As concepts closely related to microwave absorption properties,impedance matching and phase matching were rarely combined with material parameters to regulate properties and explore related mechanisms.In this work,red...As concepts closely related to microwave absorption properties,impedance matching and phase matching were rarely combined with material parameters to regulate properties and explore related mechanisms.In this work,reduction–diffusion method was innovatively applied to synthesize rare earth alloy Y_(2)Fe_(17).In order to regulate the electromagnetic parameters of absorbers,the Y_(2)Fe_(17)N_(3-δ)particles were coated with silica(Y_(2)Fe_(17)N_(3-δ)@SiO_(2))and absorbers with different volume fractions were prepared.The relationship between impedance matching,matching thickness,and the strongest reflection loss peak(RLmin)was presented obviously.Compared to the microwave absorption properties of Y_(2)Fe_(17)N_(3-δ)/PU absorber,Y_(2)Fe_(17)N_(3-δ)@SiO_(2)/PU absorbers are more conducive to the realization of microwave absorption material standards which are thin thickness,light weight,strong absorbing intensity,and broad bandwidth.Based on microwave frequency bands,the microwave absorption properties of the absorbers were analyzed and the related parameters were listed.As an important parameter related to perfect matching,reflection factor(√ε_(r)/μ_(r))was discussed combined with microwave amplitude attenuation.According to the origin and mathematical model of bandwidth,the formula of EAB(RL<-10 dB)was derived and simplified.The calculated bandwidths agreed well with experimental results.展开更多
We analyze the temperature dependence of the Raman intensity using the experimental data according to a power-law formula close to the order-disorder transition (Tc = 549 K) in NaNO 3. From this analysis, we extract t...We analyze the temperature dependence of the Raman intensity using the experimental data according to a power-law formula close to the order-disorder transition (Tc = 549 K) in NaNO 3. From this analysis, we extract the value of β = 0.26 as the critical exponent for the order parameter, which indicates a tricritical phase transition in this crystalline system. Using the temperature dependence of the order parameter, the Raman bandwidth is calculated at various temperatures in NaNO3. Our calculated bandwidths describe adequately the observed behaviour of the order-disorder transition in this crystal.展开更多
Perovskite LaCoO_(3)is of great potential in electromagnetic wave absorption considering its outstanding dielectric loss as well as the existing magnetic response with the magnetic doping.However,the dissipation mecha...Perovskite LaCoO_(3)is of great potential in electromagnetic wave absorption considering its outstanding dielectric loss as well as the existing magnetic response with the magnetic doping.However,the dissipation mechanism of the magnetic doping on the microwave absorption is lack of sufficient investigated.In this paper,LaCo_(1-x)Fe_(x)O_(3)(x=0,0.05,0.1,0.15,0.2,0.25,0.3,LCFOs)perovskites with different Fe doping amounts were prepared successfully by the sol-gel method and subsequent heat treatment in the air atmosphere.The structure characterization carried out by the frst-principles calculations shows the effect of Fe doping on the dielectric and magnetic properties of LCFOs and the strong hybridization of Co/Fe-3d with O-2p in the LCFOs system was successfully demonstrated.Particularly,when x=0.1 and the thickness is only 1.95 mm,the LaCo_(0.9)Fe_(0.1)O_(3)exhibits the best microwave absorption performance with the minimum reflection loss(RL)value of about-41 dB.The typical samples achieve a broad effective absorption bandwidth(EAB)of 5.16 GHz(7.92-13.08 GHz),which covers the total X band(8-12 GHz).Considering that,the especial Fe doping perovskite is promising to be a candidate as efficient microwave absorbers.展开更多
To investigate the modification effect of the B2O3 component on tellurite glass, a series of glasses with a composition of xB2O3-（80-x）TeO2-10ZnO-10Na20 （x = 0, 10, 20, 30, 40, 50, 60, 70, 80） and an additional am...To investigate the modification effect of the B2O3 component on tellurite glass, a series of glasses with a composition of xB2O3-（80-x）TeO2-10ZnO-10Na20 （x = 0, 10, 20, 30, 40, 50, 60, 70, 80） and an additional amount of 0.5% Er2Os（in molar） were prepared. The refractive index, the absorption edge of the host, the J-O parameters of Er^3＋ , the fluorescent decay time, the bandwidth, and the quantum efficiency for the 4Ⅰ13/2→4Ⅰ15/2 transition were obtained theoretically and experimentally. These results indicated that the introduction of B2O3 modified the performance of the tellurite glass. For example, with increasing content of B2O3, the refractive index of the host decreases from 1.9 to 1.5, the absorption edge of the host shifted toward the blue regime, the intensity parameter Ω6 changed from 1.08 × 10^-20（for the pure tellurite glass） to 1.98 ×10^-20 cm^2（for the pure borate glass）, the bandwidth of the 4Ⅰ13/2→4Ⅰ15/2 transition increased, and the quantum efficiency of the 4Ⅰ13/2→4Ⅰ15/2 transition decreased.展开更多
The Er^(3+)-doped TeO_2-WO_3-ZnO-ZnF_2(TWZOF) glasses were prepared. The absorption spectra, 1.5 μm emission spectra and fluorescence lifetimes of Er^(3+), excited at 970 nm, were measured. The J-O parameters Ω_ t (...The Er^(3+)-doped TeO_2-WO_3-ZnO-ZnF_2(TWZOF) glasses were prepared. The absorption spectra, 1.5 μm emission spectra and fluorescence lifetimes of Er^(3+), excited at 970 nm, were measured. The J-O parameters Ω_ t (t =2, 4, 6), absorption and emission cross-sections were calculated. The dependence of the 1.5 μm emission intensity, fluorescence lifetime and bandwidth of the Er^(3+) emission upon the contents of ZnF_2 in glass were investigated. In TWZOF glass, Er^(3+) ions had a broad emission profile around 1.5 μm with the maximum FWHM of 83 nm. With the increasing of the content of ZnF_2, the emission intensity at peak wavelength and the fluorescence lifetime of Er^(3+) at 1.5 μm increase.展开更多
One of the important aspects of seamless communication for ubiquitous computing is the dynamic selection of the best access network for a multimodal device in a heterogeneous wireless environment. In this paper, we co...One of the important aspects of seamless communication for ubiquitous computing is the dynamic selection of the best access network for a multimodal device in a heterogeneous wireless environment. In this paper, we consider available bandwidth as a dynamic parameter to select the network in heterogeneous environments. A bootstrap approximation based technique is firstly utilized to estimate the available bandwidth and compare it with hidden Markov model based estimation to check its accuracy. It is then used for the selection of the best suitable network in the heterogeneous environment consisting of 2G and 3G standards based wireless networks. The proposed algorithm is implemented in temporal and spatial domains to check its robustness. The numerical results show that the proposed algorithm gives improved performance in terms of estimation error （less than 15%）, overhead （varies from 0.45% to 72.91%） and reliability （approx. 99%）as compared to the existing algorithm.展开更多
基金Project supported by the National Key Research and Development Program of China(Grant No.2021YFB3501300)the National Natural Science Foundation of China(Grant No.51731001)the Fund from the State Key Laboratory of Baiyunobo Rare Earth Resource Researches and Comprehensive Utilization’s Key Research and Development Projects。
文摘As concepts closely related to microwave absorption properties,impedance matching and phase matching were rarely combined with material parameters to regulate properties and explore related mechanisms.In this work,reduction–diffusion method was innovatively applied to synthesize rare earth alloy Y_(2)Fe_(17).In order to regulate the electromagnetic parameters of absorbers,the Y_(2)Fe_(17)N_(3-δ)particles were coated with silica(Y_(2)Fe_(17)N_(3-δ)@SiO_(2))and absorbers with different volume fractions were prepared.The relationship between impedance matching,matching thickness,and the strongest reflection loss peak(RLmin)was presented obviously.Compared to the microwave absorption properties of Y_(2)Fe_(17)N_(3-δ)/PU absorber,Y_(2)Fe_(17)N_(3-δ)@SiO_(2)/PU absorbers are more conducive to the realization of microwave absorption material standards which are thin thickness,light weight,strong absorbing intensity,and broad bandwidth.Based on microwave frequency bands,the microwave absorption properties of the absorbers were analyzed and the related parameters were listed.As an important parameter related to perfect matching,reflection factor(√ε_(r)/μ_(r))was discussed combined with microwave amplitude attenuation.According to the origin and mathematical model of bandwidth,the formula of EAB(RL<-10 dB)was derived and simplified.The calculated bandwidths agreed well with experimental results.
文摘We analyze the temperature dependence of the Raman intensity using the experimental data according to a power-law formula close to the order-disorder transition (Tc = 549 K) in NaNO 3. From this analysis, we extract the value of β = 0.26 as the critical exponent for the order parameter, which indicates a tricritical phase transition in this crystalline system. Using the temperature dependence of the order parameter, the Raman bandwidth is calculated at various temperatures in NaNO3. Our calculated bandwidths describe adequately the observed behaviour of the order-disorder transition in this crystal.
基金fnancial support from the National Natural Science Foundation of China(No.51971111)。
文摘Perovskite LaCoO_(3)is of great potential in electromagnetic wave absorption considering its outstanding dielectric loss as well as the existing magnetic response with the magnetic doping.However,the dissipation mechanism of the magnetic doping on the microwave absorption is lack of sufficient investigated.In this paper,LaCo_(1-x)Fe_(x)O_(3)(x=0,0.05,0.1,0.15,0.2,0.25,0.3,LCFOs)perovskites with different Fe doping amounts were prepared successfully by the sol-gel method and subsequent heat treatment in the air atmosphere.The structure characterization carried out by the frst-principles calculations shows the effect of Fe doping on the dielectric and magnetic properties of LCFOs and the strong hybridization of Co/Fe-3d with O-2p in the LCFOs system was successfully demonstrated.Particularly,when x=0.1 and the thickness is only 1.95 mm,the LaCo_(0.9)Fe_(0.1)O_(3)exhibits the best microwave absorption performance with the minimum reflection loss(RL)value of about-41 dB.The typical samples achieve a broad effective absorption bandwidth(EAB)of 5.16 GHz(7.92-13.08 GHz),which covers the total X band(8-12 GHz).Considering that,the especial Fe doping perovskite is promising to be a candidate as efficient microwave absorbers.
基金Project supported by the National Natural Science Foundation of China (50572102 ,50102006)National High Technology Re-search and Development Program ("863"Program) (2002AA311160)+1 种基金Natural Science Foundation of Jilin Province(1999514 ,20030514-2) Outstanding Young People Foundation of Jilin Province (20040113)
文摘To investigate the modification effect of the B2O3 component on tellurite glass, a series of glasses with a composition of xB2O3-（80-x）TeO2-10ZnO-10Na20 （x = 0, 10, 20, 30, 40, 50, 60, 70, 80） and an additional amount of 0.5% Er2Os（in molar） were prepared. The refractive index, the absorption edge of the host, the J-O parameters of Er^3＋ , the fluorescent decay time, the bandwidth, and the quantum efficiency for the 4Ⅰ13/2→4Ⅰ15/2 transition were obtained theoretically and experimentally. These results indicated that the introduction of B2O3 modified the performance of the tellurite glass. For example, with increasing content of B2O3, the refractive index of the host decreases from 1.9 to 1.5, the absorption edge of the host shifted toward the blue regime, the intensity parameter Ω6 changed from 1.08 × 10^-20（for the pure tellurite glass） to 1.98 ×10^-20 cm^2（for the pure borate glass）, the bandwidth of the 4Ⅰ13/2→4Ⅰ15/2 transition increased, and the quantum efficiency of the 4Ⅰ13/2→4Ⅰ15/2 transition decreased.
文摘The Er^(3+)-doped TeO_2-WO_3-ZnO-ZnF_2(TWZOF) glasses were prepared. The absorption spectra, 1.5 μm emission spectra and fluorescence lifetimes of Er^(3+), excited at 970 nm, were measured. The J-O parameters Ω_ t (t =2, 4, 6), absorption and emission cross-sections were calculated. The dependence of the 1.5 μm emission intensity, fluorescence lifetime and bandwidth of the Er^(3+) emission upon the contents of ZnF_2 in glass were investigated. In TWZOF glass, Er^(3+) ions had a broad emission profile around 1.5 μm with the maximum FWHM of 83 nm. With the increasing of the content of ZnF_2, the emission intensity at peak wavelength and the fluorescence lifetime of Er^(3+) at 1.5 μm increase.
文摘One of the important aspects of seamless communication for ubiquitous computing is the dynamic selection of the best access network for a multimodal device in a heterogeneous wireless environment. In this paper, we consider available bandwidth as a dynamic parameter to select the network in heterogeneous environments. A bootstrap approximation based technique is firstly utilized to estimate the available bandwidth and compare it with hidden Markov model based estimation to check its accuracy. It is then used for the selection of the best suitable network in the heterogeneous environment consisting of 2G and 3G standards based wireless networks. The proposed algorithm is implemented in temporal and spatial domains to check its robustness. The numerical results show that the proposed algorithm gives improved performance in terms of estimation error （less than 15%）, overhead （varies from 0.45% to 72.91%） and reliability （approx. 99%）as compared to the existing algorithm.
