全空间中带临界指数增长的Kirchhoff问题

本文考虑非齐次Kirchhoff型方程解的存在性与多解性:m(‖u‖N)(-ΔNu+V(x)|u|N-2u)=f(x,y)/|x|β+∈h(x),x∈RN,其中N≥2,‖u‖N=fRN(|▽u|N+V(x)|u|N)dx,ΔNu=div(|▽u|N-2▽u)是N-拉普拉斯算子,m:R+→R+表示Kirchhoff函数,...     

Theoretical and numerical studies on the flow multiplicity phenomenon for gas–solids two-phase flows in CFB risers

The dependence of the fully-developed flow profiles on the inlet flow conditions for gas–solids two-phase flows, i.e. the flow multiplicity phenomenon, in circulating fluidized bed (CFB) risers was proposed and discussed in this article. The flow multiplicity phenomenon for gas–solids two-phase flows was first proved mathematically based on the conservation equations of mass and momentum. Then the CFD model using Eulerian–Eulerian approach with k–ε turbulence model for each phase was further adopted to analyze the details of this flow multiplicity phenomenon. It is theoretically and numerically revealed that for gas–solids two-phase flows, the flow profiles in the fully-developed region are always dominated by the flow profiles at the inlet. The solids concentration profile is closely coupled with the velocity profile, and the inlet solids concentration and velocity profiles can largely influence the fully-developed concentration and velocity profiles.     

光电耦合器的反应堆中子辐射效应

 选择3种典型光电耦合器开展了反应堆中子辐照实验,中子注量为3×10¹¹~5×10¹²cm^-2时,位移效应导致电流传输比下降,饱和压降提高。发光器件相同,探测器为Si PIN光电二极管的光电耦合器比探测器为Si NPN光敏晶体管的光电耦合器的初始电流传输比要小,但其抗位移损伤能力更强。探测器均为Si NPN光敏晶体管,发光器件为异质结LED要比硅两性掺杂LED的光电耦合器的电流传输比抗位移损伤能力提高2个量级;以光敏晶体管为探测器的光电耦合器,在较大的正向电流和输出负载电阻条件下工作可提高抗辐射水平。此外,光电耦合器的位移损伤存在加电退火效应。     

SILEX-I装置上激光-团簇聚变实验中子产额测量

 超短超强脉冲激光与CD4团簇相互作用可以产生高能量的氘离子,从而产生DD聚变中子,这种团簇聚变中子源有着非常广阔的应用前景。在SILEX-I 100 TW飞秒激光装置上,超短超强脉冲激光与CD₄团簇相互作用实现了DD核聚变。团簇聚变的中子产额是实验中最为重要的物理量,在实验中采用高灵敏的中子探测器对团簇聚变产生的中子进行了测量,在现有实验条件下测得中子产额为10³。     

基于时标系统的条纹相机动态畸变

针对神光Ⅲ原型实验中出现的动态畸变现象,开展了条纹相机动态成像特性研究。结合实验图像,利用CST Particle Studio软件模拟了强信号下变像管的成像过程,结果表明:在强信号下,变像管的空间电荷效应会造成电子束聚焦点与理想成像面距离减小,使得图像的放大倍数变小,产生信号弯曲现象,并且这一现象随着电流强度的增加更为明显。     

超导与自旋涨落

在常规超导体中,库珀对是由于电子与声子之间的相互作用而形成的.在此过程中,人们可以只考虑电子的电荷性质与声子之间的关联.然而在所谓的非常规超导体中,人们意识到一些其他类型的元激发也可能导致超导现象,而自旋涨落则可能是其中最重要的一种.在大多数非常规超导体中,都可以发现自旋涨落的身影.而在一些重要的体系中,包括铜基超导体、铁基超导体以及一些重费米子超导体体系等,可以确切地说,自旋涨落起到了关键的作用,尽管其相对应的超导机制仍然还不清楚.文章简单介绍了自旋涨落与超导电性之间的关联.     

The discoveries of uranium 237 and symmetric fission - from the archival papers of Nishina and Kimura

Shortly before the Second World War time, Nishina reported on a series of prominent nuclear physical and radiochemical studies in collaboration with Kimura. They artificially produced (231)Th, a member of the natural actinium series of nuclides, by bombarding thorium with fast neutrons. This resulted in the discovery of (237)U, a new isotope of uranium, by bombarding uranium with fast neutrons, and confirmed that (237)U disintegrates into element 93 with a mass number of 237. They also identified the isotopes of several middle-weighted elements produced by the symmetric fission of uranium. In this review article, the highlights of their work are briefly summarized along with some explanatory commentaries.     

Magnetic properties of cobalt nanowires: Study by polarized SANS

Structural and magnetic properties of two-dimensional spatially ordered system of ferromagnetic cobalt nanowires embedded into Al₂O₃ matrix have been studied using polarized small-angle neutron scattering. A comprehensive analysis of contributions to the scattering intensity was carried out, including nonmagnetic (nuclear) contribution, magnetic contribution depending on the magnetic field, and nuclear-magnetic interference indicating the correlation between the magnetic and nuclear structures. Experiments have revealed an anomalously low value of the magnetic contribution as compared to the nuclear one. This behavior is interpreted in terms of low coherence of the magnetic structure caused by the anisotropy of Co crystallites as compared with the large coherency of nuclear structure of nanowires.     

Characterisation of novel magnetic materials using the USANSPOL technique

USANSPOL is a novel ultra-small-angle scattering technique with polarised neutrons for investigation of magnetic materials. It represents a polarised neutron extension to traditional USANS which works with unpolarised neutrons. The high angular resolution of this technique relies on the narrow reflection width of perfect crystal reflections and is employed in a double-crystal diffractometer. Corresponding to the μrad resolution of the set-up, micro-structures of the order of a few tenths of a micrometre up to a few tens of micrometres may be investigated. Neutron polarisation is achieved by insertion of birefringent magnetic prisms between the monochromator crystal and the sample. Rocking the analyser crystal produces a scattering pattern for both neutron spin states in a single measurement but well separated in reciprocal space. By this technique, we have recently studied various amorphous Galfenol soft-magnetic ribbons which were produced by spinning from melt at different manufacturing conditions. USANSPOL allows for a determination of domain sizes of the non-magnetised samples and a study of the growing of magnetically homogeneous regions with increasing externally applied magnetic field. The manufacturing process of the ribbons is reflected in the magnetic micro-structure of the different specimens.     

Interaction of neutrons with layered magnetic media in oscillating magnetic field

New experimental possibilities of investigating layered magnetic structures in oscillating magnetic fields are discussed. Spin-flip and nonspin-flip neutron reflection and transmission probabilities show a frequency dependency near the magnetic neutron resonance condition. This allows to increase the precision of the static magnetic depth profile measurements of the magnetized matter. Moreover, this opens new possibilities of measuring the induction of the oscillating field inside the matter and determining the magnetic susceptibility of the oscillating magnetic field. Refraction of neutrons as they pass through a magnetic prism in the presence of an oscillating magnetic field is also investigated. A non-polarized neutron beam splits into eight spatially separated neutron beams, whose intensity and polarization depend on the strength and frequency of the oscillating field. Also, it is shown that the oscillating magnetic permeability of an angstrom-thick layer can be measured with a neutron wave resonator.