Simulation of segregation in a fluidized bed by CFD-DEM by using similarities

Segregation happens in a fluidized bed due to particles with different sizes and/or different densities. Segregation is important for a lot of processes such as gasification, combustion and drying, but there are still a lot of unknown features. CFD coupled with DEM (discrete element model) is a powerful tool to investigate segregation in fluidized beds, but the computational load by this approach is too heavy to perform simulations in large-scale. In this study, similarities are used to decrease computational load. A fluidized bed consisting of jetsam and flotsam particles is simulated, i.e. large particles with small density and small particles with large density, respectively (Table 1). The dimensions of the fluidized bed are 1m height, 1m length and 0.037m depth. The number of real particles in the bed exceeds 1 billion, which is too large to track in a numerical simulation by computer. Therefore, in the imaginary system which is simulated the number of particles is reduced as described below. The imaginary system contains imaginary gas and imaginary particles. Each imaginary particle with a diameter K times larger than that of the real particle replaces a group of real particles. It is deduced that the segregation behavior of the imaginary system is similar to that of the real system, if the physical properties of the imaginary system are adjusted such that Reynolds and Archimedes numbers equal those of the real system (Fig.2). Enlarging the imaginary particles by a factor K can decrease the number of particles and hence the computational load by a factor of K-4.5. Please click Additional Files below to see the full abstract

THE ROLE OF SOCIAL NETWORKS IN ONLINE REVIEWING

Online reviews are a dominant resource for consumer decisions but what leads users to write reviews remains largely unexamined. Extant research on user content generation has primarily focused on what motivates users to contribute content, and less on the effects of informational and social environment surrounding these users. The aim of this study is to examine how a user’s contribution to an online review platform is affected by reviews of his/her friends from both informational and social perspectives. We expect that information, reciprocity, and social comparison are primary drivers for contribution. Among friends who wrote reviews, we predict that those who carry redundant information have less effect on the focal user’ contribution, whereas those who are strong-tie friends of the focal user have a stronger effect. Furthermore, we expect that users’ status moderates these effects such that an elite user responds more positively to friends who carry redundant information, and more negatively to those who are strong-tie friends, compared to non-elite users. Our expected findings hold implications for online review platforms in terms of highlighting the most relevant reviews generated by one’s peer

Structural basis for the regulation of L-type voltage-gated calcium channels: interactions between the N-terminal cytoplasmic domain and Ca2+-calmodulin

It is well-known that the opening of L-type voltage-gated calcium channels can be regulated by calmodulin (CaM). One of the main regulatory mechanisms is calcium-dependent inactivation (CDI), where binding of apo-CaM to the cytoplasmic C-terminal domain of the channel can effectively sense an increase in the local calcium ion concentration. Calcium-bound CaM can bind to the IQ-motif region of the C-terminal region and block the calcium channel, thereby providing a negative feedback mechanism that prevents the rise of cellular calcium concentrations over physiological limits. Recently, an additional Ca2+/CaM-binding motif (NSCaTE, N-terminal spatial Ca2+ transforming element) was identified in the amino terminal cytoplasmic region of Cav1.2 and Cav1.3. This motif exists only in Cav1.2 and Cav1.3 channels, and a pronounced N-lobe (Ca2+/CaM) CDI effect was found for Cav1.3. To understand the molecular basis of this interaction, the complexes of Ca2+/CaM with the biosynthetically produced N-terminal region (residues 1–68) and NSCaTE peptide (residues 48–68) were investigated. We discovered that the NSCaTE motif in the N-terminal cytoplasmic region adopts an α-helical conformation, most likely due to its high alanine content. Additionally, the complex exhibits an unusual 1:2 protein:peptide stoichiometry when bound to Ca2+-CaM, and the N-lobe of CaM has a much stronger affinity for the peptide than the C-lobe. The complex structures of the isolated N- and C-lobe of Ca2+/CaM and the NSCaTE peptide were determined by nuclear magnetic resonance spectroscopy and data-driven protein-docking methods. Moreover, we also demonstrated that calcium binding protein 1, which competes with CaM for binding to the C-terminal cytoplasmic domain, binds only weakly to the NSCaTE region. The structures provide insights into the possible roles of this motif in the calcium regulatory network. Our study provides structural evidence for the CaM-bridge model proposed in previous studies