关于Lovasz不等式的几类超图

本文证明了下面的定理：若超图Ｈ＝（Ｘ；Ｅ１，Ｅ２，．．．Ｅｍ）中存在浓度为Ｋ长为ｍ的圈，则有ｍ∑ｉ＝１（│Ｅｉ│－ｋ）＞ｎ－ｋ。     

Big deformation in ~(17)C

Reaction and interaction cross sections of ¹⁷C on a carbon target have been re-analyzed using the modified Glauber model. The analysis with a deformed Woods-Saxon density/potential suggests a big deformation structure for ¹⁷C. The existence of a tail in the density distribution supports the possibility of it being a one-neutron halo structure. Under a deformed core plus a single-particle assumption, analysis shows a dominant d-wave of the valence neutron in ¹⁷C.     

用两台装置找出两个坏硬币的最优化方法

本文探讨从一堆硬币中以最少次数用规定的方法挑选出其中坏硬币的问题。由于给定的模型不同,这一问题有多种不同的形式。其中,用一台装置挑选出至多两个坏硬币的问题已得到广泛研究,且已有了一些好结果。本文考虑的是用两台平行装置挑选两个坏硬币的情形。我们特别考虑了装置只能区分是否在某装置中同时放入了两个坏硬币这一模型M。以t_k表示关于模型M的一个过程t在k次测试中所能鉴别的最大硬币数目,以n_k表示关于模型M在k次测试中所能鉴别的最大硬币数目。我们找到了关于模型M的一个过程t,使得t_k/n_k>0.994(k≥20)。     

Graphene-based heterojunction for enhanced photodetectors

Graphene has high light transmittance of 97.7% and ultrafast carrier mobility, which means it has attracted widespread attention in two-dimensional materials. However, the optical absorptivity of single-layer graphene is only 2.3%, and the corresponding photoresponsivity is difficult to produce at normal light irradiation. And the low on—off ratio resulting from the zero bandgap makes it unsuitable for many electronic devices, hindering potential development. The graphene-based heterojunction composed of graphene and other materials has outstanding optical and electrical properties, which can mutually modify the defects of both the graphene and material making it then suitable for optoelectronic devices. In this review, the advantages of graphene-based heterojunctions in the enhancement of the performance of photodetectors are reviewed. Firstly, we focus on the photocurrent generation mechanism of a graphene-based heterojunction photodetector, especially photovoltaic, photoconduction and photogating effects. Secondly, the classification of graphene-based heterojunctions in different directions is summarized. Meanwhile, the latest research progress of graphene-transition metal dichalcogenide (TMD) heterojunction photodetectors with excellent performance in graphene-based heterostructures is introduced. Finally, the difficulties faced by the existing technologies of graphene-based photodetectors are discussed, and further prospects are proposed.     

Nonlinear optical rectification of GaAs/Ga1-xAlxAs quantum dots with Hulthén plus Hellmann confining potential

We investigate the nonlinear optical rectification (NOR) of spherical quantum dots (QDs) under Hulthén plus Hellmann confining potential with the external tuning elements. Energy and wavefunction are determined by using the Nikiforov-Uvarov method. Expression for the NOR coefficient is derived by the density matrix theory. The results show that the applied external elements and internal parameters of this system have a strong influence on intraband nonlinear optical properties. It is hopeful that this tuning of the nonlinear optical properties of GaAs/Ga_1-xAl_xAs QDs can make a greater contribution to preparation of new functional optical devices.