• Macromolecular Research
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• v.12 no.1
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• pp.141-143
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• 2004

We have investigated the dynamic mechanical behavior of ultra-high molecular weight polyethylene (UHMWPE) irradiated with varying doses of gamma rays. A relaxation peak in the loss factor curve, which has not been reported previously in the literature, is observed at a temperature above the crystal melting temperature. The peak is unique to UHMWPE and appears to be related to the high degree of entanglement. Because the temperature and intensity of the peak are reduced by irradiation-induced chain scission and crosslinking, respectively, we believe that the peak is associated with disentanglement relaxation. The behavior of the storage modulus in the melt state agrees with the classical theory of rubber elasticity.

• Bulletin of the Korean Chemical Society
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• v.32 no.12
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• pp.4397-4402
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• 2011

The NF-${\kappa}B$ system of transcription factors plays a crucial role in inflammatory diseases, making it an important drug target. We combined quantitative structure activity relationships for predicting the activity of new compounds and quantitative dynamic models for the NF-${\kappa}B$ network with intracellular concentration models. GFA-MLR QSAR analysis was employed to determine the optimal QSAR equation. To validate the predictability of the $IKK{\beta}$ QSAR model for an external set of inhibitors, a set of ordinary differential equations and mass action kinetics were used for modeling the NF-${\kappa}B$ dynamic system. The reaction parameters were obtained from previously reported research. In the IKKb QSAR model, good cross-validated $q^2$ (0.782) and conventional $r^2$ (0.808) values demonstrated the correlation between the descriptors and each of their activities and reliably predicted the $IKK{\beta}$ activities. Using a developed simulation model of the NF-${\kappa}B$ signaling pathway, we demonstrated differences in $I{\kappa}B$ mRNA expression between normal and different inhibitory states. When the inhibition efficiency increased, inhibitor 1 (PS-1145) led to long-term oscillations. The combined computational modeling and NF-${\kappa}B$ dynamic simulations can be used to understand the inhibition mechanisms and thereby result in the design of mechanism-based inhibitors.

• BMB Reports
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• v.50 no.2
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• pp.55-57
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• 2017

Toll-like receptor 4 (TLR4) together with MD2, one of the key pattern recognition receptors for a pathogen-associated molecular pattern, activates innate immunity by recognizing lipopolysaccharide (LPS) of Gram-negative bacteria. Although LBP and CD14 catalyze LPS transfer to the TLR4/MD2 complex, the detail mechanisms underlying this dynamic LPS transfer remain elusive. Using negative-stain electron microscopy, we visualized the dynamic intermediate complexes during LPS transfer-LBP/LPS micelles and ternary CD14/LBP/LPS micelle complexes. We also reconstituted the entire cascade of LPS transfer to TLR4/MD2 in a total internal reflection fluorescence (TIRF) microscope for a single molecule fluorescence analysis. These analyses reveal longitudinal LBP binding to the surface of LPS micelles and multi-round binding/unbinding of CD14 to single LBP/LPS micelles via key charged residues on LBP and CD14. Finally, we reveal that a single LPS molecule bound to CD14 is transferred to TLR4/MD2 in a TLR4-dependent manner. These discoveries, which clarify the molecular mechanism of dynamic LPS transfer to TLR4/MD2 via LBP and CD14, provide novel insights into the initiation of innate immune responses.

• Membrane Journal
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• v.4 no.2
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• pp.96-105
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• 1994

Theoretical model for membrane transport of large polye!ectroiyte is presented. When the electric field is applied, the molecular conformation quickly orients in the field direction showing overshooting orientation. the predicted dependence of overshoot time and orientation upon field intensity and molecular size aids to understand the dynamic motion of molecules in membrane transport. The dynamics of the overshoot is associated with self-trapping conformations of molecule. The understanding of these effects supports evidences for the electrophoretic filtration of polydectrolyte in the polymeric membrane. This paper shows one example for molecular study in the theoretical review paper of membrane transport.

• Journal of Mechanical Science and Technology
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• v.17 no.9
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• pp.1332-1338
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• 2003

To estimate the true wear rate of polyethylene acetabular cups used in total hip arthroplasty, the dynamic compressive creep deformation of ultra-high molecular weight polyethylene (UHMWPE) was quantified as a function of time, load amplitude, and radial location of the specimen in the extruded rod stock. These data were also compared with the creep behavior of polyethylene observed under static loading. Total creep strains under dynamic loading were only 64％, 70％, and 61％ of the total creep strains under static loading at the same maximum pressures of 2 MPa,4 MPa, and 8 MPa, respectively. Specimens cut from the periphery of the rod stock demonstrated more creep than those cut from the center when they were compressed in a direction parallel to the extrusion direction (vertical loading) whereas the opposite was observed when specimens were compressed in a direction perpendicular to the extrusion direction (transverse loading). These findings show that creep deformation of UHMWPE depends upon the orientation of the crystalline lamellae.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.547-550
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• 2004

We present a multiscale scheme which describes the dynamic pictures of atoms in the multiple length-scale systems. Large-scale atomic systems are reduced to coarse grained system by the quasicontinuum, of which the dynamic pathways are rendered by the action-derived molecular dynamics proved effective for multiple time-scale problems such as rare events. Adatom diffusions on the metal (001) surface are selected for our numerical examples. The energy barriers of the diffusions and the real dynamic trajectories of the adatoms are calculated.

• Multiscale and Multiphysics Mechanics
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• v.1 no.4
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• pp.327-340
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• 2016

Poly(${\epsilon}$-caprolactone) (PCL) diol, with good biodegradation and biocompatibility, is one of the widely used soft segments (SSs) in composing bio-polyester-urethanes (Bio-PUs), which show great potential in both biomedical and tissue engineering applications. Properties of Bio-PUs are tunable by combining SS monomers with different molecular weights, structures, modifications, and ratio of components. Although numbers of research have reported many Bio-PUs properties, few studies have been done at the molecular scale. In this study, we use molecular dynamic (MD) simulation to construct atomistic models for two commonly used PCL diol SSs with different molecular weights 1247.58 Da and 1932.42 Da. We compare the simulation results by using two widely used classical force fields for organic molecules: Consistent Valence Force Field (CVFF) and CHARMM General Force Field (CGenFF), and discuss the validity and accuracy. Melt density, volume, polymer conformations, transition temperature, and mechanical properties of PCL diols are calculated and compared with experiments. Our results show that both force fields provide accurate predictions on the properties of PCL diol system at the molecular scale and could help the design of future Bio-PUs.

• Bulletin of the Korean Chemical Society
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• v.29 no.5
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• pp.1075-1078
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• 2008

• Bulletin of the Korean Chemical Society
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• v.28 no.2
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• pp.325-328
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• 2007

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.6
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• pp.1487-1494
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• 1990

In this paper the dynamic characteristics of self acting air lubricated slider bearing of hard disk/head system are investigated. The dynamic equations of magnetic head mechanism considering both parallel and pitch motion and the time dependent modified Reynolds equation are analyzed and the dynamic pressure distribution of air film is numerically calculated in frequency domain by small perturbation method and finite difference scheme with variable grid. The dynamic response of the slider spacing is obtained accordingly as the moving recording surface vibrates in parallel mode.