润滑油对基于制冷循环的喷雾冷却系统性能的影响

针对高功率固体激光器的散热需求,设计了一种基于制冷循环的喷雾冷却系统,并对其换热性能进行研究。由于制冷系统的压缩机需要润滑,冷却液中不可避免地会混有润滑油。润滑油会对冷却液的粘度、表面张力产生影响,并可能产生油膜,从而对冷却液的换热过程产生强化或抑制。因此,通过实验研究,分析了润滑油对喷雾冷却换热性能的影响。实验结果表明,冷却液中存在润滑油,会增大冷却液流经喷嘴过程中的阻力,减小流量,但根据本系统的应用情况,可以忽略;在低热流密度时,含有一定量的润滑油更有利于热源表面温度的均匀分布,高热流密度时,2%(质量分数)的含油量对温度分布不均的影响可以忽略;润滑油的存在可以提高临界热流密度,使得系统的散热能力得到提高,更有利于其在高功率固体激光器散热领域的应用。     

Production and constraints for a massive dark photon at electron-positron colliders

Dark sector may couple to the Standard Model via one or more mediator particles.We discuss two types of mediators:the dark photon A’and the dark scalar mediatorΦ.The total cross-sections and various differential distributions of the processes e+e-→qqA’and e+e→qqφ(q=u,d,c,s and b quarks)are discussed.We focus on the study of the invisible due to the cleaner background at future e+e-colliders.It is found that the kinematic distributions of the two-jet system could be used to identify(or exclude)the dark photon and the dark scalar mediator,as well as to distinguish between them.We further study the possibility of a search for dark photons at a future CEPC experiment with s1/2=91.2 GeV and 240 GeV.With CEPC running at s1/2=91.2 GeV,it would be possible to perform a decisive measurement of the dark photon(20 GeV相似文献   

Zero-temperature magnetic transition in an easy-axis Kondo lattice model

We address the quantum transition of a spin-1/2 antiferromagnetic Kondo lattice model with an easy-axis anisotropy using the extended dynamical mean field theory. We derive results in real frequency by using the bosonic numerical renormalization group (BNRG) method and compare them with quantum Monte Carlo results in Matsubara frequency. The BNRG results show a logarithmic divergence in the critical local spin susceptibility, signaling a destruction of Kondo screening. The T=0 transition is consistent with being second order. The BNRG results also display some subtle features; we identify their origin and suggest means for further microscopic studies.     

分辨率对大气中痕量污染气体的DOAS测量性能影响研究

在差分吸收光谱(DOAS)测量过程中,光谱分辨率的选择直接决定了污染气体浓度的测量准确度.主要研究了光谱分辨率对污染气体被榆测到的特征吸收结构形状的影响,以及差分吸收截面随分辨率的变化趋势,从而确定了光谱分辨率对污染气体最低可检测浓度的影响,通过研究分辨率与光强的关系,确定了分辨率与信噪比(S/N)的函数关系式,得出了DOAS测量NO2,O3,和SO2的最佳信噪比范围,对多种污染物标准气体进行了同时监测,计算出标准气体在不同光谱分辨率下的测量误差,确定了对NO2,O3和SO2监测的最适用的分辨率范围.在此分辨率范围既能够实现对痕量气体的准确定性定量测量,又能达到测量所需要的高灵敏度,强选择性和适用的时间分辨率.通过在北京丰台区的实际监测得到了与点式仪器测量结果很好的一致性.     

A NECESSARY AND SUFFICIENT CONDITION FOR THE COEXISTENCE OF A CLASS OF CUBIC CURVE SEPARATRIX CYCLES AND LIMIT CYCLES TO THE CUBIC SYSTEM

In this paper, we give the necessary and sufficient condition for the coexistence of a class of cubic curve separatrix cycles and limit cycles to the cubic system, and study their topological structures.     

An improved evaluation of the neutron background in the PandaX-Ⅱ experiment

In dark matter direct detection experiments,neutron is a serious source of background,which can mimic the dark matter-nucleus scattering signals.In this paper,we present an improved evaluation of the neutron background in the PandaX-II dark matter experiment by a novel approach.Instead of fully relying on the Monte Carlo simulation,the overall neutron background is determined from the neutron-induced high energy signals in the data.In addition,the probability of producing a dark-matter-like background per neutron is evaluated with a complete Monte Carlo generator,where the correlated emission of neutron(s)andγ(s)in the(α,n)reactions and spontaneous fissions is taken into consideration.With this method,the neutron backgrounds in the Run 9(26-ton-day)and Run 10(28-ton-day)data sets of PandaX-II are estimated to be(0.66±0.24)and(0.47±0.25)events,respectively.     

理想弹塑性固体Riemann问题的解结构与初值条件

针对理想弹塑性固体材料的一维Riemann问题,在不考虑真空的情况下,讨论其所有可能存在的解结构,给出每一种解结构下对应的初值条件且证明该系列初值条件的完备性,即任意给定的物理量初值均有且只有一种解结构与之对应.基于该理论,在设计精确或近似理想弹塑性Riemann问题求解器时,可以依据初值条件对任意物理量初值直接判断其对应的解结构,从而提高求解器的精度和效率.数值试验验证了该系列初值条件的正确性和有效性.     

Multi-pass,multi-bunch beam breakup for 9-cellTesla cavities in the ERL

Generally, the Energy Recovery Linac (ERL) needs specially designed high current superconducting RF cavities. In this paper, the threshold current of beam breakup for compact ERL facilities with 9-cell Tesla type cavities are investigated. The results show that it is feasible to adopt the 9-cell Tesla cavity for compact ERL test facilities with just a few cavities and beam current around 10 mA.     

基于随机矩阵理论的城市人群移动行为分析

移动通信应用为人类移动规律的研究提供了独特的数据来源. 本文通过城市手机用户的分布数据,研究城市移动人群的整体动力学行为. 借助随机矩阵理论的方法,通过比较移动人群数据与随机数据在互相关矩阵谱分布上的差异,发现移动人群数据互相关矩阵的相关系数均值、最大本征值及其对应的本征向量明显偏离于随机互相关矩阵的分布,指出这种差异体现了城市移动人群的整体行为特性,且这种差异在不同时间段也会有所不同. 研究结果体现出相关系数的均值和最大本征值的波动趋势,并指出本征向量成员权重的时空模式与城市移动人群整体行为特征的波动过 关键词： 随机矩阵理论 移动人群 宏观行为     

Mott transition in modulated lattices and parent insulator of (K,Tl)(y)Fe(x)Se(2) superconductors

The degree of electron correlations remains a central issue in the iron-based superconductors. The parent iron pnictides are antiferromagnetic, and their bad-metal behavior has been interpreted in terms of proximity to a Mott transition. We study such a transition in multiorbital models on modulated lattices containing an ordered pattern of iron vacancies, using a slave-rotor method. We show that the ordered vacancies lead to a band narrowing, which pushes the system to the Mott insulator side. This effect is proposed to underlie the insulating behavior observed in the parent compounds of the newly discovered (K,Tl)(y)Fe(x)Se(2) superconductors.