Keywords resonant column, frozen silt, shear modulus, damping ratio, Hardin-Drnevich model IntroductionLarge frozen regions are distributed around the world, as in subarctic countries [1,2]. Compared to soil under normal conditions (15°C to 25°C), under which pore water remained in a liquid state inside the soil, the dynamics of frozen ground varies significantly with the seasons, resulting in different vibratory responses for building and civil engineering structures; even seismic damage is related to the season. The seasonal influences were demonstrated in the seismic damage caused by the earthquake swarm that occurred in Dedu county, China, in 1986. These earthquakes occurred in the summer and winter; the stiffer buildings suffered more during the winter earthquake events, while the more flexible buildings were damaged during the summer events [3]. Research on the frequency of building during an Alaskan winter illustrates that the firstorder mode frequency of reinforced concrete frame structures with a shallow foundation increases nearly 50% over construction performed during the summer [4].There are many researchers studying the shear modulus and damping ratio of normal soil [5][6][7][8][9][10], also some researchers have made significant achievements using specific soils [11][12][13][14][15]. Common used testing devices are resonant column apparatus (RCA) and dynamic triaxial apparatus (DTA), and the utilization frequency of DTA is higher than RCA. But in fact, the resonant column test (RCT) at normal temperatures (15°C to 25°C) is relatively reliable, and certain codes, such as the Chinese standard (SL237-1999) and the American standard (D4015-92) [16,17], have proven to be useful.In contrast, research on the shear modulus and damping ratio of frozen soil is limited [3,[18][19][20]. These researches revealed each factor that affects the modulus and damping to a different extent. However, the equipment performance and technological level required for a low temperature environment are more complex than those found in normal temperature tests. For all of the research noted above, there is a limit to the equipment's capabilities as well as some issues with the methodology, as shown in the following list.
Glutathione (GSH) plays critical roles in the inflammatory response by acting as the master substrate for antioxidant enzymes and an important anti-inflammatory agent. In the early phase of the inflammatory response of macrophages, GSH content is decreased due to the down regulation of the catalytic subunit of glutamate cysteine ligase (GCLC). In the current study we investigated the underlying mechanism for this phenomenon. In human THP1-differentiated macrophages, GCLC mRNA had a half-life of 4 h under basal conditions, and it was significantly reduced to less than 2 h upon exposure to lipopolysaccharide (LPS), suggesting an increased decay of GCLC mRNA in the inflammatory response. The half-life of GCLC protein was >10 h under basal conditions, and upon LPS exposure the degradation rate of GCLC protein was significantly increased. The pan-caspase inhibitor Z-VAD-FMK but not the proteasome inhibitor MG132, prevented the down regulation of GCLC protein caused by LPS. Both caspase inhibitor Z-LEVD-FMK and siRNA of caspase-5 abrogated LPS-induced degradation of GCLC protein. In addition, supplement with γ-GC, the GCLC product, efficiently restored GSH content and suppressed the induction of NF-κB activity by LPS. In conclusion, these data suggest that GCLC down-regulation in the inflammatory response of macrophages is mediated through both increased mRNA decay and caspase-5-mediated GCLC protein degradation, and γ-GC is an efficient agent to restore GSH and regulate the inflammatory response.
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