HIGH-TEMPERATURE GAS-COOLED REACTOR CRITICAL EXPERIMENT AND ITS APPLICATION

Two types of critical experiments were conducted in support of the 40- Mw(e) Peach Bottom HTGR nucleardesign program. The first was the test-lattice experiment, where detailed measurements of reaction rates were examined in a lattice having a cold neutron spectrum characteristic of the HTGR. This program provided a method for checking the resonance integral of thorium, the Doppler coeificient of thorium, the detailed flux distribution in the lattice, and control-rod effectiveness within a cell. The second experiment was designed as a gross test of the calculational procedures and data. A small critical experiment having a clean geometry and a composition similar to that of the HTGR was constructed. This assembly had approximately one-sixth the volume of the HTGR core and was surrounded on all sides by a 2-ft graphite reflector. Owing to the small core size and the large reflector area, this experiment provided a severe test of the calculational methods. Experiments with this facility encompassed reactivity-coefficient measurements, neutron-flux distributions, effectiveness of groups of control rods, and a measurement of the overall temperature coefficient. (N.W.R.

Predicting the occurrence of grind hardening in cubic boron nitride grinding of crankshaft steel

Grind hardening is a stock removal grinding operation in which the heat generated in the grinding zone is used to heat-treat the workpiece surface to a specified depth. A thermal model to describe this process has been developed from the original Jaeger modelling and has been used to predict subsurface time-temperature profiles in the dry cylindrical grinding of 42CrMo4 crankshaft steel using cubic boron nitride (CBN) wheels. By comparing with experimental hardness depths, partition ratios were calculated and a polynomial fit applied to the proportion of specific energy entering the workpiece as heat, as a function of specific removal rate. By using this polynomial to provide the heat input to the thermal model, a theoretical chart of workpiece surface speed against depth of cut has been produced, which shows the regions in which grind hardening can be achieved to specified depths. The chart shows lower limits where the martensitic transformation temperature has been reached at certain specified depths and an upper limit where melting starts at the contact surface between the CBN grinding wheel and the workpiece. This chart has then been compared with experimental results for the specific case of a hardened depth of 0.5 mm or greater, with good agreement. The predictions indicate that there is an upper limit on workpiece speed if grind hardening is to be achieved, and that the limiting speed reduces as the required hardness depth increases. The predictions also indicate that there is an optimum work speed of around 10 mm/s for hardness depths below 1.5mm and an upper limit below 4 mm/s for hardness depths around 2 mm

Effect of Dickkopf-1 (Dkk-1) and SP600125, a JNK Inhibitor, on Wnt Signaling in Canine Prostate Cancer Growth and Bone Metastases

Human Dickkopf-1 (Dkk-1) upregulates a noncanonical Wnt/JNK pathway, resulting in osteoclast stimulation, cell proliferation, and epithelial-to-mesenchymal transition (EMT) of cancer cells. Ace-1-Dkk-1, a canine prostate cancer (PCa) cell line overexpressing Dkk-1, was used to investigate Wnt signaling pathways in PCa tumor growth. SP600125, a JNK inhibitor, was used to examine whether it would decrease tumor growth and bone tumor phenotype in canine PCa cells in vitro and in vivo. Ace-1-VectorYFP-Luc and Ace-1-Dkk-1YFP-Luc cells were transplanted subcutaneously, while Ace-1-Dkk-1YFP-Luc was transplanted intratibially into nude mice. The effects of Dkk-1 and SP600125 on cell proliferation, in vivo tumor growth, and bone tumor phenotype were investigated. The mRNA expression levels of Wnt/JNK-related genes were measured using RT-qPCR. Dkk-1 significantly increased the mRNA expression of Wnt/JNK-signaling-related genes. SP600125 significantly upregulated the mRNA expression of osteoblast differentiation genes and downregulated osteoclastic-bone-lysis-related genes in vitro. SP600125 significantly decreased tumor volume and induced spindle-shaped tumor cells in vivo. Mice bearing intratibial tumors had increased radiographic density of the intramedullary new bone, large foci of osteolysis, and increased cortical lysis with abundant periosteal new bone formation. Finally, SP600125 has the potential to serve as an alternative adjuvant therapy in some early-stage PCa patients, especially those with high Dkk-1 expression