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  • 1
    In: Nature, Springer Science and Business Media LLC, Vol. 534, No. 7609 ( 2016-06-30), p. 652-657
    Type of Medium: Online Resource
    ISSN: 0028-0836 , 1476-4687
    RVK:
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    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2016
    detail.hit.zdb_id: 120714-3
    detail.hit.zdb_id: 1413423-8
    SSG: 11
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  • 2
    Online Resource
    Online Resource
    Oxford University Press (OUP) ; 2021
    In:  Publications of the Astronomical Society of Japan Vol. 73, No. 2 ( 2021-04-05), p. 439-449
    In: Publications of the Astronomical Society of Japan, Oxford University Press (OUP), Vol. 73, No. 2 ( 2021-04-05), p. 439-449
    Abstract: Computation resource is the limiting factor in higher operational accuracy of field-programmable gate arrays (FPGAs) in solar radio digital receivers. The data truncation strategy which determines the accuracy of data is then the essential technology in the design of a receiving system. Based on the solar radio spectrometer (dual channel, 14 bit, 1.25 gigasamples per second) at the Chashan Solar Radio Observatory (CSO), this paper presents a data truncation strategy which can realize real-time solar radio observation (35–40 GHz) with high time and frequency resolution as well as a large dynamic range, and at the same time saves the computation resource to a large extent. Simulations of truncations during signal processing are carried out in MATLAB, and the best truncation mechanisms are deduced for windowing and fast Fourier transform (FFT). Using the simulation results, the best truncation strategies have been implemented in the solar radio receiver at CSO with the result that the best truncation bits for the windowing operation are [27 : 14], with an error of 2.5 × 10−4, and the best truncation bits for the FFT output are [20 : 5] with an error of 1.5 × 10−3. Compared with the processing of full-precision data, occupation of the computation resources in the FPGA can be reduced significantly. For instance, the lookup table, lookup table RAM, flip flop, and digital signal processing slices are reduced by 7.36%, 14.65%, 8.38%, and 24.94%, respectively, which guarantees broad-band real-time solar radio observations (35–40 GHz).
    Type of Medium: Online Resource
    ISSN: 0004-6264 , 2053-051X
    RVK:
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 2021
    detail.hit.zdb_id: 2206640-8
    detail.hit.zdb_id: 2083084-1
    SSG: 16,12
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  • 3
    Online Resource
    Online Resource
    Society of Exploration Geophysicists ; 2022
    In:  GEOPHYSICS Vol. 87, No. 6 ( 2022-11-01), p. T417-T433
    In: GEOPHYSICS, Society of Exploration Geophysicists, Vol. 87, No. 6 ( 2022-11-01), p. T417-T433
    Abstract: Wave-equation simulation based on the k-space method produces nearly dispersion-free wavefields and enhances simulation stability. However, for simulation in heterogeneous media, the conventional first-order k-space method requires many mixed-domain operators, which are the most expensive part of the wave-extrapolation process. We have analyzed and summarized the problem of the conventional k-space method as symmetrical factorization of the wave propagators. Based on this analysis, we develop a novel asymmetrical factorization-based k-space method that can significantly reduce the number of mixed-domain operators without compromising modeling accuracy. By using this method, the number of mixed-domain operators is reduced by half, and thus, the computational cost decreases significantly. Furthermore, we have compared our method to the conventional pseudospectral method. The comparison finds that, at comparable accuracy, our method is more efficient due to its ability to use a larger time step. Acoustic and elastic examples demonstrate the correctness and effectiveness of our method.
    Type of Medium: Online Resource
    ISSN: 0016-8033 , 1942-2156
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    Language: English
    Publisher: Society of Exploration Geophysicists
    Publication Date: 2022
    detail.hit.zdb_id: 2033021-2
    detail.hit.zdb_id: 2184-2
    SSG: 16,13
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  • 4
    Online Resource
    Online Resource
    World Scientific Pub Co Pte Ltd ; 2020
    In:  Modern Physics Letters B Vol. 34, No. Supp01 ( 2020-12-31), p. 2150008-
    In: Modern Physics Letters B, World Scientific Pub Co Pte Ltd, Vol. 34, No. Supp01 ( 2020-12-31), p. 2150008-
    Abstract: For the fabricated AlGaN/GaN high electron mobility transistors (HEMTs) with different Ohmic contact widths, the gate-channel electron mobility is obtained experimentally. Mobility curves show very different values and trends. This phenomenon is investigated with the scattering theory in AlGaN/GaN HEMTs. The reason for the different mobility curves is found to be attributed to the different polarization charge distributions at the AlGaN/GaN interface. The AlGaN/GaN HEMT with a smaller Ohmic contact width corresponds to positive additional polarization charge near the Ohmic contact. The AlGaN/GaN HEMT with a larger Ohmic contact width corresponds to negative additional polarization charge near the Ohmic contact. Changing the Ohmic contact width will be a new dimension to optimize the characteristics of AlGaN/GaN HEMTs effectively.
    Type of Medium: Online Resource
    ISSN: 0217-9849 , 1793-6640
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    Language: English
    Publisher: World Scientific Pub Co Pte Ltd
    Publication Date: 2020
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  • 5
    Online Resource
    Online Resource
    American Astronomical Society ; 2022
    In:  The Astrophysical Journal Supplement Series Vol. 258, No. 2 ( 2022-02-01), p. 25-
    In: The Astrophysical Journal Supplement Series, American Astronomical Society, Vol. 258, No. 2 ( 2022-02-01), p. 25-
    Abstract: Most solar radio telescopes operate below ∼18 GHz and cannot realize a complete frequency coverage of the microwave spectrum, especially in the optically thin regime during solar bursts, which can provide unique information about the magnetic field in the burst area in the solar corona. Therefore, the development of high-frequency microwave observation equipment is demanded by the solar radio community. In this paper, we present a microwave spectrum observation system operating at 35–40 GHz. In this system, the solar radio signal is acquired by an 80 cm Cassegrain circularly polarized antenna, which is then downconverted and channelized by a 35–40 GHz analog front end. The processed signal is finally sent to the digital receiver to generate the microwave dynamic spectrum, which is transmitted by gigabit Ethernet transmission to a host computer. The system performance has been tested and obtained as follows: a noise figure of ∼300 K, system linearity of 〉 0.9999, time resolution of about 134 ms (default), and frequency resolution of 153 kHz. We further conduct calibration for this system and find that the observed Sun–Moon ratio is about 43.1–53.3 @ 35.25 GHz during the new Moon, and is quite close to the theoretical value. The coefficient of variation of the system is ∼0.61% in a 9 hr test. The system has been designed, developed, and tested for over 1 yr in Chashan Solar Observatory and is expected to play an important role in the microwave burst study in the 25th solar cycle.
    Type of Medium: Online Resource
    ISSN: 0067-0049 , 1538-4365
    RVK:
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2022
    detail.hit.zdb_id: 2006860-8
    detail.hit.zdb_id: 2207650-5
    SSG: 16,12
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  • 6
    Online Resource
    Online Resource
    IOP Publishing ; 2022
    In:  Applied Physics Express Vol. 15, No. 4 ( 2022-04-01), p. 042004-
    In: Applied Physics Express, IOP Publishing, Vol. 15, No. 4 ( 2022-04-01), p. 042004-
    Abstract: We demonstrate the excellent nonlinear optical absorption of CuFeO 2 (CFO) microcrystals (MCs) and realise nanosecond passively Q-switched erbium-doped fiber laser (EDFL) based on CFO MCs as saturable absorber (SA). The CFO MCs-based SA has a modulation depth of 13.5% and an unsaturated loss of 12.6%. The threshold of stable Q-switched EDFL is only 30 mW, and the obtained repetition rate and pulse duration are 70.9 KHz and 690 ns respectively under 225 mW pump power. High signal-to-noise ratio of up to 70 dB proves its stability. Our results show that CFO MCs are a promising material for optoelectronic devices.
    Type of Medium: Online Resource
    ISSN: 1882-0778 , 1882-0786
    RVK:
    Language: Unknown
    Publisher: IOP Publishing
    Publication Date: 2022
    detail.hit.zdb_id: 2417569-9
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