Pre-osteoblast MC3T3-E1 cells were cultured in hyaluronic acid-modified chitosan/collagen/nano-hydroxyapatite (HA-CS/Col/nHAP) composite scaffolds and treated with phytoestrogen α-zearalanol (α-ZAL) to improve bone tissue formation for bone tissue engineering. Perfusion and dynamic strain were applied to three-dimensional (3D) cultured cells, which simulates mechanical microenvironment in bone tissue and solves mass transfer issues. The morphology of cell-scaffold constructs in vitro was then examined and markers of osteogenesis were assessed by immunohistochemistry staining and western blotting. The results showed that cells expanded their pseudopodia in an irregular manner and dispersed along the walls in 3D-dynamic culture. Osteogenic phenotype was increased or maintained by enhanced collagen I (COLI) levels, decreased osteopontin expression and having little effect on osteocalcin expression during the 12 days of in vitro culture. In response to α-ZAL, the cell-scaffold constructs showed inhibited cellular proliferation, enhanced the alkaline phosphatase (ALP) activity and increased ratio of osteoprotegerin to receptor activator of nuclear factor kappa B (NF-κB) ligand (RANKL). Application of perfusion and dynamic strain to cells-scaffold constructs treated with α-ZAL represents a promising approach in the studies of osteogenesis stimulation of bone tissue engineering.

For earthquakes (M ≥ 4.9) that occurred in the region limited by latitudes 2°S–16°N and longitudes 90°E–101°E from 1 January 1973 to 25 December 2004, we investigated temporal variations of the b value in the aftershock zone to determine its abnormal characteristics prior to the 2004 M_w9.0 Sumatra earthquake. The b value was estimated via the maximum likelihood method. We found that the b value significantly decreased by ∼36% in the aftershock zone from January 1990 to December 1999. From 2000 onwards until the Sumatra earthquake, the b value was persistently low (between 1.0 and 1.2). Furthermore, we calculated the spatial distribution of the relative changes in b value from 1990 to 1999. Only one area of larger relative declines in b value (>25%) was located very near to the epicentre of the Sumatra event. We also calculated the b values as a function of time for earthquakes in this area and its immediate vicinity. The result shows that the changes of b value with time around the epicentre is similar to that in the aftershock zone, but the relative decline amount is ∼40% around the epicentre, greater than that in the aftershock zone. Therefore, if our finding is confirmed, it will help to better constrain the location of future great earthquakes in seismic hazard analysis.

For earthquakes (M ≥ 2.0) occurring in and around the aftershock zone of the M7.1 Ridgecrest earthquake between January 2000 and June 2019, we analyzed the correlation between the phase of Earth's rotation and the occurrence of earthquakes. The Schuster's test and the two-rate Poisson model were used to statistically examine the correlation between the phase of Earth's rotation and the occurrence of earthquakes. For the Schuster's test, the results were judged based on the P-value. When the P-value is smaller, the correlation is higher. In general, if P ≤ 5%, the correlation is significant. For the two-rate Poisson model, the results were evaluated by R. When the 95% confidence lower limit on R (R_L) is over one, earthquakes could be non-random. We calculated the temporal variation on the P-value for earthquakes that occurred in the study region and found lower P-values, corresponding to significant correlation for earthquakes (2.0 ≤ M ≤ 2.4) occurring before the M7.1 event. When the P-value reached to the lowest, the earthquake nucleated when the Earth's acceleration of rotation is increasing or near the peak acceleration. This correlation is also confirmed by the two-rate Poisson model. The spacial distribution of the P-values for earthquakes (2.0 ≤ M ≤ 2.4) occurring from Jul. 2013 to Jun. 2019 shows that areas of low P-value were located mainly in and around the northwest segment of the aftershock zone of the M7.1 Ridgecrest earthquake. The lower P-value obtained in this study emphasises that the Earth's rotation can triggered earthquakes in and around the aftershock zone prior to the M7.1 Ridgecrest earthquake and hence it may be considered as one of the precursors.

The earthquake prediction released by USGS in 1985 to the public stated that there was an M_w6.0 earthquake occurring in the Parkfield area by January 1993 with a 95% chance. This prediction has proved unsuccessful. Some researchers analyzed the reasons for the failure of the prediction on the basis of statistics. In this study, we explored this problem by means of b-value and the Earth's rotation-correlated seismicity. The results show that an increasing trend in b-value occurred prior to May 1992 and a decreasing trend with a relative decrease of more than 35% from June 1992 to early 1999. In several years before the 2004 M_w 6.0 Parkfield earthquake, the b-value remained stable at the lowest level. A significant correlation between seismic activity and Earth's rotation occurred only when the 2004 mainshock was approaching. It has been well- known that when a stressed focal medium is approaching failure due to action of a critical stress, the focal medium will reach a critical state. At this point, seismicity could be significantly correlated to Earth's rotation. So, significantly Earth's rotation-related seismic activity indicated that the focal medium in the Parkfield area was at a critical state. Since the decline in b-value corresponds to increasing stress and the significantly Earth's rotation-related seismic activity indicates the critical state of the focal medium, we suggest that two precursors are the decline (several years to more than a decade) in b-value and the significantly Earth's rotation-related seismic activity. These two precursors did not emerge during or before the 1985 Parkfield earthquake prediction period. Instead, they appeared preceding the 2004 M_w 6.0 Parkfield mainshock. This may be the reason that the M_w 6 Parkfield earthquake did not occurred till 2004.