Unsteady simulations of horizontal ribbon growth of silicon were performed that included both Marangoni and buoyancy effects. A chaotic flow was observed dominated by strong Marangoni-driven jets ...emerging near the local temperature minima on the free surface. This oscillatory flow caused the vertical position of the leading edge of the sheet to fluctuate, resulting in corrugations on the top surface of the ribbon. Additionally, larger amplitude and wavelength nonuniformities appeared on the bottom of the sheet resulting in a sheet with varying thickness. Lastly, the unsteady flow caused temporal variations in growth rate, which when converted to distance using the pull speed, matched the wavelengths observed on the top surface. All three of these phenomena have been observed experimentally: The median of the surface wavelengths and amplitudes decreased with increasing temperature sensitivity of surface tension and had wavelengths on the same order as experiments for a sensitivity corresponding to uncontaminated silicon. Oscillations in growth rate have been observed using passive antimony demarcation and thickness variations have been measured after sheet removal. These results indicate that the chaotic flow makes producing thin uniform sheets using HRG challenging.
•Buoyancy and thermal Marangoni (thermocapillary) effects result in a chaotic flow.•The chaotic flow caused small-amplitude corrugations on the top of the silicon sheet.•The chaotic flow caused large variations in growth rate of silicon.•The chaotic flow caused large sheet thickness non-uniformities.•These phenomena have all been observed experimentally.
•SiC MOSFETs static characteristic parameters are affected by temperature variation.•The HTGB project will affect the threshold voltage of the device.•The HTRB project will affect the Idss and ...threshold voltage of the device.
Reliability characteristics play a critical role in studied of SiC MOSFETs, including gate oxygen, long-term and short circuit reliability. This article presents a long-term reliability and device high temperature performance. Firstly, the static performance evaluation of the device at high temperature is introduced. Next, the gate bias test induces the threshold voltage shift, arguing that the instability is due to the capture of electrons by the SiC/SiO2 interface traps and the gate dielectric near-interface traps. Finally, the reliability characterization is verified using the common methods of high temperature reverse bias and high temperature gate bias tests. The results exhibit the superior reliability and performance of 1200 V SiC MOSFETs.
In a crystal growth experiment conducted on the Japanese Experiment Module “Kibo” aboard the International Space Station, an unknown phenomenon, i.e., spontaneous oscillation of the growth rate of ...ice-crystal basal faces in supercooled water containing antifreeze glycoprotein (AFGP), was observed. In this study, we modeled growth-inhibiting and growth-promoting effects of the AFGP adsorbed on the ice-crystal basal face and discussed the mechanism of the spontaneous oscillatory growth. The normal growth rate of the basal face depends on the amount of AFGP adsorbed on the basal face. Simultaneously, the amount of adsorbed AFGP is controlled by the crystal growth, because the higher the growth rate, the more frequently the crystal surface is renewed. The normal growth rate and the amount of adsorbed AFGP can be determined as a steady state that satisfies the interdependence between these quantities. By formulating the interdependence and finding the steady state, we demonstrated the appearance of two different stable steady states in a certain range of supercooling (bistability). This is theoretical proof of a crystal growth hysteresis, in which the trace of the growth rate varies with when the degree of supercooling is increased or decreased. We also clarified that the spontaneous oscillation of the growth rate is triggered by the release of the latent heat of crystallization. Our findings herein provide novel possibilities for the effect of AFGP on ice-crystal growth.
•Antifreeze glycoproteins cause oscillatory growth of ice crystal in microgravity.•This is a first theory that explains this oscillatory growth mechanism.•Glycoproteins are repeatedly adsorbed and desorbed on ice surface.•Glycoproteins act as impurities that inhibit or promote ice-crystal growth.•Release of latent heat of crystallization triggers oscillatory growth.
Chemokine-controlled arterial leukocyte recruitment is a crucial process in atherosclerosis. Formyl peptide receptor 2 (FPR2) is a chemoattractant receptor that recognizes proinflammatory and ...proresolving ligands. The contribution of FPR2 and its proresolving ligand annexin A1 to atherosclerotic lesion formation is largely undefined.
Because of the ambivalence of FPR2 ligands, we here investigate the role of FPR2 and its resolving ligand annexin A1 in atherogenesis.
Deletion of FPR2 or its ligand annexin A1 enhances atherosclerotic lesion formation, arterial myeloid cell adhesion, and recruitment. Mechanistically, we identify annexin A1 as an endogenous inhibitor of integrin activation evoked by the chemokines CCL5, CCL2, and CXCL1. Specifically, the annexin A1 fragment Ac2-26 counteracts conformational activation and clustering of integrins on myeloid cells evoked by CCL5, CCL2, and CXCL1 through inhibiting activation of the small GTPase Rap1. In vivo administration of Ac2-26 largely diminishes arterial recruitment of myeloid cells in a FPR2-dependent fashion. This effect is also observed in the presence of selective antagonists to CCR5, CCR2, or CXCR2, whereas Ac2-26 was without effect when all 3 chemokine receptors were antagonized simultaneously. Finally, repeated treatment with Ac2-26 reduces atherosclerotic lesion sizes and lesional macrophage accumulation.
Instructing the annexin A1-FPR2 axis harbors a novel approach to target arterial leukocyte recruitment. With the ability of Ac2-26 to counteract integrin activation exerted by various chemokines, delivery of Ac2-26 may be superior in inhibition of arterial leukocyte recruitment when compared with blocking individual chemokine receptors.
•The evolution and stability of a particle in a binary alloy melt is studied.•The critical nucleation radius in a binary alloy melt is determined.•Absolute and relative stability criteria of a ...particle in a binary alloy are shown.•Solute concentration first suppresses and then enhances the stability of the particle.•Minimum solute concentration for critical stability radius is determined.
The evolution and morphological stability of a particle in a binary alloy melt is re-examined using the asymptotic method. The resulting asymptotic solution of the dynamics model of the particle reveals that the temporal evolution and morphological stability of the particle vary continuously as functions of solute concentration. In particular, (1) the critical nucleation radius of the particle in the binary alloy melt is determined. When solute is rejected from solid phase to liquid phase, the initial concentration increases the critical nucleation radius and depresses the growth velocity of the particle. When solute is incorporated into the solid, the initial concentration decreases the critical nucleation radius. (2) The absolute and relative stability criteria of the particle in the binary alloy melt are shown on the basis of Mullins and Sekerka’s work in the pure melt. The critical stability radii for the absolute and relative stability criteria of the particle in the binary alloy melt are determined. The growth ratio of the critical stability radius to the critical nucleation radius in the binary melt does not exceed that in the pure melt. (3) When the segregation coefficient is less than one, with the growth of the particle, the initial concentration in the binary alloy melt first suppresses and then enhances the morphological stability of the particle. There exists a minimum solute concentration in the binary alloy melt such that when the initial concentration is lower than the minimum solute concentration, the stability of the particle decreases with the increase of solute concentration, whereas when the initial concentration is higher than the minimum solute concentration, the stability of the particle increases with the solute concentration. As the initial concentration increases, the critical stability radius first decreases to the minimum solute concentration at a certain solute concentration, and then increases with the solute concentration. This may control the morphological stability of particles by changing the addition of solute in the alloy melt.
The diffusion-controlled growth of a spherical particle embedded in a solid matrix of infinite size has been theoretically investigated for binary alloys, in the framework of the ...diffusion-under-stress formalism developed by Cahn-Larché. Assuming a composition stress develops in the particle, both concentrations of the diffusing species have been determined in the particle and in the matrix, as well as the interface velocity. The dependence on the composition stress and heterogeneous shear moduli of the concentrations in the particle and the interface growth rate has been characterized.
•The interface equilibrium equations of a growing particle in a solid matrix with composition stress have been established.•The concentrations of the species in both phases have been determined.•The interface growth rate has been determined.•The effects of the composition stress and shear modulus heterogeneity have been analyzed.
Subcellular membrane-less organelles consist of proteins with low complexity domains. Many of them, such as hnRNPA1, can assemble into both a polydisperse liquid phase and an ordered solid phase of ...amyloid fibril. The former mirrors biological granule assembly, while the latter is usually associated with neurodegenerative disease. Here, we observe a reversible amyloid formation of hnRNPA1 that synchronizes with liquid-liquid phase separation, regulates the fluidity and mobility of the liquid-like droplets, and facilitates the recruitment of hnRNPA1 into stress granules. We identify the reversible amyloid-forming cores of hnRNPA1 (named hnRACs). The atomic structures of hnRACs reveal a distinct feature of stacking Asp residues, which contributes to fibril reversibility and explains the irreversible pathological fibril formation caused by the Asp mutations identified in familial ALS. Our work characterizes the structural diversity and heterogeneity of reversible amyloid fibrils and illuminates the biological function of reversible amyloid formation in protein phase separation.
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