Yong-Soo Kim

A Phenome-Based Functional Analysis of Transcription Factors in the Cereal Head Blight Fungus, Fusarium graminearum

Fusarium graminearum is an important plant pathogen that causes head blight of major cereal crops. The fungus produces mycotoxins that are harmful to animal and human. In this study, a systematic analysis of 17 phenotypes of the mutants in 657 Fusarium graminearum genes encoding putative transcription factors (TFs) resulted in a database of over 11,000 phenotypes (phenome). This database provides comprehensive insights into how this cereal pathogen of global significance regulates traits important for growth, development, stress response, pathogenesis, and toxin production and how transcriptional regulations of these traits are interconnected. In-depth analysis of TFs involved in sexual development revealed that mutations causing defects in perithecia development frequently affect multiple other phenotypes, and the TFs associated with sexual development tend to be highly conserved in the fungal kingdom. Besides providing many new insights into understanding the function of F. graminearum TFs, this mutant library and phenome will be a valuable resource for characterizing the gene expression network in this fungus and serve as a reference for studying how different fungi have evolved to control various cellular processes at the transcriptional level.

A study on the incidence of ABL gene deletion on derivative chromosome 9 in chronic myelogenous leukemia by interphase fluorescence in situ hybridization and its association with disease progression.

Fluorescence in situ hybridization for the BCR/ABL rearrangement in 138 bone marrow specimens from 59 Philadelphia+ (Ph+) chronic myelogenous leukemia (CML) patients, 35 Ph+ acute lymphoblastic leukemia (ALL) patients, and 57 Ph− ALL patients was used. Sixteen (27.1%) of the 59 CML patients had deletions of the residual ABL gene on the derivative chromosome 9. During the study period, 32 of the 59 CML patients progressed to blast crisis or accelerated phase. Of these, nine patients had residual ABL gene deletions on the derivative chromosomes 9 and 23 patients had no deletions. The mean duration from first diagnosis to blast crisis or accelerated phase for the nine patients with ABL deletions was 32.8 months, and for the 23 patients without ABL deletions, it was 62.4 months (P = 0.017). The overall survival time for the 16 patients with deletions was 32.8 months, and for the 43 patients without deletions, it was 60.1 months (P = 0.164). ABL deletions were not detected among the 35 ALL patients (17 with major BCR/ABL, 18 with minor BCR/ABL), and it appears that this deletion occurs rarely or not at all in Ph+ ALL patients, which is in contrast to the CML patients (27.1%). However, we detected two ALL cases with ABL deletion but without BCR/ABL rearrangement among 49 Ph− ALL and 66 Ph− AML patients. In conclusion, patients with ABL deletions progress to blast crisis or accelerated phase in a significantly shorter time than do those without such deletions. It is therefore suggested that the ABL deletion is an indicator of a poor prognosis in CML.

Molecular cloning and complete cDNA sequence of UBH1 in mouse testis.

We have identified a full-length mouse UBH1 cDNA, encoding a putative deubiquitinating enzyme, from the testis by RT-PCR using primers prepared from sequences conserved amongst deubiquitinating enzymes. Sequence analysis predicts that the UBH1 cDNA encodes a 355 amino acid polypeptide with the molecular weight of approximately 39 kDa containing the highly conserved Cys, Asp, and His domains characteristic of the ubiquitin-specific processing proteases. Biochemical assay revealed that the mouse UBH1 has deubiquitinating enzyme activity and sequence analysis showed 98.3% amino acid identity with human UBH1.

Integral test and engineering analysis of coolant depletion during a large-break loss-of-coolant accident

This study concerns the development of an integrated calculation methodology with which to continually and consistently analyze the progression of an accident from the design-basis accident phase via core uncovery to the severe accident phase. The depletion rate of reactor coolant inventory was experimentally investigated after the safety injection failure during a large-break loss-of-coolant accident utilizing the Seoul National University Integral Test Facility (SNUF), which is scaled down to 1/6.4 in length and 1/178 in area from the APR1400 [Advanced Power Reactor 1400 MW(electric)]. The experimental results showed that the core coolant inventory decreased five times faster before than after the extinction of sweepout in the reactor downcomer, which is induced by the incoming steam from the intact cold legs. The sweepout occurred on top of the spillover from the downcomer region and expedited depletion of the core coolant inventory. The test result was simulated with the MAAP4 severe accident analysis code. The calculation results of the original MAAP4 deviated from the test data in terms of coolant inventory distribution in the test vessel. After the calculation algorithm of coolant level distribution was improved by including the subroutine of pseudo pressure buildup, which accounts for the differential pressure between the core and downcomer in MAAP4, the core melt progression was delayed by hundreds of seconds, and the code prediction was in reasonable agreement with the overall behavior of the SNUF experiment.

Thermal-Hydraulic Analyses of Steam Generator Tube Rupture Accident for the Kori Nuclear Unit 1 Pressurized Thermal Shock Study

Abstract This paper discusses a thermal-hydraulic analysis methodology using RETRAN-3D and assembles system analyses for pressurized thermal shock resulting from a steam generator tube rupture accident in Kori Nuclear Unit 1. Through a systematic definition of sequences and thermal-hydraulic analyses using RETRAN-3D, the most important parameters on downcomer overcooling were identified. The break location that leads to the most significant overcooling was found to be the hot leg side in the loop that does not contain the charging flow inlet. The initial power level had a large effect on the downcomer overcooling. The closure failure of the pressurizer power operated relief valves and the termination failure of the safety injection were found to be the most significant operator actions. In contrast, auxiliary feedwater control failure had little effect on overcooling, and the steam dump valve closure failure merely resulted in a temperature rise in the latter half of the transient. Through these analyses, recommendations for sequence grouping and against downcomer overcooling are provided.

AN EXPERIMENTAL STUDY WITH SNUF AND VALIDATION OF THE MARS CODE FOR A DVI LINE BREAK LOCA IN THE APR1400

In order to analyze thermal hydraulic phenomena during a DVI (Direct Vessel Injection) line break LOCA (Loss-of-Coolant Accident) in the APR1400 (Advanced Power Reactor 1400 MWe), we performed experimental studies with the SNUF (Seoul National University Facility), a reduced-height and reduce-pressure integral test loop with a scaled down APR1400. We performed experiments dealing with eight test cases under varied tests. As a result of the experiment, the primary system pressure, the coolant temperature, and the occurrence time of the downcomer seal clearing were affected significantly by the thermal power in the core and the SI flow rate. The break area played a dominant role in the vent of the steam. For our analytical investigation, we used the MARS code for simulation of the experiments to validate the calculation capability of the code. The results of the analysis showed good and sufficient agreement with the results of the experiment. However, the analysis revealed a weak capability in predicting the bypass flow of the SI water toward the broken DVI line, and it was insufficient to simulate the streamline contraction in the broken side. We, hence, need to improve the MARS code.

Analysis of Main-Steam-Line-Break Accidents Using RETRAN-3D for Pressurized Thermal Shock Evaluation of the Kori Nuclear Unit-1 Power Plant

Abstract A thermal-hydraulic analysis methodology is established for a pressurized thermal shock (PTS) analysis of the Kori Nuclear Unit-1 (KNU-1) power plant using RETRAN-3D. The effects of the important parameters on PTS are evaluated, such as the initial power level, break size, isolation of the depressurized steam generator (SG), and charging flow runback. As a result, the most dominant factors are revealed as the initial power level and break flow rate. Auxiliary feedwater (AFW) to the depressurized SG should be isolated by operator action as soon as possible to minimize break flow. To mitigate the risk of PTS by reducing both steam flow rate and operator response time of depressurized SG isolation, the installation of check valves to block the cross flow between two steam lines is recommended. An efficient grouping methodology is proposed using these results. Groups should be divided according to the break size, the initial power level, and the AFW isolation to a depressurized SG. Charging flow runback is revealed to have little effect on downcomer overcooling.

Magnetoluminescence Study on the Low-Dimensionality of Excitons Confined in a Narrow GaAs/AlGaAs Quantum Well

Low-dimensional characteristics of excitons confined in a quantum well (QW) are studied by applying a high magnetic field (B). The diamagnetic shift is best fit with a linear combination of linear and quadratic terms of B. From the quadratic dependence of B, it is obtained that the exciton becomes two-dimensional (2-D) like when the QW width decreases to 15 monolayers (ML). However, the 2-D confinement becomes weak when the width becomes smaller than 10 ML. In large B, the field confinement becomes significant in the electron-hole recombination, and the population inversion of the photo-generated carriers in the islands of ML fluctuation was observed.

Development of sweepout model in APR1400 during an LBLOCA

Abstract As a result of experiments with the Upper Plenum Test Facility and the 1400-MW(electric) Advanced Power Reactor (APR1400), sweepout in the downcomer has been identified as playing an important role in the depletion of the core coolant inventory during a large-break loss-of-coolant accident. In order to identify the sweepout mechanism and estimate the amount of coolant discharged during sweepout, separate-effects tests were performed in a rectangular-type test apparatus 1/5 the scale of the APR1400 downcomer. The experimental results showed that the sweepout was dominantly influenced by the hydraulic behaviors of coolant and steam near the intact cold leg. A sweepout model was developed by correlating the experimental results to analytically derived nondimensional parameters. The developed model showed applicability to the prototype, as the experimental results of the counterpart tests were in good agreement, within <25.0% of the uncertainty band.