Water and ions transport in calcium silicate hydrate: a molecular dynamics study

Transport properties of water and ions in calcium silicate hydrate (C-S-H) greatly affect the durability of cementitious materials. In this study, molecular dynamics (MD) technique is used to investigate the transport behaviors of NaCl solution in C-S-H nanopores with different sizes (from 0.5 nm to 5 nm), and the hindering effect of C-S-H on the diffusion of water molecules and Cl ions is further explored in the case of a 5 nm pore. Results show that the diffusion coefficients of water molecules and Cl ions in C-S-H nanopores increase with the expansion of nanopore. At the atomic scale, the Ca-rich C-S-H forms Ca-O and Ca-Cl clusters with water molecules and Cl ions, respectively, and the Si-O tetrahedra on silicate chains can also build hydrogen bonding interactions with water molecules, which constrain the transport behaviors of water and ions. From the molecular perspective, this study innovatively investigates the effect of C-S-H pore size on the diffusion capacity of water and ions, and reveals the chemical bonding mechanism between water molecules, Cl ions and C-S-H, which provides a theoretical basis for studying the resistance of concrete to ionic attack

Stochasticity overrides deterministic processes in structuring macroinvertebrate communities in a plateau aquatic system

Deterministic and stochastic processes are two major factors shaping community dynamics, but their relative importance remains unknown for many aquatic systems, including those in the high-elevation Qinghai–Tibet Plateau. Here, we explored the causes of multidimensional beta diversity patterns (i.e., taxonomic, functional, and phylogenetic) of a macroinvertebrate metacommunity in this large aquatic system by using multiple approaches (i.e., null models, phylogenetic signal testing, and ordination-based approaches). To obtain insights into community assembly mechanisms, we also analyzed beta diversity in two deconstructed sub-metacommunities (e.g., different tributaries and the main lake body). We found that most functional traits showed significant phylogenetic signals, indicating that the functional traits were profoundly influenced by evolutionary history. The null models showed randomness of functional and phylogenetic beta diversities for the whole basin and its tributaries, confirming the importance of stochasticity over deterministic processes in controlling community structure. However, both phylogenetic and functional community structures were clustered in the Qinghai Lake, probably reflecting the importance of environmental filtering. Ordination-based approaches also revealed that both environmental factors and spatial processes accounted for variation in taxonomic, functional, and phylogenetic beta diversity. More specifically, environmental filtering was more important than spatial processes for the functional dimension, but the opposite was true for the taxonomic and phylogenetic dimensions. The paleogeographic history of the Qinghai Lake basin may have contributed substantially to the prevalence of stochastic processes. Overall, this study provides a better understanding of ecological patterns and assembly mechanisms of macroinvertebrate communities across this poorly known high-elevation aquatic system that is highly sensitive to climate warming

A TRPV4-dependent neuroimmune axis in the spinal cord promotes neuropathic pain

Microglia, resident macrophages of the CNS, are essential to brain development, homeostasis, and disease. Microglial activation and proliferation are hallmarks of many CNS diseases, including neuropathic pain. However, molecular mechanisms that govern the spinal neuroimmune axis in the setting of neuropathic pain remain incompletely understood. Here, we show that genetic ablation or pharmacological blockade of transient receptor potential vanilloid type 4 (TRPV4) markedly attenuated neuropathic pain-like behaviors in a mouse model of spared nerve injury. Mechanistically, microglia-expressed TRPV4 mediated microglial activation and proliferation and promoted functional and structural plasticity of excitatory spinal neurons through release of lipocalin-2. Our results suggest that microglial TRPV4 channels reside at the center of the neuroimmune axis in the spinal cord, which transforms peripheral nerve injury into central sensitization and neuropathic pain, thereby identifying TRPV4 as a potential new target for the treatment of chronic pain