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1.
针对线性相控阵列在固体介质中的声场聚焦特性及参数优化问题,该文给出了一个线性阵列的纵波瞬态聚焦声场模型。数值结果表明,当阵元被短时脉冲信号激励时,瞬态聚焦声场中不会形成栅瓣,突破了传统稳态理论模型中对阵元间距的限制;同时由于横纵波在聚焦区域内可完全分离,声束旁瓣的幅值也得到了抑制。其次,增大阵元间距能够显著提高聚焦性能,但会导致聚焦声场能量减弱,综合考虑后,最佳的阵元间距为一个波长左右。并且发现,阵元宽度对于聚焦性能几乎没有影响,但宽阵元能够提高聚焦能量。此外,受到纵波激发特性的影响,使得相控阵只能在低偏转角处获得理想的纵波聚焦性能。最后,采用不同阵元间距的相控阵探头对试块进行成像实验,观察到大阵元间距可以显著改善缺陷成像分辨率,从而验证了理论分析的结果。  相似文献   
2.
延安是中国共产党领导革命的中心和战略总后方,是革命的红色摇篮。延安时期出版了大量具有历史、文化以及教育意义的红色文献,这些红色文献记载了中国共产党波澜壮阔的发展历程,也反映了延安时期不断发展的科技生产水平与独特的制浆造纸工艺,具有重要的研究价值。然而,延安时期出版的红色文献虽距今不到百年时间,但其保存现状不容乐观,普遍存在纸张老化、焦脆易碎等问题,大量文献急需科学检测与修复保护,以延长其保存寿命。目前,针对延安时期红色文献的检测研究仍存在较大空白。考虑到红色文献的珍贵性与特殊性,应当尽可能选择无损检测方法对其分析检测。基于衰减全反射-傅里叶变换红外光谱法(ATR-FTIR),以木素1 510 cm-1处特征峰与纤维素1 030 cm-1处特征峰的强度作为定量依据,建立了造纸原料与红色文献纸张中木素相对含量的无损检测方法。通过检测不同碱强度与碱浓度处理后的构皮、苦竹与杨木的木素含量,考察了制浆过程中碱处理条件对造纸原料脱木素程度的影响,同时体现了红外光谱法测定木素相对含量的普适性。以复旦大学图书馆藏的76册延安时期红色文献为研究对象,分析了红色文献的纸张木素含量与纸张pH值以及纸张氧化度的相互关系。结果表明,木素相对含量高于25%的红色文献,其纸张pH集中在3~4之间且纸张氧化度较高,文献整体保存状况堪忧;而木素相对含量低于25%的红色文献,其纸张氧化度与酸度较低,文献整体保存情况较好。以上结果验证了红外光谱无损检测法用于延安时期红色文献木素含量分析的可行性,并结合纸张氧化度与酸度数据提出了纸张木素含量的合适范围,为制浆造纸中植物原料的脱木素过程提供参考。拓展了红外光谱法在红色文献无损检测中的应用范围,以期为延安时期红色文献的修复与保护研究提供科学依据。  相似文献   
3.
建立了氟化氢铵消解地球化学样品,电感耦合等离子体质谱(ICP-MS)法测定样品中钨、锡和钼的方法。方法经过国家土壤和水系沉积物标准参考物质验证,方法的检出限钨为0.048μg/g、锡为0.079μg/g、钼为0.063μg/g,准确度(相对误差)钨为0.64%~6.28%、锡为0.29%~3.74%、钼为2.12%~7.41%,精密度(相对标准偏差)钨为0.13%~0.72%、锡为0.05%~1.2%、钼为0.03%~1.1%,能够满足《地质矿产实验室测试质量管理规范》的质量要求。方法具有操作简便、测试成本低、分析效率高、环境污染小等特点,适合于批量样品的分析测试。  相似文献   
4.
李军  姚道新 《中国物理 B》2022,31(1):17403-017403
This article reviews the basic theoretical aspects of octagraphene, an one-atom-thick allotrope of carbon, with unusual two-dimensional(2 D) Fermi nesting, hoping to contribute to the new family of quantum materials. Octagraphene has an almost strongest sp2hybrid bond similar to graphene, and has the similar electronic band structure as iron-based superconductors, which makes it possible to realize high-temperature superconductivity. We have compared various possible mechanisms of superconductivity, including the unconventional s;superconductivity driven by spin fluctuation and conventional superconductivity based on electron–phonon coupling. Theoretical studies have shown that octagraphene has relatively high structural stability. Although many 2 D carbon materials with C;carbon ring and C;carbon ring structures have been reported, it is still challenging to realize the octagraphene with pure square-octagon structure experimentally.This material holds hope to realize new 2 D high-temperature superconductivity.  相似文献   
5.
Ruppeiner geometry has been successfully applied in the study of the black hole microstructure by combining with the small–large black hole phase transition, and the potential interactions among the molecular-like constituent degrees of freedom are uncovered. In this paper, we will extend the study to the triple point, where three black hole phases coexist acting as a typical feature of black hole systems quite different from the small–large black hole phase transition. For the six-dimensional charged Gauss–Bonnet anti-de Sitter black hole, we thoroughly investigate the swallow tail behaviors of the Gibbs free energy and the equal area laws. After obtaining the black hole triple point in a complete parameter space, we exhibit its phase structures both in the pressure–temperature and temperature–horizon radius diagrams. Quite different from the liquid–vapor phase transition, a double peak behavior is present in the temperature–horizon radius phase diagram. Then we construct the Ruppeiner geometry and calculate the corresponding normalized curvature scalar. Near the triple point, we observe multiple negatively divergent behaviors. Positive curvature scalar is observed for the small black hole with high temperature, which indicates that the repulsive interaction dominates among the microstructure. Furthermore, we consider the variation of the curvature scalar along the coexisting intermediate and large black hole curves. Combining with the observation for different fluids, the result suggests that this black hole system behaves more like the argon or methane. Our study provides a first and preliminary step towards understanding black hole microstructure near the triple point, as well as uncovering the particular properties of the Gauss–Bonnet gravity.  相似文献   
6.
Liang'an Huo 《中国物理 B》2022,31(3):30202-030202
The appearance of rumors intensifies people's panic and affects social stability. How to control the spread of rumors has become an important issue which is worth studying. In order to more accurately reflect the actual situation in the real world, a stochastic model incorporating media coverage and Lévy noise is proposed to describe the dynamic process of rumor propagation. By introducing two control strategies of popular science education and media coverage in an emergency event, an near-optimal control problem that minimizes the influence and control cost of rumor propagation is proposed. Sufficient conditions for near-optimal control of the model are established by using a Hamiltonian function. Then the necessary conditions for near-optimal control are obtained by using the Pontryagin maximum principle. Finally, the effect of popular science education, media coverage and Lévy noise on rumor propagation process control is verified by numerical simulation.  相似文献   
7.
Lijun Ni 《中国物理 B》2022,31(12):128504-128504
We report the temperature dependence of the spin pumping effect for Y3Fe5O12 (YIG, 0.9 μm)/NiO (tNiO)/W (6 nm) (tNiO = 0 nm, 1 nm, 2 nm, and 10 nm) heterostructures. All samples exhibit a strong temperature-dependent inverse spin Hall effect (ISHE) signal Ic and sensitivity to the NiO layer thickness. We observe a dramatic decrease of Ic with inserting thin NiO layer between YIG and W layers indicating that the inserting of NiO layer significantly suppresses the spin transport from YIG to W. In contrast to the noticeable enhancement in YIG/NiO (tNiO ≈ 1-2 nm)/Pt, the suppression of spin transport may be closely related to the specific interface-dependent spin scattering, spin memory loss, and spin conductance at the NiO/W interface. Besides, the Ic of YIG/NiO/W exhibits a maximum near the TN of the AF NiO layer because the spins are transported dominantly by incoherent thermal magnons.  相似文献   
8.
We devote to the calculation of Batalin–Vilkovisky algebra structures on the Hochschild cohomology of skew Calabi–Yau generalized Weyl algebras. We first establish a Van den Bergh duality at the level of complex. Then based on the results of Solotar et al., we apply Kowalzig and Krähmer's method to the Hochschild homology of generalized Weyl algebras, and translate the homological information into cohomological one by virtue of the Van den Bergh duality, obtaining the desired Batalin–Vilkovisky algebra structures. Finally, we apply our results to quantum weighted projective lines and Podleś quantum spheres, and the Batalin–Vilkovisky algebra structures for them are described completely.  相似文献   
9.
Kelvin−Helmholtz (KH) instability is a fundamental fluid instability that widely exists in nature and engineering. To better understand the dynamic process of the KH instability, the influence of the tangential velocity on the compressible KH instability is investigated by using the discrete Boltzmann method based on the nonequilibrium statistical physics. Both hydrodynamic and thermodynamic nonequilibrium (TNE) effects are probed and analyzed. It is found that, on the whole, the global density gradients, the TNE strength and area firstly increase and decrease afterwards. Both the global density gradient and heat flux intensity in the vertical direction are almost constant in the initial stage before a vortex forms. Moreover, with the increase of the tangential velocity, the KH instability evolves faster, hence the global density gradients, the TNE strength and area increase in the initial stage and achieve their peak earlier, and their maxima are higher for a larger tangential velocity. Physically, there are several competitive mechanisms in the evolution of the KH instability. (i) The physical gradients increase and the TNE effects are strengthened as the interface is elongated. The local physical gradients decrease and the local TNE intensity is weakened on account of the dissipation and/or diffusion. (ii) The global heat flux intensity is promoted when the physical gradients increase. As the contact area expands, the heat exchange is enhanced and the global heat flux intensity increases. (iii) The global TNE intensity reduces with the decreasing of physical gradients and increase with the increasing of TNE area. (iv) The nonequilibrium area increases as the fluid interface is elongated and is widened because of the dissipation and/or diffusion.  相似文献   
10.
基于水声超材料吸声机理和多层平行介质平面波理论,建立局域共振型水声超材料结构,通过COMSOL进行建模计算,研究该结构的吸声性能机理,此外为了验证钢背衬的隔声性能,在该水声超材料结构基础上添加一层0.005m厚的钢背衬进行仿真对比。研究结果表明,在频段为200Hz-4000Hz时,水声超材料声学性能较好,吸声性能整体较优,且添加钢背衬的水声超材料隔声性能较优,甚至在某频率点达到15dB的隔声差值;此外通过位移场图进一步揭示水声超材料的吸声机理,发现水声超材料结构的位移场和钢背衬都对吸声性能会产生影响,钢背衬通过影响共振吸收来影响吸声性能,而位移场则通过位移幅度大小影响吸声性能。  相似文献   
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