分类： 机械工程 >> 机械设计 提交时间： 2024-04-01
摘要： Overstaffing production in underground coal mining is not convenient for daily management, and incomplete information of coal miners hinders the rescue process of firefighters during mine accidents. To address this safety sustainability issue, a novel face recognition method based on an improved multiscale neural network is proposed in this paper. A new depthwise seperable (DS)-inception block is designed and a joint supervised loss function based on center loss theory is developed to constructe a new multiscale model. The miniers can be recognized in the harsh underground environment during the life rescue. Experimental results show that the accuracy, recall and F1-score indexes of the proposed method for the miner face recognition in the underground mining environment are 97.26%, 94.17% and 95.42%, respectively. Transfer model with joint supervised loss can effectively improve the recognition accuracy by about 0.5~1.5%. In addition, the average recognition accuracy of the proposed face recognition method achieves to 91.34% and the miss detection rate is less than 5% in the dugout tunnel of coal mine.
分类： 能源科学 >> 储能技术 提交时间： 2024-03-31
摘要： This work experimentally explores the influence of thesodiumchloride pollution on thePEMFC performancein the marine saltsprayenvironment by analyzing the concentration diffusion characteristics of the sodium chloride in thePEMFC membraneelectrodes. Firstly, a set of experiments were carried out to determine the distribution of the sodium chloride components in the membrane electrodes, where five different salt spray environments (i.e., 100mg/L, 200mg/L, 300mg/L, 400mg/L, and 500mg/L of the salt component, respectively) were used/employed to analyze the concentration diffusion characteristics of the sodium chloride. Then, the obtained samples were microscopically characterized and elementally analyzed by thefield emission scanning electron microscopy(FESEM) and the energy spectrometry. Subsequently, a least squares-based model was proposed to predict the diffusion rate of the contaminatingions inthe membrane electrodes. Lastly, the pollution of the sodium chloride was evaluated/assessed to reveal theperformance degradationof the PEMFCs. The experimental results demonstrated that (1) the sodium chloride fraction existed as crystals orions inthe membrane electrodes in the marine salt spray environment; (2) the sodium chloride poisoning was founded in theproton exchange membranein the form ofsodium ions; (3) and the sodium-to-chloride ratio was proportional to the contamination time and the salt spray in the proton exchange membrane.
分类： 机械工程 >> 刀具技术 提交时间： 2024-03-31
Nikodem Wrobel
Michal Rejek
Jolanta Krolczyk
Mateusz Franka
Munish K. Gupta
Marcin Sliwinski
Grzegorz Krolczyk
Z. Li
摘要： The present article describes a new and innovative method of producing an inseparablejointwith the use of expansion jaws. The effect of jaw tool geometry on the reaction forces and ultimate strength of an inseparable joint formed on a prototype stand was analyzed. The results are also compared of joints produced by jaws with single movement method and with complex movement method. The tool responds with bending and pressing one part into the other, which results in their permanent connection. In the tests, differentiation was introduced with regard to the height of the applied force to the collar of the connection pipe. A novelty is also a solution based on a complex, parameterized trajectory of the stamp movement consisting of horizontal and vertical displacements. This paper presents the tests of the joints formed at the stand. The new approach described in this article has resulted in a joint strength increase of approximately 30% using the innovative complex jaw movement of the biaxial clinching process. A jointtensile strengthclose to 1000N was achieved.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
X. H. Xu
Y. Wang
F. S. Wei
X. S. Feng
M. H. Bo
H. W. Tang
D. S. Wang
B. Lei
B. Y. Wang
P. B. Zuo
C. W. Jiang
X. J. Xu
Z. L. Zhou
Z. Li
P. Zou
L. D. Wang
Y. X. Gu
Y. L. Chen
W. Y. Zhang
P. Sun
摘要： Analyzing the effects of space weather on aviation is a new and developing topic. It has been commonly accepted that the flight time of the polar flights may increase during solar proton events because the flights have to change their route to avoid the high-energy particles. However, apart from such phenomenon, researches related to the flight time during space weather events is very rare. Based on the analyses of 39 representative international air routes around westerlies, it is found that 97.44% (94.87%) of the commercial airplanes on the westbound (eastbound) air routes reveal shorter (longer) flight time during solar proton events compared to those during quiet periods, and the averaged magnitude of change in flight time is ~10 min or 0.21%-4.17% of the total flight durations. Comparative investigations reassure the certainty of such phenomenon that the directional differences in flight time are still incontrovertible regardless of over-land routes (China-Europe) or over-sea routes (China-Western America). Further analyses suggest that the solar proton events associated atmospheric heating will change the flight durations by weakening certain atmospheric circulations, such as the polar jet stream. While the polar jet stream will not be obviously altered during solar flares so that the directional differences in flight time are not found. Besides the conventional space weather effects already known, this paper is the first report that indicates a distinct new scenario of how the solar proton events affect flight time. These analyses are also important for aviation since our discoveries could help the airways optimize the air routes to save passenger time costs, reduce fuel costs and even contribute to the global warming issues.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Y. Wang
X. H. Xu
F. S. Wei
X. S. Feng
M. H. Bo
H. W. Tang
D. S. Wang
L. Bian
B. Y. Wang
W. Y. Zhang
Y. S. Huang
Z. Li
J. P. Guo
P. B. Zuo
C. W. Jiang
X. J. Xu
Z. L. Zhou
P. Zou
摘要： Although the sun is really far away from us, some solar activities could still influence the performance and reliability of space-borne and ground-based technological systems on Earth. Those time-varying conditions in space caused by the sun are also called space weather, as the atmospheric conditions that can affect weather on the ground. It is known that aviation activities can be affected during space weather events, but the exact effects of space weather on aviation are still unclear. Especially how the flight delays, the top topic concerned by most people, will be affected by space weather has never been thoroughly researched. By analyzing huge amount of flight data (~5X106 records), for the first time, we demonstrate that space weather events could have systematically modulating effects on flight delays. The average arrival delay time and 30-minute delay rate during space weather events are significantly increased by 81.34% and 21.45% respectively compared to those during quiet periods. The evident negative correlation between the yearly flight regularity rate and the yearly mean total sunspot number during 22 years also confirms such delay effects. Further studies indicate that the interference in communication and navigation caused by geomagnetic field fluctuations and ionospheric disturbances associated with the space weather events will increase the flight delay time and delay rate. These results expand the traditional field of space weather research and could also provide us with brand new views for improving the flight delay predications.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
K. Abe
Y. Haga
Y. Hayato
K. Hiraide
K. Ieki
M. Ikeda
S. Imaizumi
K. Iyogi
J. Kameda
Y. Kanemura
Y. Kataoka
Y. Kato
Y. Kishimoto
S. Miki
S. Mine
M. Miura
T. Mochizuki
S. Moriyama
Y. Nagao
M. Nakahata
摘要： We present the development of neutron-tagging techniques in Super-Kamiokande IV using a neural network analysis. The detection efficiency of neutron capture on hydrogen is estimated to be 26%, with a mis-tag rate of 0.016 per neutrino event. The uncertainty of the tagging efficiency is estimated to be 9.0%. Measurement of the tagging efficiency with data from an Americium-Beryllium calibration agrees with this value within 10%. The tagging procedure was performed on 3,244.4 days of SK-IV atmospheric neutrino data, identifying 18,091 neutrons in 26,473 neutrino events. The fitted neutron capture lifetime was measured as 218 \pm 9 \mu s.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
X. H. Xu
Y. Wang
F. S. Wei
X. S. Feng
M. H. Bo
H. W. Tang
D. S. Wang
L. Bian
B. Y. Wang
W. Y. Zhang
Y. S. Huang
Z. Li
J. P. Guo
P. B. Zuo
C. W. Jiang
X. J. Xu
Z. L. Zhou
P. Zou
摘要： Solar flare is one of the severest solar activities on the sun, and it has many important impacts on the near-earth space. It has been found that flight arrival delays will increase during solar flare. However, the detailed intrinsic mechanism of how solar flares influence the delays is still unknown. Based on 5-years huge amount of flight data, here we comprehensively analyze the flight departure delays during 57 solar flares. It is found that the averaged flight departure delay time during solar flares increased by 20.68% (7.67 min) compared to those during quiet periods. It is also shown that solar flare related flight delays reveal apparent time and latitude dependencies. Flight delays during dayside solar flares are more serious than those during nightside flares, and the longer (shorter) delays tend to occur in the lower (higher) latitude airport. Further analyses suggest that flight delay time and delay rate would be directly modulated by the solar intensity (soft X-ray flux) and the Solar Zenith Angle. For the first time, these results indicate that the communication interferences caused by solar flares will directly affect flight departure delay time and delay rate. This work also expands our conventional understandings to the impacts of solar flares on human society, and it could also provide us with brand new views to help prevent or cope with flight delays.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Synchronized rotation of unit cells in a periodic structure provides a novel design perspective for manipulation of band topology. We then design a two-dimensional version of higher-order topological insulators (HOTI), by such rotation in a triangular photonic lattice with $\mathcal{C}_3$ symmetry. This HOTI supports the hallmark zero-dimensional corner states and simultaneously the one-dimensional edge states. We also find that our photonic corner states carry chiral orbital angular momenta locked by valleys, whose wavefunctions are featured by the phase vortex (singularity) positioned at the maximal Wyckoff points. Moreover, when excited by a fired source with various frequencies, the valley topological states of both one-dimensional edges and zero-dimensional corners emerge simultaneously. Extendable to higher or synthetic dimensions, our work provides access to a chiral vortex platform for HOTI realisations in the THz photonic system.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： There exists the phase ambiguity problem in the coherent beam combining (CBC) system with centrosymmetric arrays, which means that multiple different piston aberrations may generate the same far-field image. This will cause that the far-field image can not correctly reflect the phase information, resulting in the performance degradation of image-based intelligent algorithms. In this paper, we make a theoretical analysis on phase ambiguity. To the best of our knowledge, we give the number and descriptions of all solutions of the phase ambiguity problem in above system for the first time. A method to solve phase ambiguity is proposed, which requires no additional optical devices. We designed simulations to verify our conclusions and methods. We believe that our work solves the phase ambiguity problem in theory and is conducive to improving the performance of image-based algorithms. In addition, we designed a two-stage algorithm to generate Bi-beam, which have valuables application in laser propagation.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
H. Li
W. Wan
Z. Li
J. C. Cao
S. Lepillet
J-F. Lampin
K. Froberger
L. Columbo
M. Brambilla
S. Barbieri
摘要： Mode-locking operation and multimode instabilities in Terahertz (THz) quantum cascade lasers (QCLs) have been intensively investigated during the last decade. These studies have unveiled a rich phenomenology, owing to the unique properties of these lasers, in particular their ultrafast gain medium. Thanks to this, in QCLs a modulation of the intracavity field intensity gives rise to a strong modulation of the population inversion, directly affecting the laser current. In this work we show that this property can be used to study the real-time dynamics of multimode THz QCLs, using a self-detection technique combined with a 60GHz real-time oscilloscope. To demonstrate the potential of this technique we investigate a free-running 4.2THz QCL, and observe a self-starting periodic modulation of the laser current, producing trains of regularly spaced, ~100ps-long pulses. Depending on the drive current we find two regimes of oscillation with dramatically different properties: a first regime at the fundamental repetition rate, characterised by large amplitude and phase noise, with coherence times of a few tens of periods; a much more regular second-harmonic-comb regime, with typical coherence times of ~105 oscillation periods. We interpret these measurements using a set of effective semiconductor Maxwell-Bloch equations that qualitatively reproduce the fundamental features of the laser dynamics, indicating that the observed carrier-density and optical pulses are in antiphase, and appear as a rather shallow modulation on top of a continuous wave background. Thanks to its simplicity and versatility, the demonstrated technique is a powerful tool for the study of ultrafast dynamics in THz QCLs.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Progress on two-dimensional materials has shown that valleys, as energy extrema in a hexagonal first Brillouin zone, provides a new degree of freedom for information manipulation. Then valley Hall topological insulators supporting such-polarized edge states on boundaries were set up accordingly. In this paper, a two-dimensional valley photonic crystal composed of six tunable dielectric triangular pillars in unit cells is proposed in the photonic sense of a deformed Su-Schrieffer-Heeger (SSH) model. We reveal the vortex nature of valley states and establish the selection rules for valley polarized states. Based on the valley topology, a rhombus-shaped beam splitter waveguide is designed to verify the valley-chirality selection above. Our numerical results entail that this topologically protected edge states still maintain robust transmission at sharp corners, henceforth providing a feasible idea for valley photonic devices in THz regime.
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