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Titanium (Ti) has been commonly used as an implant material in dentistry and bone surgery for several decades. Meanwhile, surface modification of titanium can enhance the osseointegration of implants. In this study, a graphene oxide/chitosan/hydroxyapatite (GO/CS/HA) composite coating was fabricated by electrophoretic deposition on Ti substrates. Subsequently, the surface morphology, phase composition, wettability, and bonding strength of this composite coating were researched. Additionally, in vitro cytological examination was performed, including evaluations of cell adhesion, cell viability, cell differentiation, cell mineralization, and osteogenetic factor expression. Finally, the in vivo osteogenetic properties were evaluated through an animal study, including a histological analysis, a microcomputed tomography, and biomechanical tests. The results showed that a homogeneous and crack-free GO/CS/HA composite coating was coated on Ti, and the wettability and bonding strength of the GO/CS/HA composite coating were enhanced compared with HA, GO/HA, and CS/HA coatings. Furthermore, the GO/CS/HA coating greatly heightened the cell-material interactions in vitro. Additionally, this GO/CS/HA-Ti implant could enhance osseointegration in vivo. Consequently, GO/CS/HA-Ti may have potential applications in the field of dental implants. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2018.

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The modular multilevel converter (MMC) provides promising development for high-voltage direct current (HVDC) applications, including multiterminal HVDC (MTDC) and renewable energy integration. This paper, considering an offshore wind farm (OWF) integrated MMC MTDC system, investigates its start-up process with three main developments: 1) it further develops the mathematical model of MTDC with active networks and proposes a hierarchical start-up control scheme; 2) for the terminal which connects the OWF, it proposes a reduced dc voltage control scheme of mitigating the current surges with deblocking the converter at zero voltage difference on submodules (SMs) and proposes an overall sequential start-up control scheme for the offshore integrated MTDC; and 3) it analyzes and compares different start-up control schemes. To evaluate the proposed sequential start-up control scheme, an offshore MMC HVDC system is established on the RTDS. The simulation results verify effectiveness of the proposed scheme on the MMC MTDC system with two control paradigms, i.e., master-slave control and droop control, respectively. In comparison with different start-up control schemes, the superiority of the mitigation of voltage spikes and current surges are shown using the proposed scheme with less complexity and easier implementation.Index Terms-Droop control, master-slave control, modular multilevel converter (MMC), multiterminal HVDC (MTDC), offshore wind farm (OWF), sequential start-up control.

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ABSTRACT. Glacier albedo controls the surface energy budget, the variability of which affects the glacier surface melt rate and, in turn, impacts the mass balance of the glacier. During 2013 and 2014, spatial and temporal variations of albedo were investigated using 18 Landsat images of Urumqi Glacier No. 1. Factors influencing these spatiotemporal profiles were analyzed. An established retrieval process, including geolocation, radiometric calibration, atmospheric, topographic, and anisotropic correction and narrow-to broadband conversion, was applied for the first time to Landsat-8 images. Differences between Landsat image derived albedo values and albedo values measured using a handheld spectroradiometer ranged from −0.024 to 0.049. Spatial and temporal variations of surface albedo were significant, especially in the ablation area. The variability of the values of ice albedo ranged from 0.06 to 0.44 due to topographic effects and light-absorbing impurities. The results suggest that this retrieval method can be used to investigate the spatial and temporal variability of surface albedo from Landsat-8 images on mountain glaciers. Moreover, as constant albedo values for ice and snow cannot be assumed, the distribution of albedo was not completely dependent on altitude under conditions of more intense ablation, and by reason of light-absorbing impurities during the melt season.