Yusic Kim

PREDICTION OF ASPHALT MIX FATIGUE LIFE WITH VISCOELASTIC MATERIAL PROPERTIES

A simplified fatigue model is presented that can predict the fatigue life of asphalt mixes using viscoelastic properties only. This fatigue model was originally developed with the elastic-viscoelastic correspondence principle and continuum damage mechanics and was reduced to a simple version that can predict fatigue life with viscoelastic properties only. On the basis of the experimental study conducted on 12 different types of asphalt mixes, it was observed that the fatigue behavior of asphalt mixes is affected by both the viscoelastic properties and the fatigue characteristics, but mostly by the viscoelastic properties. In addition, it was found that the coefficient of conventional strain-based fatigue models could be expressed in terms of viscoelastic material properties. In the verification study, the fatigue model was able to predict the fatigue life of various types of mixes at the same level of prediction accuracy without change in model coefficients. The fatigue model was also able to accurately predict the changes in the fatigue life of an asphalt mix due to the changes in the volumetric mix properties.

Conformationally resolved structures of jet-cooled acetaminophen by UV–UV hole-burning spectroscopy

The conformational structures of jet-cooled acetaminophen were investigated in the gas phase by resonant 2-photon ionization and UV-UV hole-burning spectroscopy. In contrast to the results from a previous study, two nearly isoenergetic conformers were distinctly found in a supersonic molecular beam expansion and positively identified as the cis and trans isomers of acetaminophen by UV-UV hole-burning spectroscopy. The 0-0 bands of the cis and trans isomers were found at 33518.7 and 33485.6 cm(-1), respectively. The vibronic bands of the two isomers are close-lying and/or partially overlapping due to the small energy difference (33 cm(-1)) between the two 0-0 bands. As a consequence, the recorded resonant 2-photon ionization spectrum is highly congested in the low excitation energy region, which develops continuously into a featureless, broadened spectrum in the high energy region.

Qualification Test Results of the KSTAR Superconducting Coils From the Construction to the Commissioning Steps

To achieve the first plasma of the Korea superconducting tokamak advanced research (KSTAR), the KSTAR superconducting coils were tested in advance. As they should operate in excessively low temperature of 4.5 K and high magnetic field environment of 7.5 T, it is crucial to monitor the cryogenic and the structural behaviors of KSTAR device during the commissioning period including a cool-down. The temperatures of the KSTAR toroidal field (TF) coil and the poloidal field (PF) coils were measured during the entire operating period. The mechanical stresses on the TF and PF structures were continuously monitored to check if they go beyond the limiting value calculated through the simulation. The alignment of the KSTAR device was checked by using displacement sensors. The TF coils were successfully supplied with 15 kA DC current for 8 hours, and the maximum 5 kA/s current variation of the PF coils were tested. For the main experiment, the interlock test of the quench detection system for the KSTAR coils was carried out at reduced currents of 1 kA. From these results the quench protection circuit, and the current-flow of the KSTAR superconducting coils proved to be well performed for the first plasma operation.

Pressure Drop of CICC From Manufacturing Stage to Plasma Operation in KSTAR Superconducting Magnet System

The Korea Superconducting Tokamak Advanced Research (KSTAR) is a superconducting tokamak that consists of cable-in-conduit conductors (CICCs) and has been successfully operated since 2008. KSTAR toroidal field (TF) and poloidal field (PF) coils are cooled by forced-flow supercritical helium of about 4.5 K. The complicated behaviors of the supercritical helium affect the plasma operation and the efficiency of the helium refrigerator system by means of, for instance, pressure drop. The annual measurements of pressure drop of PF coils are carried out including the manufacturing stage at room temperature to check the inside status of the cable-in-conduit conductor. The mass flow distribution of TF coils has also been checked since the individual coil stage. During current charging of the TF coil, we confirmed the change of pressure drop, and the friction factor of PF coils are compared to the ITER case. In this paper, the latest hydraulic behaviors based on pressure drop of the KSTAR superconducting magnet are presented.

Finite-temperature corrections in the dilated chiral quark model

We calculate the finite-temperature corrections in the dilated chiral quark model using the effective potential formalism. Assuming that the dilaton limit is applicable at some short length scale, we interpret the results to represent the behavior of hadrons in dense and hot matter. We obtain the scaling law, f{sub {pi}}(T)/f{sub {pi}} = m{sub Q}(T)/m{sub Q} {approx_equal} m{sub {sigma}}(T)/m{sub {sigma}}while we argue, using PCAC, that pion mass does not scale within the temperature range involved in our Lagrangian. It is found that the hadron masses and the pion decay constant drop faster with temperature in the dilated chiral quark model than in the conventional linear sigma model that does not take into account the QCD scale anomaly. We attribute the difference in scaling in heat bath to the effect of baryonic medium on thermal properties of the hadrons. Our finding would imply that the AGS experiments (dense and hot matter) and the RHIC experiments (hot and dilute matter) will ``see`` different hadron properties in the hadronization exit phase.