新型铁基超导体角分辨光电子能谱研究

最近发现的新型122结构的铁基超导体掀起了铁基高温超导研究的又一轮热潮.文章利用角分辨光电子能谱实验手段,研究了这类新型铁基材料的电子结构、费米面拓扑和超导能隙.实验结果表明,其在布里渊区中心的能带结构及费米面与其他铁基超导体存在明显差异,并导致嵌套在粒子-空穴通道的费米面消失.另外,在布里渊区边缘的电子型费米面发现了较强的并且有各向同性的超导能隙.这些结果对可能的超导配对机制提出了严格的限制.     

Competing phases in the cuprates: Charge vs spin order

We have investigated magnetic and charge instabilities of the cuprates within the Gutzwiller approximation RPA (GA+RPA). Interestingly, in GA the dressed Hubbard U is not a single parameter, but has different forms in the spin and charge responses, with distinct doping dependencies. While there are a number of competing magnetic instabilities for hole-doped cuprates, we fail to find any purely electronic charge density waves. The dominant magnetic instabilities are associated with ‘double nesting’, and the phase diagrams are material dependent, with LSCO differing from other cuprates.     

EC and α decays of 235Am

EC and decays of ²³⁵Am have been studied using a gas-jet coupled on-line isotope separator. Excited states in ²³⁵Pu have been established for the first time by means of -ray spectroscopy following the EC decay of ²³⁵Am. The deduced log ft value suggests that the ground state of ²³⁵Am should have the 5/2^-[523] configuration. The - coincidence result has revealed that the 5/2^-[523] state in ²³¹Np populated by the favored transition of ²³⁵Am is located at < 15 keV, which allows us to precisely determine the Q value of ²³⁵Am.     

Medium-spin excitations of the neutron-rich 84Se isotope: Possible decrease in energy of the N = 50 neutron-core excitation

The ⁸⁴Se nucleus has been produced as fission fragment in the fusion reaction ¹⁸O + ²⁰⁸Pb at 85MeV bombarding energy and studied with the Euroball IV array. Medium-spin states of this neutron-rich isotope have been identified for the first time. Its level scheme has been obtained up to 4.9MeV excitation energy and spin I 7. Its structure is interpreted by analogy with those of the stable heavier isotones. The evolution of the energy of the N = 50 neutron-core excitation is discussed as a function of the proton number.     

Direct visualization of the vortex distributions in a superconducting film with a Penrose array of magnetic pinning centers: Symmetry induced giant vortex state

Using scanning Hall probe microscopy a direct visualization of the flux distribution in a Pb film covering a fivefold Penrose array of Co dots is obtained. We demonstrate that stable vortex configurations can be found for fields H ∼ 0.8H₁, H₁ and 1.6H₁, where H₁ corresponds to one flux quantum per pinning site. The vortex pattern at 0.8H₁ corresponds to one vacancy in one of the vertices of the thin tiles whereas at 1.6H₁ the vortex structure can be associated with one interstitial vortex inside each thick tile. Strikingly, for H = 1.6H₁ interstitial and pinned vortices arrange themselves in ring-like structures (“vortex corrals”) which favor the formation of a giant vortex state at their center.     

一种改进的直方图均衡化

从理论上分析了直方图均衡化过程中灰度级合并的原因,给出了简单的物理解释和解析推导,并讨论了该算法的缺点。为了使图像保留更多的细节信息、消除虚假轮廓且保持连续性,提出了保留灰度级的直方图均衡化算法,并分析了其基本原理。实验结果表明:通过该算法处理的图像比采用传统直方图均衡化算法处理的图像效果好。     

X-ray spectra induced by ~(129)Xe~(q+) impacting the metal surface

Using the slow highly charged ions 129 Xe q+ (q=25,26,27;initial kinetic T0≤4.65 keV/a.u.)to impact Au surface,the Au atomic Mαcharacteristic X-ray spectrum is induced.The result shows that as long as the charge state of projectile is high enough,the heavy atomic characteristic X-ray can be effectively excited even though the incident beam is very weak(nA magnitude),and the X-ray yield per ion is in the order of 10-8and increases with the kinetic energy and potential energy of projectile.By measuring the Au Mα-X-ray spectra,Au atomic N-level lifetime is estimated at about 1.33×10-18s based on Heisenberg uncertainty relation.     

BE-代数的广义模糊理想

利用模糊拓扑中模糊点重于和属于模糊集概念研究模糊代数结构,在BE-代数中引入(∈,∈∨q)-模糊理想的概念,并研究这类模糊理想的重要性质.得到了BE-代数中(∈,∈∨q)-模糊理想的若干等价条件,研究了BE-代数的模糊理想和(∈,∈∨q)-模糊理想的关系,特别是利用上水平集和∈∨q-水平集刻画了(∈,∈∨q)-模糊理想.本文拓展了模糊代数结构的研究内容和方法.此结果和方法稍作修改可用于工程、计算机科学、人工智能和其他模糊代数结构等研究领域.     

Precise determination of the neutron scattering length of lead isotopes <Superscript>204</Superscript>Pb, <Superscript>207</Superscript>Pb and <Superscript>208</Superscript>Pb by neutron interferometry

Excited states of ⁶⁸Ga have been investigated through the ⁵⁵Mn(¹⁶O, 2pn) reaction at projectile energy 55 MeV. The level scheme has been extended up to 7.8 MeV. Altogether six new excited levels could be identified and twelve previously unobserved γ-transitions have been placed in the modified level scheme. Received: 19 June 2000 / Accepted: 20 October 2000     

渐开线斜齿轮短齿廓修形降噪分析

为了降低特定工况下减速箱的噪声特性,找到相对最佳的渐开线斜齿轮修形方式,该文基于专业的齿轮修形软件Kisssoft和多学科一体化软件LMS Virtual Lab,根据短齿廓修形可以改变渐开线斜齿轮的端面、轴向重合度的原理,比较了未修形和经过不同短齿廓修形方式达到特定重合度后的渐开线斜齿轮减速箱声功率级的大小。分析了经过短齿廓修形后的减速箱声功率级在转速500～2000 r/min之间显著下降的原因,并对经过短齿廓修形后的减速箱声功率级在2500 r/min和3000 r/min时并未明显下降的原因做了解释。最后根据减速箱声功率级在转速500～2000 r/min之间的平均降幅,认为通过齿形鼓形修形使得渐开线斜齿轮的端面、轴向重合度分别为1.516、0.864时,减速箱声功率级降幅最大,降噪效果最好。