• Journal of the Korean Ceramic Society
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• v.43 no.12 s.295
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• pp.839-845
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• 2006

Graphite has hexagonal closed packing structure with two bonding characteristics; (1) van der waals bonding between c axis, and (2) covalent bonding in the a and b axis. The weak van der waals bonds cause self-lubricant property, and the strong covalent bonds cause excellent electric and thermal conductivity. Furthermore, graphite is chemically very inert because of the material composed of only carbon elements. Thus, graphite is very useful for mechanical sealing materials. However, Graphite have porous microstructure because starting materials of graphite produce many volatile during the manufacturing processes. This causes low density of graphite, which is unsuitable for the mechanical sealing materials. Thus, further impregnation process is generally needed to enhance the graphite density. In this work, high density graphite is prepared with the principle of densification when coke and pitch binder, prepared from thermal treatment of coal tar pitch, become dehydrogenation during graphitization or carbonization.

• Bulletin of the Korean Chemical Society
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• v.34 no.5
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• pp.1555-1558
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• 2013

• International journal of steel structures
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• v.18 no.5
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• pp.1483-1496
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• 2018

Negligible research has been conducted to date on how to analyse weakened columns, thus safety risks are still involved when structures are weakened prior to demolition. There are various methods available for demolishing steel structures. One of the most effective methods that has been developed involves pre-cutting steel columns at a certain height, so that the least effort can be used to collapse the structure by means of pulling out some of the columns. This paper presents (a) an experimental setup developed to test the capacity of axially loaded weakened columns, which is used to (b) validate a finite element (FE) model. The two pre-cuts that are presented in this paper are (1) the double window cut and (2) the triangular window cut, which are both commonly used in industry. A column weakened with a double window cut or triangular window cut reduces the axial load capacity by up to 50 and 40%, respectively. The FE models developed predict the axial failure load of weakened columns for a double window cut and triangular window cut are generally within an accuracy of less than 8 and 10%, respectively. It is shown at higher slendernesses the influence of column cuts is less than would be intuitively expected because global buckling becomes dominant.

• Journal of Magnetics
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• v.20 no.4
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• pp.336-341
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• 2015

MnBi alloys were fabricated by arc melting and annealing at 573 K. The heat treatment enhanced the content of the low-temperature phase (LTP) of MnBi up to 83 wt%. The Bi-excess assisted LTP MnBi alloys were used in the hybridization with the Nd-Fe-B commercial Magnequench ribbons to form the hybrid magnets (100-x)NdFeB/xMnBi, x = 20, 30, 40, 50, and 80 wt%. The as-milled powder mixtures of Nd-Fe-B and MnBi were aligned in a magnetic field of 18 kOe and warm-compacted to anisotropic and dense bulk magnets at 573 K by 2,000 psi for 10 min. The magnetic ordering of two hard phase components strengthened by the exchange coupling enhanced the Curie temperature ($T_c$) of the magnet in comparison to that of the powder mixture sample. The prepared hybrid magnets were highly anisotropic with the ratio $M_r/M_s$ > 0.8. The exchange coupling was high, and the coercivity $_iH_c$ of the magnets was ~11-13 kOe. The maximum value of the energy product $(BH)_{max}$ was 8.4 MGOe for the magnet with x = 30%. The preparation of MnBi alloys and hybrid magnets are discussed in details.

• Korean Journal of Crystallography
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• v.5 no.2
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• pp.108-112
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• 1994

C19H20O5, Mr=314.337, triclinic,PI, a=10.291(2)A, b=11.218(3)A, c=3.059(1)A, α=74.54(2)°, β=1148.84(1)°, r=109.84(2)°, V=883.283(2)A3, λ(Mo Kα)=0.71069A, μ=0.47 mm-1, F(000)=324, 296K, Z=2, Dx=1.18Mgm-3. Final R=0.0580 for 1637[F>3σ(F)]unique refledtions. α,β-diphenylsuccinic acid, C16H14O4, are connedted with the solvent actone by hydrogen bond O(4)-H˙˙˙O(5), forming a dimer related by related by centrosymmentry thorough intermolecualr carboxylic hydrogen bond O(1)-H˙˙˙O(2)(-x,-y,-z). The nearest distance 3.288A[O(2)˙˙˙O(2)(-x,-y,-z)] between the dimers shows that the packing of the dimer is govermed by van der Waals'force.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39B no.11
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• pp.743-754
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• 2014

Recently, Information-Centric Networking(ICN), different from traditional IP-based networking, has been highlighted. Content-Centric Networking(CCN), proposed by Van Jacobson, is a representative scheme of the ICN architectures. It can deliver messages slightly faster than the IP-based networking by focusing on the access and delivery to the content itself. However, CCN is restricted to distribute the information without transmitting the request packet in advance because it is pull-based architecture by content requester. In addition, it has a problem that the Pending Interest Table(PIT) could be overloaded easily when DDoS attack happens. In this paper, we suggest an algorithm using a push-based scheme without request packets and overcoming PIT overload situation by Interest Group Push Table(IGPT). The proposed scheme enables to transmit a large amount of content than an existing scheme during the same amount of time in terms of timely-delivery and security.

• Journal of the Korean Chemical Society
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• v.43 no.6
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• pp.656-662
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• 1999

We have obtained retention data of benzene, toluene, ethylbenzene, phenol, and acetophenone at 25, 30, 35, 40, 45 and 50 $^{\circ}C$ in 30/70, 40/60, 50/50, 60/40, 70/30, and 80/20 (v/v %) methanol/water eluents using a $C_18$ phase with a high ligand density. We drew van't Hoff plots from the data, and computed enthalpies and entropies of solute transfer from the mobile to the stationary phase. The cavity formation effect was found the major factor that governs the solute distribution between the mobile and stationary phases. The hydrophobic effect became significant in highly aqueous mobile phases. We also concluded that the Shodex C18-5B stationary phase was a polymer-like phase with a high ligand density, and followed a partially adsorption-like mechanism.

• Journal of the Korean Chemical Society
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• v.54 no.3
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• pp.275-282
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• 2010

2-Fluorocyclopropanemethanol and 2-chlorocyclopropanemethanol have been studied with MP2 and B3LYP methods with 6-311++G(d,p) basis set. The optimized structures show several stable conformers. The most stable conformer show the possibility of intramolecular hydrogen bonding, but the distance between $H{\cdots}F$, or $H{\cdots}Cl$ is longer than van der Waals radii and it may not be strong covalent bonding. Rather the second stable conformer has optimum structure for intramolecular hydrogen bonding but the energy of the conformer is 5 ~ 7 kJ higher than the most stable conformer. When the methanol group and the F or Cl atom have opposite direction, the conformers are less stable than the most stable conformer.

• Journal of Broadcast Engineering
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• v.20 no.3
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• pp.398-407
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• 2015

Compressive sensing (CS) has drawn much interest as a novel sampling technique that enables sparse signal to be sampled under the Nyquitst/Shannon rate. By noting that the block-based CS can still keep spatial correlation in measurement domain, this paper proposes to adapt sampling rate of each block in frame according to its characteristic defined by edge information. Specifically, those blocks containing more edges are assigned more measurements utilizing block-wise correlation in measurement domain without knowledge about full sampling frame. For natural image, the proposed adaptive rate allocation shows considerable improvement compared with fixed subrate block-based CS in both terms of objective (up to 3.29 dB gain) and subjective qualities.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.148-148
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• 2011

Riemann 문제는 천수방정식과 같은 쌍곡선형 방정식과 단일한 도약에 의해 불연속인 어떤 점의 좌 우에서 상수인 자료로 구성되는 초기치 문제로서 그 해법은 Godunov 방법과 같이 정확해에 의하면 정확 Riemann 해법, 근사 기법에 의하면 근사 Riemann 해법으로 불린다. 지금까지 이용되는 근사 Riemann 해법으로는 1981년에 P. L. Roe가 제안한 Roe의 선형화 기법과 1983년에 A. Harten, P. D. Lax, 그리고 B. van Leer가 제안한 HLL 기법의 수정 기법들이다. 최대 및 최소 파속만 고려하는 것으로 알려진 HLL 기법은 1988년에 B. Einfeldt의 제안에 의해 두 파속의 결정에서 Roe의 선형화 기법에 따른 고유치와 비교하는 것으로 수정되었다(HLLE 기법). 또한, 1994년에 E. F. Toro 등은 접촉파를 고려하기 위해 선형화된 지배방정식의 정확해로부터 중앙 파속을 고려하는 기법을 제안하였고, 이를 HLLC 기법으로 불렀다. 2002년에 T. Linde는 중앙 파속을 평가하기 위해 일반화된(수학적) 엔트로피 함수를 도입하였으며, van Leer는 이를 HLLL 기법으로 불렀다. 이 기법에서는 접촉파의 평가를 위해 보존변수에 대한 일반화된 엔트로피 함수로부터 중앙 파속이 유도되며, 이것과 특성 속도의 비교를 통해 최대 및 최소 파속이 결정된다. 따라서 이 기법에서는 모든 파속이 초기치로부터 결정되므로 HLLE 기법과 달리 Roe의 선형화 기법과 완전히 결별되고 HLLC 기법과 달리 정확해에 의존되지 않는 점에서 HLLL 기법은 모태인 HLL 기법의 온전한 계승으로 볼 수 있다. HLLL 기법은 여러 분야에 적용된 바 있으나, 수공학 분야에 적용된 사례는 알려진 바 없다. 이는 천수방정식에 대한 (물리적) 엔트로피 함수가 명확하지 않기 때문인 것으로 보인다. 이 연구에서는 보존변수로부터 정의되는 총 에너지를 일반화된 엔트로피 함수로 간주하여 모형을 구성하고, 정확해가 알려진 1차원 문제에 대해 적용성을 검토하였다. 정확해가 알려진 경우에 대해 모의한 결과, 1차 정도 수치해의 한계에도 불구하고, HLLL 기법의 결과는 대체로 정확해와 잘 일치하였으며 그 외의 HLL-형 기법의 그것에 비해 우수한 것으로 나타났다. 특히, 물이 빠져 바닥이 드러나는 상태에 대한 접촉 파속의 추정에서 Riemann 불변량을 이용하는 HLLC 기법에 비해 물이 빠지는 전선을 더 정확하게 포착하는 HLLL 기법의 결과는 매우 고무적이었다.