Since the discovery of carbon nanotubes in 1991 by Iijima, there has been great interest in creating long, continuous nanotubes for applications where their properties coupled with extended lengths ...will enable new technology developments. For example, ultralong nanotubes can be spun into fibres that are more than an order of magnitude stronger than any current structural material, allowing revolutionary advances in lightweight, high-strength applications. Long metallic nanotubes will enable new types of micro-electromechanical systems such as micro-electric motors, and can also act as a nanoconducting cable for wiring micro-electronic devices. Here we report the synthesis of 4-cm-long individual single-wall carbon nanotubes (SWNTs) at a high growth rate of 11 μm s−1 by catalytic chemical vapour deposition. Our results suggest the possibility of growing SWNTs continuously without any apparent length limitation.
Gravitational‐wave high‐energy Electromagnetic Counterpart All‐sky Monitor (GECAM) is a space‐borne instrument dedicated to monitoring high‐energy transients, including Terrestrial Gamma‐ray Flashes ...(TGFs) and Terrestrial Electron Beams (TEBs). We implemented a TGF/TEB search algorithm for GECAM, with which 147 bright TGFs, 2 typical TEBs and 2 special TEB‐like events are identified during an effective observation time of ∼9 months. We show that, with gamma‐ray and charged particle detectors, GECAM can effectively identify and distinguish TGFs and TEBs, and measure their temporal and spectral properties in detail. A very high TGF‐lightning association rate of ∼80% is obtained between GECAM and GLD360 in east Asia region.
Plain Language Summary
Terrestrial gamma‐ray flashes (TGFs) and Terrestrial Electron Beams (TEBs) represent the most energetic radioactive phenomena in the atmosphere of the Earth. They reflect a natural particle accelerator that can boost electrons up to at least several tens of mega electron volts and produce gamma‐ray radiation. With novel detection technologies, Gravitational‐wave high‐energy Electromagnetic Counterpart All‐sky Monitor (GECAM) is a new powerful instrument to observe TGFs and TEBs, as well as study their properties. For example, it is difficult for most space‐borne high‐energy instruments to distinguish between TGFs and TEBs. However, we show here that, with the joint observation of gamma‐ray and charged particle detectors, GECAM can effectively identify TGFs and TEBs. GECAM can also reveal their fine features in the light curves and spectra.
Key Points
During 9‐month observation, Gravitational‐wave high‐energy Electromagnetic Counterpart All‐sky Monitor (GECAM) has detected 147 bright Terrestrial Gamma‐ray Flashes (TGFs), 2 typical Terrestrial Electron Beams (TEBs), and 2 special TEB‐like events
With novel detector design, GECAM can effectively classify TGFs and TEBs, and reveal their fine temporal features
We obtained a very high TGF‐lightning association rate (∼80%) between GECAM and GLD360 in east Asia region
ABSTRACT
Fast transitions between different types of power density spectra (PDS) happening over time-scales of several tens of seconds are rare phenomena in black hole X-ray binaries. In this paper, ...we report a broad-band spectral-timing analysis of the fast transitions observed in the 2021 outburst of GX 339−4 using NICER and Insight-HXMT observations. We observe transitions between band-limited noise-dominated PDS and type-B quasi-periodic oscillations (QPOs), and their rapid appearance or disappearance. We also make a detailed comparison between the fast transitions in GX 339−4 with those seen in MAXI J1820+070 and MAXI J1348−630. By comparing the spectra of the periods with and without type-B QPOs, we find that the spectral ratios above 10 keV are nearly constant or slightly decreasing, and the values are different between sources. Below 10 keV, the flux change of the Comptonization component is inversely proportional to the flux change of the thermal component, suggesting that the appearance of type-B QPOs is associated with a redistribution of the accretion power between the disc and the Comptonizing emission region. The spectral ratios between the periods with type-B QPO and those with broad-band noise are significantly different from that with type-B QPO and without type-B QPO, where the ratios (type-B QPO/broad-band noise) show a maximum at around 4 keV and then decrease gradually towards high energies. Finally, we discuss the possible change of the geometry of the inner accretion flow and/or jet during the transitions.
938,720 Giants from LAMOST I Zhang, X.; Zhao, G.; Yang, C. Q. ...
Publications of the Astronomical Society of the Pacific,
09/2019, Letnik:
131, Številka:
1003
Journal Article
Recenzirano
Odprti dostop
Extracting accurate atmospheric parameters and elemental abundances from stellar spectra is crucial for studying the Galactic evolution. In this paper, a deep neural network architecture named ...StarNet is used to estimate stellar parameters (T
eff, log g, M/H), α-elements as well as C and N abundances from LAMOST spectra, using stars in common with APOGEE survey as training data set. With the spectral signal-to-noise ratio (S/N) in g band (S/N
g
) larger than 10, the test indicates our method yields uncertainties of 45 K for T
eff, 0.1 dex for log g, 0.05 dex for M/H, 0.03 dex for α/M, 0.06 dex for C/M and 0.07 dex for N/M. Because of few stars with M/H < −1.0 dex in the training set, the uncertainties are dominated by stars with M/H > −1.0 dex. Based on test results, we think StarNet is valid for measuring parameters from low-resolution spectra of the LAMOST survey. The trained network is then used to predict parameters for 938,720 giants from LAMOST DR5. Within the range of stellar parameters 4000 K < T
eff < 5300 K, 0 dex < log g < 3.8 dex and −2.5 dex < M/H < 0.5 dex, the comparisons with high-precision measurements (e.g., PASTEL, asteroseismic log g) yield uncertainties of 100 K for T
eff, 0.10 dex for log g, 0.12 dex for M/H. Our estimations are consistent with values from the high-precision measurements. In this research, a deep neural network is successfully applied on the numerous spectra from LAMOST. The deep neural network shows an excellent performance, which demonstrates that deep learning can effectively reduce the inconsistencies between parameters measured by the individual survey pipelines.
Photosynthesis is a critical function that allows adaptation to drought stress in maize (
Zea mays
L.). Therefore, elucidation of the genetic control of photosynthetic performance under drought ...stress and the associated molecular markers is of great importance for marker-assisted selection (MAS). Here, we detected 54 quantitative trait loci (QTLs) affecting the net photosynthetic rate (
P
n
), stomatal conductance (
G
s
), intercellular CO
2
concentration (
C
i
), transpiration rate (
Tr
), ribulose 1,5-biphosphate carboxylase activity (RuBP), and water use efficiency (WUE) of the ear leaf across two F4 populations in drought-stressed and well-watered environments by single-environment mapping with composite interval mapping (CIM), and 43 QTLs identified under drought stress, indicating that the tolerance to photoinhibition is a key factor affecting drought stress tolerance in maize. We further dissected 54 QTLs via joint analysis of all environments with mixed-linear-model-based CIM (MCIM), including 24 involved in QTL-by-environment interactions (QEIs), 87.5% QEIs identified under drought stress, 14 pairs showing epistatic interactions with dominance-by-additive/dominance effects under contrasting environments. We further identified eight constitutive QTLs (cQTLs) across two populations by CIM/MCIM, which could be used for genetic improvement of maize via QTL pyramiding. The co-localization of five cQTLs in bin 1.07_1.10/6.05/7.02_7.04/8.03/10.03 under contrasting environments in both populations strongly supported pleiotropy. Additionally, 17 candidate genes located at the above-mentioned cQTLs were involved in photomorphogenesis, photosynthesis, and stress response. These results provide insights into the genetic mechanisms responsible for photosynthesis under different water availability conditions, and reveal alleles that could potentially be used for MAS-based development of drought tolerant maize cultivars.
•Anisotropic grain boundary diffusion of NdFeB magnet is studied by micromagnetism.•Anisotropic diffusion is due to anisotropic distribution of demagnetizing field.•Diffusion parallel to easy axis is ...the most effective way to improve coercivity.•To enhance coercivity only a limited diffusion depth along easy axis is needed.
A systematic investigation on the anisotropic grain boundary diffusion in sintered Nd-Fe-B magnets is carried out by micromagnetic simulation. The results indicate that the critical reason for the anisotropic diffusion effect is not the difference in the amount of Dy diffused along different directions but the macroscopic demagnetizing field. The diffusion parallel to the easy axis from both pole surfaces of the magnet can increase the nucleation fields in the two major regions with large macroscopic demagnetizing fields, where the reverse domains can nucleate easily. As a consequence, the grain boundary diffusion along the directions parallel to the easy axis from two pole surfaces is more effective to improve the coercivity of the magnets than that along other directions. It is also found that, to enhance the coercivity, only a limited diffusion depth is required. The present result is in good agreement with the recent experimental findings.
It has been understood that the use of cation-exchange membranes (CEM) and alkali-doped polybenizimidazole membranes (APM) in alkaline direct ethanol fuel cells (DEFC) with an added base in the fuel ...exhibits performance similar to the use of anion-exchange membranes (AEM). The present work is to assess the suitability of the three types of membrane to alkaline DEFCs by measuring and comparing the membrane properties including the ionic conductivity, the species permeability, as well as the thermal and mechanical properties. The comparison shows that: (i) the AEM is still the most promising membrane for the alkaline DEFC, although the thermal stability needs to be further enhanced; (ii) before solving the problem of the poor thermal stability of AEMs, the CEM is another choice for the alkaline DEFC running at high temperatures (<90 °C); and (iii) the APM can also be applied to the alkaline DEFC operating at high temperatures, but its mechanical property needs to be substantially enhanced and the species permeability needs to be dramatically decreased.
► This work is to compare the properties of three types of membrane, including AEM, CEM and APM. ► The AEM is found to be the most promising membrane for alkaline DEFCs. ► The CEM and APM can also be applied to alkaline DEFCs operating at high temperatures.
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