利用飞行时间法测定锶原子5s5p3P1亚稳态能级寿命

本文结合TOF法和吸收光谱测量技术,利用连续光场测定了锶原子亚稳态能级的寿命。实验中,利用689nm激光连续泵浦基态锶原子至5s5p3P1亚稳态能级,然后在距泵浦区域不同距离处观测处于5s5p3P1态的原子对688nm探测光的吸收强度,得到锶原子5s5p3P1态的能级寿命,我们利用TOF法实验得到的能级寿命为21.9±0.8μs。本文给出的方法具备实验装置简单的优点,同时可获得较高的测量精度。     

Inversion algorithm based on the generalized objective functional for compressed sensing

Owing to providing a novel insight for signal and image processing, compressed sensing (CS) has attracted increasing attention. The accuracy of the reconstruction algorithms plays an important role in real applications of the CS theory. In this paper, a generalized reconstruction model that simultaneously considers the inaccuracies on the measurement matrix and the measurement data is proposed for CS reconstruction. A generalized objective functional, which integrates the advantages of the least squares (LSs) estimation and the combinational M-estimation, is proposed. An iterative scheme that integrates the merits of the homotopy method and the artificial physics optimization (APO) algorithm is developed for solving the proposed objective functional. Numerical simulations are implemented to evaluate the feasibility and effectiveness of the proposed algorithm. For the cases simulated in this paper, the reconstruction accuracy is improved, which indicates that the proposed algorithm is successful in solving CS inverse problems.     

Thermal-transport studies on two-dimensional quantum spin liquids

Quantum spin liquids (QSLs) are fluidlike states of quantum spins in which the long-range ordered state is destroyed by quantum fluctuations. The ground state of QSLs and their exotic phenomena, which have been extensively discussed for decades, have yet to be identified. We employ thermal-transport measurements on newly discovered QSL candidates κ-(BEDT-TTF)(2)Cu(2)(CN)(3) and EtMe(3)Sb[Pd(dmit)(2)](2), and report that the two organic insulators have different QSLs characterized by different elementary excitations. In κ-(BEDT-TTF)(2)Cu(2)(CN)(3), heat transport is thermally activated at low temperatures, and this suggests the presence of a spin gap in this QSL. In stark contrast, in EtMe(3)Sb[Pd(dmit)(2)](2), a sizable linear temperature dependence of thermal conductivity is clearly resolved in the zero-temperature limit, and shows gapless excitation with a long mean free path (ca. 1000 lattice distances). Such a long mean free path demonstrates a novel feature of QSL as a quantum-condensed state with long-distance coherence.     

Minimal violation of flavour and custodial symmetries in a vectophobic Two-Higgs-Doublet-Model

Tree-level accidental symmetries are known to play a fundamental role in the phenomenology of the Standard Model (SM) for electroweak interactions. So far, no significant deviations from the theory have been observed in precision, flavour and collider physics. Consequently, these global symmetries are expected to remain quite efficient in any attempt beyond the SM. Yet, they do not forbid rather unorthodox phenomena within the reach of current LHC experiments. This is illustrated with a vectophobic Two-Higgs-Doublet-Model (2HDM) where effects of a light, flavour-violating and custodian (pseudo)scalar might be observed in the _Bs→μ⁺μ⁻$B_s\to {\mu }^{+}{\mu }^{-}$ decay rate and in the diphoton invariant mass spectrum at around 125 GeV.     

一些典型的软物质物理中的非平衡自组织现象

在软物质物理中经常有自组织(self-organization)现象发生.这一现象通常在非平衡的过程中产生,并生成非常美丽和有趣的图案与结构.具体例子包括胶体颗粒的扩散限制凝聚(diffusion limited aggregation,DLA),Hele-Shaw盒中产生的流体分形结构,凝胶的形成(gelation),生物体自组织聚集,以及颗粒类物质(granular material)运动产生的规则图案等.这些现象在软物质物理研究中产生了很多重要结果.文章以比较浅显的文字介绍这些软物质物理中的非平衡自组织现象.     

高能量密度氘、氦的第一原理研究进展

极端条件下氘、氦的研究对于凝聚态物理、等离子体物理、天体物理以及惯性约束聚变的研究具有重要意义.文章综述了近年来温稠密区、热稠密区以及低温高压区的最新研究进展,归纳了尚待解决的科学问题,从而为进一步的研究提供参考.     

核物理与核探测、核分析技术的应用

文章概要介绍了随着核物理研究发展起来的辐射和粒子探测的原理、方法和主要技术,举例介绍了相关核物理与核探测、核分析的典型技术及其在高精度测量和医学中的广泛应用,如活化分析技术、穆斯堡尔谱学、核磁共振技术、加速器质谱技术、核医学成像、同步辐射技术、中子散射分析、放射性示踪技术等等.     

Nanoscience of single polymer chains revealed by nanofishing

The invention of atomic force microscopy (AFM) enabled us to study the statistical properties of single polymer chains by a method called "nanofishing," which stretches a single polymer chain adsorbed on a substrate with its one end by picking it at the other end. A force-extension curve obtained for a single polystyrene chain in a Theta solvent (cyclohexane) shows good agreement with a worm-like chain model and, therefore, gives microscopic information about entropic elasticity. Furthermore, the nanofishing technique can be used for dynamic viscoelastic measurement of single polymer chains. An AFM cantilever is mechanically oscillated at its resonant frequency during the stretching process. This technique enables the estimation of quantitative and simultaneous elongation-dependent changes of stiffness and viscosity of a single chain with the use of a phenomenological model. In this study, the effect of solvent on viscosity in low extension regions reveals that the viscosity is attributed to monomer-solvent friction. Thus, static and dynamic nanofishing techniques are shown to give powerful experimental proofs for several basic questions in polymer physics. The techniques are expected to reveal hidden properties of polymer chains or polymer solutions by any types of macroscopic measurements in the future.     

Rare tau decays from BABAR

The BABAR experiment has now completed data taking and with an integrated luminosity of 531 fb^-1 of e^＋e^- collision data has recorded some 480 million tau-pair events. Various studies of suppressed, rare and forbidden decays of the tau have been conducted, including searches for high-multiplicity decays, for second-class hadronic weak currents, and for lepton-flavour violation.