Effect of contact plasticity on the seismic response of a 7-duct bundle immersed in fluid

In the reactor core, the ducts, submerged under fluid, are closely packed. As a result, the collision between ducts is inevitable during the seismic load. Understanding seismic response of the ducts needs to consider both the collision between ducts and the inertial effect from the surrounding fluid. For the collision model, we proposed a nonlinear contact model from a full scale simulation to consider the plastic effect during collision; For the fluid effect, we built an acoustic-structural model to obtain the added mass coefficient depending on the duct's location. Next, we integrated the effects from plastic collision and the fluid inertia into a beam model to study the seismic response of a 7-duct bundle, and then discussed the plastic effect on the contact forces, contact durations and duct acceleration. Results show that although contact plasticity hardly affects the ducts' motion, it has a noticeable effect on both contact force and contact energy dissipation. In addition, our result shows that the contact duration for one typical type of collisions tends to be constant

Identification and mRNA Expression of Antioxidant Enzyme Genes in the Mud Crab (Scylla paramamosain) in Response to Acute Ammonia and Nitrite Exposure

Thioredoxin reductase (TrxR) is a conserved protein that is involved in protecting organisms against various oxidative stresses. In this study, a thioredoxin reductase gene was cloned from the mud crab Scylla paramamosain (SpTrxR). The full-length cDNA of SpTrxR is comprised of 2724 bp with a 1791 bp open reading frame that encodes a putative protein of 596 amino acids. The deduced amino acid sequence of SpTrxR contains the typical TrxR domain. Quantitative real-time PCR analysis revealed that the SpTrxR mRNA was distributed abundantly in mud crabs, while strong expression was observed mainly in the gills. The expression of antioxidant enzyme genes (SpTrxR, SpTrx, SpSOD, and SpCAT) was measured using quantitative real-time PCR after acute ammonia and nitrite exposure. The results show that antioxidant enzyme genes (SpTrxR, SpTrx, SpSOD, and SpCAT) were modulated by acute ammonia and nitrite exposure. These results suggest that antioxidant enzyme genes play an important role in protecting organisms against oxidative stres