温度对核电站传热管阵列声透射特性的影响

为了研究温度分布对于管阵列结构中的声透射特性的影响，以核电站的实际工况为背景，构建了不同的温度场以及周期性变化的非均匀温度场，利用有限元方法进行数值模拟。结果表明：（1）温度分布会改变管阵列声透射频谱的“禁带”宽度以及中心频率位置。在同一介质中，温度变化对频率较高位置的影响大于频率较低的位置。（2）在同样为10℃的温度差下，当水的平均声速为1 653 m·s^-1、饱和水蒸气的平均声速为522.5 m·s^-1时，介质为水时的禁带宽度及中心频率位置变化较大，即声速大的介质的频谱对于温度的变化更敏感。（3）当温度差在10℃以内，在周期性变化的非均匀温度场和与均匀温度场中管阵列声透射特性在第一中心频率23 996.1 Hz之前，两频谱差别很小，在第一禁带之后会出现明显区别。该研究成果对完善核电站应用的声学检测提供了理论基础。     

Feasibility of high performance in p-type Ge1−xBixTe materials for thermoelectric modules

GeTe is a promising candidate for the fabrication of high-temperature segments for p-type thermoelectric (TE) legs. The main restriction for the widespread use of this material in TE devices is high carrier concentration (up to ∼ 10²¹ cm⁻³), which causes the low Seebeck coefficient and high electronic component of thermal conductivity. In this work, the band structure diagram and phase equilibria data have been effectively used to attune the carrier concentration and to obtain the high TE performance. The Ge_1−xBi_xTe (x = 0.04) material prepared by the Spark plasma sintering (SPS) technique demonstrates a high power factor accompanied by moderate thermal conductivity. As a result, a significantly higher dimensionless TE figure of merit ZT = 2.0 has been obtained at ∼ 800 K. Moreover, we are the first to propose that application of the developed Ge_1−xBi_xTe (x = 0.04) material in the TE unicouple should be accompanied by SnTe and CoGe₂ transition layers. Only such a unique solution for the TE unicouple makes it possible to prevent the negative effects of high contact resistance and chemical diffusion between the segments at high temperatures.     

Influence of Al3+ doping for V5+ on the structural,optical, thermal and electrical properties of V2-xAlxO5-δ (x=0–0.20) ceramics

This paper reports an investigation on the structure-properties correlation of trivalent metal oxide (Al₂O₃)-doped V₂O₅ ceramics synthesized by the melt-quench technique. XRD patterns confirmed a single orthorhombic V₂O₅ phase formation with increasing strain on the doping of Al₂O₃ in place of V₂O₅ in the samples estimated by Williamson-Hall analysis. FTIR and Raman investigations revealed a structural change as [VO₅] polyhedra converts into [VO₄] polyhedra on the doping of Al₂O₃ into V₂O₅. The optical band gap was found in a wide semiconductor range as confirmed by UV–visible spectroscopy analysis. The thermal and conductivity behavior of the prepared samples were studied using thermal gravimetric analysis (TGA) and impedance analyzer, respectively. All the prepared ceramics exhibit good DC conductivity (0.22–0.36 Sm^-1) at 400 ?C. These materials can be considered for intermediate temperature solid oxide fuel cell (IT-SOFC)/battery applications due to their good conductivity and good thermal stability.     

Impact of bismuth oxide on the structure,optical features and ligand field parameters of borosilicate glasses doped with nickel oxide

Understanding the impact of bismuth cations on the optical properties of borosilicate glass is significant for manipulating borate glass applications. In this paper, the influence of bismuth cations on both structural and optical properties of borosilicate glass doped with NiO was investigated. Different glass samples, containing different amounts of Bi₂O₃ and a constant amount of NiO, were prepared and studied. Infrared (IR) analysis was carried out to study the internal structure within the investigated glass samples. Optical absorption studies were performed to investigate the impact of Bi₂O₃ content on optical properties of the BiBaNiB-glasses. Astonishingly, with Bi₂O₃ addition, an absorption band at 380 nm has appeared. Moreover, this band is overlapped with the Urbach edge; which regularly produced an artificial edge-like feature at ~450 nm. A detailed deconvolution protocol has been implemented for an appropriate understanding of these spectra and unraveling the hidden Urbach edge. Optical band gap energy, linear and nonlinear refractive index for each BiBaNiB sample were calculated. Furthermore, the metallization criterion was calculated to examine the metallic or insulating nature of the BiBaNiB-glasses. The values of the nonlinear third-order susceptibility and nonlinear refractive index were increased with Bi₂O₃ doping. The BiBaNiB-glasses exhibited outstanding stability and optical band gap than the pristine glass sample, which makes it possible for practical applications.     

Insights into charge transition within band structure of amorphous SiCNO ceramic

SiCNO ceramic is prepared by pyrolyzing modified polysilazane. Its microstructure feature, dielectric properties and charge transition mechanisms are studied based on the analysis of effects of pyrolysis temperature on AC electrical performance. The Tauc band and the energy states density at Fermi level are studied by ultraviolet absorption and dielectric tests. The charge transition in the silicon-based matrix was analyzed according to Jonscher's dielectric relaxation theory. Results show that SiCNO ceramic obtained at 1000–1300?°C is amorphous with chemical stability. Three types of charge transition, that is, excitation from deep traps into the delocalized bands and the corresponding reverse capture processes, hopping near the Fermi level, and localized hopping of an electron in a potential double well, are enhanced as annealing temperature increases, which occur within energy band of Si-based matrix.     

Characterization of Bi2O3 thin films for doping photoluminescent Er3+ ions

Undoped and Er³⁺-doped Bi₂O₃ thin films were sputter-deposited on Si(100) substrates. Sufficiently oxidized Bi₂O₃ films with refractive indices between 2.17?2.23 were obtained at a wavelength of 633 nm; these values are comparable to those of bulk Bi₂O₃ crystals. While the film composition was stable for deposition temperatures between room temperature (RT) and 450 °C, the refractive index steeply decreased above 450 °C and reached 1.4 at 600 °C. The lowering of the optical transmittance spectra indicated aggregation of metallic Bi and darkening of the film. All films exhibited X-ray diffraction patterns of α-Bi₂O₃. The direct and indirect bandgap energies derived from the Tauc plots were 3.4–3.7 eV and 1.9–2.5 eV, respectively, depending on the O₂ flow rate and deposition temperature. Upon excitation of Er³⁺-doped Bi₂O₃ films at 532 nm, Er³⁺ emissions peaking at 1537 and 1541 nm appeared, and the photoluminescence spectra included fine structures reflecting crystal-field splitting. Resonant excitation of Er³⁺ 4f levels and indirect excitation via the defect levels of Bi₂O₃ followed by energy transfer to Er³⁺ contributed to the emission. The films deposited at RT with Er concentrations of 2 at.% had the emission intensity of Er³⁺, but concentration quenching strongly suppressed the Er³⁺ emission because the doped Er³⁺ ions stayed inside the Bi₂O₃ crystals. At deposition temperatures above 400 °C, the concentration quenching was mitigated possibly because out-diffusion of Er³⁺ ions reduced the effective number of Er³⁺ ions in the Bi₂O₃ crystalline domains.     

Polyaniline-based networks combined with Fe3O4 hollow spheres and carbon balls for excellent electromagnetic wave absorption

Polyaniline (PANI)-based networks combined with Fe₃O₄ hollow spheres and carbon balls (FCP) for improved electromagnetic wave (EMW) absorption were investigated using an easy-to-industrialize solvothermal and physical method. Hollow structure Fe₃O₄ spheres with a lower density than that of the common solid sphere were prepared. As a thin and light magnetic material, Fe₃O₄ hollow spheres generate magnetic loss, carbon balls and PANI networks generate dielectric loss. The magnetic and conductive parts play appropriate roles in achieving complementarity in the EMW absorption. The relatively high specific surface area introduced by PANI networks promotes interfacial polarization and further supports dielectric loss. In conclusion, the above reasons provide multiple attenuation mechanisms. Samples FCP1 (?65.109 dB, at 12.800 GHz, 1.966 mm, from 5.6 to 18.0 GHz) and FCP2 (?61.033 dB, at 8.480 GHz, 3.328 mm, from 4.3 to 18.0 GHz) demonstrated a wide bandwidth, a small thickness, a minimum reflection loss (R_L), and a low loading ratio (25%) in paraffin-based composites. Specifically, their loading ration of 25% is much lower than the loading ratio of conventional materials (usually 50% and above). In addition, the bandwidth is excessively wide, above 12 GHz, possessing good absorption performance in continuous intervals with different thicknesses. Such excellent characteristics have rarely been reported in literature.     

Structural,electrical, and linear/nonlinear optical characteristics of thermally evaporated molybdenum oxide thin films

Homogeneous thin films of Molybdenum oxide (MoO₃) were grown on quartz and glass substrates using the thermal evaporation method. XRD results showed that the MoO₃ powder has a polycrystalline structure with an orthorhombic crystal system whereas the MoO₃ thin films have amorphous nature. SEM images showed that the MoO₃ thin films have a nearly uniform surfaces with worm-like shape grains. The film thickness influences on the linear and nonlinear optical characteristics of MoO₃ thin films that were examined using spectrophotometric measurements and from which, the linear optical constants of the MoO₃ thin films were estimated. The electronic transition type was determined as a direct allowed one. The values of the optical band gap were obtained to be in the range of 3.88–3.72 eV. The dispersion parameters, third-order nonlinear optical susceptibility, and the nonlinear refractive index of the MoO₃ thin films were determined and interpreted in the light of the single oscillator model. The temperature dependence of the DC electrical conductivity and the corresponding conduction mechanism for the MoO₃ films were investigated at temperatures ranging from 303 to 463 K.     

基于K-AP算法的高光谱图像波段选择方法

在高光谱图像分析领域中，波段选择是一种能有效减少高光谱图像维度的方法。K类仿射传播算法是一种高效的聚类算法，已成功地应用于人脸识别和数据分析等领域，但在高光谱图像分析领域还少有成功的应用。提出将K-AP算法应用于高光谱图像波段选择，对高光谱图像进行有效的数据压缩。针对K-AP算法的特点，基于Kullback-Leibler散度定义了新的相似度矩阵，对波段进行度量，再使用K-AP算法进行聚类，选择最有代表性的波段。实验结果表明，与常用的波段选择方法相比，所提出的方法有更好的表现。     

ACCUGRAM: A novel approach based on classification to frequency band selection for rotating machinery fault diagnosis

Frequency band selection (FBS) in rotating machinery fault diagnosis aims to recognize frequency band location including a fault transient out of a full band spectrum, and thus fault diagnosis can suppress noise influence from other frequency components. Impulsiveness and cyclostationarity have been recently recognized as two distinctive signatures of a transient. Thus, many studies have focused on developing quantification metrics of the two signatures and using them as indicators to guide FBS. However, most previous studies almost ignore another aspect of FBS, i.e. health reference, which significantly affect FBS performance. To address this issue, this paper investigates importance of a health reference and recognize it as the third critical aspect in FBS. With help of the health reference, the frequency band where the fault transient exists could be located. A novel approach based on classification is proposed to integrate all three aspects (impulsiveness, cyclostationarity, and health reference) for FBS. Classification accuracy is developed as a novel indicator to select the most sensitive frequency band for rotating machinery fault diagnosis. The proposed method (coined by accugram) has been validated on benchmark and experiment datasets. Comparison results show its effectiveness and robustness over conventional envelope analysis, the kurtogram, and the infogram.