Titanium dioxide has attracted considerable interest as a prototypical semiconductor photocatalyst. However, because of the relative large bandgap energy, further application of TiO2 photocatalyst is limited by its inefficient solar energy conversion. Various attempts have been made to broaden the light absorption window of the TiO2, such as growth of TiO2-based heterostructures. Herein, a novel three-component system, Ag2O/TiO2/V2O5 one-dimensional nanoheterostructures with enhanced solar light absorption, is prepared by depositing Ag2O nanoparticles onto the surface of TiO2/V2O5 nanofibers through a two-step synthetic process. This three-component system exhibits excellent solar-driven photocatalytic activity, far exceeding those of the single- and two-component systems, as a result of extended solar light absorption and efficient electron-hole separation. Furthermore, the photocatalytic performance of Ag2O/TiO2/V2O5 one-dimensional nanoheterostructures is very stable for recycling use.

Hierarchical nanostructures with much increased surface-to-volume ratio have been of significant interest for prototypical gas sensors. Herein we report a novel resistive gas sensor based on TiO2/V2O5 branched nanoheterostructures fabricated by a facile one-step synthetic process, in which well-matched energy levels induced by the formation of effective heterojunctions between TiO2 and V2O5, a large Brunauer-Emmett-Teller surface area and complete electron depletion for the V2O5 nanobranches induced by the branched-nanofiber structures are all beneficial to the change of resistance upon ethanol exposure. As a result, the ethanol sensing performance of this device shows a lower operating temperature, faster response/recovery behavior, better selectivity and about seven times higher sensitivity compared with pure TiO2 nanofibers. This study not only confirms the gas sensing mechanism for performing enhancement of branched nanoheterostructures, but also proposes a rational approach to the design of nanostructure-based chemical sensors with desirable performance.

A new black hole X-ray binary (BHXRB) MAXI J1535-571 was discovered by MAXI during its outburst in 2017. Using observations taken by the first Chinese X-ray satellite, the Hard X-ray Modulation Telescope (dubbed as Insight -HXMT), we perform a joint spectral analysis (2-150 keV) in both energy and time domains. The energy spectra provide the essential input for probing the intrinsic Quasi-Periodic Oscillation (QPO) fractional rms spectra (FRS). Our results show that during the intermediate state, the energy spectra are in general consistent with those reported by Swift/XRT and NuSTAR. However, the QPO FRS become harder and the FRS residuals may suggest the presence of either an additional power-law component in the energy spectrum or a turn-over in the intrinsic QPO FRS at high energies.

Much greater surface-to-volume ratio of hierarchical nanostructures renders them attract considerable interest as prototypical gas sensors. In this work, a novel resistive gas sensor based on TiO2/Ag0.35V2O5 branched nanoheterostructures is fabricated by a facile one-step synthetic process and the ethanol sensing performance of this device is characterized systematically, which shows faster response/recovery behavior, better selectivity, and higher sensitivity of about 9 times as compared to the pure TiO2 nanofibers. The enhanced sensitivity of the TiO2/Ag0.35V2O5 branched nanoheterostructures should be attributed to the extraordinary branched hierarchical structures and TiO2/Ag0.35V2O5 heterojunctions, which can eventually result in an obvious change of resistance upon ethanol exposure. This study not only indicates the gas sensing mechanism for performance enhancement of branched nanoheterostructures, but also proposes a rational approach to design nanostructure based chemical sensors with desirable performance.

Ceramics typically have very high hardness, but suffer from poor toughness. Here, we use graphene to enhance the toughness of bulk boron carbide ceramics. The reduced graphene oxide (rGO) platelets are homogenously dispersed with boron carbide particles after sintering at 1350°C, under high pressure of 4.5 GPa with a multi-anvil apparatus. Fracture toughness of the composites is increased~131% (from~3.79 tõ 8.76 MPaÁm 1/2 ) at 1.5 vol% rGO platelets as a result of a toughing effect of graphene along with a little sacrificing of the hardness and elastic modulus, compared with those of pure boron carbide. The remarkably enhanced fracture toughness in the boron carbide ceramics is associated with graphene sheets crack bridging and graphene interface sliding effect. This study holds much significance for the understanding and development of high-performance graphene reinforcing ceramics.

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GSN 069 is a recently discovered quasi-periodic eruption (QPE) source recurring about every 9 hr. The mechanism for the QPEs of GSN 069 is still unclear. In this work, a disk instability model is constructed to explain GSN 069 based on Pan et al. (PLC21), where the authors proposed a toy model for the repeating changing-look active galactic nuclei. We improve the work of PLC21 by including a nonzero viscous torque condition on the inner boundary of the disk and adopting a general form for the viscous stress torque in the Kerr metric. It is found that the 0.4–2 keV light curves, the light curves at different energy bands, and the phase-resolved X-ray spectrum of GSN 069 can all be qualitatively reproduced by our model. Furthermore, the profiles of light curves in QPEs can be significantly changed by the parameter μ in the viscous torque equation, which implies that our model may also be applied to other QPEs.

We report results on the joint-fit of the NuSTAR and HXMT data for the black hole X-ray binary candidate MAXI J1535-571. The observations were obtained in 2017 when the source evolved through the hard, hard-intermediate and soft-intermediate states over the rising phase of the outburst. After subtracting continuum components, X-ray reflection signatures are clearly showed in those observations. By modeling the relativistic reflection in detail, we find that the inner radius Rin is relatively stable with Rin ≲ 1.55Rg during the three states, which implies that the inner radius likely extends to the innermost stable circular orbit even in the bright hard state. When adopting Rin = RISCO, the spin parameter is constrained to be $0.985_{-0.004}^{+0.002}$ at 90 per cent confidence (statistical only). The best-fitting results reveal that the inclination of the inner accretion disc is ∼70 − 74 degrees, which notably conflicts with the apparent orientation of the ballistic jet (≤45 degrees). In addition, both the photon index and the electron temperature increase during the transition from hard to soft state. It seems that the corona evolves from dense low-temperature in the LHS to tenuous high-temperature after the state transition, which indicates that the state transition is accompanied by the evolution of the coronal properties.