► Amorphous MnO2 nanoparticles were firstly prepared by reducing KMnO4 in N,N-dimethylformamid. ► Asymmetric MnO2/graphene supercapacitor has been constructed using 1molL−1 Na2SO4. ► The asymmetric ...MnO2/graphene supercapacitor could operate reversibly at cell voltage of 2.0V. ► The asymmetric cell shows an energy density of 25.2Whkg−1 at a power density of 100Wkg−1.
Asymmetric supercapacitor cells based on MnO2 as positive electrode and graphene as negative electrode have been constructed with 1M Na2SO4 aqueous electrolyte. Amorphous MnO2 nanoparticles were prepared by reducing KMnO4 in N,N-dimethylformamid (DMF). Graphene was prepared by hydrothermal reduction of exfoliated graphite oxide sheets. The MnO2/graphene asymmetric supercapacitor could operate reversibly at a high cell voltage of 2.0V, showing an energy density of 25.2Whkg−1 at a power density of 100Wkg−1, which is much higher than those of symmetric supercapacitors based on MnO2/MnO2 (4.9Whkg−1) and graphene/graphene (3.6Whkg−1). Moreover, the asymmetric system exhibits capacitance retention of 96% after 500 cycles.
A facile co-electrodeposition method has been developed to fabricate reduced graphene oxide/polypyrrole (rGO/PPy) composite films, with sodium dodecyl benzene sulfonate as both a surfactant and ...supporting electrolyte in the precursor solution. The introduction of rGO into the PPy films forms porous structure and enhances the conductivity across the film, leading to superior electrochemical performance. By controlling the deposition time and rGO concentration, the highest area capacitance can reach 411 mF/cm2 (0.2 mA/cm2) for rGO/PPy films, whereas optimized specific capacitance is as high as 361 F/g (0.2 mA/cm2). All of the composite films exhibit excellent rate capability (at least 175 F/g at the current density of 12 mA/cm2) compared with pure PPy film (only 12 F/g at the current density of 12 mA/cm2). The rGO/PPy composite exhibits excellent cycling stability that maintains 104% of its initial capacitance after cycling for 2000 cycles and 80% for 5000 cycles. The two-electrode solid-state supercapacitor (SC) based on rGO/PPy composite electrodes demonstrates good rate performance, excellent cycling stability, as well as a high area capacitance of 222 mF/cm2. The solid-state planar SC based on the rGO/PPy composite exhibits an area capacitance of 9.4 mF/cm2, demonstrating great potential for fabrication of microsupercapacitors.
Abstract
An updated catalog consisting of 1092 6.7 GHz methanol maser sources is reported in this work. Additionally, the NH
3
(1, 1), NH
3
(2, 2), and NH
3
(3, 3) transitions were observed toward ...214 star-forming regions using the Shanghai Tianma radio telescope in order to examine the differences in physical environments, such as the excitation temperature and column density of molecular clouds associated with methanol masers on the Galactic scale. Statistical results reveal that the number of 6.7 GHz methanol masers in the Perseus arm is significantly lower than that in the other three main spiral arms. In addition, the Perseus arm also has the lowest gas column density among the main spiral arms traced by the NH
3
observations. Both findings suggest that the Perseus arm has the lowest rate of high-mass star formation compared to the other three main spiral arms. We also observed a trend in which both the luminosity of the 6.7 GHz methanol masers and the ammonia gas column density decreased with the galactocentric distance. This finding indicates that the density of material in the inner Milky Way is generally higher than that in the outer Milky Way. This further suggests that high-mass stars are more easily formed at the head of the spiral arms. Furthermore, we found that the column density of ammonia gas is higher in the regions on the arms than in the inter-arm regions, supporting that the former is more likely to be the birthplace of high-mass stars.
Three-dimensional (3D) graphene oxide/polypyrrole (GO/PPy) composite electrodes have been fabricated viaone-step electrochemical co-deposition in an aqueous solution containing pyrrole monomers, GO ...and LiClO sub(4). The concentration of GO in the solution plays an important role in controlling the morphologies of the as-deposited GO/PPy composites, and a relatively low concentration of 0.1 mg mL super(-1) is favorable for the formation of a 3D interconnected structure. The unique 3D interconnected structure ensures fast diffusion of electrolyte ions through the electrode. As a result, the GO/PPy composite electrode with a mass loading of 0.26 mg cm super(-2) exhibits the highest specific capacitance of 481.1 F g super(-1), while the electrode with a larger mass loading of 1.02 mg cm super(-2) delivers the best area capacitance of 387.6 mF cm super(-2), at a current density of 0.2 mA cm super(-2). Moreover, the GO/PPy composite electrodes exhibit good rate capability with capacitance retentions over 80% when the current density load increases from 0.2 to 10 mA cm super(-2). Both the aqueous and solid-state supercapacitors based on GO/PPy composite electrodes show excellent capacitive properties with good cycling stability, indicating their suitability for applications in energy storage and management.
The motion of grain boundary (GB) dislocations, via a combination of glide and climb, mediates GB plasticity during processes such as creep and GB stress relaxation. Creep within the low stress ...regime, where non-Newtonian GB creep occurs, remains poorly understood. Models for GB dislocation nucleation rate limited creep, however, have not been sufficiently developed previously in the literature. Herein, a model for nucleation rate limited kinetics is developed and demonstrated to describe existing creep data reasonably well, using physically realistic materials properties as inputs to the model.
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Platycodin D (PD) is a potent bioactive constituent in the medicinal herb Platycodon grandiflorum. It has shown anticancer properties, particularly against glioblastoma (GB) and other human ...malignancies. DEPDC1B (DEP domain-containing protein 1B) is an oncogene associated with epithelial–mesenchymal transition (EMT). It is highly expressed in GB and correlated with tumor grade and patient prognosis. In this study, we investigated whether the antiglioma effect of PD was associated with downregulation of DEPDC1B.
Gene expression and clinical data were obtained from the China Glioma Genome Atlas and The Cancer Genome Atlas databases for glioma samples. In vitro experiments were conducted using Cell Counting Kit-8 and Transwell assays to assess the impact of PD on the proliferation, migration, and invasion of GB cells. mRNA and protein expression was evaluated using real-time polymerase chain reaction and western blotting, respectively.
PD exerted inhibitory effects on the proliferation and motility of GB cells. PD downregulated DEPDC1B protein as well as several markers associated with EMT, namely N-cadherin, vimentin, and Snail. The suppressive effects of PD were enhanced when DEPDC1B was knocked down in GB cells, while overexpression of DEPDC1B in cells reversed the inhibitory effects of PD.
PD exerts an antiglioma effect by regulating DEPDC1B-mediated EMT.
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Solid-state ASC based on rGO/MnO2/CB (positive electrode) and rGO/CB (negative electrode) shows extended cell voltage of 1.8V and excellent power capability.
Reduced graphene ...oxide/manganese dioxide/carbon black (rGO/MnO2/CB) ternary film is prepared by a simple vacuum filtration method. MnO2 nano particles grow on both sides of the graphene layers serving as active sites for the electrochemical reactions which remarkably enhance the specific capacitance. While CB acts as spacers between the graphene layers preventing the restacking of graphene sheets and improves the conductivity between the basal planes of graphene sheets, leading to a better rate performance. Thanks to the synergistic effects of CB and MnO2, the capacitanceis improved to 209Fg−1, which is much better than that of the binary graphene/CB film (96Fg−1) and maintains at 77Fg−1 even at a fastscan rate of 1Vs−1. The 1.8V aqueous asymmetric supercapacitor based on rGO/MnO2(2.5)/CB (positive electrode) and rGO/CB (negative electrode) exhibits a large energy density of 24.3Whkg−1 especially a high power delivery capability with an energy density of 10Whkg−1 at the power density of 45kWkg−1. Furthermore, the energy density of the flexible solid-state asymmetric device based on this ternary film reaches 20Whkg−1 and maintains 10Whkg−1 at the power density of 21kWkg−1.
Abstract
The young, compact, very high surface brightness but low excitation planetary nebula (PN) BD+30°3639 is one of the very few PNe that have been reported to exhibit the 21 cm H
i
emission ...line. As part of a long-term program to search for circumstellar atomic hydrogen, we observed the 21 cm feature toward BD+30°3639 with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Assuming a direct association between the PN and the detected H
i
emission, these new observations show that this surrounding emission is significantly more spatially extended than indicated by previous interferometric observations and can be resolved into two velocity components. The estimated H
i
mass is larger than 100
M
⊙
, invalidating an origin from the host star itself or its ejecta for the emitting material. We discuss the possibility that the extended H
i
emission stems from the interstellar medium (ISM) swept out over time by the stellar wind. Moreover, we report tentative detections of H
i
absorption features lying near and blueward of the systemic velocity of this PN, which are probably from a stalled asterosphere at the outer boundary of the expanding ionized region. The mass of the gas producing the H
i
absorption is insufficient to solve the so-called “PN missing mass problem.” We demonstrate the capability of FAST to investigate the interaction process between a PN and the surrounding ISM.
Solid lubricants are described as solid materials of intentionally introduced or in situ formed on contact surfaces in relative motion for the purpose of lowering friction and wear and providing ...protection from damage. Solid lubricants and advanced self-lubricating materials are widely used in modern industries, especially in aerospace, aviation, automotive, metallurgy, materials forming, and machining industries, and have attracted great interest in lubrication applications under very severe circumstances such as elevated temperatures, heavy loads, ultrahigh vacuum, extreme radiation, strong oxidation, and chemical reactivity environments. Many efforts have been made to develop self-lubricating composites by a variety of material preparation techniques, which include powder metallurgy, physical/chemical vapor depositions, thermal spraying, electrodeposition, laser cladding, and additive manufacturing. Although several reviews on the development of high-temperature solid lubricants have been published, most of them only focus on a type of material, a specific process, or application. In this paper, a comprehensive review is provided to present the state-of-the-art progress in solid lubricants, self-lubricating composites/coatings, and their effective functions that can be used over a wide variety of environmental conditions, especially at elevated temperatures. The solid lubricants considered include representative soft metals, layered structure materials (e.g., graphite, hexagonal boron nitride, transition metallic dichalcogenides, MAX phase), chemically stable fluorides, binary or ternary metallic oxides, especially alkaline earth chromates, and sulfates, and synergistic effects from these solid lubricants. This paper also provides new insights into design considerations of environmental adaptive solid lubrication, and the challenges and potential breakthroughs are further highlighted for high-temperature solid lubrication applications.
A nucleation rate limited sintering model was recently developed based on observations of bicrystal sintering. This work validates the applicability of this model for sintering of polycrystalline ...clusters of Al2O3-SmAlO3 at high temperature in the range of 1130–1610 ℃. The model fits the data well and agrees with trends observed during bicrystal sintering. A temperature dependence to the dominant sintering strain deformation modes is observed from in situ heating experiments performed in a transmission electron microscope (TEM). The observations provide insights into how temperature influences the early stages of sintering by affecting the pore size distribution through local de-sintering. This provides insights into the role heating rate and sintering schedule play in microstructural evolution that influences the grain size versus density trajectory.
