- 标题
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- 实验方案
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A Method to Reconstruct the Solar-Induced Canopy Fluorescence Spectrum from Hyperspectral Measurements
摘要： A method for canopy Fluorescence Spectrum Reconstruction (FSR) is proposed in this study, which can be used to retrieve the solar-induced canopy fluorescence spectrum over the whole chlorophyll fluorescence emission region from 640–850 nm. Firstly, the radiance of the solar-induced chlorophyll fluorescence (Fs) at five absorption lines of the solar spectrum was retrieved by a Spectral Fitting Method (SFM). The Singular Vector Decomposition (SVD) technique was then used to extract three basis spectra from a training dataset simulated by the model SCOPE (Soil Canopy Observation, Photochemistry and Energy fluxes). Finally, these basis spectra were linearly combined to reconstruct the Fs spectrum, and the coefficients of them were determined by Weighted Linear Least Squares (WLLS) fitting with the five retrieved Fs values. Results for simulated datasets indicate that the FSR method could accurately reconstruct the Fs spectra from hyperspectral measurements acquired by instruments of high Spectral Resolution (SR) and Signal to Noise Ratio (SNR). The FSR method was also applied to an experimental dataset acquired in a diurnal experiment. The diurnal change of the reconstructed Fs spectra shows that the Fs radiance around noon was higher than that in the morning and afternoon, which is consistent with former studies. Finally, the potential and limitations of this method are discussed.
关键词： Fluorescence Spectrum Reconstruction (FSR),solar-induced chlorophyll fluorescence (Fs),Spectral Fitting Method (SFM),Fraunhofer Line Discriminator (FLD),hyperspectral remote sensing,Singular Vector Decomposition (SVD)
更新于2025-09-04 15:30:14
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Enhanced Index Modulated OFDM Spread Spectrum
摘要： Index modulated OFDM spread spectrum (OFDM-IM-SS) is a recently proposed scheme, which transmits the additional bits (index bits) through the code domain. In this paper, we propose a novel variant of OFDM-IM-SS, called index modulated OFDM with in-phase/quadrature spread spectrum (OFDM-IM-SS-IQ), to increase the spectrum efficiency of OFDM-IM-SS. In OFDM-IM-SS-IQ, the transmitted symbols are divided into in-phase and quadrature parts, which are combined by the corresponding spreading codes selected by their respective index bits. A low complexity detection algorithm for OFDM-IM-SS-IQ is investigated to relieve the computational complexity of the optimal maximum-likelihood detection. A closed-form of the upper bound on the bit error rate is then derived to evaluate the error performance of OFDM-IM-SS-IQ. In addition, a diversity-enhancing scheme of OFDM-IM-SS, named index modulated OFDM spread spectrum enhancement (OFDM-IM-SS-E), is also designed to achieve a full diversity order. Computer simulation results validate the theoretical analysis and show that OFDM-IM-SS-IQ outperforms the conventional OFDM-IM-SS scheme. They also prove that the proposed OFDM-IM-SS-E obtains full diversity and achieves a better bit error rate performance than OFDM-IM-SS.
关键词： diversity,OFDM,index modulation,low complexity,spread spectrum
更新于2025-09-04 15:30:14
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Photocontrol of magnetic structure in an itinerant magnet
摘要： We study the photoinduced magnetic transition in an itinerant magnet described by the double-exchange model, in which conduction electrons couple with localized spins through the ferromagnetic (FM) Hund coupling. It is shown that intense light applied to the FM ground state induces an antiferromagnetic (AFM) order, in contrast to the AFM-to-FM transition due to the photocarrier injection. In particular, we focus on the mechanism for instability of the FM structure by the light irradiation. The magnon spectrum in the Floquet state is formulated on the basis of the perturbative expansion of the Floquet Green’s function. The magnon dispersion shows softening at momentum (π, π ) in the square lattice with increasing the light amplitude, implying photoinduced AFM instability. This result is mainly attributed to a nonequilibrium electron distribution, which promotes low-energy Stoner excitations. The transient optical conductivity spectra characterized by interband excitations and Floquet sidepeaks are available to identify the photoinduced AFM state.
关键词： photoinduced magnetic transition,magnon spectrum,double-exchange model,itinerant magnet,optical conductivity,Floquet state
更新于2025-09-04 15:30:14
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Revision of the Sun’s Spectral Irradiance as Measured by SORCE SIM
摘要： The Spectral Irradiance Monitor (SIM) instrument on board the Solar Radiation and Climate Experiment (SORCE) performs daily measurements of the solar spectral irradiance (SSI) from 200 to 2400 nm. Both temporal and spectral corrections for instrument degradation have been built on physical models based on comparison of two independent channels with different solar exposure. The present study derives a novel correction for SIM degradation using the total solar irradiance (TSI) measurements from the Total Irradiance Monitor (TIM) on SORCE. The correction is applied to SIM SSI data from September 2004 to October 2012 over the wavelength range from 205 nm to 2300 nm. The change in corrected, integrated SSI agrees within 0.1 W m?2 (1σ ) with SORCE TIM TSI and independently shows agreement with the SATIRE-S and NRLSSI2 solar models within measurement uncertainties.
关键词： Solar spectral irradiance,Degradation correction,Solar spectrum,Solar variability,Solar cycle
更新于2025-09-04 15:30:14
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Systematic analysis of the fine structure of energy level structures and spin-Hamiltonian parameters of V3+ ion in corundum with dynamic Jahn-Teller effect
摘要： Systematic analysis of fine structure of the whole energy levels and spin-Hamiltonian parameters ( zero-field splitting (ZFS) parameter D and g-factors g// and g?) for the ground state 3A2 ( 3T1 ) of V3+ ion in corundum are presented in detail with complete diagonalization method (CDM) of 45×45 energy matrix, in which the full configuration interactions are taken in account . The reduction of the splittings of excited electronic 3T2 ( t2ge ) term with orbital triplet degenerate caused by spin-orbit (SO) and lower trigonal crystal field (CF) is studied by T2?e model dynamic Jahn-Teller theory, and Ham deduction factor , the Jahn-Teller energy EJT and Huang-Rhys factor S are estimated. The studies are performed within the strong-field scheme with molecular orbit (MO) approximation, in which the two SO coupling parameter model is used and the SO contributions from both the central 3d ion and ligands are taken in account.The calculated results are in good agreement with the experimental data, and the local structure of [VO6]9- cluster with C3 point group symmetry are determined quantitatively.
关键词： Dynamic Jahn-Teller effect,Electron paramagnetic resonance,V3+ ion,Optical spectrum,Complete diagonalization method
更新于2025-09-04 15:30:14
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Quantum and spectral properties of the Labyrinth model
摘要： We consider the Labyrinth model, which is a two-dimensional quasicrystal model. We show that the spectrum of this model, which is known to be a product of two Cantor sets, is an interval for small values of the coupling constant. We also consider the density of states measure of the Labyrinth model and show that it is absolutely continuous with respect to Lebesgue measure for almost all values of coupling constants in the small coupling regime.
关键词： coupling constant,density of states measure,quasicrystal,Labyrinth model,spectrum
更新于2025-09-04 15:30:14
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Current‐Enhanced Broadband THz Emission from Spintronic Devices
摘要： An ultra-broadband terahertz (THz) emitter covering a wide range of frequencies from 0.1 to 10 THz is highly desired for spectroscopy applications. So far, spintronic THz emitters have been proven as one class of efficient THz sources with a broadband spectrum while the performance in the lower THz frequency range (0.1–0.5 THz) limits its applications. In this work, a novel concept of a current-enhanced broad spectrum from spintronic THz emitters combined with semiconductor materials is demonstrated. A 2–3 order enhancement of the THz signals in a lower THz frequency range (0.1–0.5 THz) is observed, in addition to a comparable performance at higher frequencies from this hybrid emitter. With a bias current, there is a photoconduction contribution from semiconductor materials, which can be constructively interfered with the THz signals generated from the magnetic heterostructures driven by the inverse spin Hall effect (ISHE). These findings push forward the utilization of metallic heterostructure-based THz emitters on the ultra-broadband THz emission spectroscopy.
关键词： spintronic devices,broadband spectrum,photoconduction,terahertz emitters
更新于2025-09-04 15:30:14
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Renormalized Spectrum of Three-Level Localized Quasiparticle Interacting with Polarization Phonons at Cryogenic Temperature
摘要： Based on the generalized method of Feynman–Pines diagram technique, a new method of calculation of the mass operator in the Fourier image of Green’s function is proposed for the system of a three-level localized quasiparticle interacting with polarization phonons at T = 0 K. The revealed main class of diagrams gives the opportunity to write the renormalized mass operator in a form of continuous branch chain fraction with typical links. Such presentation allows effective accounting of multi-phonon processes. It is shown that the renormalized energy spectrum contains the complexes of bound-to-phonon states of the quasiparticle. These complexes essentially differ for the resonant and non-resonant systems.
关键词： Spectrum,Quasiparticle,Phonon,Mass operator,Green’s function
更新于2025-09-04 15:30:14