Kim Yh

A climatology of medium‐scale gravity wave activity in the midlatitude/low‐latitude daytime upper thermosphere as observed by CHAMP

We report on a detailed global climatology of medium-scale (150–600 km) thermospheric gravity wave (GW) activity using mass density observations onboard the CHAMP satellite from 2001 to 2010. Our study focuses mainly on daytime (09–18 h in local time) and midlatitude/low-latitude upper thermosphere between 300 km and 400 km altitudes. Midlatitude GW activity is strongest in the winter hemisphere. GW activity during June solstice adjacent to the Andes and Antarctic Peninsula is stronger than in any other season or location. GW activity in the low-latitude summer hemisphere is stronger above continents than above oceans: especially during December solstice and equinoxes. In terms of relative density variation, GW activity is stronger during solar minimum than solar maximum. These results agree well with the characteristics of stratospheric GWs, implying that the CHAMP GWs are mainly caused by GWs from tropospheric/stratospheric processes. Using mesosphere/lower thermosphere wind observations at a Korean Antarctic station, we investigated at which altitudes the upper thermospheric GW climatology becomes visible. While the correlation is insignificant at z=82–88 km, it becomes significant for most cases at z=90–98 km, suggesting that the upper thermospheric GW climatology may start to emerge at z≥90 km.

Outcome of pediatric patients with severe brain injury in Korea : a comparison with reports in the West

Abstract There have been relatively wide variations in the results of studies examining the outcomes of severe brain injury in children. Among the reasons for these variations in outcome, prehospital care can be considered as one of the factors. In Korea, major hospitals use an aggressive and sophisticated management policy very similar to that practiced in the West. However, effective prehospital management, such as emergency care at the scene of injury and during transport by paramedics, have not yet been established. In order to evaluate the influence of prehospital care on the outcome in severely brain-injured children, we report the outcome recorded in 73 pediatric patients treated in our hospital following severe brain injury and compare these results with those reported from centers in the western community, where well-trained paramedic care and an excellent transfer system are in operation. The overall mortality rate in our patients was 23%; 41% had a good recovery, 22% moderate disability, and 12% severe disability, and 1% remained in a vegetative state. In conclusion, we would like to suggest that prehospital care does not remarkably influence mortality rates in severely brain-injured children.

Investigation of bleeding focus in the intracranial vertebral artery with the use of posterior neck dissection method in traumatic basal subarachnoid hemorrhage

Traumatic basal subarachnoid hemorrhage caused by minor blunt trauma to the head or neck can lead to rapid collapse and death. The vertebral arteries are the vessels most commonly involved in such cases, but it is very difficult to find the bleeding focus in the vertebral arteries in routine autopsy because of the location of these vessels. Using the posterior neck dissection method, which is relatively easy and avoids artificial damage to the intracranial portion of the vertebral arteries, authors have identified tear sites in the intracranial artery in four out of five consecutive traumatic basal subarachnoid hemorrhage cases. In this report we show that this new method is useful for cases of traumatic basal subarachnoid hemorrhage.

Environmental Fatigue Evaluation for Primary Components of APR1400 Reactor Coolant System

USNRC Regulatory Guide (RG) 1.207 provides a guideline for evaluating fatigue analyses due to the environmental effects on the new light water reactor (LWR). The environmental correction factor (Fen ) is used to incorporate the LWR environmental effect into fatigue analyses of ASME Class 1 components. In this paper, the environmental fatigue evaluation is applied to some primary components with 60 year design life of Advanced Power Reactor (APR1400). The materials sampled from Class 1 components are the low alloy steel for the reactor vessel (RV) outlet nozzle and the carbon steel for the hot leg which are attached to the outlet nozzle. The simplified method, time-based integral method and strain-based integral method are used to compute the Fen values. The calculated fatigue usage factors including the environmental effects are compared with those obtained using the current ASME Code rules. As the calculated cumulative fatigue usage factor considering environmental effects (CUFen ) is below 1.0, there is no concern for the RV outlet nozzle to implement design for environmental fatigue effects.Copyright

An Analysis of Residual Stress Improvement for a Dissimilar Metal Nozzle-to-Pipe Weld by Using the Heat Sink Method

This study is concerned with the mechanics analysis of residual stress improvement by the heat sink method applied to a dissimilar metal weld (DMW) for the use in nuclear power plants. The DMW joint considered here is composed of ferritic low-alloy steel nozzle, austenitic stainless steel safe-end, and nickel-base alloy A52 weld metal. To prepare the DMW joint with a narrow-gap, the gas tungsten arc welding (GTAW) process is utilized, and the heat sink method is employed to control thermal gradients developed in the critical region of work pieces during welding. Weld residual stresses are computed by the non-linear thermal elasto-plastic analysis using the axisymmetric finite element (FE) model, for which temperature-dependent thermal and mechanical properties of the materials are considered. A full-scale mock-up test is conducted to validate analytical solution for the DMW joint, and residual stresses are measured by using the hole-drilling method. Results of the FE modeling and mock-up test for the DMW joint are compared and effects of the heat sink method are discussed. It is found that a significant amount of residual compressive stresses can be developed on the inner surface of the DMW joint by using the heat sink method, which can effectively reduce the susceptibility of the welded materials to stress corrosion or fatigue cracking.© 2008 ASME