• Journal of Korean Society of Forest Science
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• v.77 no.3
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• pp.283-293
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• 1988

Anatomical features of the secondary xylem were described in the branches, stems, and roots of Salix glandulosa and Quercus variavilis. In Quercus variavilis, the stem shows ring-porous wood, while the root shows diffuse-porous wood. In both species, it is found that the boundaries between the growth rings are not well defined in the roots. Both vessel elements and fibers are the longest in the roots followed by the sterns and the branches in turn and diameter of vessel elements shows the same trend. In cross section, the number of vessels per unit area are the longest in the branches followed by the stems and the roots in turn as well. Perforation plates are simple in both species and their angles are wide in the root, intermediate in the stems, and narrow in the branches. In tangential section, height of rays is taller in the roots than in the stem and branches.

• Journal of IKEEE
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• v.18 no.2
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• pp.214-219
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• 2014

In this paper, the usage of tilt-implanted trench Schottky diode(TITSD) based on silicon carbide is proposed. A tilt-implanted trench termination technique modified for SiC is proposed as a method to keep all the potentials confined in the trench insulator when reverse blocking mode is operated. With the side wall doping concentration of $1{\times}10^{19}cm^{-3}$ nitrogen, the termination area of the TITSD is reduced without any sacrifice in breakdown voltage while potential is confined within insulator. When the trench depth is set to 11um and the width is optimized, a breakdown voltage of 2750V is obtained and termination area is 38.7% smaller than that of other devices which use guard rings for the same breakdown voltage. A Sentaurus device simulator is used to analyze the characteristics of the TITSD. The performance of the TITSD is compared to the conventional trench Schottky diode.

• The Transactions of the Korean Institute of Power Electronics
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• v.6 no.1
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• pp.57-63
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• 2001

The wound rotor type induction motor(WRIM) control system which is widely used in the industry has many maintenance problem because of external resistors and magnetic contactors. In this paper, the simple sensorless vector control algorithm for WRIM is proposed without any additional devices except detecting rotor currents. Because the external resistors are disconnectd and the rotor slip rings are shorten, the power loss due to external resistors is removed and the maintenance problem is improved remarkably. Also, the vector control performance becomes better because the proposed sensorless vector control algorithm does not use the rotor resistance which is usually used to estimate the slip frequency in case of indirect vector control scheme. The proposed algorithm is verified by the digital simulation and the experiment.

• Journal of the Korean Chemical Society
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• v.55 no.2
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• pp.183-188
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• 2011

The electronic structure and properties of Ni$(C_6H_{4-n}F_n)(CO)_2$ ($C_6H_4$=benzyne, n=1-4) complexes have been investigated using hybrid density functional B3LYP theory. Both aromatic natures and nucleus independent chemical shift (NICS) of the benzyne rings have been analyzed. Among mono-, di-, and tri-fluorinated complexes, 3-F, 3,6-F, and 4-H are the most stable isomers, respectively. NICS values calculated at the several points above the ring centers are consistent with those based on the relative energies of the complexes. The atoms in molecules (AIM) analysis indicates that Ni-C bond distance is well correlated with the electron density of a ring critical point (${\rho}_{rcp}$) in all species.

• Bulletin of the Korean Chemical Society
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• v.29 no.9
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• pp.1711-1716
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• 2008

The reaction of copper(II) chloride with phenyl-N-[(pyridine-2-yl)methylene]methaneamide (ppmma) leads to a new $\mu$ -chloro bridged dimeric [Cu(ppmma)$Cl_2$]$_2$ complex, whereas a reaction of copper(II) bromide with ppmma affords a monomeric Cu(ppmma)$Br_2$ complex. Both complexes have been characterized by X-ray crystallography and electronic absorption spectroscopy. The crystal structural analysis of [Cu(ppmma)$Cl_2$]$_2$ shows that the two Cu(II) atoms are bridged by two chloride ligands, forming a dimeric copper(II) complex and the copper ion has a distorted square-pyramidal geometry ($\tau$ = 0.2). The dimer units are held through a strong intermolecular $\pi-\pi$ interactions between the nearest benzyl rings. On the other hand, Cu(ppmma)Br2 displayed a distorted square planar geometry with two types of strong intermolecular π-π interaction. EPR spectrum of [Cu(ppmma)$Cl_2$]$_2$ in frozen glas s at 77 K revealed an equilibrium between the mononuclear and binuclear species. The magnetic susceptibilities data of [Cu(ppmma)$Cl_2$]$_2$ and Cu(ppmma)$Br_2$ follow the Curie-Weiss law. No significant intermolecular magnetic interactions were examined in both complexes, and magnetic exchange interactions are discussed on the basis of the structural features.

• Structural Engineering and Mechanics
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• v.66 no.3
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• pp.343-351
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• 2018

Brazilian disc test is one of the most widely used experiments in the literature of geo-mechanics. In this work, the pre-holed concrete Brazilian disc specimens are numerically modelled by a two-dimensional discrete element approach. The cracks initiations, propagations and coalescences in the numerically simulated Brazilian discs (each containing a single cylindrical hole and or multiple holes) are studied. The pre-holed Brazilian discs are numerically tested under Brazilian test conditions. The single-holed Brazilian discs with different ratios of the diameter of the holes to that of the disc radius are modelled first. The breakage load in the ring type disc specimens containing an internal hole with varying diameters is measured and the crack propagation mechanism around the wall of the ring is investigated. The crack propagation and coalescence mechanisms are also studied for the case of multi-holes' concrete Brazilian discs. The numerical and experimental results show that the breaking mechanism of the pre-holed disc specimens is mainly due to the initiation of the radially induced tensile cracks which are growth from the surface of the central hole. Radially cracks propagated toward the direction of diametrical loading. It has been observed that for the case of disc specimens with multiple holes under diametrical compressive loading, the breaking process of the modelled specimens may occur due to the simultaneous cracks propagation and cracks coalescence phenomena. These results also show that as the hole diameter and the number of the holes increases both the failure stress and the crack initiation stress decreases. The experimental results already exist in the literature are quit agree with the proposed numerical simulation results which validates this simulation procedure.

• Journal of the Korean Magnetics Society
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• v.7 no.1
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• pp.7-12
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• 1997

Amorphous $Fe_{50}Zr_{50}$ alloy has been manufactured by mechanical alloying from pure elemental powders of Fe and Zr in conventional ball mill under an Ar atmosphere. Structure and magnetic properties of the amorphous phase were studied by transmission electron microscopy and SQUID magnetometry. Selected area diffraction patterns taken from the mechanically alloyed powders showed two halo rings, indicating coexistence of Fe rich and Zr rich amorphous phases in mechanically alloyed powder. Curie temperature of the Fe rich amorphous phase, measured by Arrot plot, was 195 K. Fe content in the ferromagnetic amorphous phase, estimated from the Curie temperature, was about 65 at%. Spin wave stiffness constant of $Fe_{50} Zr_{50}$ alloys processed for 100 and 200 hrs were 52.2 and 63.8 meV, respectively. The higher spin wave stiffness constant in 200 hrs milled powders may arise from the precipitation of $\alpha$-Fe by partial crystallization of amorphous phase.

• Maxillofacial Plastic and Reconstructive Surgery
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• v.27 no.6
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• pp.545-551
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• 2005

Purpose: The effect of orthognathic surgery on the temporomandibular dysfunction has been controversial. The purpose of this study is to prove statistically that early removal of fixation plate at postoperative 2 weeks with active exercise of mouth opening could relieve preoperative temporomandibular dysfunction and reposition of temporomandibular joint. Patients and Methods: All 28 subject patients underwent mandibular setback with BSSRO in Kyunghee medical center by one surgeon. The fixation plates used for rigid fixation were removed at postoperative 2 weeks and we had the patients excercise active mouth opening with intermaxillary rubber rings for the guiding proper postoperative occlusion. Temporomandibular symptoms were checked and radiographs were taken before surgery, within a month after surgery, six to twelve months after surgery respectively. Results: The temporomandibular dysfunction symptoms were relieved after the surgery and the condyle was displaced inferior-posteriorly immediate after surgery and repositioned toward its original position during follow-up periods. Conculusion: Orthognathic surgery may benefit temporomandibular joint dysfunction by obtaining a postoperative stable occlusion and more physiologic neuromuscular function. The early removal of fixation plates after BSSRO could reposition the temporomandibular joint to physiologic position and relieve the symptoms of temporomandibular dysfunction by permitting movement of proximal segment.

• The Korea Journal of Herbology
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• v.30 no.6
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• pp.25-32
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• 2015

Objectives : The purpose of this study was to investigate the endothelium-dependent vasorelaxation effect of Cynomorii Herba(CH) extract on contracted rabbit carotid artery.Methods : To clarify the vasorelaxation effect of CH extract, arterial strips with intact was used, to endothelium -dependent vasorelaxation effect of CH extract, arterial strips damaged endothelium was used for experiment using organ bath. Arterial strips was contracted with phenylephrine(PE) before treated with CH extract(0.01, 0.03 and 0.1 ㎎/㎖). To study mechanisms of CH-induced vasorelaxation effect, CH extract infused into arterial rings after treatment by indomethacin(IM), tetraethylammonium chloride(TEA), Nω-nitro-L-arginine (L-NNA), methylene blue(MB) for comparing with non-treated. And calcium chloride(Ca²⁺) 1 mM was treated into precontracted arterial ring induced by PE after treatment of CH extract in Ca²⁺-free krebs solution. Cytotoxic activity of CH extract on human umbilical vein endothelial cell(HUVEC) was measured by MTT assay, and nitric oxide(NO) concentration was measured by Griess reagent.Results : PE-induced arterial strips was significantly relaxed, but the damaged endothelium arterial ring wasn't relaxed by CH extract. Pretreatment of IM, TEA didn't inhibit the vasorelaxation of CH extract, but pretreatment of L-NNA, MB inhibited the vasorelaxation of CH extract. Pretreatment of CH extract reduced the increase of contraction by influx of extracellular Ca²⁺ in contracted arterial ring induced by PE, CH extract increased nitric oxide concentration on HUVEC significantly.Conclusions : This study shows that CH extract have the vasorelaxation effect by blocking the influx of extracellular Ca²⁺ through the activating NO-cGMP system.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.6
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• pp.8-12
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• 2008

A ring resonator based band-pass filter enabling enhanced sideband suppression was proposed and demonstrated. It is composed of a single-ring based band-pass section combined with a band-rejection section based on two different coupled rings. The sideband region of the transfer characteristics of the first band-pass filter section was selectively suppressed by means of the band-rejection section without causing any excessive insertion loss. As a result, the overall transfer characteristics of the proposed filter was unproved so that its sideband suppression was elevated to allow for sharper roll-off and narrower bandwidth. In this work, a conventional single-ring band-pass filter and a proposed filter including the band-rejection section were designed and fabricated. As for the achieved device performance, with the center frequency at about 4 GHz, the sideband suppression ratio was increased as much as 8 dB and the 3-dB bandwidth was reduced from 98 MHz to 48 MHz by about 51% with no remarkable excessive insertion loss as expected. And the quality factor of the device was increased by about 105%.