We report on the discovery of eight repeating fast radio burst (FRB) sources found using the Canadian Hydrogen Intensity Mapping Experiment (CHIME) telescope. These sources span a dispersion measure ...(DM) range of 103.5-1281 pc cm−3. They display varying degrees of activity: six sources were detected twice, another three times, and one 10 times. These eight repeating FRBs likely represent the bright and/or high-rate end of a distribution of infrequently repeating sources. For all sources, we determine sky coordinates with uncertainties of ∼10′. FRB 180916.J0158+65 has a burst-averaged DM = 349.2 0.3 pc cm−3 and a low DM excess over the modeled Galactic maximum (as low as ∼20 pc cm−3); this source also has a Faraday rotation measure (RM) of −114.6 0.6 rad m−2, which is much lower than the RM measured for FRB 121102. FRB 181030.J1054+73 has the lowest DM for a repeater, 103.5 0.3 pc cm−3, with a DM excess of ∼70 pc cm−3. Both sources are interesting targets for multi-wavelength follow-up due to their apparent proximity. The DM distribution of our repeater sample is statistically indistinguishable from that of the first 12 CHIME/FRB sources that have not yet repeated. We find, with 4 significance, that repeater bursts are generally wider than those of CHIME/FRB bursts that have not repeated, suggesting different emission mechanisms. Many of our repeater events show complex morphologies that are reminiscent of the first two discovered repeating FRBs. The repetitive behavior of these sources will enable interferometric localizations and subsequent host galaxy identifications.
Carbon nanotubes reinforced aluminum matrix composites were fabricated by isostatic pressing followed hot extrusion techniques. Differential scanning calorimetric, X-ray diffraction, field emission ...scanning electron microscopy, transmission electron microscopy has been carried out to examine the reaction condition of nanotubes and aluminum, and to analyze the composites structure. The effects of nanotubes content on mechanical properties of composites were investigated. Experimental results showed that nanotubes are homogeneously distributed in the composites. Some nanotubes act as bridges across cracks, others are pulled-out on fracture surfaces of composites. However, nanotubes react with aluminum and form Al
4C
3 phases when the temperature is above 656.3
°C. The nanotubes content affects significantly mechanical properties of composites. Meanwhile, the 1.0
wt.% nanotube/2024Al composite is found to exhibit the highest tensile strength and Young's modulus. The maximal increments of tensile strength and Young's modulus of the composite, compared with the 2024Al matrix, are 35.7% and 41.3%, respectively.
A practice of cemented backfill technology with ultra-fine tailings in a gold mine was comprehensively presented, and a series of tests were conducted in accordance with the peculiar properties of ...ultra-fine tailings and the mining technology conditions. The test results show that, the tailings from Shuiyindong Gold Mine have a great grinding fineness, with the average particle diameter 22.03 μm, in which the ultra-fine particles with the diameter below 20 μm occupying 66.13%. The analysis results of chemical components of tailings indicate that the content of SiO2 is relatively low, i.e., 33.08%, but the total content of CaO, MgO and Al2O3 is relatively high i.e., 36.5%. After the settlement of 4–6 h, the tailing slurry with the initial concentration of 40% has the maximum settling concentration of 54.692%, and the corresponding maximum settling unit weight is 1.497 g/cm3. During the field application, the ultra-fine tailings and PC32.5 cement were mixed with the cement-tailings ratios of 1:3–1:8, and the slurry concentration of 50 wt% was prepared. Using the slurry pump, the prepared cemented backfill slurries flowed into the goaf, and then the strength of the cemented backfill body met the mining technique requirements in Shuiyindong Gold Mine, where the ore body has a smooth occurrence, with the average thickness of approximately 2 m and the inclination angle ranging from 5 to 10°.
•Taking the goaf as the tailing dam to dispose the ultra-fine tailings.•A large number of concrete columns can be replaced by the cemented tailing backfill body.•The cemented backfill slurry with ultra-fine tailings is optimal when the concentration is approximately 50%.•The risk of tailings dam break can be significantly reduced.
The egg-laying interval (LI) directly reflects the laying performance of breeding pigeons, influenced by reproductive hormones. This study aimed to assess reproductive hormone levels in serum and the ...expression of related genes and their receptors in the hypothalamus and pituitary gland in 4 stages: first (LI1), third (LI3), fifth (LI5), and seventh (LI7) days. The results showed that serum gonadotropin-releasing hormone (GnRH) level decreased from LI1 to LI7 (P < 0.01) and peaked in LI1. The serum follicle-stimulating hormone (FSH) and luteinizing hormone (LH) levels stayed at high levels from LI1 to LI5. The FSH level decreased slightly from LI5 to LI7 (P > 0.05), but the LH level decreased rapidly (P < 0.01). The prolactin (PRL) levels significantly increased in LI5 (P < 0.01) compared with LI1 and then stayed at a high level. The GnRH1 expression in the hypothalamus had no significant change in LI (P > 0.05). However, the GnRHR first decreased from LI1 to LI3 (P < 0.05) and then increased. The FSH mRNA level in the pituitary gland decreased from LI1 to LI3 and slightly increased in LI5 (P > 0.05). The change pattern of FSHR was similar to that of FSH and peaked in LI5 (P < 0.05). The LH expression level was the highest in LI5 and significantly higher than that in LI3 and LI7 (P < 0.05). However, the LHR mRNA level decreased in LI (P < 0.05). The expression patterns of PRL and PRLR were similar; they were upregulated in LI and peaked in LI7 (P < 0.01). The expression pattern of GnRHR was similar to that of FSH, LH, and FSHR, suggesting the critical role of GnRHR in LI. Furthermore, the expression levels of these genes peaked in LI5, closely correlating with the maturation of the first largest follicle in pigeons. PRL–PRLR signaling inhibited GnRH activity to promote ovulation. This study provided a basis for further investigating the molecular mechanisms underlying the regulation of reproduction in pigeons.
The dry sliding friction and wear behavior of nano/ultrafine-grained (NG/UFG), heterogeneous ultrafine-grained (HUFG), and coarse-grained (CG) austenitic stainless steels was studied. The results ...revealed that the wear resistance of the samples increased with an increase in hardness under the applied load of 10 N. However, under the applied loads of 20 N and 30 N, the HUFG steel presented the best wear resistance. Analysis of the wear mechanism revealed that the HUFG structure with good comprehensive performances formed a continuous hardened layer early, which did not delaminate and peel off prematurely, thereby effectively resisting the damage of a Si3N4 ball. The ε- and α′-martensite were generated below the wear surfaces of the NG/UFG, HUFG, and CG samples after wear.
•NG/UFG and HUFG steels were obtained by strain-induced martensite reversion process.•The HUFG steel exhibited the best wear resistance under the high applied loads of 20 N and 30 N.•A continuous hardened layer formed on the HUFG steel, which did not peel off prematurely, efficiently resisted the wear.•The ε- and α′-martensite phases were generated below the wear surfaces of the NG/UFG, HUFG, and CG steels.
The Binchang area of southwestern Ordos Basin is one of the most promising areas for low-rank coalbed methane (CBM) in China. This work investigates the Jurassic Yanan Formation coal and CBM geology ...and accumulation characteristics of CBM in the southwestern Ordos Basin based on data from 46 wells and laboratory measurements of 14 coal samples from 7 mines. The results show that coal rank in the Binchang area is mainly sub-bituminous A and high-volatile C bituminous (0.46%–0.73%Ro). Coals are dominated by inertinite (14.7–85.6%); less abundant are vitrinite (8.5–77.7%) and liptinite (1.5–15.2%). Minerals are found only in small amounts (0.4–8.3%). Permeability is between 0.04 and 25.3mD, and porosity ranges from 2.4% to 20.1%. Most coal pores are less than 100nm in diameter, making them favorable for gas adsorption but unfavorable for gas permeability. Pore morphology is represented mainly by micro- and mesopores with a well-connected and ink-bottle shaped (narrow throat and wide body) morphology. These coals are characterized by a high adsorption volume of more than 3.0×10−3ml/g. Methane isothermal adsorption measurements of 12 coal samples revealed that their maximum adsorption capacity (on a dry and ash-free basis) varies from 5.06 to 13.37m3/t, depending on moisture content. However, under the influence of gas preservation conditions, the in-place gas content is generally 0.11–6.26m3/t. Finally, based on a comprehensive analysis of coal thickness, gas content, hydrogeology conditions, roof, floor, and depth properties, this study indicated that the best prospective target areas for CBM production are forecasted to be the Tingnan and Dafosi areas, which are located in the syncline, central south part of the study area.
► The physical properties of low-rank CBM reservoirs are characterized. ► The low-rank CBM enrichment and accumulation model is provided. ► The favorable exploration areas of low-rank CBM are pointed out.
Here we report a new crystallographic orientation relationship (OR) between MC-type carbide (M = metal) and ferrite matrix, observed in the specimen held isothermally at 600 °C for 20 min, named ...NEU-OR. The 〈110〉carbide//〈110〉 ferrite alignment is the main difference from the well-known Baker–Nutting (BN) OR. NEU-OR is related to BN OR by the relative rotation of 45° about the zone axis of 〈110〉carbide. The interfacial energy between carbide and ferrite with NEU-OR is lower than that with BN OR based on semi-coherent dislocation theory, which benefits increases in the number density of precipitates.
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The effect of adding trace amounts of Nd to Mg–3Zn-0.5Zr alloy was systematically investigated in this work. With the introduction of Nd, the composition of the second phase changed significantly in ...the as-cast Mg–3Zn-0.5Zr–x Nd (ZKN) alloy (x=0,0.3,0.6,0.9wt%). The volume fraction of the second phases increased with increasing of Nd content, and the distribution gradually changed from a discontinuous point to a semi-continuous reticular structure and then to a continuous reticular structure. Furthermore, it was found that the degree of dynamic recrystallization (DRX) and the sizes of DRXed grains gradually decreased with increasing Nd content (0 wt% ∼ 0.6 wt%) after extrusion, as well as the texture intensity gradually increased. However, when the Nd content was greater than 0.6 wt%, the DRXed grain sizes and the degree of DRX had not changed significantly. In addition, the volume fraction of the precipitates first increased and then decreased as the Nd content increased. High ultimate tensile strength (450–510 MPa), yield strength (400–476 MPa), and acceptable elongation (4.1% ∼ 11.0%) could be obtained in the extruded ZKN alloys. The prodigious increase in strength was mainly caused by grain boundary strengthening, dislocation strengthening, and Orowan strengthening. Low alloying content and traditional extrusion processes contribute to current low-cost and high-strength alloys that have substantial commercial application potential.
●A new phase was discovered in Mg–3Zn-0.5Zr- x Nd (ZKN) alloys.●The transformation of the second phases was clarified in ZKN alloys.●Ultra-fine grains were formed in the ZKN alloys after extrusion.●The ZKN alloys exhibited YS of 400–476 MPa and El. of 4.1%–11.0%.
We elucidate here the strengthening mechanisms in titanium microalloyed low-carbon steels, which were rolled into plates of 12 mm thickness using a combination of thermomechanical controlled ...processing (TMCP) and ultrafast cooling (UFC). The ultrafast cooling combined with thermomechanical controlled processing is referred by us as new generation (NG)-TMCP. Chemical phase analysis, small-angle X-ray scattering (SAXS) and high-resolution transmission electron microscopy (TEM) were used to study the characteristics of nanoscale cementite precipitates and microalloyed precipitates. Besides nanoscale TiC, cementite precipitates of size less than ∼35 nm with high volume fraction were observed in Ti-microalloyed steel. Cementite with high volume fraction had a stronger precipitation strengthening effect than nanometer-sized TiC. The precipitation strengthening contribution of nanoscale precipitates of different types and size was estimated together with solid solution strengthening and grain refinement strengthening contribution. The estimated yield strength was consistent with the experimental value.
TEM micrograph of (a) interphase TiC, (b) random TiC, (c) Fe3C, (d) HRTEM image, (e) corresponding FFT diffractogram, and (f) IFFT lattice image interphase TiC. Display omitted
•A good combination of strength and toughness can be obtained controlled by NG-TMCP.•Nanoscale cementite was observed in Ti-microalloyed steel except for TiC.•The contribution of precipitates to yield strength can be greater than ∼300 MPa.
Although electromagnetic brain stimulation is a promising treatment in neurology and psychiatry, clinical outcomes are variable, and underlying mechanisms are ill-defined, which impedes the ...development of new effective stimulation protocols. Here, we show, in vivo and ex vivo, that repetitive transcranial magnetic stimulation at low-intensity (LI-rTMS) induces axon outgrowth and synaptogenesis to repair a neural circuit. This repair depends on stimulation pattern, with complex biomimetic patterns being particularly effective, and the presence of cryptochrome, a putative magnetoreceptor. Only repair-promoting LI-rTMS patterns up-regulated genes involved in neuronal repair; almost 40% of were cryptochrome targets. Our data open a new framework to understand the mechanisms underlying structural neuroplasticity induced by electromagnetic stimulation. Rather than neuronal activation by induced electric currents, we propose that weak magnetic fields act through cryptochrome to activate cellular signaling cascades. This information opens new routes to optimize electromagnetic stimulation and develop effective treatments for different neurological diseases.
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