膨胀的热的富重子夸克─胶子物质的双轻子产生的抑制

从完全核阻止的假定出发基于３＋１维ＲＨＥ研究了双轻子谱，并得到结论：如果在极端相对论性原子核碰撞中富重子的夸克－胶子物质真地产生了，那么随着初始重子密度的增加，在不变质量２ｍπ和１ＧｅＶ之间双轻子的产生将会显示出强烈的抑制，而且将有一个反常的峰出现在不变质量０．７５ＧｅＶ附近．这些预言可以在ＣＥＲＮ和Ｂｒｏｏｋｈａｖｅｎ即将开展的实验中得到检验．     

夸克－胶子等离子体对高能碰撞多重产生的可能描述

以ＱＣＤ袋模型和统计流体力学模型为基础，在二维平衡态近似下得到多重数和质心系能量的关系式，和高能　碰撞非单衍过程产生的多重数实验数据吻合得很好；在三维平衡态近似下得到中心在快度较大区域的产生粒子的源Ⅱ的大小和横动量的关系，关系式和三火球模型计算结果符合．     

PGNAA系统中D-T中子管的慢化装置优化设计

为了提高PGNAA系统中D-T中子管的中子慢化效率,获得更高的热中子产额,借助蒙特卡罗模拟,确定了以铅为中子反射层、5个聚乙烯层和铅层相互交替作为中子慢化层、碳化硼含量为3%的含硼聚乙烯作为中子吸收层以及铅作为γ屏蔽层的中子慢化装置模型。针对中子产额为3×107 n/s 的D-T中子管,该慢化装置输出面低于5 eV中子通量可达5.28×106 n/s,占总中子通量的30.8%,有效提高了中子慢化效率。经过验证模拟结果能够满足实验要求。To improve the moderating efficiency of D-T Neutron Generator in PGNAA system, and get higher thermal neutron yield, the Monte Carlo code MCNP was used to optimize the moderation setup. The lead was selected as neutron reflector and gamma absorber, 5 polyethylene layers and 4 lead layers constituted the neutron moderator and 3% boron-doping polyethylene was selected as neutron absorber. For the yield of 3107 n/s D-T Neutron Generator, this moderation setup can provide a yield of lower than 5 eV of 5.28106 n/s, accounting for 30.8% of total neutron yield, dramatically improves the moderating efficiency. It is proved that the simulation results can satisfy the requirement of PGNAA system by preliminary experimental verification.     

标量介子f0(980)光生过程γp→pf0(980)的研究

轻标量介子性质研究是当今中高能核物理研究中的热点问题之一,特别是质量低于1 GeV的标量介子f₀（980）的内部结构一直存在争议,至今未达成共识。基于前人的研究结果,运用有效拉氏量方法,对f₀（980）粒子的光生过程γp→pf₀（980）进行了更深入的理论研究。探讨了两种传播子形式下得矢量介子ρ和ω交换的贡献,第一种是选择雷吉传播子,第二种是选择普通费曼传播子。第二种形式的微分散射截面理论结果与现有实验数据符合比第一种形式的结果好。基于此,计算了两种形式的总截面,两种形式给出的理论结果相差很大。另外,给出了γp→pf₀（980）→pπ+π-过程的π+π-不变质量分布的理论预言,发现π+π-不变质量分布对于f₀（980）于K-K的耦合常数（g_f0KK）有很强的依赖关系,不同的g_f0KK给出明显不同的π+π-不变质量分布。将来相关实验数据可以验证这些理论预言,并对矢量介子传播子形式和耦合常数g_f0KK做出限制,加深人们对f₀（980）粒子的认识。We study the scalar meson f0(980) in the γp→pf0(980) reaction within an effective Lagrangian approach. Based on previous studies, we calculate the differential cross sections of this reaction. We take two types of the propagators of vector mesons ρ and ω, one is the Regge form, the other one is the normal Feynman propagator. It is found that our theoretical results for the differential cross sections with the Feynman propagator are in agreement with the current experimental data. For the total cross sections, the results with the two types of propagator are much different. On the other hand, we predict the π+π- invariant mass distribution of the γp→pf0(980)→pπ+π- reaction. We find that the π+π- invariant mass distribution depends sensitively on the value of the coupling constant gf0KK. We hope that the future experiments can test our model calculation and give further constraints on the value of gf0KK and also the nature of f0(980).     

Average Property of Isospin Effects Induced by Neutron-Halo Nuclei

We study the average property of the isospin effects of reaction mechanism induced by neutron-halo nuclei within the isospin-dependent quantum molecular dynamics model. We find that the extended neutron density distribution for the neutron-halo projectile brings an important isospin effect into the reaction mechanism, which induces the decrease of nuclear stopping R; however, it induces the obvious increases of the neutron-proton ratio of nucleon emissions （n/p）nucl for all of the beam energies in this work, compared to the same mass stable colliding system.     

Two-dimensional relativistic electromagnetic dromion-like soliton in a cold transparent plasma

By using a standard multiple scale method, a Davey--Stewartson (DS) equation has been derived and also applied to a multi-dimensional analytical investigation on the interaction of an ultra-intense laser pulse with a cold unmagnetized transparent electron-ion plasma. The regions of instability are found by considering the modulation instability of a plane wave solution of the DS equation. The DS equation is just of the Davey--Stewartson 1 (DS1) type and admits a dromion solution, i.e. a two-dimensional (2D) dromion soliton decaying exponentially in all spatial directions. A 2D relativistic electromagnetic dromion-like soliton (2D REDLS) is derived for a vector potential.     

光学中一道流传甚广的典型错题

根据“用牛顿环测定透镜曲率半径实验”的原理,剖析了有关牛顿环的一道典型错题,列举了正确的例题.     

基于μ子动量谱的多群模型测量平板材料的厚度北大核心CSCD

在基于μ子多重库仑散射的断层成像技术中,天然宇宙射线中不同动量的μ子在同一目标对象中的散射特性存在明显的差异,这在一定程度上影响了成像分辨率。为了减少或消除这种不利影响,建立了一套基于天然宇宙射线μ子动量谱的多群模型,并检验其用于铅板厚度测量及平板材料识别中的性能和特征。结果表明,采用基于μ子动量谱的多群模型能够实现1~16cm范围内铅板厚度的准确测量,相对误差小于5%。此外,该多群模型还可以通过计算辐射长度来识别未知平板的材料组成,尤其是对于高原子序数材料组成的平板,其辐射长度相对误差小于4%。     

含有周期球腔的黏弹性覆盖层消声性能分析

利用散射矩阵法分析了单个球状空腔在黏弹性橡胶中的Mie散射特性以及振动模式.以此为基础，利用多重散射法分析了不同背衬条件下，含有单层周期球状空腔的橡胶覆盖层(厚度为8mm)的消声性能.结果表明，单个球腔的径向共振对覆盖层的低频消声性能有重要贡献，覆盖薄层在共振区具有良好的消声性能.最后，设计了双层消声覆盖层(厚度为20mm)，有效拓展了消声带宽. 关键词： Mie散射 多重散射法 消声材料 声子晶体     

Fermionic Zero Modes in Self-dual Vortex Background on a Torus

We study fermionic zero modes in the self-dual vortex background on an extra two-dimensional Riemann surface in （5＋1） dimensions. Using the generalized Abelian-Higgs model, we obtain the inner topological structure of the self-dual vortex and establish the exact self-duality equation with topological term. Then we analyze the Dirac operator on an extra torus and the effective Lagrangian of four-dimensional fermions with the self-dual vortex background. Solving the Dirac equation, the fermionic zero modes on a torus with the self-dual vortex background in two simple cases are obtained.