It is a challenging task to realize large-area manufacture of chiral geometries of nanoparticles in solid-state materials, which exhibit strongly chiroptical responses in the visible and ...near-infrared ranges. Herein, novel nanocomposites, made from mixtures of achiral block copolymers and nanoparticles in a geometrically confined environment, are conceptually proposed to construct the chiral assemblies of nanoparticles through a joint theoretical-calculation framework and experimental discussion. It is found that the nanochannel-confined block copolymers self-assemble into a family of intrinsically chiral architectures, which serve as structural scaffolds to direct the chiral arrangement of nanoparticles. Through calculations of chiral order parameters and simulations of discrete dipole approximation, it is further demonstrated that certain members of this family of nanoparticle assemblies exhibit intense chiroptical activity, which can be tailored by the nanochannel radius and the nanoparticle loading. These findings highlight the multiple levels of structural control over a class of chiral assemblies of nanoparticles and the functionalities of emerging materials via careful design and selection of nanocomposites.
Human pluripotent stem-cell-derived islets (hPSC-islets) are a promising cell resource for diabetes treatment
. However, this therapeutic strategy has not been systematically assessed in large animal ...models physiologically similar to humans, such as non-human primates
. In this study, we generated islets from human chemically induced pluripotent stem cells (hCiPSC-islets) and show that a one-dose intraportal infusion of hCiPSC-islets into diabetic non-human primates effectively restored endogenous insulin secretion and improved glycemic control. Fasting and average pre-prandial blood glucose levels significantly decreased in all recipients, accompanied by meal or glucose-responsive C-peptide release and overall increase in body weight. Notably, in the four long-term follow-up macaques, average hemoglobin A1c dropped by over 2% compared with peak values, whereas the average exogenous insulin requirement reduced by 49% 15 weeks after transplantation. Collectively, our findings show the feasibility of hPSC-islets for diabetic treatment in a preclinical context, marking a substantial step forward in clinical translation of hPSC-islets.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The purpose of this paper is to explore the effect of geometric position on the film properties for a complex-shaped substrate in high-power impulse magnetron sputtering (HiPIMS) discharge. The ...substrate is a trapezoidal prism, whose base has four inner corners of 60°, 120°, 75°, and 105°. A negative bias is added to this trapezoidal prism during the high-density discharge to deposit TiAlSiN films. The chemical compositions, microstructures and mechanical properties of the films at different area of the substrate are analyzed using the energy dispersive spectroscopy, X-ray diffraction, scanning electron microscope, nano-indentor and Vickers indentation tester. Systematic investigations demonstrate that the films properties have prominent differences on various planes of the trapezoidal-prism sample, due to the so-called shadowing effect. Compared with the measurements on the plane perpendicular to the target surface, there is a higher average hardness and stronger toughness on the plane facing to the target surface. However, the values of both the hardness and toughness are the lowest on the plane facing away from the target surface. Moreover, even for the same plane, the enhanced mechanical properties as well as a smoother surface and denser microstructure appear in the edge regions, with respect to that in the planar center regions. To understand these interesting phenomena, a two-dimensional particle-in-cell/Monte Carlo collision simulation (2D PIC-MCC) and Transport of Ions in Matter method (TRIM) are employed to explore the ion dynamics at the different sites of the sample. Simulation results suggest that a higher ion flux density and larger re-sputtering rate may contribute to the improved film properties in the edge regions. These results in this paper are important for broadening the industrial applications of high ion fraction plasma sources in irregular structures, especially for cutting tools.
•For a complex substrate, the film in edge regions presents obvious different mechanical properties with that in the center.•As the corner gets sharpened, its affected edge regions become wider.•The dependencies of substrate geometry on the film properties is studied by simulation method.•The mechanism of the improved mechanical properties in the edge regions may be due to the intensive ion flux density and re-sputtering rate.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZRSKP
The cathode spot is crucial to vacuum arc technology and the cathode spot theories have been widely studied. However, the study on a type of unusual erosion patterns is still very rare so far. For ...blocking this erosion patterns’ formation, a new cathode water cooling system with higher cooling efficiency was designed. The paper studies the formation of this erosion patterns by macro-particle filtered vacuum arc plasma, arc spots splitting, and arc spots movement velocity in pure argon gas and mixture gas (oxygen and argon). The ratio of oxygen to argon is from 0 to 2.5. Meanwhile, energy dispersive spectrometer (EDS) experiment was completed on the cross-section of this erosion pattern to study on the oxygen and other trace elements’ redistribution. In addition, an erosion model was proposed to explain the format process of these etching patterns. The results of this paper make a contribution to the theory of arc etching.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
To enhance the cutting performance of TiAlSiN coated cemented carbide tools by inserting Ti interlayers and to explore their mechanism, TiAlSiN/Ti multilayer coatings with different Ti thicknesses, ...including 0 nm, 25 nm, 50 nm, 100 nm, and 150 nm, were deposited onto cemented carbide (WC-10 wt%, Co) substrates by high power impulse magnetron sputtering (HiPIMS). The microstructure, hardness, grain orientation, residual stress, adhesion, and toughness of those coatings were measured, and the cutting performance against Inconel 718 was analyzed. Meanwhile, finite element method (FEM) indentation simulations were performed to gain detailed insight into the effects of Ti interlayer thickness on mechanical properties of TiAlSiN/Ti multilayer coatings. Results demonstrated that mechanical properties of TiAlSiN multilayer coatings were significantly changed after the Ti interlayer was introduced, and the multilayer coating #M2 with 25 nm Ti layer showed the excellent toughness and adhesion without sacrificing hardness too much. As Ti interlayer thickness increased, both toughness and adhesion decrease owing to the plastic mismatch between individual layers, and these changes were discussed detailedly with finite element method. Moreover, the result of the cutting experiment also revealed that the tool flank wear Vb can be reduced by the multilayer structure. This improvement is believed to be due to the increasing toughness, which alleviated the damage caused by the continuous impact load of hard phases generated by Inconel 718 during cutting.
Erosion seriously threatens the safety of high-speed rotating mechanical components in very harsh service environments, particularly for lightweight titanium alloy matrix material. In order to ...improve the erosion resistance of titanium alloy, TiAlSiN coatings with different phase compositions are deposited on TC6 titanium alloy using a high-power pulse magnetron sputtering discharge (HPPMS) system under various discharge voltages. The componential and microstructural evolution as well as mechanical properties of the TiAlSiN coatings are evaluated by X-ray diffraction, scanning electron microscopy, and nanoindentation, respectively. The erosion performance relative to titanium alloy is investigated by a sand blasting tester. With the increase in discharge voltage from −500 to −600 V, the peak of discharge current increases from 105 to 225 A. The prepared TiAlSiN coatings show a shift of the preferred crystallographic orientation from (220) to (200), but all of them have a dense nanocomposite structure. Their hardness (H) and elastic modulus (E) gradually increase before decreasing, arriving at maximum values of 35.34 and 360.5 GPa at −570 V. The erosion resistance of the TiAlSiN coatings dependent on the discharge voltage is consistent with the H/E ratio change. The TiAlSiN coatings prepared at −560 V exhibit the optimal erosion resistance, which is 15 times that of the TC6 substrate. The erosion behavior of the coatings is positively correlated with their hardness and toughness. Adjusting the discharge voltage of the HPPMS pulse is finally proved to be an effective way of tailoring the coating phase compositions to improve the erosion resistance of titanium alloy.
•HiPIMS-deposited TiAlSiN coatings show obvious improvements compared with DCMS.•The effects of bias voltage on coatings properties have evident regularity.•A coating with high hardness, low ...roughness and small grain size was attained.•An increasing plasma discharge current was detected with increasing the bias voltage.
TiAlSiN nanocomposite coatings were deposited onto cemented carbide (WC-10wt.%, Co) substrates by high power impulse magnetron sputtering (HiPIMS). The effect of substrate bias voltage on plasma discharge characterization of HiPIMS, element concentration, deposition rate, microstructure, surface/cross-sectional morphology, hardness and adhesion strength of coatings were studied. Compared with those deposited with direct current magnetic sputtering (DCMS), HiPIMS-deposited TiAlSiN coatings show improvements in some properties, including the surface roughness, the grain size, the hardness and adhesion strength, but a decrease in the deposition rate. When the bias voltage increases, the discharge current rose up from 118A to 165A. HiPIMS-deposited TiAlSiN coatings show a shift of the preferred crystallographic orientation from (220) to (200) and decreases in surface roughness from 14.1nm down to 7.4nm and grain size from 10.5nm to 7.4nm. Meanwhile, a change in crystal morphology from columnar to equiaxial and a grain refinement, as well as an increase of hardness from 30GPa up to 42GPa of those TiAlSiN coatings were observed with the increasing bias voltage and a decrease in adhesion strength from HF2 to HF5 of those coatings were revealed by indentation adhesion test.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Precise organization of nanoparticles (NPs) into regularly well-defined arrays represents a continuing challenge in the development of high-performance metamaterials. Herein, zone-annealed diblock ...copolymers provide an effective medium for construction of periodically well-ordered arrays of NPs within mechanically enhanced nanocomposites. By integrating the dynamic self-consistent field theory for diblock copolymers and molecular dynamics for NPs, it is revealed that the emergence of response layers of asymmetric diblock copolymers induces the epitaxial assembly of NPs during the processing of hot zone annealing. In particular, the ability to kinetically control the assembly pathway of NPs enables them to be organized into hexagonally packed, defect-free arrays, with essentially the individual NP in a unit cell. Our simulations also show that the moving speed of annealing fronts and the concentration and radius of NPs all play important roles in engineering both the spatial arrangement and organization of NPs in a diblock copolymer matrix. Furthermore, the information from the simulations of diblock copolymer/NP mixtures is used to deduce mechanical responses of polymeric nanocomposites by the lattice spring model. The results reveal that the spatial arrangement and organization of NPs in the diblock copolymer matrix provide additional reinforcing elements to enhance the strength of structural materials. Merging the self-assembly of nanocomposites with the zone annealing processing can provide a means of kinetically controlling the assembly pathway for the achievement of regularly well-ordered arrays of polymer-embedded NPs with structural and optoelectronic functionalities.
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IJS, KILJ, NUK, PNG, UL, UM
The integration of the dynamic self-consistent field theory for polymer molecules and molecular dynamics for nanoparticles is proposed to model the structural evolution of nanocomposites in the ...course of zone annealing. Using computational modeling, we establish an effective approach to simultaneously tailor the spatial regularity of self-assembled nanostructures of diblock copolymers and the arrangement of nanoparticles within the matrix. As the spatially localized, mobile field of zone annealing is introduced into the hybrid organic/inorganic system, the nanocomposites re-assemble from the defective nanopatterns to the periodically well-ordered nanostructures, with the nanoparticles dispersed in the energetically favorable domains. In particular, because of the presence of response layers of diblock copolymers at the annealing front, the directional motion of nanoparticles within the matrix can be achieved by finely tuning the moving velocity and minimum Flory–Huggins interaction parameter of zone annealing. Furthermore, the regularity of self-assembled nanostructures and the spatial arrangement of nanoparticles are affected by the physiochemical properties of nanoparticles. Our theoretical findings present new opportunities to kinetically manipulate the self-assembled nanostructures of both the organic and inorganic components, which will impart their collective properties and the ultimate performances of nanocomposites.
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IJS, KILJ, NUK, PNG, UL, UM
The effect of applying a positive voltage pulse (Urev = 10–150 V) directly after the negative high power impulse magnetron sputtering (HiPIMS) pulse (bipolar HiPIMS) is investigated for the reactive ...sputter deposition of TiN thin films. Energy-resolved mass spectroscopy analyses are performed to gain insight in the effect on the ion energy distribution function of the various ions. It is demonstrated that the energy of a large fraction of the ions can be tuned by a reverse target potential and gain energy corresponding to the applied Urev. Microscopy observations and x-ray reflectometry reveal densification of the films which results in an increase in the film hardness from 23.9 to 34 GPa as well as an increase in compressive film stress from 2.1 GPa to 4.7 GPa when comparing conventional HiPIMS with bipolar HiPIMS (Urev = 150 V).
•TiN films are deposited using bipolar high power impulse magnetron sputtering (HiPIMS).•The ion energy distributions are tuned when a positive target voltage is applied.•The density of the deposited films increase with the positive target voltage.•Both hardness and compressive stress are increased when using bipolar HiPIMS.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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