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An isolation bearing for highway bridges using shape memory alloys
Choi, E.,Nam, T.H.,Oh, J.T.,Cho, B.S. Elsevier 2006 Materials science & engineering. properties, micro Vol.438 No.-
<P><B>Abstract</B></P><P>Conventional lead-rubber bearings may have a problem of instability and unrecovered deformation with a strong ground motion. As a way of solving the problem, this study proposes a new concept of an isolation device in which shape memory alloy wires are incorporated in an elastomeric bearing. A three-span continuous steel bridge was used for seismic analyses to compare the performance of lead-rubber and the proposed bearings. The proposed bearings limit the deck relative displacement effectively with strong ground motions and recover almost original undeformed shape.</P>
BRCA2 Fine-Tunes the Spindle Assembly Checkpoint through Reinforcement of BubR1 Acetylation
Choi, E.,Park, P.G.,Lee, H.o.,Lee, Y.K.,Kang, G.,Lee, J.,Han, W.,Lee, H.,Noh, D.Y.,Lekomtsev, S.,Lee, H. Cell Press 2012 Developmental cell Vol.22 No.2
Germline mutations that inactivate BRCA2 promote early-onset cancer with chromosome instability. Here, we report that BRCA2 regulates the spindle assembly checkpoint (SAC). Previously, we reported that BubR1 acetylation is essential for SAC activity. In this study we show that BRCA2 recruits the PCAF acetyltransferase and aids in BubR1 acetylation during mitosis. In the absence of BRCA2, BubR1 acetylation is abolished, and the level of BubR1 decreases during mitosis. Similarly, Brca2-deficient mouse embryonic fibroblasts exhibited weak SAC activity. Transgenic mice that were engineered to have interruptions in the BRCA2-BubR1 association exhibited marked decrease of BubR1 acetylation, weakened SAC activity, and aneuploidy. These transgenic mice developed spontaneous tumors at 40% penetrance. Moreover, immunohistochemical analyses of human breast cancer specimens suggested that BRCA2 mutation and BubR1 status is closely linked. Our results provide an explanation for how mutation of BRCA2 can lead to chromosome instability without apparent mutations in SAC components.
Choi, E.,Chung, Y.S.,Park, K.,Jeon, J.S. IPC Science and Technology Press ; Elsevier Scienc 2013 Engineering structures Vol.48 No.-
In this study, the bond behavior between steel reinforcing bars and concrete confined via steel wrapping jackets is estimated. Lateral bending tests are conducted for the reinforced concrete columns with continuous longitudinal reinforcement or lap-spliced longitudinal bars confined by the steel wrapping jackets. It is found that the jackets increase the bond strength and ductile behavior due to the transfer of splitting bonding failure to pull-out bonding failure. In the column tests, the steel wrapping jackets increase the flexural strength and ultimate drift for the lap-spliced column. However, the jacket for the column with continuous longitudinal reinforcement only increases the ultimate drift since the flexural strength depends on the yield of reinforcement. Finally, this study suggests a basic concept for determination of the thickness of the steel wrapping jackets which is different from the conventional method.
Variation of mechanical properties of shape memory alloy bars in tension under cyclic loadings
Choi, E.,Nam, T.h.,Chung, Y.S. Elsevier Sequoia 2010 Materials science & engineering. properties, micro Vol.527 No.16
It is well-known that the behavior of shape memory alloys (SMAs) depends on varying the temperature and dynamic loading frequency. However, the relationship between SMA behavior and cyclic loads has not been clearly discussed. This relationship is very important in the field of seismic application of SMAs. Therefore, this study arranges several dynamic tensile tests of martensitic and austenitic SMA bars. The parameters of the tests are the initial strain of the SMA bars, the number of cycles, and the loading frequency. The hysteretic curves of the stress-strain relation are measured, and the mechanical properties of the residual strain, Young's modulus is varied at first, but becomes stable after 250 cyclic loading. However, the damping ratio decreases continuously when the number of loading cycles increased. It is found that the initial strain and loading frequency do not affect the mechanical properties significantly. Only the residual strain is influenced by the amount of initial strain but not the loading frequency.
Choi, E.,Petersen, C.P.,Lapierre, L.A.,Williams, J.A.,Weis, V.G.,Goldenring, J.R.,Nam, K.T. American Association of Pathologists and Bacteriol 2015 The American journal of pathology Vol.185 No.8
Doublecortin-like kinase 1 (Dclk1) is considered a reliable marker for tuft cells in the gastrointestinal tract. We investigated the dynamic changes of tuft cells associated with mouse models of oxyntic atrophy and metaplasia in the stomach. Increases in the numbers of Dclk1-positive tuft cells were observed in several models of parietal cell loss. However, the expanded population of Dclk1-expressing cells showed a morphologically distinct structure in apical microvilli and acetylated microtubules, which was not seen in the tuft cells present in the normal gastric mucosa. These microvillar sensory cells (MVSCs) showed no evidence of proliferation. The expansion of the MVSCs induced by oxyntic atrophy was reversible after the return of parietal cells. More important, expansion of MVSCs after induced parietal cell loss was not observed in Gast<SUP>-/-</SUP> mice. Although the Dclk1-expressing cells in the normal gastric mucosa were in part derived from Lrig1-expressing stem cells, the Lrig1-lineaged cells did not produce the expanded Dclk1-expressing cells associated with oxyntic atrophy. These studies indicate that loss of parietal cells leads to the reversible emergence of a novel Dclk1-expressing sensory cell population in the gastric mucosa.