Preparation of ordered TiO2 macroporous membrane using PBMA colloid crystal as template

Poly(butyl methacrylate) (PBMA) colloidal crystal templates were assembled orderly on the clean substrates of monocrystalline silicon by dip-drawing technique and titanium dioxide (TiO2) macroporous membranes were prepared by using sol-dipping template method to fill the interstices among the PBMA templates, followed by calcination to remove the templates at 550℃. Calcination of the PBMA templates was carried out according to the following procedure: the rate of rising temperature was 5℃/min from room temperature to 150℃, 2℃/min from 150℃ to 270℃, 1℃ /min from 270℃ to 430℃, 2℃/min from 430℃ to 550℃ and maintained it at 550℃ for 2h. X-ray diffraction (XRD) spectra indicated the macroporous materials were anatase structure. The polymerization mechanism of BMA with Fenton reagent as a new initiator was discussed, and the removal process of the PBMA templates and the formation of TiO2 pore size were investigated, respectively. The results showed that the new method of polymerization overcomes many problems associated with the conventional emulsion polymerization techniques such as long reaction time, necessary deoxygenation, and complicated operation

Characterization and Alignment of Carbon Nanofibers under Shear Force in Microchannel

This work presents a novel method to align CNFs by using shear forces in microchannels. Effect of two different microchannel sizes (1 mm × 0.1 mm and 1 mm × 0.2 mm) on CNFs alignment is investigated. SEM images of CNFs preform display significant alignment by both microchannels, which can be interpreted using a second-order alignment tensor and a manual angle meter. In the second-order alignment tensor description, an elongated ellipse can signify high degree of alignment in the direction of the major axis. When the microchannel size is 1 mm × 0.2 mm, the lengths of major and minor axes of the ellipse are 0.982 to 0.018. An angle meter manually shows that 85% of the CNFs are aligned in the direction between 60° and 90° when the microchannel is 1 mm × 0.2 mm. Both methods can demonstrate that better alignment of CNFs can be obtained using the 1 mm × 0.2 mm microchannel

Mechanical properties of atomically thin boron nitride and the role of interlayer interactions

Atomically thin boron nitride (BN) nanosheets are important two-dimensional nanomaterials with many unique properties distinct from those of graphene, but investigation into their mechanical properties remains incomplete. Here we report that high-quality single-crystalline mono-and few-layer BN nanosheets are one of the strongest electrically insulating materials. More intriguingly, few-layer BN shows mechanical behaviours quite different from those of few-layer graphene under indentation. In striking contrast to graphene, whose strength decreases by more than 30% when the number of layers increases from 1 to 8, the mechanical strength of BN nanosheets is not sensitive to increasing thickness. We attribute this difference to the distinct interlayer interactions and hence sliding tendencies in these two materials under indentation. The significantly better interlayer integrity of BN nanosheets makes them a more attractive candidate than graphene for several applications, for example, as mechanical reinforcements

Spitzer + VLTI-GRAVITY Measure the Lens Mass of a Nearby Microlensing Event

We report the lens mass and distance measurements of the nearby microlensing event TCP J05074264+2447555. We measure the microlens parallax vector ${\pi}_{\rm E}$ using Spitzer and ground-based light curves with constraints on the direction of lens-source relative proper motion derived from Very Large Telescope Interferometer (VLTI) GRAVITY observations. Combining this ${\pi}_{\rm E}$ determination with the angular Einstein radius $\theta_{\rm E}$ measured by VLTI GRAVITY observations, we find that the lens is a star with mass $M_{\rm L} = 0.495 \pm 0.063~M_{\odot}$ at a distance $D_{\rm L} = 429 \pm 21~{\rm pc}$. We find that the blended light basically all comes from the lens. The lens-source proper motion is $\mu_{\rm rel,hel} = 26.55 \pm 0.36~{\rm mas\,yr^{-1}}$, so with currently available adaptive-optics (AO) instruments, the lens and source can be resolved in 2021. This is the first microlensing event whose lens mass is unambiguously measured by interferometry + satellite parallax observations, which opens a new window for mass measurements of isolated objects such as stellar-mass black holes.Comment: 3 Figures and 6 Tables Submitted to AAS Journa

Spitzer + VLTI-GRAVITY Measure the Lens Mass of a Nearby Microlensing Event

We report the lens mass and distance measurements of the nearby microlensing event TCP J05074264+2447555 (Kojima-1). We measure the microlens parallax vector π_E using Spitzer and ground-based light curves with constraints on the direction of lens-source relative proper motion derived from Very Large Telescope Interferometer (VLTI) GRAVITY observations. Combining this π_E determination with the angular Einstein radius θ_E measured by VLTI-GRAVITY observations, we find that the lens is a star with mass M_L = 0.495±0.063 M⊙ at a distance D_L = 429 ± 21 pc. We find that the blended light basically all comes from the lens. The lens-source proper motion is Μ_(rel,hel) = 26.55±0.36 mas yr⁻¹, so with currently available adaptive-optics instruments, the lens and source can be resolved in 2021. This is the first microlensing event whose lens mass is unambiguously measured by interferometry + satellite-parallax observations, which opens a new window for mass measurements of isolated objects such as stellar-mass black holes

Dynamics and nucleation of dislocations in crystals

Hydrogen-poor superluminous supernovae (SLSNe-I) have been predominantly found in low-metallicity, star-forming dwarf galaxies. Here we identify Gaia17biu/SN 2017egm as an SLSN-I occurring in a "normal" spiral galaxy (NGC 3191) in terms of stellar mass (several times 10^10 M_sun) and metallicity (roughly Solar). At redshift z=0.031, Gaia17biu is also the lowest redshift SLSN-I to date, and the absence of a larger population of SLSNe-I in dwarf galaxies of similar redshift suggests that metallicity is likely less important to the production of SLSNe-I than previously believed. With the smallest distance and highest apparent brightness for an SLSN-I, we are able to study Gaia17biu in unprecedented detail. Its pre-peak near-ultraviolet to optical color is similar to that of Gaia16apd and among the bluest observed for an SLSN-I while its peak luminosity (M_g = -21 mag) is substantially lower than Gaia16apd. Thanks to the high signal-to-noise ratios of our spectra, we identify several new spectroscopic features that may help to probe the properties of these enigmatic explosions. We detect polarization at the ~0.5% level that is not strongly dependent on wavelength, suggesting a modest, global departure from spherical symmetry. In addition, we put the tightest upper limit yet on the radio luminosity of an SLSN-I with <5.4x10^26 erg/s/Hz (at 10 GHz), which is almost a factor of 40 better than previous upper limits and one of the few measured at an early stage in the evolution of an SLSN-I. This limit largely rules out an association of this SLSNe-I with known populations of gamma-ray burst (GRB) like central engines.Comment: Accepted for publication in ApJ. Ancillary ASCII tables added: TRL.txt -- blackbody temperature, radius and luminosity; uvw2uvm2uvw1uvu.txt -- UV photometry; BgVri.txt -- optical photometry; zJHK.txt -- NIR photometr