated a frequency of vibration using the orthotropic model, a beam or rod like models and shell models, considering the surface forces. The effects of body forces on the dynamics of the microtubules were not yet taken into account. This study seeks to capture the body force effects on the vibration modes generated and on the corresponding frequency for microtubules. An orthotropic elastic shell model for the structural details of microtubules is used for the analysis. The tests are conducted out for microtubules, exposed to electro-magnetic and gravitational forces, the transverse vibration, radial mode vibration, and axial mode of vibration have accomplished. We therefore, evaluate and compare microtubules' frequencies with prior results of vibration frequency without the effects of body force.

• Journal of KSNVE
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• v.7 no.1
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• pp.71-79
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• 1997

The objective of this study is to investigate experimentally the effect of surface conditions of the plate on the impinging jet noise. The experimental results about the spectrum, the sound pressure level and the directivity are pressented and discussed in relation with the surface conditions. Regardless of the surface conditions, the pure tones of high level are generated at the same frequency band and the overall sound power level of impinging jets is much higher than that of the free jet. However, the velocity dependence of the sound pressure level and the directivity are different between smooth surfaces and rough surfaces. The dependence of sound pressure level on the jet velocity shows that the smooth surface generates quadrupole-type sound like free jets. However, the perforated or the rough surface radiates sound power exactly proportional to the sixth power of the jet velocity, indicating that the source is fixed dipole type. The directivities of 1/3 octave band sound pressure level for both the free and impinging jet show the peak directivity at 115$^\circ$ upstream, probably due to the refraction associated with velocity gradient.

• Bulletin of the Society of Naval Architects of Korea
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• v.19 no.1
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• pp.23-32
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• 1982

Herein the motion of a freely-floating sphere in a water of finite depth is analysed within the framework of a linear potential theory. A velocity potential describing fluid motion is generated by distributing pulsating sources and dipoles on the immersed surface of the sphere, without introducing an inner flow model. The potential becomes the solution of an integral equation of Fredholm's second type. In the light of the vertical axisymmetry of the flow, surface integrals reduce to line integrals, which are approximated by summation of the products of the integrand and the length of segments along the contour. Following this computational scheme the diffraction potential and the radiation potential are determined from the same algorithm of solving a set of simultaneous linear equations. Upon knowing values of the potentials hydrodynamic forces such as added mass, hydrodynamic damping and wave exciting forces are evaluated by the integrating pressure over the immersed surface of the sphere. It is found in the case of finite water depth that the hydrodynamic forces are much different from the corresponding ones in deep water. Accordingly motion response of the sphere in a water of finite depth displays a particular behavior both in a amplitude and phase.

• International Journal of Aeronautical and Space Sciences
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• v.3 no.2
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• pp.82-87
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• 2002

Aerodynamic analysis of NACA wings moving with a constant speed over guideways are performed using an indirect boundary element method (potential-based panel method). An integral equation is obtained by applying Green's theorem on all surfaces of the fluid domain. The surfaces over the wing and the guideways are discretized as rectangular panel elements. Constant strength singularities are distributed over the panel elements. The viscous shear layer behind the wing is represented by constant strength dipoles. The unknown strengths of potentials are determined by inverting the aerodynamic influence coefficient matrices constructed by using the no penetration conditions on the surfaces and the Kutta condition at the trailing edge of the wing. The aerodynamic characteristics for the wings flying over nonplanar ground surfaces are investigated for several ground heights.

• Honam Mathematical Journal
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• v.36 no.2
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• pp.399-415
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• 2014

We study the Seifert surfaces of a link by relating the embeddings of graphs with induced graphs. As applications, we prove that every link L is the boundary of an oriented surface which is obtained from a graph embedding of a complete bipartite graph $K_{2,n}$, where all voltage assignments on the edges of $K_{2,n}$ are 0. We also provide an algorithm to construct such a graph diagram of a given link and demonstrate the algorithm by dealing with the links $4^2_1$ and $5_2$.