Phonon Thermal Transport Through Tilt Grain Boundaries in Strontium Titanate

In this work, we perform nonequilibrium molecular dynamics simulations to study phonon scattering at two tilt grain boundaries (GBs) in SrTiO3. Mode-wise energy transmission coefficients are obtained based on phonon wave-packet dynamics simulations. The Kapitza conductance is then quantified using a lattice dynamics approach. The obtained results of the Kapitza conductance of both GBs compare well with those obtained by the direct method, except for the temperature dependence. Contrary to common belief, the results of this work show that the optical modes in SrTiO3 contribute significantly to phonon thermal transport, accounting for over 50% of the Kapitza conductance. To understand the effect of the GB structural disorder on phonon transport, we compare the local phonon density of states of the atoms in the GB region with that in the single crystalline grain region. Our results show that the excess vibrational modes introduced by the structural disorder do not have a significant effect on phonon scattering at the GBs, but the absence of certain modes in the GB region appears to be responsible for phonon reflections at GBs. This work has also demonstrated phonon mode conversion and simultaneous generation of new modes. Some of the new modes have the same frequency as the initial wave packet, while some have the same wave vector but lower frequencies

Ballistic-diffusive phonon heat transport across grain boundaries

The propagation of a heat pulse in a single crystal and across grain boundaries (GBs) is simulated using a concurrent atomistic-continuum method furnished with a coherent phonon pulse model. With a heat pulse constructed based on a Bose-Einstein distribution of phonons, this work has reproduced the phenomenon of phonon focusing in single and polycrystalline materials. Simulation results provide visual evidence that the propagation of a heat pulse in crystalline solids with or without GBs is partially ballistic and partially diffusive, i.e., there is a co-existence of ballistic and diffusive thermal transport, with the long-wavelength phonons traveling ballistically while the short-wavelength phonons scatter with each other and travel diffusively. To gain a quantitative understanding of GB thermal resistance, the kinetic energy transmitted across GBs is monitored on the fly and the time-dependent energy transmission for each specimen is measured; the contributions of coherent and incoherent phonon transport to the energy transmission are estimated. Simulation results reveal that the presence of GBs modifies the nature of thermal transport, with the coherent long-wavelength phonons dominating the heat conduction in materials with GBs. In addition, it is found that phonon-GB interactions can result in reconstruction of GBs

Wnt-5a Promotes Neural Development and Differentiation by Regulating CDK5 via Ca2+/Calpain Pathway

Background/Aims: The Wnt signaling pathway has essential functions in the central nervous system, where it regulates the major physiological functions of neurons, including development, differentiation, and plasticity. Wnt signaling controls these cellular events; however, how Wnt pathways integrate into a coherent developmental program remains unclear. Methods: The expression and secretion of different WNT ligands (Wnt-1, Wnt-3a, Wnt-4, Wnt-5a, Wnt-11), and the levels and activities of cyclin-dependent kinases (CDK2, CDK4, CDK6/cyclin D, cyclin E) or CDK5 (CDK5/p35 and p25) were measured in Rat cortex at different embryonic stages, and in RA/BDNF-induced differentiated SH-SY5Y cell model, by Quantitative real-time PCR (qPCR), western blotting, ELISA, and in vitro CDK5 kinase assays. MAP2-BrdU double staining was used to assess cell differentiation and cell cycle exit in an RA/BDNF-induced differentiated SH-SY5Y cell model. The effects of CDK5 and Ca2+/calpain signaling were assessed using specific chemical inhibitors. Results: We found that Wnt-1 was unchanged and Wnt-3a was attenuated, whereas Wnt-4, Wnt-5a, and Wnt-11 were markedly up-regulated, during the development of neurons and differentiated SH-SY5Y cells. Simultaneously, the activity of CDK5 was elevated. Furthermore, we describe crosstalk between non-canonical Wnt signaling and CDK5 in the development of neurons and differentiated SH-SY5Y cells. Wnt-5a, a non-canonical Wnt ligand, regulated CDK5 via Ca2+/calpain signaling in both neuronal development and differentiation. Inhibition of Wnt-5a diminished CDK5 kinase activity via the Ca2+/calpain pathway, thereby attenuating RA-BDNF induced SH-SY5Y cell differentiation. Conclusion: Wnt-5a signaling is a significant regulator of neuronal development and differentiation and upregulates CDK5 kinase activity via Ca2+/calpain signaling

Paradoxical Leadership: A Meta-Analytical Review

This is the final version. Available on open access from Frontiers Media via the DOI in this recordThe past few decades have brought a rapid emergence of research related to paradoxical leadership behavior (PLB), yet extant research remains scattered, inconsistent and somewhat contradictory. This meta-analysis examines the association between PLB and follower/team outcomes, specifically exploring PLBs incremental validity over other established leadership styles, namely transactional, transformational and servant leadership, as well three competing mechanisms through which PLB elicits positive effects. Our findings demonstrate that PLB is consistently positively associated with follower in-role performance, organizational citizenship behaviour, creativity, voice and innovation. However, while PLB showed consistent incremental effects over transactional leadership, its incremental validity in relation to transformational and servant leadership is less clear, with the exception of predicting innovation. Finally, we found evidence that PLB is related to follower behaviors via socio-cognitive (psychological safety), role-based (role clarity), and relational (LMX) mechanisms, with these effects varying as a function of the outcome. Based on our findings, we derive several important implications for PLB theory and key implications for future research

Regioselective oxidation of heterocyclic aromatic hydrocarbons catalyzed by cytochrome P450: A case study of carbazole

Recently there are increasing interests in accurately evaluating the health effects of heterocyclic PAHs. However, the activation mechanism and possible metabolites of heterocyclic PAHs catalyzed by human CYP1A1 is still elusive to a great extent. Here, leveraged to high level QM/MM calculations, the corresponding activation pathways of a representative heterocyclic PAHs, carbazole, were systematically explored. The first stage is electrophilic addition or hydrogen abstraction from N-H group. Electrophilic addition was evidenced to be more feasible and regioselectivity at C3 and C4 sites were identified. Correlations between energy barriers and key structural/electrostatic parameters reveal that O-Cα distance and Fe-O-Cα angle are the main origin for the catalytic regioselectivity. Electrophilic addition was determined as the rate-determining step and the subsequent possible reactions include epoxidation, NIH shift (the hydrogen migration from the site of hydroxylation to the adjacent carbon) and proton shuttle. The corresponding products are epoxides, ketones and hydroxylated carbazoles, respectively. The main metabolites (hydroxylated carbazoles) are estimated to be more toxic than carbazole. The regioselectivity of carbazole activated by CYP1A1 is different from the environmental processes (gas and aqueous phase). Collectively, these results will inform the in-depth understanding the metabolic processes of heterocyclic PAHs and aid the accurate evaluation of their health effects

Ballistic-diffusive phonon heat transport across grain boundaries

The propagation of a heat pulse in a single crystal and across grain boundaries (GBs) is simulated using a concurrent atomistic-continuum method furnished with a coherent phonon pulse model. With a heat pulse constructed based on a Bose-Einstein distribution of phonons, this work has reproduced the phenomenon of phonon focusing in single and polycrystalline materials. Simulation results provide visual evidence that the propagation of a heat pulse in crystalline solids with or without GBs is partially ballistic and partially diffusive, i.e., there is a co-existence of ballistic and diffusive thermal transport, with the long-wavelength phonons traveling ballistically while the short-wavelength phonons scatter with each other and travel diffusively. To gain a quantitative understanding of GB thermal resistance, the kinetic energy transmitted across GBs is monitored on the fly and the time-dependent energy transmission for each specimen is measured; the contributions of coherent and incoherent phonon transport to the energy transmission are estimated. Simulation results reveal that the presence of GBs modifies the nature of thermal transport, with the coherent long-wavelength phonons dominating the heat conduction in materials with GBs. In addition, it is found that phonon-GB interactions can result in reconstruction of GBs.This is a manuscript of an article published as Chen, Xiang, Weixuan Li, Liming Xiong, Yang Li, Shengfeng Yang, Zexi Zheng, David L. McDowell, and Youping Chen. "Ballistic-diffusive phonon heat transport across grain boundaries." Acta Materialia 136 (2017): 355-365. DOI: 10.1016/j.actamat.2017.06.054. Copyright 2017 Acta Materialia Inc. Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0). Posted with permission

Supplementary document for Multiscale Diffractive U-Net: a robust all-optical deep learning framework modeled with sampling and skip connections - 5920110.pdf

1. Network modeling and parameter definition; 2. Features of different scales of MDUNet</p

Transitional Structures with Continuous Variations in Atomic Positions from Anatase to Rutile Improve Photocatalytic Activity

Abstract TiO2 polymorphs have distinct properties that are widely employed in various applications. However, mechanisms of transformations between these polymorphs are not fully understood, especially at atomic scale, inhibiting advancing the design and application of the transitional phases. Here, based on results from semi‐in situ transmission electron microscopy, density functional theory, and X‐ray photoemission experiments, a physical picture of transitional structures is discovered, in which continuous variations in atomic positions form along a previously unreported anatase‐to‐rutile phase transformation path of [010]A–to–[1¯1¯1]R and (004)A–to– (011)R. These gradient structures give rise to continuous band bending, which promotes electron‐hole separation and inhibits their recombination across the bulk of the particles, leading to a large functionally active volume fraction and resulting in high photoactivity. These findings suggest that interphase matter based on extended gradient structures can be designed to advance new functions not achievable using abrupt interfaces