功能性分权与中国特色权力制约监督理论的探索——评《权力法治与廉政治理》

资本是经济生活中的权力,权力是政治生活中的资本。然而,由于政治权力往往存在扩张性、腐蚀性等特征,对政治权力的合理控制就成为国家治理现代化的必然选择(何增科,2018)。也正因如此,对权力法治与廉政治理的理论探索,也成为政治学和行政学研究的核心所在。

Second-harmonic generation in periodic fork-shaped χ^((2)) gratings at oblique incidence

Three-dimensional(3D) nonlinear photonic crystals have received intensive interest as an ideal platform to study nonlinear wave interactions and explore their applications. Periodic fork-shaped gratings are extremely important in this context because they are capable of generating second-harmonic vortex beams from a fundamental Gaussian wave, which has versatile applications in optical trapping and materials engineering. However, previous studies mainly focused on the normal incidence of the fundamental Gaussian beam, resulting in symmetric emissions of the second-harmonic vortices. Here we present an experimental study on second-harmonic vortex generation in periodic fork-shaped gratings at oblique incidence, in comparison with the case of normal incidence. More quasi-phase-matching resonant wavelengths have been observed at oblique incidence, and the second-harmonic emissions become asymmetric against the incident beam.These results agree well with theoretic explanations. The oblique incidence of the fundamental wave is also used for the generation of second-harmonic Bessel beams with uniform azimuthal intensity distributions. Our study is important for a deeper understanding of nonlinear interactions in a 3D periodic medium. It also paves the way toward achieving highquality structured beams at new frequencies, which is important for manipulation of the orbital angular momentum of light.

Wavelength-dependent nonlinear wavefront shaping in 3D nonlinear photonic crystal

A 3D nonlinear photonic crystal containing four parallel segments of periodicχ^((2))grating structure is fabricated employing the femtosecond laser poling of ferroelectric Ca_(0.28)Ba_(0.72)Nb_(2)O_(6) crystal.The second harmonic generation from this foursegment structure is studied with a fundamental Gaussian wave.By tuning the wavelength of the fundamental wave,the second harmonic varies from the Laguerre-Gaussian beam(topological charge l_(c)=1)to the higher-order Hermite-Gaussian beam and Laguerre-Gaussian again(l_(c)=−1).This effect is caused by the wavelength-dependent phase delays introduced by the four-grating structure.Our study contributes to a deeper understanding of nonlinear wave interactions in 3D nonlinear photonic crystals.It also offers new possibilities for special beam generation at new frequencies and their control.

Ternary BiOBr/TiO2/Ti3C2Tx MXene nanocomposites with heterojunction structure and improved photocatalysis performance

The rational design and construction of heterojunction structure is an effective strategy to improve the photocatalytic performance.Herein,a series of BiOBr nanosheets-immobilized TiO2/Ti3C2Tx MXene hybrid materials with heterojunction structure were synthesized by a facial one-step hydrothermal method.The ternary composites show outstanding performance as photocatalysts for the degradation of rhodamine B due to the optimized synergetic effects of BiOBr,TiO2 and Ti3C2Tx.The improved photocatalytic performance is remarkably attributed to the construction of a heterojunction between TiO2 and BiOBr due to their well-matching of energy band position,which can enhance the absorption for visible light and promote the transfer of photo-generated charge carriers.Moreover,Ti3C2Tx acts as an electron trap to further accelerate the separation of photo-generated electrons and holes.

Nonlinear Talbot self-healing in periodically poled LiNbO_3 crystal [Invited]

The nonlinear Talbot effect is a near-field nonlinear diffraction phenomenon in which the self-imaging of periodic objects is formed by the second harmonics of the incident laser beam. We demonstrate the first, to the best of our knowledge, example of nonlinear Talbot self-healing, i.e., the capability of creating defect-free images from faulty nonlinear optical structures. In particular, we employ the tightly focused femtosecond infrared optical pulses to fabricate LiNbO_(3) nonlinear photonic crystals and show that the defects in the form of the missing points of two-dimensional square and hexagonal periodic structures are restored in the second harmonic images at the first nonlinear Talbot plane. The observed nonlinear Talbot self-healing opens up new possibilities for defect-tolerant optical lithography and printing.

交错桁架体系RC柱与桁架连接节点受力性能分析

交错桁架结构体系最早于20世纪60年代出现于美国,并得到了广泛应用,典型的交错桁架结构体系主要由柱、楼板及平面桁架等构件组成,柱可采用H型钢柱、钢管柱、钢管混凝土柱等,楼板可以采用空心楼板、叠合楼板、现浇钢筋混凝土楼板等,桁架可以采用空腹式桁架、帕式桁架或混合式桁架。该结构体系具有开间大、施工便捷、经济、高效、环保等优势,同时其结构质量轻、整体受力性能好,柱内力一般较小,导致采用钢柱时设计控制指标通常为长细比,造成了材料的浪费。预制钢筋混凝土(reinforced concrete,RC)柱具有实心截面且施工便捷的优势,运用在交错桁架结构体系中,可以更充分地利用柱的力学性能,进而提高交错桁架结构体系的经济效益。然而,要实现RC柱的应用必须先实现柱-桁架节点的可靠连接。中建科技有限公司设计开发了采用预制RC柱、钢桁架和预应力混凝土楼板的装配式交错桁架结构,重庆大学对该结构体系进行了静力弹塑性分析,以评估其抗震性能。国内外学者对交错桁架结构体系中的桁架及结构体系抗震性能进行了大量的试验研究与理论分析,但对于交错桁架结构体系节点仅少量学者进行了一些较为初步的研究,且主要针对钢或钢管混凝土柱-桁架节点。为研究交错桁架体系中RC柱与桁架连接节点的受力性能,基于ABSQUS有限元软件,针对该工程中采用的典型RC柱-桁架节点,即RC柱与上弦杆和斜腹杆连接处的牛腿加预埋板式节点,建立了有限元模型,对其在结构设计分析中出现的5种最不利工况下的应力分布、斜腹杆荷载-位移曲线以及弦杆截面内力进行了分析,主要研究参数包括RC柱轴压比、是否限制弦杆水平位移及斜腹杆的受力情况。研究结果表明:1)杆件内力可通过节点板传至牛腿或预埋钢板,再通过锚杆传至柱内,传力路径明确,节点设计合理。2)各类杆件均先于节点区钢筋屈服,满足“强节点,弱构件”的设计要求。3)不释放弦杆水平位移的工况中,弦杆和斜腹杆强度利用更充分,柱中钢筋应力发展程度较释放弦杆水平位移的工况弱。4)不释放弦杆水平位移时,由于此时弦杆和斜腹杆强度利用更充分,柱中钢筋应力发挥程度不高,因此承载力和位移均更大;轴压比为0的工况中,斜腹杆荷载在位移为5 mm之前随位移线性增大,5 mm之后由于节点区塑性变形增长,荷载随位移增长速率减慢。5)峰值荷载时,除轴压力为0工况的剪力外,其他工况下弦杆的弯矩和剪力均较小;限制弦杆水平位移的工况下的弦杆轴力明显大于释放弦杆水平位移的工况,且斜腹杆峰值荷载提高约10%。6)为减轻由于牛腿造成的柱偏心效应,建议适当增加钢筋混凝土的纵筋配筋率,以提高其安全储备。