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A quadrilateral Morley element for biharmonic problems
Chunjae Park,Dongwoo Sheen 한국산업응용수학회 2011 한국산업응용수학회 학술대회 논문집 Vol.6 No.1
In this talk, we propose a Morley-type finite element for quadrilateral meshes to solve bihar-monic problems. For each quadrilateral Q, the finite element space is defined by the span of P₂(Q) plus two cubic polynomials. Each of the cubic polynomials vanishes at a pair of opposite edges and the bimedian between them. We will prove the values at vertices and integrals of normal derivatives over edges are the degrees of freedom of the proposed element. An optimal order of convergence is analyzed and several numerical tests confirm it.
Analysis of recoverable current from one component of magnetic flux density in MREIT and MRCDI
Park, Chunjae,Lee, Byung Il,Kwon, Oh In Institute of Physics in association with the Ameri 2007 Physics in medicine & biology Vol.52 No.11
<P>Magnetic resonance current density imaging (MRCDI) provides a current density image by measuring the induced magnetic flux density within the subject with a magnetic resonance imaging (MRI) scanner. Magnetic resonance electrical impedance tomography (MREIT) has been focused on extracting some useful information of the current density and conductivity distribution in the subject Ω using measured <I>B<SUB>z</SUB></I>, one component of the magnetic flux density <B>B</B>. In this paper, we analyze the map <img SRC='http://ej.iop.org/images/0031-9155/52/11/005/pmb237414ieqn1.gif' ALIGN='MIDDLE' ALT='{\cal T} '/> from current density vector field <B>J</B> to one component of magnetic flux density <I>B<SUB>z</SUB></I> without any assumption on the conductivity. The map <img SRC='http://ej.iop.org/images/0031-9155/52/11/005/pmb237414ieqn2.gif' ALIGN='MIDDLE' ALT='{\cal T} '/> provides an orthogonal decomposition <B>J</B> = <B>J</B><SUP><I>P</I></SUP> + <B>J</B><SUP><I>N</I></SUP> of the current <B>J</B> where <B>J</B><SUP><I>N</I></SUP> belongs to the null space of the map <img SRC='http://ej.iop.org/images/0031-9155/52/11/005/pmb237414ieqn3.gif' ALIGN='MIDDLE' ALT='{\cal T} '/>. We explicitly describe the projected current density <B>J</B><SUP><I>P</I></SUP> from measured <I>B<SUB>z</SUB></I>. Based on the decomposition, we prove that <I>B<SUB>z</SUB></I> data due to one injection current guarantee a unique determination of the isotropic conductivity under assumptions that the current is two-dimensional and the conductivity value on the surface is known. For a two-dimensional dominating current case, the projected current density <B>J</B><SUP><I>P</I></SUP> provides a good approximation of the true current <B>J</B> without accumulating noise effects. Numerical simulations show that <B>J</B><SUP><I>P</I></SUP> from measured <I>B<SUB>z</SUB></I> is quite similar to the target <B>J</B>. Biological tissue phantom experiments compare <B>J</B><SUP><I>P</I></SUP> with the reconstructed <B>J</B> via the reconstructed isotropic conductivity using the harmonic <I>B<SUB>z</SUB></I> algorithm.</P>
Park, Chunjae,Lee, Byung Il,Kwon, Ohin,Woo, Eung Je IOP Pub 2007 PHYSIOLOGICAL MEASUREMENT Vol.28 No.2
<P>Magnetic resonance electrical impedance tomography (MREIT) measures induced magnetic flux densities subject to externally injected currents in order to visualize conductivity distributions inside an electrically conducting object. Injection currents induce magnetic flux densities that appear in phase parts of acquired MR image data. In the conventional current injection method, we inject currents during the time segment between the end of the first RF pulse and the beginning of the reading gradient in order to ensure the gradient linearity. Noting that longer current injections can accumulate more phase changes, we propose a new pulse sequence called injection current nonlinear encoding (ICNE) where the duration of the injection current pulse is extended until the end of the reading gradient. Since the current injection during the reading gradient disturbs the gradient linearity, we first analyze the MR signal produced by the ICNE pulse sequence and suggest a novel algorithm to extract the induced magnetic flux density from the acquired MR signal. Numerical simulations and phantom experiments show that the new method is clearly advantageous in terms of the reduced noise level in measured magnetic flux density data. The amount of noise reduction depends on the choice of the data acquisition time and it was about 24% when we used a prolonged data acquisition time of 10.8 ms. The ICNE method will enhance the clinical applicability of the MREIT technique when it is combined with an appropriate phase artefact minimization method.</P>
옵티컬 일루젼의 효과적인 접목을 위한 제품 디자인 사례연구
김충재 ( Chunjae Kim ),김보연 ( Bo Yeun Kim ) 커뮤니케이션디자인학회 2015 커뮤니케이션 디자인학연구 Vol.53 No.-
제품이 사용자에게 도달하기까지 수많은 생산과정과 제약을 거치면서 대칭적이고 정형화된 형태의 디자인을 갖게 된다. 하지만 현대 소비자들은 보다 빠르게 새롭고 독특한 제품을 원하고 디자이너들은 그에 따라보다 자극적이며 실험적인 형태의 제품들을 끊임없이 연구한다. 이러한 흐름에 부합하고자 본 연구는 메종&오브제 파리 2015가 선정한 올해의 디자이너인 ``오키 사토``와 그의 디자인 스튜디오 ``넨도``가 중점적으로 활용한 옵티컬 일루젼에 주목하여 옵티컬의 개념과 배경을 검토한다. 또한 그와 관련 사례들을 Wucius Wong의 체험 조형요소에 따라 면밀히 분석함으로서 앞으로의 옵티컬 일루젼이 접목된 제품디자인 방향을 논한다. Generally a product has symmetric and valanced design by being gone through many processes and regulations in its production. However, contemporary designers study more experimental design for their consumers who are eagerly looking for more unique design. In order to follow the stream of product design, this study focus on optical illusion which is recently used by the winner of Meson & Object paris 2015, ``Oki Sato``, design studio ``Nendo``. Moreover, this study explores and describes contemporary product design with optical illusion. Specifically, every product in this study was analysed by the elements of design by Wucius Wong. In conclusion, it results and suggests the future of product design.
Ad-hoc 망에서 동적 임계값을 이용한 부하균등 라우팅 프로토콜
한욱표(Ukpyo Han),이춘재(Chunjae Lee),정영준(Youngjun Chung) 한국정보과학회 2004 한국정보과학회 학술발표논문집 Vol.31 No.1A
ad-hoc 망에서 라우팅 프로토콜의 부하균등(load balancing)은 이동성과 전송 지연사이의 trade-off로 인하여 성능 관점에서 중요한 이슈가 되어왔다. 부하균등을 고려한 SLAP(Simple Load-balancing Ad-hoc routing Protocol)이 제안되었으나 혼잡이 발생하거나 망의 토폴로지가 변화하였을 때 유연하게 대처하지 못한다. 본 논문에서는 ad-hoc 망에서 트래픽 혼잡 제어와 망의 이동성에 적응하기 위하여 동적인 임계치를 사용하는 부하균등 라우팅 프로토콜을 제안하였다. 제안된 프로토콜은 성능은 GloMoSim으로 시뮬레이션을 수행하여 AODV, DSR, SLAP과 지연, 패킷 전송률 등을 비교하여 평가하였다.
SPECTRAL METHOD FOR RECONSTRUCTING PHYLOGENETIC TREE
Paeng, Seong-Hun,Park, Chunjae Korean Mathematical Society 2019 대한수학회논문집 Vol.34 No.3
A new simple method is proposed for reconstructing phylogenetic trees, which we call the spectral method. The most common distance based method is the neighbor-joining method which is based on the minimum evolution principle. The spectral method shows similar performance to the neighbor-joining method for simulated data generated by seq-gen. For real data, the spectral method shows much better performance than the neighbor-joining method. Hence it can be a complementary method for reconstructing phylogenetic trees.