Effects of seismic devices on transverse responses of piers in the Sutong Bridge

The Sutong Bridge in China opened to traffic in 2008, and is an arterial connection between the cities of Nantong and Suzhou. It is a cable-stayed bridge with a main span of 1,088 m. Due to a tight construction schedule and lack of suitable seismic devices at the time, fixed supports were installed between the piers and the girder in the transverse direction. As a result, significant transverse seismic forces could occur in the piers and foundations, especially during a return period of a 2500-year earthquake. Therefore, the piers, foundations and fixed bearings had to be designed extraordinarily strong. However, when larger earthquakes occur, the bearings, piers and foundations are still vulnerable. The recent rapid developments in seismic technology and the performance-based design approach offer a better opportunity to optimize the transverse seismic design for the Sutong Bridge piers. The optimized design can be applied to the Sutong Bridge (as a retrofit), as well as other bridges. Seismic design alternatives utilizing viscous fluid dampers (VFD), or friction pendulum sliding bearings (FPSB), or transverse yielding metallic dampers (TYMD) are thoroughly studied in this work, and the results are compared with those from the current condition with fixed transverse supports and a hypothetical condition in which only sliding bearings are provided on top of the piers (the girder can move “freely” in the transverse direction during the earthquake, except for frictional forces of the sliding bearings). Parametric analyses were performed to optimize the design of these proposed seismic devices. From the comparison of the peak bridge responses in these configurations, it was found that both VFD and TYMD are very effective in the reduction of transverse seismic forces in piers, while at the same time keeping the relative transverse displacements between piers and the box girder within acceptable limits. However, compared to VFD, TYMD do not interact with the longitudinal displacements of the girder, and have simpler details and lower initial and maintenance costs. Although the use of FPSB can also reduce seismic forces, it generally causes the transverse relative displacements to be higher than acceptable limits

Regional disparities in the beneficial effects of rising CO2 concentrations on crop water productivity

Rising atmospheric CO2 concentrations ([CO2]) are expected to enhance photosynthesis and reduce crop water use1. However, there is high uncertainty about the global implications of these effects for future crop production and agricultural water requirements under climate change. Here we combine results from networks of field experiments1, 2 and global crop models3 to present a spatially explicit global perspective on crop water productivity (CWP, the ratio of crop yield to evapotranspiration) for wheat, maize, rice and soybean under elevated [CO2] and associated climate change projected for a high-end greenhouse gas emissions scenario. We find CO2 effects increase global CWP by 10[0;47]%–27[7;37]% (median[interquartile range] across the model ensemble) by the 2080s depending on crop types, with particularly large increases in arid regions (by up to 48[25;56]% for rainfed wheat). If realized in the fields, the effects of elevated [CO2] could considerably mitigate global yield losses whilst reducing agricultural consumptive water use (4–17%). We identify regional disparities driven by differences in growing conditions across agro-ecosystems that could have implications for increasing food production without compromising water security. Finally, our results demonstrate the need to expand field experiments and encourage greater consistency in modelling the effects of rising [CO2] across crop and hydrological modelling communities

Brain Rhythms Reveal a Hierarchical Network Organization

Recordings of ongoing neural activity with EEG and MEG exhibit oscillations of specific frequencies over a non-oscillatory background. The oscillations appear in the power spectrum as a collection of frequency bands that are evenly spaced on a logarithmic scale, thereby preventing mutual entrainment and cross-talk. Over the last few years, experimental, computational and theoretical studies have made substantial progress on our understanding of the biophysical mechanisms underlying the generation of network oscillations and their interactions, with emphasis on the role of neuronal synchronization. In this paper we ask a very different question. Rather than investigating how brain rhythms emerge, or whether they are necessary for neural function, we focus on what they tell us about functional brain connectivity. We hypothesized that if we were able to construct abstract networks, or “virtual brains”, whose dynamics were similar to EEG/MEG recordings, those networks would share structural features among themselves, and also with real brains. Applying mathematical techniques for inverse problems, we have reverse-engineered network architectures that generate characteristic dynamics of actual brains, including spindles and sharp waves, which appear in the power spectrum as frequency bands superimposed on a non-oscillatory background dominated by low frequencies. We show that all reconstructed networks display similar topological features (e.g. structural motifs) and dynamics. We have also reverse-engineered putative diseased brains (epileptic and schizophrenic), in which the oscillatory activity is altered in different ways, as reported in clinical studies. These reconstructed networks show consistent alterations of functional connectivity and dynamics. In particular, we show that the complexity of the network, quantified as proposed by Tononi, Sporns and Edelman, is a good indicator of brain fitness, since virtual brains modeling diseased states display lower complexity than virtual brains modeling normal neural function. We finally discuss the implications of our results for the neurobiology of health and disease