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Novel transport materials for high-performance fluorescent and phosphorescent OLEDs
Bohm, E.,Anemian, R.,Busing, A.,Fortte, R.,Heil, H.,Kaiser, J.,Krober, J.,Leu, S.,Mujica-Fernaud, T.,Parham, A.,Pflumm, C.,Voges, F. The Korean Infomation Display Society 2011 Journal of information display Vol.12 No.3
To improve the performance of blue fluorescent and green phosphorescent organic light-emitting diode devices, Merck developed novel green phosphorescent host and electron-transporting materials. The newly developed electron-transporting material improves the external quantum efficiency of blue fluorescent devices up to 8.7%, with an excellent lifetime. In combination with the newly developed host materials, the efficiency of green phosphorescent devices can be improved by a factor of 1.7, and the lifetime by a factor of 7.
Bohm Choi,Dong-Ok Lee,Sung-Seo Mo,Seong-Hun Kim,Ki-Ho Park,Kyu-Rhim Chung,Gerald Nelson,Seong Ho Han 대한치과교정학회 2011 대한치과교정학회지 Vol.41 No.6
Objective: To evaluate the extent and aspect of stress to the cortical bone after application of a lateral force to a two-component orthodontic mini-implant (OMI, mini-implant) by using three-dimensional finite element analysis (FEA). Methods: The 3D-finite element models consisted of the maxilla, maxillary first molars, second premolars, and OMIs. The screw part of the OMI had a diameter of 1.8 mm and length of 8.5 mm and was placed between the roots of the upper second premolar and the first molar. The cortical bone thickness was set to 1 mm. The head part of the OMI was available in 3 sizes: 1 mm, 2 mm, and 3 mm. After a 2 N lateral force was applied to the center of the head part, the stress distribution and magnitude were analyzed using FEA. Results: When the head part of the OMI was friction fitted (tapped into place) into the inserted screw part, the stress was uniformly distributed over the surface where the head part was inserted. The extent of the minimum principal stress suggested that the length of the head part was proportionate with the amount of stress to the cortical bone; the stress varied between 10.84 and 15.33 MPa. Conclusions: These results suggest that the stress level at the cortical bone around the OMI does not have a detrimental influence on physiologic bone remodeling. (Korean J Orthod 011;41(6): 423-430)
Lock-In Thermography Based NDT of Parts for the Automotive Industry
Bohm, Stefan,Hellmanns, Mark,Backes, Andreas,Dilger, Klaus The Society of Adhesion and Interface 2006 접착 및 계면 Vol.7 No.4
The successful use of adhesively bonded parts depends on the defect-free bond of the components. Therefore it is necessary to detect relevant faults and defects in an early state of the production. A 100% test should be pursued, but especially at complicated structures the detection of defects is not easy. Possible testing methods, which show a high potential for the NDT of adhesively bonded parts, are thermography based NDT methods. At present mainly two different procedures of active thermography are being used: Pulse and Lock-In Thermography. With pulse thermography the examined material is warmed up with a short energy pulse (light, eddy current or ultrasonic pulse) and the heat response is recorded after a certain time. The result is an infrared image which indicates material defects in different depths. This paper presents a variety of images showing the capability of Lock-In Thermography to image subsurface defects. Several examples of adhesives joints qualify the ultrasonic Lock-In-Thermography for the in-process quality control for adhesive bonded components.
Micro Bonding Using Hot Melt Adhesives
Bohm, Stefan,Hemken, Gregor,Stammen, Elisabeth,Dilger, Klaus The Society of Adhesion and Interface 2006 접착 및 계면 Vol.7 No.4
Due to the miniaturization of MEMS and microelectronics the joining techniques also have to be adjusted. The dosing technology with viscous adhesives does not permit reproducible adhesive volumes, which are clearly under a nano-liter. A nano-liter means however a diameter of bonding area within the range of several 100 micrometers. Additional, viscous adhesives need a certain time, until they are cross linked or cured. The problem especially in the MEMS is the initial strength, since it gives the time, which is needed for joining an individual adhesive joint. The time up to the initial strength is with viscous, also with fast curing systems, within the range of seconds until minutes. Until the reach of the initial strength, the micro part must be fixed/held. Without sufficient adjustment/clamping it can come to a shift of the micro parts. Also existing micro adhesive bonding processes are not batch able, i.e. the individual adhesive joints of a micro system must be processed successively. In the context of the WCARP III 2006 now an innovative method is to be presented, how it is possible to solve the existing problems with micro bonding. i.e. a method is presented, which is batch able, possess a minimum joining geometry with some micrometers and is so fast that no problems with the initial strength arise. It is a method, which could revolutionize the sticking technology in the micro system engineering.
Valence bond solid phases on deformed kagome lattices: Application toRb2Cu3SnF12
Yang, Bohm-Jung,Kim, Yong Baek American Physical Society 2009 Physical review. B, Condensed matter and materials Vol.79 No.22
<P>Motivated by a recent experiment on Rb2Cu3SnF12, where spin-1/2 Cu2+ moments reside on the layers of kagome-like lattices, we investigate quantum ground states of the antiferromagnetic Heisenberg model on a series of deformed kagome lattices. The deformation is characterized by a weaker exchange coupling alpha J on certain lattice links appropriate for Rb2Cu3SnF12 with alpha=1 corresponding to the ideal kagome lattice. In particular, we study possible valence bond solid phases using the perturbation theory around isolated dimer limits, dimer series expansion, and self-consistent bond operator mean-field theory. It is shown that the valence bond solid phase with a 36-site unit cell of the ideal kagome lattice is quite sensitive to a small lattice distortion as the kind discovered in Rb2Cu3SnF12. As a result, we find that a more likely quantum ground state in Rb2Cu3SnF12 is the valence bond solid phase with a 12-site unit cell, where six dimers form a pinwheel structure, leading to strong modification of the elementary triplet and singlet excitation spectra in the deformed kagome lattices.</P>
치주염 및 임플란트 주위염 환자의 치은 조직에서 Real Time PCR을 이용한 Matrix Metalloproteinase (MMP)-2,9,12,13의 발현
최봄 ( Bohm Choi ),이태연 ( Tae Yeon Lee ),윤현중 ( Hyun Joong Yoon ),이원 ( Won Lee ) 한국조직공학·재생의학회 2013 조직공학과 재생의학 Vol.10 No.1s
Matrix metalloproteinases (MMPs) are known to be responsible factor in various pathological conditions including stomach ulcer, tumor metastasis, rheumatoid arthritis. In previous study, MMP-8 is kown as a key mediator in periodontitis but the exact role and functions of MMPs are still unclear. This study was to investigate the expressions of MMPs in gingival tissues from periodontally healthy individuals, chronic periodontitis patients, periimplantitis patients using real time polymerase chain reaction analysis. MMP-2, MMP-9, MMP-12, MMP-13 were analyzed in this study. mRNA level of MMP-2, MMP-9 were high in tissue extract isolated from advanced periodontitis compared to that of periodontally healthy individuals. Unlike to periodontitis, in peri-implantitis patients, only MMP-9 was slightly activated compared to periodontally healthy individuals. Otherwise, expression level of MMP- 12, MMP-13 in periodontally unhealthy patients was extremely low. In RNA level, expression profile of MMPs between periodontitis and peri-implantitis was similar but there are some different aspects in individual expression. It can imply that there be the similar mechanisms and relation between two diseases but different regulatory mechanisms can be exsist.
Topological semimetals protected by off-centered symmetries in nonsymmorphic crystals
Yang, Bohm-Jung,Bojesen, Troels Arnfred,Morimoto, Takahiro,Furusaki, Akira American Physical Society 2017 Physical Review B Vol.95 No.7
<P>Topological semimetals have energy bands near the Fermi energy sticking together at isolated points/lines/planes in the momentum space, which are often accompanied by stable surface states and intriguing bulk topological responses. Although it has been known that certain crystalline symmetries play an important role in protecting band degeneracy, a general recipe for stabilizing the degeneracy, especially in the presence of spin-orbit coupling, is still lacking. Herewe showthat a class of novel topological semimetals with point/line nodes can emerge in the presence of an off-centered rotation/mirror symmetry whose symmetry line/plane is displaced from the center of other symmorphic symmetries in nonsymmorphic crystals. Due to the partial translation perpendicular to the rotation axis/mirror plane, an off-centered rotation/mirror symmetry always forces two energy bands to stick together and form a doublet pair in the relevant invariant line/plane in momentum space. Such a doublet pair provides a basic building block for emerging topological semimetals with point/line nodes in systems with strong spin-orbit coupling.</P>