基于体积法的缺口件多轴疲劳寿命预测

针对Mod.9Cr-1Mo钢不同缺口半径下的多轴疲劳试验结果进行模拟计算,采用体积法进行疲劳寿命预测,并与等效应变法的预测结果进行了对比。模拟结果表明,各路径下缺口根部应力集中程度随缺口半径减小而更为明显,最大应力集中程度达3.45。等效应变法给出的疲劳寿命预测结果随着缺口半径的减小而偏于保守,保守量高达90倍。为克服等效应变法给出的偏于保守的结果,基于剪应力随距缺口根部距离的变化趋势进行有效距离的计算,采用体积法进行寿命预测,94.1%的预测结果位于2倍分散带内。     

Broadband and high efficiency terahertz metasurfaces for anomalous refraction and vortex beam generation

The applications of metasurfaces are currently a highly active research field due to their extraordinary ability to manipulate electromagnetic waves. The ultra-thin characteristics of metasurfaces allow the miniaturization and integration of metasurface devices. However, these devices work typically under a low efficiency and narrow bandwidth condition. In this work, we design eight multilayered unit cells with similar amplitudes and a phase interval of π/4, which convert the polarization states of the terahertz (THz) waves between two orthogonal directions. The average cross-polarized transmission amplitudes of these cells are all around 0.9 in an ultra-broad frequency range from 0.5 THz to 1.4 THz. Furthermore, unit cells are used to construct both an ultra-thin anomalous refraction metalens and a vortex phase plate. Our simulation results show that the anomalous refraction for the transmitted linear polarization component is comparable to the theoretical prediction, and the maximum error is determined to be below 4.8%. The vortex phase plate can also generate an ideal terahertz vortex beam with a mode purity of 90% and more. The distributions of longitudinal electric field, intensity, and phase illustrate that the generated vortex beam has excellent propagation characteristics and a weak divergence. Simulations of the two types of metasurface devices, based on the eight unit cells, exhibit very high efficiencies in a wide bandwidth. Our research will assist in the improvement in the practical applications of metasurfaces. It also provides a reference for the design of high efficiency and broadband devices that are applied to other frequency ranges.     

无气味、实用的缩硫醛/酮化反应试剂：2-（1，3-二噻-2-亚基）-3-羰基丁酸甲酯

a-Oxo ketene dithioacetals, methyl 2-（1,3-dithian/dithiolan-2-ylidene）-3-oxobutanoate （2a/2b） prepared in nearly quantitative yields simply from methyl acetylacetate, carbon disulfide and 1,3-dibromopropane/1,2-dibromoethane in the presence of potassium carbonate, were investigated in the thioacetalization with various carbonyl compounds 3. It has been demonstrated that methyl 2-（1,3-dithian-2-ylidene）-3-oxobutanoate （2a） could act as a nonthiolic, odorless and practical thioacetalization reagent. A range of aldehydes and ketones 3 were converted into the corresponding dithioacetals 4 in high yields （up to 91%） in the presence of 2a. Moreover, 2a showed high chemoselectivity between aldehyde and ketone in thioacetalization.     

α-溴代二硫缩烯酮的制备及其反应

α-羰基二硫缩烯酮 ( 1 )是一类重要的有机合成中间体 ,作为 1 ,3-亲核体用于酯环、苯系芳烃及芳杂环化合物的合成[1～ 4 ] .Hosomi等 [5～ 7] 用有机铜试剂或二碘化钐和 α-羰基与二甲硫缩烯酮反应 ,将与硫相连的缩烯酮碳原子转化为亲核中心 .用不同的烷硫基作为调控基团将该类中间体用于二萜 pseu-dopterosins的合成 [8～ 10 ] ,并作为替代 Peterson法合成 1 ,1 -二烷硫基 - 1 ,3-丁二烯或 1 ,1 -二烷硫基 - 1 ,3,5 -己三烯 [11,12 ] ,从不同的角度对 α-羰基二硫缩烯酮在合成上的应用进行了新的探索 .Junjappa等 [13,14 ] 曾用 NBS和 …     

α-硝基二硫缩烯酮的制备

近年来，结合烷硫基对α-羰基二硫缩烯酮反应的调控作用，我们开展了α-羰基二硫缩烯酮／二硫缩烯酮α-官能化(或α-位修饰)的研究，以期扩展二硫缩烯酮在合成中的应用。在用α-碘代脱羧和α-溴代脱乙酰基反应分别成功地制备了α-碘代-α’-肉桂酰基二硫缩烯酮Ⅲ和α-溴代二硫缩烯酮嘲的基础