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구형 및 평면 원자현미경 탐침에 대한 2차원 소재의 마찰 특성
Bien-Cuong Tran Khac,정구현 한국트라이볼로지학회 2019 한국트라이볼로지학회지 (Tribol. Lubr.) Vol.35 No.4
Two-dimensional materials such as graphene, h-BN, and MoS2 have attracted increased interest as solid lubricant and protective coating layer for nanoscale devices owing to their superior mechanical properties and low friction characteristics. In this work, the frictional properties of single-layer graphene, h-BN, and MoS2 are experimentally investigated under various normal forces using atomic force microscope (AFM) tips with a spherical and flat end, with the aim to gain a better understanding of frictional behaviors. The nonlinear relationship between friction and normal force friction was clearly observed for single-layer graphene, h-BN, MoS2 specimens slid against the spherical and flat AFM tips. The results also indicate that single-layer graphene, h- BN, MoS2 exhibit low frictional properties (e.g., friction coefficient below 0.1 under 70~100 nN normal force). In particular, graphene is found to be superior to h-BN and MoS2 in terms of frictional properties. However, the friction of single-layer graphene, h-BN, MoS2 against the flat tip is larger than that against the spherical tip, which may be attributed to the relatively large adhesion. Furthermore, it is shown that the fluctuation of friction is more significant for the flat tip than the spherical tip. The resutls of this study may be helpful to elucidate the feasibility of using two-dimensional materials as solid lubricant and protective coating layer for nanoscale devices.
Bi-directional semantic similarity for gene ontology to optimize biological and clinical analyses
Bien, Sang Jay,Park, Chan Hee,Shim, Hae Jin,Yang, Woongcheol,Kim, Jihun,Kim, Ju Han BMJ Group 2012 Journal of the American Medical Informatics Associ Vol.19 No.5
<P><B>Background</B></P><P>Semantic similarity analysis facilitates automated semantic explanations of biological and clinical data annotated by biomedical ontologies. Gene ontology (GO) has become one of the most important biomedical ontologies with a set of controlled vocabularies, providing rich semantic annotations for genes and molecular phenotypes for diseases. Current methods for measuring GO semantic similarities are limited to considering only the ancestor terms while neglecting the descendants. One can find many GO term pairs whose ancestors are identical but whose descendants are very different and vice versa. Moreover, the lower parts of GO trees are full of terms with more specific semantics.</P><P><B>Methods</B></P><P>This study proposed a method of measuring semantic similarities between GO terms using the entire GO tree structure, including both the upper (ancestral) and the lower (descendant) parts. Comprehensive comparison studies were performed with well-known information content-based and graph structure-based semantic similarity measures with protein sequence similarities, gene expression-profile correlations, protein–protein interactions, and biological pathway analyses.</P><P><B>Conclusion</B></P><P>The proposed bidirectional measure of semantic similarity outperformed other graph-based and information content-based methods.</P>
ON SOME SUBGROUPS OF D<sup>*</sup> WHICH SATISFY A GENERALIZED GROUP IDENTITY
BIEN, MAI HOANG Korean Mathematical Society 2015 대한수학회보 Vol.52 No.4
Let D be a division ring and w($x_1,\;x_2,\;{\ldots},\;x_m$) be a generalized group monomial over $D^*$. In this paper, we investigate subnormal subgroups and maximal subgroups of $D^*$ which satisfy the identity $w(x_1,\;x_2,\;{\ldots},\;x_m)=1$.
Subunit Principle of Vulvar Reconstruction: Algorithm and Outcomes
Bien-Keem Tan,Gavin Chun-Wui Kang,Eng Hseon Tay,Yong Chen Por 대한성형외과학회 2014 Archives of Plastic Surgery Vol.41 No.4
Background: Vulvar defects result chiefly from oncologic resection of vulvar tumors. Reconstructionof vulvar defects restores form and function for the purpose of coitus, micturition,and defecation. Many surgical options exist for vulvar reconstruction. The purpose of thisarticle is to present our experience with vulvar reconstruction. Methods: From 2007 to 2013, 43 women presented to us with vulvar defects for reconstruction. Their mean age at the time of reconstruction was 61.1 years. The most commoncause of vulvar defect was from resection of vulvar carcinoma and extramammary Paget’sdisease of the vulva. Method s of reconstruction ranged from primary closure to skin graftingto the use of pedicled flaps. Results: The main complications were that of long term hypertrophic and/or unaestheticscarring of the donor site in 4 patients. Twenty-two patients (51%) were able to resume sexualintercourse. There were no complications of flap loss, wound dehiscence, and urethral stenosis. Conclusions: We present a subunit algorithmic approach to vulvar reconstruction based ondefect location within the vulva, dimension of the defect, and patient age and comorbidity. The gracilis and gluteal fold flaps are particularly versatile and aesthetically suited for reconstructionof a variety of vulvar defects. From an aesthetic viewpoint the gluteal fold flap wassuperior because of the well-concealed donor scar. We advocate the routine use of these 2flaps for vulvar reconstruction.
Bien Dong Che,Le-Thu T. Nguyen,Bao Quoc Nguyen,Ha Tran Nguyen,Thang Van Le,Nieu Huu Nguyen 한국고분자학회 2014 Macromolecular Research Vol.22 No.11
Radar absorbing materials (RAMs) for practical applications are expected not only to have strong microwaveabsorption and a wide absorption bandwidth, but also to be lightweight, to have a fine thickness and acceptablestructural performance, as well as being cost-effective. Although the dispersion of carbon-nanofillers in polymermatrices is a key factor determining the microwave absorbing properties of the composites, there have few studieson these effects. To our knowledge, to date, the realization of pristine multi-walled carbon nanotube (MWCNT)/polymercomposites as RAMs in industrial production has been restricted, due to high CNT contents or large composite thicknesses. Thus, in this work, two MWCNT dispersion processing methods, a solution process with surfactant-aid anda ball-milling dispersion, were investigated to fabricate pristine MWCNT/epoxy nanocomposites. The effects of thedifferent dispersion processes, CNT loading, and composite thickness on CNT dispersion in the matrix, were observedby TEM, and the electrical conductivity and X-band absorbing performance of the composites were assessed. Theuse of an ionic surfactant to aid the dispersion of CNTs in solution resulted in the best RAMs, with a good compromiseamong effective X-band absorption, small composite thickness, and very low CNT content. The ball-millingmethod also resulted in materials with a low CNT content and microwave absorbing performance acceptable forindustrial applications. Moreover, it offers a very simple and efficient route suitable for low-cost, mass productionof RAMs. The results showed that by facile approaches of dispersing pristine commercial MWCNTs in an epoxyresin matrix, composites of only 2-3 mm thickness and as little as 0.25-0.5 wt% CNT loading could be obtained,with a relatively wide X-band operating bandwidth and maximum absorptions exceeding 18-25 dB.
A NOTE ON LOCAL COMMUTATORS IN DIVISION RINGS WITH INVOLUTION
Bien, Mai Hoang Korean Mathematical Society 2019 대한수학회보 Vol.56 No.3
In this paper, we consider a conjecture of I. N. Herstein for local commutators of symmetric elements and unitary elements of division rings. For example, we show that if D is a finite dimensional division ring with involution ${\star}$ and if $a{\in}D^*=D{\setminus}\{0\}$ such that local commutators $axa^{-1}x^{-1}$ at a are radical over the center F of D for every $x{\in}D^*$ with $x^{\star}=x$, then either $a{\in}F$ or ${\dim}_F\;D=4$.