自适应非凸稀疏正则化下自适应光学系统加性噪声的去除

自适应光学系统可以实时测量并校正波前信息,但是系统中大量的噪声严重影响了系统的探测精度.自适应光学系统中一般为加性噪声,本文提出一种全新的变分处理模型去除加性噪声,该模型采用自适应非凸正则项.非凸正则项在保持图像细节上较凸正则项具有更好的效果,能更好地保持点源目标的完整性.另外,根据不同区域的噪声水平自适应地构建正则化参数,使不同区域的像素点受到不同程度的噪声抑制,可以更好地保持目标的边缘细节.在算法实现上,为了解决非凸正则项收敛性较差的缺陷,采用分裂Bregman算法及增广拉格朗日对偶算法进行计算.实验及数值仿真结果都表明,该方法能够较好地去除系统中的加性噪声,且光斑信号保存得较为完整,处理后的质心探测精度及信噪比较高.     

基于BiFeO_3/ITO复合膜表面钝化的黑硅太阳电池性能研究

采用金属银辅助化学刻蚀法在制绒的硅片表面刻蚀纳米孔形成微纳米双层结构,以期获得高吸收率的太阳能电池用黑硅材料.鉴于微纳米结构会在晶硅表面引入大量的载流子复合中心,利用磁控溅射技术在黑硅太阳电池表面制备了BiFeO_3/ITO复合膜,并对其表面性能和优化效果进行了探索.实验制备的具有微纳米双层结构的黑硅纳米线长约180—320 nm,在300—1000 nm波长范围内入射光反射率均在5%以下.沉积BiFeO_3/ITO复合薄膜后的黑硅太阳能电池反射率略有提高,但仍然具有较强的光吸收性能;采用BiFeO_3/ITO复合膜的黑硅太阳能电池开路电压和短路电流密度分别由最初的0.61 V和28.42 mA/cm~2提升至0.68 V和34.57 mA/cm~2,相应电池的光电转化效率由13.3%上升至16.8%.电池综合性能的改善主要是因为沉积BiFeO_3/ITO复合膜提高了电池光生载流子的有效分离,从而增强了黑硅太阳电池短波区域的光谱响应,表明具有自发极化性能的BiFeO_3薄膜对黑硅太阳能电池的表面性能可起到较好的优化作用.     

非晶物质中的临界现象

非晶态材料有着复杂的原子结构(短程有序、长程无序)和特殊的物理性质,其临界现象和相变问题一直受到学术界关注.非晶合金,又称为金属玻璃,是一种新型的非晶态材料,具有很高的强度和优异的弹性.从微观的角度来看,非晶合金可以看作是一个多粒子系统.临界现象的研究对认识和理解多粒子系统之间的相互作用有深刻的意义.本文主要讨论非晶合金中的临界现象,包括非晶合金从制备过程、微观结构到宏观的力学性能以及磁性方面存在的临界现象,并分析这些临界现象之间的内在联系,进而深入理解非晶合金的微观结构对其宏观性质的影响.这为认识非晶合金的形成本质,提高服役可靠性,探索具有实际应用价值的非晶合金提供理论依据.     

基于原位等离子体氮化及低压化学气相沉积-Si_3N_4栅介质的高性能AlGaN/GaN MIS-HEMTs器件的研究

通过对低压化学气相沉积(LPCVD)系统进行改造,实现在沉积Si_3N_4薄膜前的原位等离子体氮化处理,氮等离子体可以有效地降低器件界面处的氧含量和悬挂键,从而获得了较低的LPCVD-Si_3N_4/GaN界面态,通过这种技术制作的MIS-HEMTs器件,在扫描栅压范围V_(G-sweep)=(-30 V,+24 V)时,阈值回滞为186 mV,据我们所知为目前高扫描栅压V_(G+)(20 V)下的最好结果.动态测试表明,在400 V关态应力下,器件的导通电阻仅仅上升1.36倍(关态到开态的时间间隔为100μs).     

剪切光束成像技术对纵深目标的成像

剪切光束成像技术是一种能透过大气湍流对远距离目标实现高分辨率成像的主动成像技术.现有相关研究中所采用的目标均为二维平面目标,然而现实中的目标一般都具有三维形貌,目标纵深对回波信号产生的延迟或对成像质量产生不利影响.从剪切光束成像理论出发,在二维目标成像模型的基础上建立了三维纵深目标成像模型,并利用该模型研究了两剪切光与参考光间的频差及目标纵深对成像的影响.仿真结果表明,随着拍频的增大,重构图像质量逐渐下降.剪切光束成像技术可通过减小拍频来提高真实目标成像质量.     

单晶金刚石氢终端场效应晶体管特性

基于微波等离子体化学气相淀积生长的单晶金刚石制作了栅长为2μm的耗尽型氢终端金刚石场效应晶体管,并对器件特性进行了分析.器件的饱和漏电流在栅压为-6 V时达到了96 mA/mm,但是在-6 V时栅泄漏电流过大.在-3.5 V的安全工作栅压下,饱和漏电流达到了77 mA/mm.在器件的饱和区,宽5.9 V的栅电压范围内,跨导随着栅电压的增加而近线性增大到30 mS/mm.通过对器件导通电阻和电容-电压特性的分析,氢终端单晶金刚石的二维空穴气浓度达到了1.99×10~(13)cm~(-2),并且迁移率和载流子浓度均随着栅压向正偏方向的移动而逐渐增大.分析认为,沟道中高密度的载流子、大的栅电容以及迁移率的逐渐增加是引起跨导在很大的栅压范围内近线性增加的原因.     

A search for sterile neutrinos with the latest cosmological observations

We report the result of a search for sterile neutrinos with the latest cosmological observations. Both cases of massless and massive sterile neutrinos are considered in the \(\Lambda \)CDM cosmology. The cosmological observations used in this work include the Planck 2015 temperature and polarization data, the baryon acoustic oscillation data, the Hubble constant direct measurement data, the Planck Sunyaev–Zeldovich cluster counts data, the Planck lensing data, and the cosmic shear data. We find that the current observational data give a hint of the existence of massless sterile neutrino (as dark radiation) at the 1.44\(\sigma \) level, and the consideration of an extra massless sterile neutrino can indeed relieve the tension between observations and improve the cosmological fit. For the case of massive sterile neutrino, the observations give a rather tight upper limit on the mass, which implies that actually a massless sterile neutrino is more favored. Our result is consistent with the recent result of neutrino oscillation experiment done by the Daya Bay and MINOS collaborations, as well as the recent result of cosmic ray experiment done by the IceCube collaboration.     

Structural and electronic properties of potassium-doped 1,2;8,9-dibenzopentacene superconductor: comparing with doped [7]phenacenes

Polycyclic aromatic hydrocarbons doped by metal have exhibited the potential of high temperature superconductivity. Understanding the basic properties of materials is the key to reveal the superconductivity. Here, a systemically theoretical study has been done to explore crystal structures and electronic properties of pristine and potassium-doped 1,2;8,9-dibenzopentacene, compared with [7]phenacenes case. We determined that vdW-DF2 functional is more suitable to describe the non-local interaction in a molecular crystal. Based on this functional, we predicted the crystal structures and investigated in detail the K atomic positions in a system. It was found that the intralayer doping leads to lower total energy. From the calculated formation energy, for each 1,2;8,9-dibenzopentacene molecule, the doping of two electrons is more stable under the relatively K-poor condition while the doping of four electrons is more stable under the K-rich condition. Between these two phases, the three-electron doping phase stabilises in a narrow region of K chemical potential. Combining with the electronic states at Fermi level, we analysed the reasons of superconductivity enhancement in doped 1,2;8,9-dibenzopentacene. This work further deepens the understanding of 1,2;8,9-dibenzopentacene superconductor.     

Physicochemical properties of nanoparticles affect translocation across pulmonary surfactant monolayer

Interaction between nanoparticles (NPs) and pulmonary surfactant monolayer is one of the most important parts in NP-based pulmonary drug delivery system, which can affect the result of the inhaled nano-drugs and their potential efficacy. Here, we show how surface charge of NPs affects translocation across pulmonary surfactant monolayer with coarse-grained molecular dynamics simulations. The results reveal that the surface charge position of NPs can determine the fate of the inhaled NPs about whether they can have the ability of translocation across the pulmonary surfactant monolayer, which is that NPs with face surface charge can penetrate the pulmonary surfactant monolayer and NPs with edge surface charge cannot. Besides, dynamic process, phase state and the potential of mean force profiles further confirm this result. Moreover, compared to anionic NPs, there is a greater chance for cationic NPs to be adsorbed on the surface of the pulmonary surfactant monolayer, which can further decrease the thickness of the pulmonary surfactant monolayer and reduce the distance between charged NPs and the pulmonary surfactant monolayer. Our researches provide a novel simulation model of NPs on translocation across pulmonary surfactant monolayer and the study of NP-based pulmonary drug delivery system should consider the surface charge of NPs.