考虑最小尺寸精确控制的SIMP和MMC混合拓扑优化方法

拓扑优化作为一种先进设计方法, 已被成功用于多个学科领域优化问题求解, 但从拓扑优化结果到其工程应用之间仍存在诸多阻碍, 如在结构设计中存在难以制造的小孔或边界裂缝和单铰链连接等. 在拓扑优化设计阶段考虑结构最小尺寸控制是解决上述问题的一种有效手段. 在最小尺寸控制的结构拓扑优化方法中, 通用性较强的固体各向同性材料惩罚法SIMP优化结果边界模糊不光滑, 包含精确几何信息的移动变形组件法MMC对初始布局具有较强依赖性. 本文提出一种考虑最小尺寸精确控制的SIMP和MMC混合拓扑优化方法. 所提方法继承了二者优势, 避免了各自缺点. 在该方法中, 首先采用活跃轮廓算法ACWE获取SIMP输出的拓扑结构边界轮廓数据, 提出了SIMP优化结果到MMC组件初始布局的映射方法. 其次, 通过引入组件的3个长度变量, 建立了半圆形末端的多变形组件拓扑描述函数模型. 最后, 以组件厚度变量为约束, 构建了考虑结构最小尺寸控制的拓扑优化模型. 采用最小柔度问题和柔性机构问题验证了所提方法的有效性. 数值结果表明, 所提方法在无需额外约束的条件下, 仅通过组件厚度变量下限设置, 可实现整体结构的最小尺寸精确控制, 并获得了具有全局光滑的拓扑结构边界.      

稀有衰变B0(Bs)→γνν 分支比的计算

在标准模型中, 三体稀有衰变B⁰(B_s)→γνν只有通过箱图和企鹅图才可以发生.这个过程对于确定B介子的衰变常数及其波函数有着较重要的物理意义,由于这些衰变道的分支比较小, 因此也是探测新物理理论的比较好的场所.利用B介子强衰变确定的波函数, 得到 B⁰(B_s)→γνν的分支比的数量级是10^－9(10^－8), 这些结果可以在未来的实验上得到检验.     

近紫外宽带激发LED用红色荧光粉(Gd_(1-x)Eu_x)6(Te_(1-y)Mo_y)O_(12)的制备与性能

利用高温固相法制备了一种新型红色荧光粉(Gd_(1-x)Eu_x)_6(Te_(1-y)Mo_y)O_(12),研究了Eu~(3+)单掺和Eu~(3+),Mo~(6+)共掺Gd_6TeO_(12)荧光粉的结构、形貌和荧光性能.实验结果表明,所合成的粉体为纯相.在393 nm近紫外光激发下,(Gd_(1-x)Eu_x)_6(Te_(1-y)Mo_y)O_(12)荧光粉发出特征红光,位于632 nm处的发射主峰属于Eu~(3+)的~5D_0→~7F_2跃迁.当Eu~(3+)掺杂浓度超过20%(物质的量分数)时发光出现浓度淬灭,经证实这是由电偶极-电偶极相互作用造成的.随着工作温度升高,荧光粉发光强度减小,计算得到Eu~(3+)热淬灭过程中的激活能为0.1796 eV.当(Gd_(0.8)Eu_(0.2))_6TeO_(12)中共掺Mo~(6+_(取代Te~(6+)),该荧光粉发射光谱的峰位、强度变化不大,但是Mo~(6+)-O~(2-)电荷迁移态显著增大了近紫外波段的激发带宽度,可以有效提高激发效率.具有近紫外宽带激发特征的(Gd_(0.8)Eu_(0.2))_6(Te_(0.6)Mo_(0.4))O_(12)是一种潜在的白光LED用荧光粉材料.     

基于多轴应力损伤的薄板花瓣型破口形成机理研究

开展了多种应力状态下的船用钢力学特性实验,基于多轴应力状态损伤的失效准则研究了局部冲击荷载作用下圆形板的花瓣型破口形成过程,划分了花瓣型破口形成的3个阶段,分析了裂纹区域、非裂纹区域应力状态变化过程及损伤情况。得到:(1)考虑多轴应力损伤的舰船用钢失效准则能有效预测受力状态复杂的花瓣状破口;(2)花瓣型破口的形成主要分为蝶形凹陷、中心区域裂纹扩展、花瓣形成与翻转等3个阶段;(3)花瓣型破口的裂纹区和非裂纹区均受力复杂,破口预测须考虑应力状态对损伤特性的影响;(4)花瓣形成过程中,第1阶段和第3阶段均匀变形,第2阶段损伤局部化明显,花瓣卷曲会造成花瓣根部的二次损伤。     

氦在方解石和文石中的扩散:基于第一性原理的研究

研究碳酸盐矿物中氦的扩散行为对理解地球脱气过程中的物理化学性质和动力过程具有重要意义。基于密度泛函理论研究了氦在方解石和文石矿物中的扩散机理,计算了氦在地表和地幔条件下的扩散路径、激活能和频率因子(v)。计算结果表明:氦在方解石中的扩散具有明显的各向异性,沿a(b)轴方向的扩散更快;文石呈现中等的各向异性,沿c轴的扩散速率低于a轴。在高压条件下,文石的激活能随压力的增大而增大。方解石晶体在[010]方向的封闭温度为–54～–25℃,沿[100]方向的封闭温度为–12～23℃。在地表条件下,氦在文石中的滞留能力比在方解石中强,与以往的实验研究结果一致。     

Low-dimensional phases engineering for improving the emission efficiency and stability of quasi-2D perovskite films

The two-dimensional (2D) Ruddlesden-Popper-type perovskites, possessing tunable bandgap, narrow light emission, strong quantum confinement effect, as well as a simple preparation method, are identified as a new generation of candidate materials for efficient light-emitting diodes. However, the preparation of high-quality quasi-2D perovskite films is still a challenge currently, such as the severe mixing of phases and a high density of defects within the films, impeding the further promotion of device performance. Here, we prepared the quasi-2D PEA₂MA_n-1Pb_nBr_3n+1 perovskite films by a modified spin-coating method, and the phases with large bandgap were effectively suppressed by the vacuum evaporation treatment. We systematically investigated the optical properties and stability of the optimized films, and the photoluminescence (PL) quantum yield of the treated films was enhanced from 23% to 45%. We also studied the emission mechanisms by temperature-dependent PL spectra. Moreover, the stability of films against moisture, ultraviolet light, and heat was also greatly improved.     

New physics search in the doubly weak decay ■→K~+π~(-*)

The doubly weak transition b-dd■ is highly suppressed in the Standard Model,which makes it a potential channel for exploring new physics signals.We present a study of the exclusive two-body wrong sign weak decay ■→K+π-,which belongs to this class,in the perturbative QCD framework.We perform a model independent analysis for various effective dimension-6 operators for which large effects are possible.We further analyze the considered process in the Randall-Sundrum model,including the custodially protected and the bulk-Higgs Randall-Sundrum models.Exploring the experimentally favored parameter space of these models leads to a large and significant enhancement of the decay rate compared to the Standard Model,which might be accessible in future experiments.We propose to search for the wrong sign decay ■→K+π-via flavor-tagged time-dependent analyses,which can be performed at LHCb and Belle-Ⅱ.     

铝离子聚合物固态电解质

铝离子电池因其材料成本低、大倍率性能优异和循环寿命超长等优势,而被认为在大规模静态储能应用中具有广阔前景.目前的铝离子电池大部分采用离子液体、尿素和熔融盐等液态电解液,其在实际工程化应用当中存在电解液渗漏的风险.相对而言,全固态电池则可以避免电解液渗漏的问题,还具有因去除隔膜和简化封装所带来的电池整体能量密度提升的优点.但是,目前领域内少有关于全固态铝离子电池的研究.基于此,采用溶液浇筑法,以冠醚作为添加剂和配位基团、以聚乙二醇（PEO）作为基底,制备出无定型结构的聚合物固态铝离子电解质.其中,冠醚不仅作为配位基团与铝离子进行配位提高铝离子的稳定性,而且作为相容性高的添加剂降低聚合物结晶度,从而提高固态电解质的离子电导率.测试表明,制备出的18-6/PEO/Al（CF₃SO₃）₃体系聚合物固态铝离子电解质是非晶态为主的晶态与非晶态共存的薄膜,且具备很高的离子电导率（室温,5.5×10^-6 S/cm;100℃高温,1.86×10^-3 S/cm）和较宽的电化学稳定窗口（0~3 V）,这为全固态铝离子电池的研发奠定了基础.     

并列双圆柱绕流特性和互扰效应数值模拟研究

基于CFD方法,对不同间距比(1.25≤T*≤5)下的二维双圆柱绕流进行了数值模拟研究.初步研究结果表明:当1.25＜T*≤2.2时尾流不能达到稳定,两圆柱交替对下游流场起主导作用;当T*＞2.2时尾流能达到稳定且上下侧圆柱涡的脱落出现同步,即流场趋于稳定的临界值为T ≈2.2.进一步研究发现:当2.2＜T*≤3.3时...     

Spin-excited states and rectification in an organic spin rectifier

Spin-excited states in an asymmetric magnetic organic co-oligomer diode are investigated theoretically. The results demonstrate that the structural asymmetry of the co-oligomer is modulated by the spin-excited states, which is embodied in the wave functions of the eigenstates as well as the spin density wave. By calculating the transport property, a robust spin-current rectification concomitant with a charge-current rectification is observed in all spin-excited states. However, the current through the diode is suppressed distinctly by the spin-excited states, while the rectification ratios may be reduced or enhanced depending on the bias and the excited spins. The intrinsic mechanism is analyzed from the spin-dependent trans- mission combined with the change of molecular eigenstates under bias. Finally, the temperature-induced spin excitation is simulated. Significant rectification behavior is obtained even at room temperature.