Anthropogenic climate change is altering species distributions globally.While species distributions are expected to shift to higher latitudes and elevations under global warming,empirical evidence on distribution shif...Anthropogenic climate change is altering species distributions globally.While species distributions are expected to shift to higher latitudes and elevations under global warming,empirical evidence on distribution shifts is mixed,and factors mediating the direction and magnitude of range shifts remain unclear.Using a dataset of 132new provincial records for 96 resident bird species from 2000 to 2023,we measured geographic distance,latitudinal shift,and temperature shift from each new record to the historical range for each species to test for poleward shifts.We assessed taxonomic variation in the magnitude of range shifts and used phylogenetic generalized linear mixed models to quantify relationships between species traits and the extent of range shifts.Our results revealed that new records occurred at a mean geographic distance of 420 km from historical ranges,with mean latitudinal shifts of+1.68°(poleward)and temperature shifts of-1.33℃(toward colder climates).The magnitude of geographic range shifts was strongly constrained by phylogenetic relatedness.Habitat breadth,habitat openness,and centroid latitude of historical ranges emerged as significant predictors of range shifts.Our results suggest that resident bird species'geographic ranges in China are shifting poleward,but the magnitude of these shifts is non-random across lineages.Species with broader habitat preferences and those from warmer climates are more likely to shift farther from their historical ranges and toward higher latitudes.This study emphasizes taxonomic variation in species range shifts and highlights the need for species-and site-specific conservation strategies under global warming.展开更多
The Tibetan Plateau(TP),known as the“Third Pole of Earth”,and its ecosystem is quite sensitive to climate change(Yao et al.,2012;Qiu,2008).In recent decades,the main TP has experienced warming and humidification(alt...The Tibetan Plateau(TP),known as the“Third Pole of Earth”,and its ecosystem is quite sensitive to climate change(Yao et al.,2012;Qiu,2008).In recent decades,the main TP has experienced warming and humidification(although there has been a drying trend in the southern region),and researchers anticipate that this change will continue in the future(Jiang et al.,2023;Sun et al.,2020;Chen et al.,2015).展开更多
Standard perturbation theory is employed to calculate the mass shifts of the 2^(1)S_(0)-^(3)S_(1)and 2^(3)S_(1)-2^(3)P_(J)transitions for^(4,6,8)He.High-precision results are obtained for the mass shifts in the isotop...Standard perturbation theory is employed to calculate the mass shifts of the 2^(1)S_(0)-^(3)S_(1)and 2^(3)S_(1)-2^(3)P_(J)transitions for^(4,6,8)He.High-precision results are obtained for the mass shifts in the isotope pairs 6He-4He and 8He-4He,with uncertainties below 1 part per million(ppm).Our analysis provides a complete set of isotope-shift results and systematically examines their sensitivity to nuclear charge-radius differences.Once experimental measurements reach a precision comparable to that of the calculated mass shifts,the squared differences of nuclear charge radii can be determined with an accuracy of approximately 0.4%-0.6%,representing an order-of-magnitude improvement over current values.展开更多
Fifty-three samples of multi-substituted benzylideneanilines XArCH=NArYs （abbreviated XBAYs） were synthesized and their NMR spectra were determined. An extensional study of substituent effects on the 1H NMR chemical...Fifty-three samples of multi-substituted benzylideneanilines XArCH=NArYs （abbreviated XBAYs） were synthesized and their NMR spectra were determined. An extensional study of substituent effects on the 1H NMR chemical shifts （δH（CH=N）） and 13C NMR chemical shifts （δc（CH=N）） of the CH=N bridging group from di-substituted to multi-substituted XBAYs was made based on a total of 182 samples of XBAYs, together with the NMR data of other 129 samples of di-substituted XBAYs quoted from literatures. The results show thatthe substituent specific cross-interaction effect parameter （△（∑σ）2） plays an important role in quantifying the δc（CH=N） values of XBAYs, but it is negligible for quantifying the δH （CH=N） values; the other substituent parameters also present different influences on the δc （CH=N） and （δH （CH=N）. On the whole, the contributions of X and Y to the δc （CH=N） of XBAYs are balanced, but the δH（CH=N） values of XBAYs mainly rely on the contributions of X.展开更多
The Doppler-limited absorption spectra of ^14N and ^15N atoms were measured around 800 nm using concentration modulation spectroscopy to study their isotope shifts. The nitrogen atoms were generated by discharging mol...The Doppler-limited absorption spectra of ^14N and ^15N atoms were measured around 800 nm using concentration modulation spectroscopy to study their isotope shifts. The nitrogen atoms were generated by discharging molecular nitrogen buffered with helium in a homemade discharge tube. The isotope shifts of four multiplets （3s^4PJ→3p^4D^oJ, 3s^4PJ→3p^4P^oJ, 3s^2DJ→5s^2P^oJ, and 3p^2P^oJ→5s^2D^oJ） were measured and their J-dependent specific mass shifts were observed and discussed.展开更多
The transition energies of the 1s^(2)2s^(2)S_(1/2)→1s^(2)2p^(2)p_(1/2,3/2)transitions in Li-like Th87+ions were calculated by combining the multi-configuration Dirac-Hartree-Fock(MCDHF)method with the model-quantum e...The transition energies of the 1s^(2)2s^(2)S_(1/2)→1s^(2)2p^(2)p_(1/2,3/2)transitions in Li-like Th87+ions were calculated by combining the multi-configuration Dirac-Hartree-Fock(MCDHF)method with the model-quantum electrodynamics(modelQED)approach.The effects of electron correlation,Breit interaction,and QED effects were analyzed in detail.The isotope shifts,including the mass shifts and field shifts,due to the 2s2S_(1/2)→2p^(2)P_(1/2,3/2)transitions were then calculated using two different methods,namely,the MCDHF method and the finite-field method.The results show that these two methods are in excellent agreement.展开更多
According to the 2024 China Marine Economy Statistical Bulletin(hereinafter“the Bulletin”),China’s marine economy surpassed the 10 trillion yuan(US$1.38 trillion)mark for the first time in 2024,0.9 percentage point...According to the 2024 China Marine Economy Statistical Bulletin(hereinafter“the Bulletin”),China’s marine economy surpassed the 10 trillion yuan(US$1.38 trillion)mark for the first time in 2024,0.9 percentage points higher than the growth rate of the national GDP.展开更多
We investigate theoretically the effects of chirped laser pulses on high-order harmonic generation(HHG)from solids.We find that the harmonic spectra display redshifts for the driving laser pulses with negative chirp a...We investigate theoretically the effects of chirped laser pulses on high-order harmonic generation(HHG)from solids.We find that the harmonic spectra display redshifts for the driving laser pulses with negative chirp and blueshifts for those with positive chirp,which is due to the change in the instantaneous frequency of the driving laser for different chirped pulses.The analysis of crystal-momentum-resolved(k-resolved)HHG reveals that the frequency shifts are equal for the harmonics generated by different crystal momentum channels.The frequency shifts in the cutoff region are larger than those in the plateau region.With the increase of the absolute value of the chirp parameters,the frequency shifts of HHG become more significant,leading to the shifts from odd-to even-order harmonics.We also demonstrate that the frequency shifts of harmonic spectra are related to the duration of the chirped laser field,but are insensitive to the laser intensity and dephasing time.展开更多
We propose a novel approach for investigating the tunable Goos–H?nchen(GH)shift via an all-dielectric metasurface that incorporates phase change materials(PCMs).By introducing material asymmetry through the reconfigu...We propose a novel approach for investigating the tunable Goos–H?nchen(GH)shift via an all-dielectric metasurface that incorporates phase change materials(PCMs).By introducing material asymmetry through the reconfigurable characteristic of PCMs while maintaining fixed geometric parameters,we can achieve tunable dual quasi-bound states in the continuum with ultrahigh quality factors(Q factors).Enabled by such tunable dual modes with significant phase changes,the PCM-based metasurface exhibits giant-tunable bidirectional GH shifts compared to conventional metasurfaces.Notably,the GH shift exhibits multidimensional tunability,including PCM-driven switching(amorphous to crystalline),incident-angle dependence(θ),and wavelength selectivity(λ).The maximum observed shift reaches approximately 104 wavelengths,accompanied by a corresponding Q factor of 107.Our work demonstrates its potential for applications in ultrahigh-precision multifunctional devices,from biosensing to reconfigurable nanophotonic switches.展开更多
The complete characterizations of the spectra and their various parts of hyponormal unilateral and bilateral weighted shifts are presented respectively in this paper. The results obtained here generalize the correspon...The complete characterizations of the spectra and their various parts of hyponormal unilateral and bilateral weighted shifts are presented respectively in this paper. The results obtained here generalize the corresponding work of the references.展开更多
The special mass shift coefficient and field parameter factor of four multiples,3s^4P→3p4P°,3s^4P→3p^4D°,3s^2D→5p^2D°,and 3s^2P→3p^2P°,of ^14N and ^15N were studied using the multi-configuratio...The special mass shift coefficient and field parameter factor of four multiples,3s^4P→3p4P°,3s^4P→3p^4D°,3s^2D→5p^2D°,and 3s^2P→3p^2P°,of ^14N and ^15N were studied using the multi-configuration Dirac-Hartree-Fock method and the relativistic configuration interaction approach.The normal mass shifts,special mass shifts,field shifts,and isotope shifts of N(I)were derived from the theoretical calculated normal mass shift parameter,special mass shift parameter and field parameter factor,and compared with the reported experimental measurements and theoretical results.展开更多
Study results in this paper have indicated that the Holocene climate in Xinjiang, Northwestem China has been alternating between wet and dry conditions, and was punctuated with a series of abrupt climate shifts. A sed...Study results in this paper have indicated that the Holocene climate in Xinjiang, Northwestem China has been alternating between wet and dry conditions, and was punctuated with a series of abrupt climate shifts. A sediment core taken from Barkol Lake in the northern Xinjiang of Northwest China was analyzed at 1 cm interval for grain-size distribution. Abrupt climate shifts revealed by the grain-size proxy occurred at ca 1.4, 3.0, 4.3, 5.6, 8.0 cal kyr B.E, which were well correlated to both the abrupt shifts recorded in the North Atlantic Ocean （NAO） and the Holocene sea surface temperature （SST） cooling events in the Arabian Ocean. The correlation indicated that the climatic changes in the extreme arid Northwest China were associated with the NAO, probably via the North Atlantic Oscillation-affected westerly winds. The strength and position of westerly winds probably modulated the Siberian-Mongolian high- pressure system （winter monsoon）, and played an important role in climate change of Northwest China. Moreover, an evident drought interval during the middle Holocene was also revealed by grain-size proxy.展开更多
In this article, we mainly devote to proving uniqueness results for entire functionssharing one small function CM with their shift and difference operator simultaneously. Letf（z） be a nonconstant entire function of ...In this article, we mainly devote to proving uniqueness results for entire functionssharing one small function CM with their shift and difference operator simultaneously. Letf（z） be a nonconstant entire function of finite order, c be a nonzero finite complex constant, and n be a positive integer. If f（z）, f（z＋c）, and △n cf（z） share 0 CM, then f（z＋c）≡Af（z）, where A（≠0） is a complex constant. Moreover, let a（z）, b（z）（ O） ∈ S（f） be periodic entire functions with period c and if f（z） - a（z）, f（z ＋ c） - a（z）, △cn f（z） - b（z） share 0 CM, then f（z ＋ c） ≡ f（z）.展开更多
Reconfigurable intelligent surface(RIS)for wireless networks have drawn lots of attention in both academic and industry communities.RIS can dynamically control the phases of the reflection elements to send the signal ...Reconfigurable intelligent surface(RIS)for wireless networks have drawn lots of attention in both academic and industry communities.RIS can dynamically control the phases of the reflection elements to send the signal in the desired direction,thus it provides supplementary links for wireless networks.Most of prior works on RIS-aided wireless communication systems consider continuous phase shifts,but phase shifts of RIS are discrete in practical hardware.Thus we focus on the actual discrete phase shifts on RIS in this paper.Using the advanced deep reinforcement learning(DRL),we jointly optimize the transmit beamforming matrix from the discrete Fourier transform(DFT)codebook at the base station(BS)and the discrete phase shifts at the RIS to maximize the received signal-to-interference plus noise ratio(SINR).Unlike the traditional schemes usually using alternate optimization methods to solve the transmit beamforming and phase shifts,the DRL algorithm proposed in the paper can jointly design the transmit beamforming and phase shifts as the output of the DRL neural network.Numerical results indicate that the DRL proposed can dispose the complicated optimization problem with low computational complexity.展开更多
Age and body size can influence predation risk and hence habitat use. Many species undergo ontogenetic shifts in habitat use as individuals grow larger and have different age-specific predation pressures. On coral ree...Age and body size can influence predation risk and hence habitat use. Many species undergo ontogenetic shifts in habitat use as individuals grow larger and have different age-specific predation pressures. On coral reefs, a number of fish species are more tolerant of threats in structurally complex habitats that contain more refuges than in less structurally complex habitats. However, we do not know how risk perception varies with age, and whether age interacts with habitat complexity. Adults and juveniles, because of their size, may face different risks in structurally simple versus complex habitats. We used flight initiation distanee as a metric to analyze perceptions of risk in a species of damselfish Stegastes nigricans. All else being equal, fish fleeing at greater distances are inferred to perceive higher risk. We targeted juvenile and adult damselfish to assess whether there are ontogenetic shifts in perceptions of safety in relation to structural complexity, inferred based on percent coral cover and rugosity. We found that adult damselfish tolerated closer approach in more complex habitats as measured by percent coral cover, but not rugosity, whereas juvenile fish always allowed closer approach than adult fish regardless of complexity. This ontogenetic shift in habitat use may result from juvenile fish taking bigger risks to maximize growth, whereas older animals, who are closer to their maximum body size, can afford to take fewer risks and protect their assets.展开更多
After the geometry optimization at B3LYP/6-31＋G（d,p） level,the NMR calcula-tions of a series of fluorenone analogues have been carried out by GIAO method at HF/6-31＋G（d） level and B3LYP/6-311G＋（2d,p） level,re...After the geometry optimization at B3LYP/6-31＋G（d,p） level,the NMR calcula-tions of a series of fluorenone analogues have been carried out by GIAO method at HF/6-31＋G（d） level and B3LYP/6-311G＋（2d,p） level,respectively.The 13C NMR chemical shifts calculated at HF/6-31＋G（d） level show better agreement with the observed values.By a series of linear correction equations （δpred=a ＋ bδcalc）,accurate prediction of 13C chemical shifts was achieved for the new fluorenone compound.The linear correlation of δpred with δexptl is excellent,and the square of correlation coefficient,r2,is up to 0.994.The maximum absolute difference between δpred and δexptl,Δδ,is 4.6 ppm,and the root-mean-square error between δpred and δexptl is only 2.6 ppm.展开更多
Quantum chemical calculations on some possible equilibrium geometries of C24O2 isomers derived from C24 （D6） and C24O have been performed using density functional theory （DFT） method. The geometric and electronic ...Quantum chemical calculations on some possible equilibrium geometries of C24O2 isomers derived from C24 （D6） and C24O have been performed using density functional theory （DFT） method. The geometric and electronic structures as well as the relative energies and thermal stabilities of various C24O2 isomers at the ground state have been calculated at the B3LYP/6-31G（d） level of theory. And the 1,4,2,5-C24O2 isomer was found to be the most stable geometry where two oxygen atoms were added to the longest carbon-carbon bonds in the same pentagon from a thermodynamic point of view. Based on the optimized neutral geometries, the vertical ionization potential and vertical electron affinity have been obtained. Meanwhile, the vibrational frequencies, IR spectrum, and 13C chemical shifts of various C24O2 isomers have been calculated and analyzed.展开更多
Frequency shifts of the acetylene saturated absorption lines at 1.5μm with temperature, gas pressure and laser power have been investigated in detail. The second-order Doppler effect, the recoil effect, the Zeeman ef...Frequency shifts of the acetylene saturated absorption lines at 1.5μm with temperature, gas pressure and laser power have been investigated in detail. The second-order Doppler effect, the recoil effect, the Zeeman effect, the pressure shift and the power shift are taken into consideration. The magnitudes of those shifts caused by various effects are evaluated. In order to reproduce the stability of 5.7 × 10^-14 obtained by Edwards, all necessary conditions are given. The results show that when there is a larger external magnetic field, the Zeeman shift could not be neglected, so that the shield should be employed. And the design of a long cavity is advantageous to reduce the influence of the second-order Doppler effect. The results also show that at least 4-2.5℃ temperature control for cavity can effectively prevent several effects and improve the frequency stability.展开更多
The total ionizing dose(TID) effect is a key cause for the degradation/failure of semiconductor device performance under energetic-particle irradiation. We developed a dynamic model of mobile particles and defects by ...The total ionizing dose(TID) effect is a key cause for the degradation/failure of semiconductor device performance under energetic-particle irradiation. We developed a dynamic model of mobile particles and defects by solving the rate equations and Poisson's equation simultaneously, to understand threshold voltage shifts induced by TID in silicon-based metal–oxide–semiconductor(MOS) devices. The calculated charged defect distribution and corresponding electric field under different TIDs are consistent with experiments. TID changes the electric field at the Si/SiO_(2) interface by inducing the accumulation of oxide charged defects nearby, thus shifting the threshold voltage accordingly. With increasing TID, the oxide charged defects increase to saturation, and the electric field increases following the universal 2/3 power law. Through analyzing the influence of TID on the interfacial electric field by different factors, we recommend that the radiation-hardened performance of devices can be improved by choosing a thin oxide layer with high permittivity and under high gate voltages.展开更多
基金supported by grants from the National Natural Science Foundation of China(Grant No.32271733)Guangdong Basic and Applied Basic Research Foundation(Grant No.2023A1515011045)+1 种基金Science and Technology Projects in Guangzhou(Grant No.2023A04J0121)SCNU Training Program of Innovation for Undergraduates,China。
文摘Anthropogenic climate change is altering species distributions globally.While species distributions are expected to shift to higher latitudes and elevations under global warming,empirical evidence on distribution shifts is mixed,and factors mediating the direction and magnitude of range shifts remain unclear.Using a dataset of 132new provincial records for 96 resident bird species from 2000 to 2023,we measured geographic distance,latitudinal shift,and temperature shift from each new record to the historical range for each species to test for poleward shifts.We assessed taxonomic variation in the magnitude of range shifts and used phylogenetic generalized linear mixed models to quantify relationships between species traits and the extent of range shifts.Our results revealed that new records occurred at a mean geographic distance of 420 km from historical ranges,with mean latitudinal shifts of+1.68°(poleward)and temperature shifts of-1.33℃(toward colder climates).The magnitude of geographic range shifts was strongly constrained by phylogenetic relatedness.Habitat breadth,habitat openness,and centroid latitude of historical ranges emerged as significant predictors of range shifts.Our results suggest that resident bird species'geographic ranges in China are shifting poleward,but the magnitude of these shifts is non-random across lineages.Species with broader habitat preferences and those from warmer climates are more likely to shift farther from their historical ranges and toward higher latitudes.This study emphasizes taxonomic variation in species range shifts and highlights the need for species-and site-specific conservation strategies under global warming.
基金supported by the Basic Science Center for Tibetan Plateau Earth System(No.41988101)the Science and Technology Plan Project of the Xizang Autonomous Region(No.XZ202201ZD0005G01)。
文摘The Tibetan Plateau(TP),known as the“Third Pole of Earth”,and its ecosystem is quite sensitive to climate change(Yao et al.,2012;Qiu,2008).In recent decades,the main TP has experienced warming and humidification(although there has been a drying trend in the southern region),and researchers anticipate that this change will continue in the future(Jiang et al.,2023;Sun et al.,2020;Chen et al.,2015).
基金supported by the National Natural Science Foundation of China(Grant Nos.12204412,12274423,12174402,12393821,and 12004124)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant Nos.XDB0920100 and XDB0920101)support from the Natural Sciences and Engineering Research Council of Canada.All calculations were performed on the APM-Theoretical Computing Cluster(APM-TCC).
文摘Standard perturbation theory is employed to calculate the mass shifts of the 2^(1)S_(0)-^(3)S_(1)and 2^(3)S_(1)-2^(3)P_(J)transitions for^(4,6,8)He.High-precision results are obtained for the mass shifts in the isotope pairs 6He-4He and 8He-4He,with uncertainties below 1 part per million(ppm).Our analysis provides a complete set of isotope-shift results and systematically examines their sensitivity to nuclear charge-radius differences.Once experimental measurements reach a precision comparable to that of the calculated mass shifts,the squared differences of nuclear charge radii can be determined with an accuracy of approximately 0.4%-0.6%,representing an order-of-magnitude improvement over current values.
基金supported by the National Natural Science Foundation of China(No.21672058 and No.21272063)
文摘Fifty-three samples of multi-substituted benzylideneanilines XArCH=NArYs （abbreviated XBAYs） were synthesized and their NMR spectra were determined. An extensional study of substituent effects on the 1H NMR chemical shifts （δH（CH=N）） and 13C NMR chemical shifts （δc（CH=N）） of the CH=N bridging group from di-substituted to multi-substituted XBAYs was made based on a total of 182 samples of XBAYs, together with the NMR data of other 129 samples of di-substituted XBAYs quoted from literatures. The results show thatthe substituent specific cross-interaction effect parameter （△（∑σ）2） plays an important role in quantifying the δc（CH=N） values of XBAYs, but it is negligible for quantifying the δH （CH=N） values; the other substituent parameters also present different influences on the δc （CH=N） and （δH （CH=N）. On the whole, the contributions of X and Y to the δc （CH=N） of XBAYs are balanced, but the δH（CH=N） values of XBAYs mainly rely on the contributions of X.
文摘The Doppler-limited absorption spectra of ^14N and ^15N atoms were measured around 800 nm using concentration modulation spectroscopy to study their isotope shifts. The nitrogen atoms were generated by discharging molecular nitrogen buffered with helium in a homemade discharge tube. The isotope shifts of four multiplets （3s^4PJ→3p^4D^oJ, 3s^4PJ→3p^4P^oJ, 3s^2DJ→5s^2P^oJ, and 3p^2P^oJ→5s^2D^oJ） were measured and their J-dependent specific mass shifts were observed and discussed.
基金Project supported by the National Key Research and Development Program of China(Grant No.2022YFA1602500)the National Natural Science Foundation of China(Grant Nos.1236040286,12474250,12174316,12464036,and12404306)+1 种基金the Young Teachers Scientific Research Ability Promotion Plan of Northwest Normal University(Grant No.NWNU-LKQN2020-10)the Funds for Innovative Fundamental Research Group Project of Gansu Province(Grant No.20JR5RA541)。
文摘The transition energies of the 1s^(2)2s^(2)S_(1/2)→1s^(2)2p^(2)p_(1/2,3/2)transitions in Li-like Th87+ions were calculated by combining the multi-configuration Dirac-Hartree-Fock(MCDHF)method with the model-quantum electrodynamics(modelQED)approach.The effects of electron correlation,Breit interaction,and QED effects were analyzed in detail.The isotope shifts,including the mass shifts and field shifts,due to the 2s2S_(1/2)→2p^(2)P_(1/2,3/2)transitions were then calculated using two different methods,namely,the MCDHF method and the finite-field method.The results show that these two methods are in excellent agreement.
文摘According to the 2024 China Marine Economy Statistical Bulletin(hereinafter“the Bulletin”),China’s marine economy surpassed the 10 trillion yuan(US$1.38 trillion)mark for the first time in 2024,0.9 percentage points higher than the growth rate of the national GDP.
基金Project supported by the Natural Science Foundation of Jilin Province of China(Grant No.20230101014JC)the National Natural Science Foundation of China(Grant No.12374265)。
文摘We investigate theoretically the effects of chirped laser pulses on high-order harmonic generation(HHG)from solids.We find that the harmonic spectra display redshifts for the driving laser pulses with negative chirp and blueshifts for those with positive chirp,which is due to the change in the instantaneous frequency of the driving laser for different chirped pulses.The analysis of crystal-momentum-resolved(k-resolved)HHG reveals that the frequency shifts are equal for the harmonics generated by different crystal momentum channels.The frequency shifts in the cutoff region are larger than those in the plateau region.With the increase of the absolute value of the chirp parameters,the frequency shifts of HHG become more significant,leading to the shifts from odd-to even-order harmonics.We also demonstrate that the frequency shifts of harmonic spectra are related to the duration of the chirped laser field,but are insensitive to the laser intensity and dephasing time.
基金Project supported by the National Natural Science Foundation of China(Grant No.12274225)the Fundamental Research Funds for the Central Universities(Grant No.NS2023056)+1 种基金the Natural Science Foundation of Hebei Province,China(Grant No.B2024209014)the Basic Scientific Research Project of Hebei Provincial Department of Education(Grant No.JJC2024059)。
文摘We propose a novel approach for investigating the tunable Goos–H?nchen(GH)shift via an all-dielectric metasurface that incorporates phase change materials(PCMs).By introducing material asymmetry through the reconfigurable characteristic of PCMs while maintaining fixed geometric parameters,we can achieve tunable dual quasi-bound states in the continuum with ultrahigh quality factors(Q factors).Enabled by such tunable dual modes with significant phase changes,the PCM-based metasurface exhibits giant-tunable bidirectional GH shifts compared to conventional metasurfaces.Notably,the GH shift exhibits multidimensional tunability,including PCM-driven switching(amorphous to crystalline),incident-angle dependence(θ),and wavelength selectivity(λ).The maximum observed shift reaches approximately 104 wavelengths,accompanied by a corresponding Q factor of 107.Our work demonstrates its potential for applications in ultrahigh-precision multifunctional devices,from biosensing to reconfigurable nanophotonic switches.
文摘The complete characterizations of the spectra and their various parts of hyponormal unilateral and bilateral weighted shifts are presented respectively in this paper. The results obtained here generalize the corresponding work of the references.
基金supported by the National Natural Science Foundation of China(No.11674096,No.11874151,and No.11834003)Shanghai Pujiang Talents Plan(No.18PJ1403100).
文摘The special mass shift coefficient and field parameter factor of four multiples,3s^4P→3p4P°,3s^4P→3p^4D°,3s^2D→5p^2D°,and 3s^2P→3p^2P°,of ^14N and ^15N were studied using the multi-configuration Dirac-Hartree-Fock method and the relativistic configuration interaction approach.The normal mass shifts,special mass shifts,field shifts,and isotope shifts of N(I)were derived from the theoretical calculated normal mass shift parameter,special mass shift parameter and field parameter factor,and compared with the reported experimental measurements and theoretical results.
基金Under the auspices of National Natural Science Foundation of China (No. 49761007)Open Foundation of National Laboratory of Western China’s Environmental Systems,Lanzhou University
文摘Study results in this paper have indicated that the Holocene climate in Xinjiang, Northwestem China has been alternating between wet and dry conditions, and was punctuated with a series of abrupt climate shifts. A sediment core taken from Barkol Lake in the northern Xinjiang of Northwest China was analyzed at 1 cm interval for grain-size distribution. Abrupt climate shifts revealed by the grain-size proxy occurred at ca 1.4, 3.0, 4.3, 5.6, 8.0 cal kyr B.E, which were well correlated to both the abrupt shifts recorded in the North Atlantic Ocean （NAO） and the Holocene sea surface temperature （SST） cooling events in the Arabian Ocean. The correlation indicated that the climatic changes in the extreme arid Northwest China were associated with the NAO, probably via the North Atlantic Oscillation-affected westerly winds. The strength and position of westerly winds probably modulated the Siberian-Mongolian high- pressure system （winter monsoon）, and played an important role in climate change of Northwest China. Moreover, an evident drought interval during the middle Holocene was also revealed by grain-size proxy.
基金supported by the Natural Science Foundation of Guangdong Province in China(2014A030313422,2016A030310106,2016A030313745)
文摘In this article, we mainly devote to proving uniqueness results for entire functionssharing one small function CM with their shift and difference operator simultaneously. Letf（z） be a nonconstant entire function of finite order, c be a nonzero finite complex constant, and n be a positive integer. If f（z）, f（z＋c）, and △n cf（z） share 0 CM, then f（z＋c）≡Af（z）, where A（≠0） is a complex constant. Moreover, let a（z）, b（z）（ O） ∈ S（f） be periodic entire functions with period c and if f（z） - a（z）, f（z ＋ c） - a（z）, △cn f（z） - b（z） share 0 CM, then f（z ＋ c） ≡ f（z）.
文摘Reconfigurable intelligent surface(RIS)for wireless networks have drawn lots of attention in both academic and industry communities.RIS can dynamically control the phases of the reflection elements to send the signal in the desired direction,thus it provides supplementary links for wireless networks.Most of prior works on RIS-aided wireless communication systems consider continuous phase shifts,but phase shifts of RIS are discrete in practical hardware.Thus we focus on the actual discrete phase shifts on RIS in this paper.Using the advanced deep reinforcement learning(DRL),we jointly optimize the transmit beamforming matrix from the discrete Fourier transform(DFT)codebook at the base station(BS)and the discrete phase shifts at the RIS to maximize the received signal-to-interference plus noise ratio(SINR).Unlike the traditional schemes usually using alternate optimization methods to solve the transmit beamforming and phase shifts,the DRL algorithm proposed in the paper can jointly design the transmit beamforming and phase shifts as the output of the DRL neural network.Numerical results indicate that the DRL proposed can dispose the complicated optimization problem with low computational complexity.
文摘Age and body size can influence predation risk and hence habitat use. Many species undergo ontogenetic shifts in habitat use as individuals grow larger and have different age-specific predation pressures. On coral reefs, a number of fish species are more tolerant of threats in structurally complex habitats that contain more refuges than in less structurally complex habitats. However, we do not know how risk perception varies with age, and whether age interacts with habitat complexity. Adults and juveniles, because of their size, may face different risks in structurally simple versus complex habitats. We used flight initiation distanee as a metric to analyze perceptions of risk in a species of damselfish Stegastes nigricans. All else being equal, fish fleeing at greater distances are inferred to perceive higher risk. We targeted juvenile and adult damselfish to assess whether there are ontogenetic shifts in perceptions of safety in relation to structural complexity, inferred based on percent coral cover and rugosity. We found that adult damselfish tolerated closer approach in more complex habitats as measured by percent coral cover, but not rugosity, whereas juvenile fish always allowed closer approach than adult fish regardless of complexity. This ontogenetic shift in habitat use may result from juvenile fish taking bigger risks to maximize growth, whereas older animals, who are closer to their maximum body size, can afford to take fewer risks and protect their assets.
文摘After the geometry optimization at B3LYP/6-31＋G（d,p） level,the NMR calcula-tions of a series of fluorenone analogues have been carried out by GIAO method at HF/6-31＋G（d） level and B3LYP/6-311G＋（2d,p） level,respectively.The 13C NMR chemical shifts calculated at HF/6-31＋G（d） level show better agreement with the observed values.By a series of linear correction equations （δpred=a ＋ bδcalc）,accurate prediction of 13C chemical shifts was achieved for the new fluorenone compound.The linear correlation of δpred with δexptl is excellent,and the square of correlation coefficient,r2,is up to 0.994.The maximum absolute difference between δpred and δexptl,Δδ,is 4.6 ppm,and the root-mean-square error between δpred and δexptl is only 2.6 ppm.
文摘Quantum chemical calculations on some possible equilibrium geometries of C24O2 isomers derived from C24 （D6） and C24O have been performed using density functional theory （DFT） method. The geometric and electronic structures as well as the relative energies and thermal stabilities of various C24O2 isomers at the ground state have been calculated at the B3LYP/6-31G（d） level of theory. And the 1,4,2,5-C24O2 isomer was found to be the most stable geometry where two oxygen atoms were added to the longest carbon-carbon bonds in the same pentagon from a thermodynamic point of view. Based on the optimized neutral geometries, the vertical ionization potential and vertical electron affinity have been obtained. Meanwhile, the vibrational frequencies, IR spectrum, and 13C chemical shifts of various C24O2 isomers have been calculated and analyzed.
基金Project supported by the Provincial Natural Science Funds of Shanxi Province, China (Grant No 20041037)the Industrial R&D Programme of Shanxi Province, China (Grant No 2006031118-04)
文摘Frequency shifts of the acetylene saturated absorption lines at 1.5μm with temperature, gas pressure and laser power have been investigated in detail. The second-order Doppler effect, the recoil effect, the Zeeman effect, the pressure shift and the power shift are taken into consideration. The magnitudes of those shifts caused by various effects are evaluated. In order to reproduce the stability of 5.7 × 10^-14 obtained by Edwards, all necessary conditions are given. The results show that when there is a larger external magnetic field, the Zeeman shift could not be neglected, so that the shield should be employed. And the design of a long cavity is advantageous to reduce the influence of the second-order Doppler effect. The results also show that at least 4-2.5℃ temperature control for cavity can effectively prevent several effects and improve the frequency stability.
基金Project supported by the Science Challenge Project of China (Grant No.TZ2018004)the National Natural Science Foundation of China (Grant Nos.11975018 and 11775254)+1 种基金the National MCF Energy R&D Program of China (Grant No.2018YEF0308100)the outstanding member of Youth Innovation Promotion Association CAS (Grant No.Y202087)。
文摘The total ionizing dose(TID) effect is a key cause for the degradation/failure of semiconductor device performance under energetic-particle irradiation. We developed a dynamic model of mobile particles and defects by solving the rate equations and Poisson's equation simultaneously, to understand threshold voltage shifts induced by TID in silicon-based metal–oxide–semiconductor(MOS) devices. The calculated charged defect distribution and corresponding electric field under different TIDs are consistent with experiments. TID changes the electric field at the Si/SiO_(2) interface by inducing the accumulation of oxide charged defects nearby, thus shifting the threshold voltage accordingly. With increasing TID, the oxide charged defects increase to saturation, and the electric field increases following the universal 2/3 power law. Through analyzing the influence of TID on the interfacial electric field by different factors, we recommend that the radiation-hardened performance of devices can be improved by choosing a thin oxide layer with high permittivity and under high gate voltages.
