Fabrication and high heat flux test of the first wall mock-ups for the Korean He Cooled Test Blanket (KO HCML TBM)

Korea has proposed and designed a Helium Cooled Molten Lithium (HCML) Test Blanket Module (TBM) to be tested in the International Thermonuclear Experimental Reactor (ITER). Ferrite Martensitic (FM) steel is designed to be used as a structural material in this design. Three mock-ups, especially for the first wall channels, were fabricated with a Hot Isostatic Pressing (HIP, 1050 °C, 100 MPa, 2 h) in order to develop the fabrication technology. One of them was used to observe the microstructure and it was found that there are no pores and cracks. Other mock-ups were used with high heat flux (HHF) tests performed with 20 cycles under 0.5 and 1.0 MW/m² heat fluxes in order to evaluate the integrity of the fabricated mock-ups. Here, HHF test conditions were determined with an ANSYS-CFX analysis. And then, the mock-ups were tested and broken under a 1.5 MW/m² heat flux, which is about the Critical Heat Flux (CHF) at the wall.     

Methodology for quantitative hazard assessment for tunnel collapses based on case histories in Korea

In this paper we propose the KICT Tunnel Collapse Hazard Index (KTH-Index), an index system for assessing the hazard level of collapse at a tunnel face. To establish the index system, a logical process is proposed for “objectively” assessing the index based on a sensitivity analysis for a well-arranged database containing past collapse cases. For the sensitivity analysis, a neural network based technique is employed which has no restriction, in contrast to conventional sensitivity analysis based on mathematics or statistics. The proposed process is based on the concept of the interaction matrix, a tool for comprehensively expressing the influences among major factors of consideration. Each component of the interaction matrix represents the influential sensitivity between both factors horizontally and vertically linked on the matrix. Since the KTH-Index is assessed based on a database compiled and constructed from collapsed tunnel sites, reliability is compromised for collapse modes and characteristics of sites that are not included in the database. In addition, the characteristics of data available in the database in terms of each major factor must be understood prior to applying the proposed index. Accordingly, this paper includes a basic statistic of the data prepared for the study. The assessment system is applied to the section of the SYK tunnel where large-scale collapses have already occurred, and it is found that the predicted hazard levels are in good agreement with the field data already known.     

Constrained simulated annealing for stability margin computation in a time‐delay system

The stability margin of a time‐delay system is formulated via factorization. This paper provides a numerical method for computing the stability margin of time‐delay linear time‐invariant systems with delay dependence by using a constrained simulated annealing algorithm. The constrained simulated annealing is used to solve a nonlinear continuous constrained optimization problem, which is derived from computing the stability margin of a delay system. Illustrative examples show that the established method can verify the stability for a class of time‐delay systems. Copyright © 2006 John Wiley & Sons, Ltd.     

Effect of Si and Zr on the interdiffusion of U-Mo alloy and Al

We investigated the effect of Zr additions to U-Mo and Si additions to Al on interdiffusion between U-Mo and Al by employing diffusion couple tests. We examined the phase stability of the γ-heat-treated alloys by high-temperature annealing tests. Using X-ray diffraction, we observed that the γ-phase U-7Mo-Zr alloys with more than 2 wt% Zr decomposed faster than the U-7Mo alloys. The diffusion couples showed that a Zr addition to U-7Mo and the addition of Si in Al reduced the interaction layer growth rates. However, Zr additions to U-Mo are most effective in reducing the overall interdiffusion rates when combined with Si additions to Al. The decomposition of the metastable U-Mo γ-phase during the diffusion test appears to have a significant effect on the overall interdiffusion rates.     

Starch consolidation of alumina: Fabrication and mechanical properties

A consolidation technique based on gelling property of starch was used to prepare alumina ceramics. Slurry containing alumina powder, dispersant and small amount of starch (2–3.5 wt.% of powder weight) was cast into a nonporous mould and heated to gelation temperature to produce a rigid green body. A defect free green body was obtained and the total linear shrinkage during drying was 2–3% and the green density observed was 64% of theoretical value. After complete drying, ceramic compacts were sintered without debinding operation. Sintered density of 99.4% was achieved after sintering at 1600 °C for 2 h. Flexural strength values of dried and sintered alumina were ～10 and 247 MPa, respectively. The sintered ceramics showed an extremely dense microstructure.     

A Closed-Form Expression of the Positional Uncertainty for 3D Point Clouds

We present a novel closed-form expression of positional uncertainty measured by a near-monostatic and time-of-flight laser range finder with consideration of its measurement uncertainties. An explicit form of the angular variance of the estimated surface normal vector is also derived. This expression is useful for the precise estimation of the surface normal vector and the outlier detection for finding correspondence in order to register multiple three-dimensional point clouds. Two practical algorithms using these expressions are presented: a method for finding optimal local neighbourhood size which minimizes the variance of the estimated normal vector and a resampling method of point clouds.     

Dna2 of Saccharomyces cerevisiae possesses a single-stranded DNA-specific endonuclease activity that is able to act on double-stranded DNA in the presence of ATP

To gain further insights into the biological functions of Dna2, previously known as a cellular replicative helicase in Saccharomyces cerevisiae, we examined biochemical properties of the recombinant Dna2 protein purified to homogeneity. Besides the single-stranded (ss) DNA-dependent ATPase activity as reported previously, we were able to demonstrate that ssDNA-specific endonuclease activity is intrinsically associated with Dna2. Moreover, Dna2 was capable of degrading duplex DNA in an ATP-dependent fashion. ATP and dATP, the only nucleotides hydrolyzed by Dna2, served to stimulate Dna2 to utilize duplex DNA, indicating their hydrolysis is required. Dna2 was able to unwind short duplex only under the condition where the endonuclease activity was minimized. This finding implies that Dna2 unwinds only partially the 3'-end of duplex DNA and generates a stretch of ssDNA of limited length, which is subsequently cleaved by the ssDNA-specific endonuclease activity. A point mutation at the conserved ATP-binding site of Dna2 inactivated concurrently ssDNA-dependent ATPase, ATP-dependent nuclease, and helicase activities, indicating that they all reside in Dna2 itself. By virtue of its nucleolytic activities, the Dna2 protein may function in the maintenance of chromosomal integrity, such as repair or other related process, rather than in propagation of cellular replication forks.     

Identification of a high-affinity glycine betaine transport system in Staphylococcus aureus

Staphylococcus aureus accumulates proline and glycine betaine when cells are grown at low water activity. In the present study, we have identified a high-affinity glycine betaine transport system in this bacterium. Optimal activity for this transport system was measured in the presence of high NaCl concentrations, but transport activity was not stimulated by high concentrations of other solutes.     

Critical Concentration of MgO for the Prevention of Abnormal Grain Growth in Alumina

The effects of MgO on sintering and grain growth of alumina in the absence of any other impurities as well as in the presence of various amounts of CaO were investigated using ultrapure (>99.999%) alumina and sintering at 1900°C for 1 h in a clean contamination-free condition. Critical concentrations of MgO required for the prevention of abnormal grain growth were linearly dependent on the CaO concentration. For a given concentration of CaO, at least the same amount of MgO has to be added to prevent abnormal grain growth. MgO addition alone to the ultrapure alumina enhanced both grain growth and densification kinetics during pressureless sintering. The beneficial effect of MgO doping could not be explained based on the solute drag (or pinning) model. It was more likely to be understood in terms of either a glass modification model or a solid–liquid interface modification model.