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A Novel Nonlinear Disturbance Observer Embedded Second-Order Finite Time Tracking-Based Controller for Robotic Manipulators
No full textRobotic manipulators are complex and dynamic nonlinear mechanical systems subject to numerous uncertainties, such as payload variations, frictions, and unmodeled dynamics. To mitigate the uncertainty caused by these disturbances and minimize the tracking errors of the controllers, this study proposed a finite time tracking-based controller (FTC) that embeds a (NDO) and a second-order sliding-mode modifier (SOSM). The NDO was incorporated to compensate for the system's global bounded uncertainty and the SOSM used a robust nonsingular terminal sliding-mode modifier to stabilize the controller. The theoretical analysis showed that the tracking error could quickly converge in finite time. Simulation on a typical robotics manipulator demonstrated the practical appeal of the proposed scheme
Martensitic transformation and elastocaloric effect of Co51.5+xV31.5-xGa17 (x=0.1, 0.2, 0.3) alloys
No full textCo-V-Ga alloy, a newly discovered multifunctional material based on martensitic transformation (MT), has promising application prospects in spintronics and solid-state refrigeration fields. In this work, we investigated the MT behaviors and the elastocaloric effect (eCE) of Co51.5+xV31.5-xGa17 (x = 0.1, 0.2, 0.3) alloys. The alloys undergo a MT from paramagnetic austenite to paramagnetic martensite, accompanying by a large latent heat (about 6-9 J g-1). The MT temperature increases with the increase of the ratio of Co to V. The digital image correlation (DIC) combined with infrared thermography (IR) techniques were utilized to in situ characterize the stress-induced MT and temperature change of the sample. For the sample of x = 0.2, at a testing temperature of 301 K, it heats with a giant adiabatic temperature change up to 13.4 K upon loading, while cools only 2.4 K when stress releasing, showing an irreversible eCE. Raising the test temperature (319, 327 and 333 K) can greatly improve the reversibility of the eCE. Such an asymmetric elastocaloric temperature change at 301 K is closely related to the irreversibility of stress-induced MT, which can be attributed to several factors including the selfcooling effect, heat dissipative mechanism and the valence bond structure of Co-V-Ga alloys
Robust and transparent superamphiphobic coating prepared via layer-by-layer spraying
No full textSuperamphiphobic surfaces have received extensive attention in fundamental research and practical application. However, it is still a challenge to use a convenient method to fabricate a superamphiphobic surface with high transparency and mechanical robustness. Here, we proposed a simple spray-coating method to prepare a superamphiphobic coating with a thickness of similar to 8.2 mu m that has both high transmittance (>80%) and mechanical robustness. The prepared superamphiphobic coating has a micro-/nano-reentrant coordinated microstructure, which was formed by self-assembly of highly fluorinated micro-diatomite, nano-SiO2 particles, and transparent silicone resin. Tests of contact angles (CAs) and sliding angles (SAs) of the liquids with the surface tension gamma >= 30.7 mN/m on the surfaces were performed using a volume of 3 mu L. The results show that their CAs and SAs are larger than 150 degrees and lower than 10 degrees, respectively. Furthermore, the coating can retain both water and oil repellency even after 2.2 m abrasions with 1000 grit sandpaper under a load of 50 g or water jetting 10 min (pressure similar to 100 kPa). Thus, the superamphiphobic coating may be suitable for a wide range of applications, for its unique properties and the relatively low-cost fabrication
Fluorescent pyrene-imidazole material for deep-blue organic light-emitting devices
No full textNumerous endeavors have been exerted to devise deep-blue light-emitting materials (LEMs) for organic light-emitting devices (OLEDs). Nevertheless, deep-blue light-emitting materials exhibiting high efficiency for simple-structured OLEDs are still scarce. Herein, a donor-acceptor based LEM, 4'-(4, 5-diphenyl-1-(3-(pyren-1-yl) phenyl)-1H-imidazole-2-yl)-N,N-diphenylbiphenyl-4-amine (TPA-PyI) is developed by merging imidazole, triphenyl-amine and pyrene units for OLEDs. TPA-PyI is used as the emitting layer in OLED device, which emits a deep-blue fluorescence at 444 nm. With a current efficiency (CE) of 3.05 cd/A and a power efficiency (PE) of 2.95 lm/W, an EQE of 2.97% is achieved. High thermal-stability is achieved with decomposition-temperature (T-d) of 516 degrees C
Study of NaCl-induced hot-corrosion behavior of TiN single-layer and TiN/Ti multilayer coatings at 500 degrees C
No full textTiN coatings suffer severe hot corrosion under the synergistic effect of NaCl and mid-temperature oxidation. Multilayer microstructure is expected to improve the corrosion resistance of the TiN coatings. In this work, NaCl-induced hot corrosion behavior and mechanism of TiN single-layer coating and TiN/Ti multilayer coating at 500 degrees C were studied. The TiN coating was seriously corroded along the grain boundary after the hot corrosion test. However, the Ti sublayer of the TiN/Ti coating was severely corroded, while the TiN sublayer was only slightly corroded and remaining intact. The results demonstrate that the formation of micro cells corrosion is one of the reasons for the severe corrosion of the Ti sublayer in the multilayer coating in the presence of solid NaCl electrolyte
Effect of Pitch Error on Static and Dynamic Characteristics of Hydrostatic Worm-Rack-Drive
No full textHydrostatic worm-rack-drive has obvious advantages on large-sized machine tools, and its performance is significantly affected by pitch errors. This paper theoretically researches the axial static and dynamic characteristics of hydrostatic worm-rack-drive, including the effects of the amplitude, period, and phase of pitch errors. Based on the expanded view of the helicoid of threads, a numerical calculation method is implemented where the Reynolds' equation and flow continuity equation are solved simultaneously. The influence rule of pitch errors on pocket pressure, flow, axial fluid-film force, axial stiffness coefficient, and axial damping coefficient are discussed in detail, for providing beneficial guidance for the design and performance optimization of hydrostatic worm-rack-drive
A fuel cell type gas sensor based on Pt/NbN for highly selective detection of hydrogen sulfide
No full textHydrogen sulfide (H2S) is considered a highly hazardous toxic gas. H2S sensors are therefore of paramount significance for real-time leak detection. However, existing solutions do not meet the strict performance targets set by stakeholders, while deactivation due to surface area of sensing materials decrease and contamination is a widely unsolved problem. Presented here is a new support material, mesoporous niobium nitride (NbN), which improve the long-term stability largely via enhancing the interaction between metal and support. Simultaneously, sensor devices using NbN as support show enlarged sensitivity, enhanced limit of detection and well repeatability when compared with these sensors using traditional carbon black support. In a wider perspective, our work suggests strategies for enhancing long-stability of next-generation chemical gas sensors by optimizing metal-support interaction
Improved tribological behavior of plasma-nitrided AlCrTiV and AlCrTiVSi high-entropy alloy films
No full textPlasma nitriding was used to improve the tribological properties of AlCrTiV and AlCrTiVSi high-entropy alloy (HEA) films. The results indicated that after plasma nitriding, the microstructure and tribological property were improved greatly. For plasma-nitrided AlCrTiV, it is still composed of a single BCC solid solution but with a decreased lattice constant, while for plasma-nitrided AlCrTiVSi, a new V4.75Si3N0.58 nitride phase forms in the amorphous matrix, which all lead to the increase of nano-hardness, promoting the reduction of wear degree or wear rate against GCr15 and Al2O3. Due to the perfect balance of hardness and toughness, the plasma-nitrided AlCrTiV HEA film has the lowest friction coefficient (against Al2O3) and the best wear-resistance
Polypyrrole-based nanotheranostic agent for MRI guided photothermal-chemodynamic synergistic cancer therapy
No full textPolypyrrole (PPy) nanoparticles have been widely studied in tumor photothermal therapy (PTT) for their significant photostability, good biocompatibility, and excellent photothermal performance. Herein, we report bovine serum albumin (BSA) stabilized PPy that were mineralized by MnO2 nanozyme on the surface (PPy@BSA-MnO2) to achieve synergistic photothermal and chemodynamic therapy (CDT) for breast cancer. In this multifunctional nanoplatform, the surface-loaded MnO2 undergoes a redox reaction with glutathione (GSH) to generate glutathione disulfide (GSSG) and Mn2+. Then, Mn2+ can convert H2O2 into a highly cytotoxic OH to achieve chemodynamic therapy (CDT) and possess good magnetic resonance (MR) T-1-weighted imaging capabilities to realize contrast imaging of the 4T1 tumor-bearing mouse models. In addition, PPy nanoparticles can efficiently convert near-infrared light energy into heat and achieve PTT. Most importantly, PPy@BSA-MnO2 nanoprobes have excellent in vitro 4T1 cell-killing effect and in vivo tumor-suppressive properties. The acute toxicity assessment results indicate that PPy@BSA-MnO2 nanoprobes have good biological safety. Therefore, the as-prepared multifunctional PPy@BSA-MnO2 nanoprobes possess excellent performance to promote MRI-guided PTT/CDT synergistic therapy for breast cancer treatment and have extensive clinical transformation and application prospects
Optimization of Tunnel-Junction for Perovskite/Tunnel Oxide Passivated Contact (TOPCon) Tandem Solar Cells
No full textA systematic study of the formation of the tunnel-junction for perovskite/TOPCon tandem solar cells is presented, which consists of a B-doped poly-Si (p(+)-poly-Si) and P-doped poly-Si (n(+)-poly-Si) double-layer structure. The rear emitter double-side TOPCon solar cell is selected as the bottom cell in tandem solar cells, where a p(+)-poly-Si/SiOx forms the rear emitter and an n(+)-poly-Si/SiOx forms the front field with the poly-Si layer deposited by plasma-enhanced vapor deposition (PECVD) and crystallized in a furnace. The tunnel-junction is formed by depositing an additional B-doped a-Si:H (p(+)-a-Si:H) on the front n(+)-poly-Si and following a rapid thermal anneal (RTA) to partially crystallize the p(+)-a-Si:H with minimized interdiffusion of B and P. The tunnel-junction is systematically optimized and it is found that the RTA process at 700 degrees C produces the optimized tunnel-junction with the minimal contact resistivity of approximate to 16 m omega cm(2). The tunnel-junction formation affects the passivation of the front field TOPCon, but the losses in the passivation quality can be recovered by a forming gas annealing. This process provides a simple and useful method for making the tunnel-junction in perovskite/TOPCon tandem solar cells