1+1维QCD中格点哈密顿量的一种改进形式

给出1+1维QCD中格点哈密顿量的一种简单有效的改进形式,并用它对矢量介子质量谱M_v在手征极限下的大N_c行为进行格点研究,数值计算的结果与强耦合分析的结果相一致.     

冷原子干涉仪中的相干动量操控

原子物质波的干涉现象是原子物理和量子光学的一个重要分支,肇始于原子在晶体表面的衍射和原子钟中的分离场技术。由于极高的稳定性和准确性,原子干涉已成为一个成熟而强大的工具,在现代科学技术中特别是在惯性测量领域都有非常重要的应用。回顾了原子干涉仪中用到的相干动量操控技术,包括Raman双光子跃迁、Bragg衍射以及Bloch振荡等,并在此基础上进一步总结了大动量转移技术的实现方式,对比了不同方式的优缺点,重点介绍了各种方法的使用范围及最新研究进展。     

光腔衰荡光谱法测量大气中的NO3和N2O5

本文应用基于二极管激光器的双路光腔衰荡光谱技术,分别对大气中NO₃和N₂O₅浓度进行监测. 通过使用实验室标准样校正有效吸收腔长比R_L和系统的总损耗系数?,并获得了NO₃有效吸收截面. 该装置在时间分辨率为1 s时,对NO₃的测量灵敏度达到1.1 pptv,N₂O₅被在线转换成NO₃,从而被另一路光腔衰荡光谱装置探测. 利用该装置,对合肥市区冬季夜间大气中的NO₃,N₂O₅浓度进行了实时监测. 通过对比一次大气快速清洁过程中氮氧化物、臭氧、PM_2.5等组分的浓度变化,讨论了大气环境下可能影响NO₃及N₂O₅浓度的因素.     

低温液体流动沸腾数值计算中的动量模拟

采用双流体模型计算了液氮在垂直管内的过冷流动沸腾过程,着重考察了相间动量传输模型对数值预测结果准确性的影响。研究表明,相间非曳力,尤其是壁面润湿力对于数值预测的准确性有着决定性的作用。此外,正确地估计沸腾系统中气泡的平均直径对于两相流传输特性的准确预测也有着十分重要的作用。     

偶偶核基带的量子群Uqp(u2)模型的理论分析

通过对锕系和稀土偶偶核基带转动谱实验数据的拟合和Mallmann图的研究,系统地分析了量子群U_qp(u₂)模型对原子核转动谱的适用性.结果表明,U_qp(u₂)模型的理论值与实验值比较接近,明显优于单参数形变量子代数SU_q(2)模型.此外,还建立了U_qp(u₂)的形变参量q、p与核软度的关系.     

量子群Uqp(u2)模型对A～190区超形变带研究

用双参数量子群U_qp(u₂)理论模型公式对A～190区47条超形变(SD)转动带进行了系统分析.计算得到的Eγ跃迁谱与实验较好地吻合;按转动带自旋指定的3种方案确定¹⁹⁴Hg(1),¹⁹⁴Pb(1)的带首自旋,结果与实验一致.此外,进一步讨论了核软度参数σ1的物理意义,发现一对旋称对偶带的σ1几乎全等.     

Jaynes-Cummings模型中辐射场的振幅N次方压缩特性

本文研究了一初始处于激发态的二能级原子与相干态光场相互耦合的Jaynes-Cummings模型中场的振幅N次方压缩特性,给出了其压缩度随光场的初始平均光子数和压缩阶数的变化规律。     

多层膜外退火方法制备MgB2超导薄膜

报道了利用电子束蒸发的Mg/B多层膜作为前驱体，然后退火制备MgB₂薄膜的工作. 实验中发现，采用翻转膜面的退火处理方式可以有效地避免降温过程中Mg蒸气在薄膜表面形成的颗粒凝结，由此稳定地实现了面积为10 mm×10 mm，均匀、平整的超导薄膜的制备，T_c达35 K，转变宽度为0.8 K，在5 μm×5 μm的区域内薄膜的平均粗糙度小于10 nm. 为了便于后续器件制作过程中的微加工工艺，研究了膜厚小于1000 ?时薄膜的成相规律，发现当样品厚度减薄后，T_c会有明显降低. 通过调整前驱薄膜中的不同分层厚度，仍可实现转变温度达30 K以上、厚度约600 ?的MgB₂薄膜，在20 K时的临界电流密度为2.4×10⁶ A/cm².     

在手征么正模型中0+重介子是否存在分子态结构

在分子态结构的假设下, 利用手征么正模型研究了D₀(2308)和B₀的可能结构. 通过研究重子-赝标介子相互作用, 找到了一些可能的分子态. 结果表明: 在带奇异数的系统中, 存在一个质量为2.312±0.041GeV的DK束缚态, 它可以被解释为实验上发现的D_s0(2317). 与此同时, 在非奇异系统中, 存在一个与之对应的、质量为2.1GeV的宽度较大的态和一个对应的、质量为2.44GeV的宽度较小的态. 这两个态应对应于D₀. 因此, 分子态结构只能是D₀(2308)一个分量. 计算结果还预言了一些B_s0和B₀态. 其中质量为5.725±0.039GeV的BK束缚态可以被解释为B_s0(5725), 而预言的B₀(5536)和B₀(5819)应为与B_s0(5725)相对应的非奇异态.     

Zn Belavin模型反射方程的多参数解

利用A_(n－1)⁽¹⁾面模型反射方程的对角解,得到了ZnBelavin模型反射方程的含有n+1个参数的解.当n=2时,其结果与侯伯宇等人给出的8项角反射方程的解是一致的.     

Massive Meson Fluctuation in NJL Model

Based on the self-consistent scheme beyond the mean-field approximation in the large N_c expansion, including current quark mass explicitly, a general scheme of SU(2) NJL model is developed. To ensure the quark self-energy expanded in the proper order of N_c,an approximate internal meson propagator is deduced, which is in order of O(l/N_c). In our scheme, adopting the method of external momentum expansion, all the Feynman diagrams are calculated in a unified way by only expanding the quark propagator. Our numerical results show that, different &om the mean-field approximation in which the explicitly chiral symmetry breaking is invisible, the effect of finite pion mass can be seen clearly when beyond the meanfield approximation.     

The Dyson-Schwinger Method of the NJL Model Beyond the Mean Field Approximation

By making use of the generating functional method we derive the Dyson-Schwinger equations in the NJL model and obtain the revised quark gap equation due to the meson dressing effects (usually called beyond the mean-field correction), and finally analyze its influence on the meson properties as well as the nucleon sigma term.     

光束截面的动量守恒及动量衍射发散度

在忽略了瞬逝波的条件下，证明真空中单色标量光场的光束截面的动量及其任一分量都与轴向坐标无关，为守恒量；文中还给出了动量衍射发散度的表达式。     

Propagators for Scalar Bound States at Finite Temperature in an NJL Model

We re-examine physical causal propagators for scalar and pseudoscalar bound states at finite temperaturein a chiral Ut(1) x UR(1) NJL model, defined by four-point amputated fimctions subtracted through the gap equation,and prove that they are completely equivalent in the imaginary-time and real-time formalisms by separating carefiullythe imaginary part of the zero-temperature loop integral. It is shown that the same thermal transformation matrix ofthe matrix propagators for these bound states in the real-time formalism is precisely the one of the matrix propagatorfor an elementary scalar particle and this fact shows the similarity of thermodynamic property between a composite andelementary scalar particle. The retarded and advanced propagators for these bound states are also given explicitly fromthe imaginary-time formalism.     

The 1/Nc Expansion in Hadron Effective Field Theory

We study the N_c scalings of pion-nucleon and nucleon-nucleon scatterings in hadron effective field theory. By assuming Witten's counting rules are applied to matrix elements or scattering amplitudes, which use the relativistic normalization for the nucleons, we find that the nucleon axial coupling g_A is of order N_c0, and a consistent large N_c counting can be established for the pion-nucleon and nucleon-nucleon scatterings. We also justify the nonperturbative treatment of the low energy nucleon-nucleon interaction with the large N_c analysis and find that the deuteron binding energy is of order 1=N_c.     

Self-consistent mean field approximation and application in three-flavor NJL model

In this study, we apply a self-consistent mean field approximation of the three-flavor Nambu–Jona-Lasinio(NJL) model and compare it with the two-flavor NJL model. The self-consistent mean field approximation introduces a new parameter, α, that cannot be fixed in advance by the mean field approach itself. Due to the lack of experimental data, the parameter, α, is undetermined. Hence, it is regarded as a free parameter and its influence on the chiral phase transition of strong interaction matter is studied based on this self-consistent mean field approximation. α affects numerous properties of the chiral phase transitions, such as the position of the phase transition point and the order of phase transition. Additionally, increasing α will decrease the number densities of different quarks and increase the chemical potential at which the number density of the strange quark is non-zero. Finally, we observed that α affects the equation of state(EOS) of the quark matter, and the sound velocity can be calculated to determine the stiffness of the EOS, which provides a good basis for studying the neutron star mass-radius relationship.     

Au-Au碰撞中大横动量双轻子对的产生(英文)

运用微扰QCD讨论了重离子碰撞中大横动量轻子对的分布, 计算了Au-Au碰撞中两个部分子产生的轻子对的贡献。引入了轻子对产生的直接单光子过程和分解单光子过程。大横动量情况下的所有过程都包括在内, 而且考虑了核遮蔽效应和同位旋效应, 作为QGP背景的双轻子信号有了一个好的修正。The large transverse momentum distribution of lepton pairs produced in heavy-ion collisions has been studied, making use of the perturbative QCD. The contribution of the two parton production process into lepton pairs in Au Au collisions is calculated. Lepton pair production with the direct single photon process and the resolved single photon process are introduced. We believe that the photon processes are significant. The complete processes at large transverse momentum are included, and moreover, the effect of shadowing and isospin of nucleus are also considered in heavy ion collisions. Dilepton signals to regard the background of QGP have a good correction.     

Two-Point Function Reduction of Four-Point Amputated Functions and Transformations in FF and RA Basis in a Real-Time Finite Temperature NJL Model

Based on a general analysis of Green functions in the real-time thermal field theory, we have proven that the four-point amputated functions in an NJL model in the fermion bubble diagram approximation behave like usual two-point functions. We expound the thermal transformations of the matrix propagators for a scalar bound state in the FF basis and in the RA basis respectively. The resulting physical causal, advanced and retarded propagators are respectively identical to corresponding ones derived in the imaginary-time formalism, and this shows once again the complete equivalence of the two formalisms of thermal field theory on the discussed problem in the NJL model.     

Decomposition for a 2+1-Dimensional Discrete Integrable Model

A 2＋1-dimensional discrete is presented, which is decomposed into a new integrable symplectic map and a class of finite-dimensional integrable Hamiltonian systems, with aid of the nonlineaxization of Lax pairs. The system is completely integrable in the Liouville sense.     

Linked-Cluster Expansion of the Ising Model

The linked-cluster expansion technique for the high-temperature expansion of spin modes is reviewed. A new algorithm for the computation of three-point and higher Green's functions is presented. Series are computed for all components of two-point Green's functions for a generalized 3D Ising model, to 25th order on the bcc lattice and to 23rd order on the sc lattice. Series for zero-momentum four-, six-, and eight-point functions are computed to 21st, 19th, and 17th order respectively on the bcc lattice.