To meet the demand for the new generation of neutron absorber materials (NAMs) for the dry storage of the spent nuclear fuels, (B4C + Al2O3)/Al composites were fabricated by powder metallurgy ...technique using ultrafine Al powders. The composites designed with various fabricating parameters and fabricated at various sintering temperatures were characterized by electron microscopy and mechanically tested. The sample sintered at 450 °C shows the best strength-ductility balance at 350 °C (106.2 MPa in ultimate tensile strength and 9.6% in elongation). Addition of B4C particles and increase of the Al2O3 film thickness could enhance the strength of the composites at room temperature but showed no obvious effect on the strength at 350 °C. When sintering temperature of the composites increased from 450 °C to 550 °C, the transformation of amorphous Al2O3 lamellae to γ-Al2O3 particles led to deterioration of the strength of the composites. Based on the analyses of both high-temperature deformation mechanism and strengthening mechanism, it was considered that the amorphous Al2O3 could pin the grain boundaries and prevent them from gliding, which was the main factor to significantly increase the high-temperature strength. Based on the results, a strategy to design the aluminium matrix NAMs with excellent high-temperature strength was proposed.
ABSTRACT
The follow-up timing observations were carried out for 24 pulsars discovered with the Five-hundred-meter Aperture Spherical radio Telescope (FAST) in Commensal Radio Astronomy FAST Survey. ...We report their phase-connected timing ephemeris, polarization pulse profiles, and Faraday rotation measurements. With their spin periods spanning from 2.995 ms to 4.34 s, their period derivatives were determined to spread between 7.996(8) × 10−21 and 9.83(3) × 10−15 s s−1, which imply that they have characteristic ages from 1.97 × 106 to 5.93 × 109 yr. It is inferred that PSRs J0211+4235 and J0518+2431 are beyond the ‘traditional death line’. PSR J0211+4235 is beyond the ‘death valley’. The death line model of Zhang et al. also cannot explain the radio presence of PSR J0211+4235. This suggests that radiation theory needs to be improved. Besides, ten of the 22 canonical pulsars show nulling phenomena. Moreover, PSR J1617+1123 exhibits variation of emission and J0540+4542 shows subpulse drifting. The DM of five pulsars is larger than the estimated by the YMW16 electron density model, which could suggest that electron density models need updates for higher Galactic latitude regions. PSRs J0447+2447 and J1928−0548 are isolated millisecond pulsars. With their flux densities spanning from 5(1)–553(106) μJy, some of these new pulsars found by FAST are distant, dim, and low-$\dot{E}$ ones and are suitable for testing pulsar emission theories.
Three-dimensional (3D) graphene networks are attracting ever-increasing attention in the field of energy storage because their unique architecture at macroscopic scales is beneficial for effective ...electron and ion transport. Herein, a novel interconnected 3D graphene mesh network (3D GMN) was successfully designed and fabricated by folded Ni meshes assisted chemical vapor deposition method. The structure parameters of 3D GMN can be controlled well by tuning the period of Ni mesh and the electroplating time. With the increase of the density of 3D GMN, the electrical conductivity of 3D GMN and the thermal conductivity of 3D GMN/epoxy composite are greatly improved compared to that of the 3D graphene foam. This 3D GMN enables the high capacity of 57 mA h g −1 in an aluminum ion battery at the ultra-high rate of 40C with capacity retention of 96.5% after 200 cycles.
Regional environmental evaluation often requires a large amount of spatial information. Remote sensing (RS) and geographic information systems (GIS) are capable of managing large amounts of spatially ...related datum, and providing the ability to integrate multiple layers and to derive additional information. A methodological reference framework, using RS, GIS, and AHP (the analytic hierarchy process), is developed for environmental vulnerability assessment. Using this proposed method, we carried out a case study in the Tibetan Plateau. An environmental vulnerability index (EVI) proposed incorporates 15 factors covering natural conditions, environmental issues, and human activities. According to the EVI values, the vulnerability was classified into five levels: slight (EVI<2.2), light (2.2⩽EVI<2.7), moderate (2.7⩽EVI<3.0), heavy (3.0⩽EVI⩽3.4), and extreme vulnerability (>3.4). The case study showed that the majority of the area in the Tibetan Plateau is ecologically lightly (light level; 22% of the total area), moderately (moderate level; 27%), and heavily (heavy level; 30%) vulnerable. Except for a clearly horizontal distribution, the environmental vulnerability increased clearly with increasing elevation (vertical distribution). The case study verified the usefulness and feasibility of the methods developed, for the results gained reflect the reality of the Tibetan environment closely. Further use in other regions should pay attention to what factors seem to be important in determining the local environmental vulnerability, and how is the impact of each factor on the complex environment.
It has been puzzling whether and how a plant could exert a strong allelopathic inhibition to the target organisms by releasing low concentrations of allelochemicals. Plant allelochemicals have been ...proposed to be released continuously, however, direct evidence from specific allelochemicals is urgently required. In the present study, the toxicity of allelochemical N-phenyl-1-naphthylamine (NPN) towards the cyanobacterium Microcystis aeruginosa by two different exposure patterns was compared. One was low-dosage repeated exposure (LRE), in which 50 μg L−1 NPN was repeatedly dosed to simulate the continual release of allelochemicals, and the other one was high-dosage single exposure (HSE) as per the routine toxicity assay. The results showed a significant growth inhibition to M. aeruginosa in the LRE group, where the inhibition rate reached above 90% from day 6 to day 9. The cell-membrane damage ratio increased from 64.05% on day 5 up to 96.60% on day 9. PSII photosynthesis activity expressed as Fv/Fm, ΦPSII, NPQ and ETRmax was also thoroughly inhibited in this group. Whereas the growth and PSII photosynthesis activity of M. aeruginosa in the HSE group were inhibited initially, but recovered gradually from day 4 or 5, which was accompanied by a continuous reduction of NPN content in culture solutions. Although NPN content in the LRE group was relatively lower, it remained at a more stable level throughout the experiment. These results indicate that continual release of low-dosage allelochemicals by aquatic plants plays crucial roles in their potent inhibition against cyanobacteria. Low-dosage continual exposure pattern needs to be investigated further.
•Severe damage on M. aeruginosa exposed repeatedly to low-dosage N-phenyl-1-naphthylamine (NPN) was observed.•Continual stress of low-dosage allelochemicals was proved to be a potent mode for allelopathy of aquatic plants.•It is essential to introduce low-dosage continual exposure pattern of allelochemicals into further research.
Utilizing the dataset corresponding to an integrated luminosity of 2.93 fb-1 at s√=3.773 GeV collected by the BESIII detector, we report the first amplitude analysis and branching fraction ...measurement of the D0→K-π+π0π0 decay. We investigate the sub-structures and determine the relative fractions and the phases among the different intermediate processes. Our results are used to provide an accurate detection efficiency and allow measurement of B(D0→K-π+π0π0)=(8.86±0.13(stat)±0.19(syst))%.
By means of the measurement of the residual stress and friction properties, the observation of the microstructure by the SEM, the X-ray diffraction (XRD) was used to phase analysis and the ...nano-bainite structure was determined by transmission electron microscopy (TEM). The effect of nano-bainite microstructure and residual stress on friction properties of M50 bearing steel was analyzed after austempered at 200 °C for 2 h, 16 h and 32 h. Results show that nano-bainite structure is composed of thin film austenite and bainite ferrite, the mean thickness of bainite ferrite lath is about 90 ± 10 nm. The contents of nano-bainite are 15.772%, 33.951% and 50.332% respectively after austempered for 2 h, 16 h and 32 h. The hardness increases from 2 to 16 h, which is related to the precipitation of secondary carbides in bainite. And the hardness decreases after 16 h due to the fact that the bainite content is the largest. The fluctuation range of the residual stress of the sample austempered for 32 h + tempering is the smallest and the distribution is the most uniform. Wear resistance of the sample gradually increases with the extension of austempering time which is mainly related to hardness, residual stress state and thermal stability.
An amplitude analysis of the pi(0)pi(0) system produced in radiative J/psi decays is presented. In particular, a piecewise function that describes the dynamics of the pi(0)pi(0) system is determined ...as a function of M pi(0)pi(0) from an analysis of the (1.311 +/- 0.011) x 10(9) J/psi decays collected by the BESIII detector. The goal of this analysis is to provide a description of the scalar and tensor components of the pi(0)pi(0) system while making minimal assumptions about the properties or number of poles in the amplitude. Such a model-independent description allows one to integrate these results with other related results from complementary reactions in the development of phenomenological models, which can then be used to directly fit experimental data to obtain parameters of interest. The branching fraction of J/psi -> pi(0)pi(0) is determined to be (1.15 +/- 0.05) x 10(-3), where the uncertainty is systematic only and the statistical uncertainty is negligible.
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