张英逊
,
卢晓华
,
赵凯
,
李祝霞
,
P．Danielewicz
,
M．B．Tsang
原子核物理评论
对称能的密度依赖形式对于中子星结构及其演化规律、不稳定核结构及其反应等都有非常重要的影响。由于目前理论上预言的对称能密度依赖形式有很大的不确定性,因此确定对称能的密度依赖形式已经成为目前核物理研究的一个重要课题。丰中子核重离子碰撞是目前在实验室条件下确定对称能密度依赖形式的一种重要手段,其主要的理论依据就是微观输运理论。首先回顾了目前输运理论的两个处理方法,即Boltzmann-Uehling-Uhlenbeck（BUU）和量子分子动力学（QMD）方法,并重点介绍了改进的量子分子动力学模型（ImQMD05）。利用ImQMD05对中能重离子碰撞的一些基本观测量,如碎块分布、集体流、核核碰撞的阻止本领等进行了详细研究,通过与实验数据的比较,确定了ImQMD05中同位旋无关部分的平均场、介质中核子-核子散射截面。为了从重离子碰撞的实验数据确定对称能的密度依赖形式,详细研究了输运理论中对称势以及同位旋相关的介质中核子-核子散射截面对于同位旋敏感观测量的影响。研究显示,对于Fermi能附近的重离子碰撞,输运理论预言的同位旋敏感的观测量,如DR（n/p）和Ri,强烈依赖于对称势的软硬,而不敏感于介质中同位旋相关的核子-核子散射截面。多重碎裂作为中能重离子碰撞的一个主要特点,本文论述的研究显示碎块发射机制对同位旋敏感的观测量,出射核子的双中子质子之比DR（n/p）和同位旋转移之比Ri,都有重要影响。以重碎块的同位旋不对称度为探针得到的同位旋转移之比Ri（δZmax〉20）要大于Ri（δ）,这些测量能够在NSCL/RIKEN的相关实验上进行测量。同时,这一现象的研究对于理解碎块的发射机制及碎块发射的特征时间等问题将有重要的帮助。为此,采用ImQMD05研究了112,124Sn＋112,124Sn在入射能量50MeV/u,不同碰撞参数条件下的多个实验观测量,如DR（n/p）、同位旋扩散Ri以及同位旋转移之比的快度分布。研究表明,模型能够同时自洽地解释这几个实验观测量,并通过与这些实验数据的分析比较,自洽地确定出低密区对称能密度依赖形式的范围。
关键词:
对称能
,
重离子碰撞
,
集体流
,
核核碰撞的阻止本领
Journal of the Less-Common Metals
High-field magnetization measurements were performed on magnetically aligned samples of quasi-ternary compounds of the Pr2(Fe,M)14B series with M = Al, Ga and Si at 4.2 K in magnetic fields up to 35 T. The saturation magnetization and anisotropy constants were derived as functions of composition. The results suggest that the transition in the magnetization curves of these series is probably not a first-order magnetization process (FOMP).
关键词:
crystal;anisotropy;pr2fe14b
Journal of Applied Physics
The magnetic properties of nanocomposite multilayer magnets of the (Nd,Dy)(Fe,Co,Nb,B)(5.5)/M (M=Co,FeCo) on Ti-buffered Si substrates have been investigated. X-ray diffraction results reveal that the Nd2Fe14B-type phase in almost all the films is randomly oriented. Different thickness x (nm) for Co layers and y (nm) for FeCo layers were adopted in the multilayers. It is found that high remanence is achieved in the nanocomposite multilayer films consisting of the Nd2Fe14B-type phase and soft magnetic phase for Co with 6greater than or equal toxgreater than or equal to4 and for FeCo with 10greater than or equal toygreater than or equal to6. The enhancement of the remanence in the nanocomposite multilayer films is attributed to the exchange coupling between the magnetically soft and hard phases. Increasing the soft magnetic components results in a continuously decreasing coercivity. (C) 2002 American Institute of Physics.
关键词:
remanence enhancement;fe;films
Journal of Magnetism and Magnetic Materials
Phase constitution and magnetic properties of Nd10Fe76B4M10 and Nd10Fe76B2M12 (M = Fe,Ti,V,Cr, Mn,Co and Al) alloys prepared by mechanical alloying and subsequent annealing have been systematically studied. It is found that the components of phases in the alloys critically depend on the additive transition metals M. In all the alloys, only the addition of Ti give significant enhancement to the permanent-magnetic properties. The increase of the Curie temperature in the Ti-doped alloys with an excessively low B content implies that part of the Ti atoms may occupy crystalline sites other than the Fe sites. In all the M additive alloys, with increasing content of the additive elements, the quantity of 1:7 phase increases and that of Nd2Fe14B-type phase decreases, (C) 2000 Elsevier Science B.V. All rights reserved.
关键词:
phase constitution;structure;magnetic properties;alloys;mechanical;alloying;nd;coercivity
SUN LilingInstitute of Metal Research
,
Chinese Academy of Sciences
,
Shenyang
,
ChinaWU QiShenyang College of Technology
,
Shenyang
,
ChinaZHANG Zhiya
,
HU ZhuangqiInstitute of Metal Research
,
Chinese Academy of Sciences
,
Shenyang
,
China
金属学报(英文版)
The effect of trace element B on microstructure of directionally solidified new type Co-base superalloy is studied systematically in this paper. It is found that the addition of B makes the incipient melting temperature of the alloy decline remarkably. Compared with the alloy having a boron content of 0.05 %, the incipient melting temperature of the alloy with 0.7 % B decreases by 197℃. The primary and secondary dendrite arm spacings increase and the volume fraction of interdendritic carbides with fine microstructure becomes bigger with the enhancement of boron content. When the alloy is with 0.7wt %B, M3B2 precipitates in the interdendrites.
关键词:
horon
,
null
,
null
,
null
邢峰
,
江潮
,
何文望
金属学报
本文研究了Nd_2(Fe_(1-x)M_x)_(14)B的磁性。少量类金属原子C和Si取代部分Fe,能形成四方结构,且具有单轴各向异性。碳取代Fe,使化合物的Curie温度降低,低温下粘结体样品的内禀矫顽力减少;而Si对Fe的取代可使Curie温度升高,并在x=0.15附近达到极大值。含Si样品在0≤x≤0.10范围内,矫顽力显著增加,室温下从x=0的62.7kA/m增加到x=0.06的138.7 kA/m,并且在x=0.06附近,剩磁有一个极值,饱和磁化强度减少不多。
关键词:
Nd-Fe-B合金
,
magnetic properties
,
Curie temperature
李玉清
金属学报
在NiFeCrWMoTiAl合金断口的萃取碳复型上,观察到:合金中的硼可以减少和消除能脆化合金晶界的Ti_4C_2S_2脆性薄片;硼含量为0.025—0.050％和0.075—0.100％时,M_3B_2分别呈薄片(或枝晶薄片)状和块状;在1200℃以下温度加热时,颗粒状M_3B_2沉淀,而且薄片状M_3B_2向颗粒状M_3B_2转变。
关键词:
董琰峰
,
周石山
,
杨修春
功能材料
以V2P5为原料,采用无机溶胶-凝胶法制备出V2O5粉体,在H2气氛下热处理得到了VO2(B)粉体,再在Ar气氛下热处理VO2(B)粉体,制备出了VO2(M)粉体.采用X射线衍射(XRD)、红外吸收光谱(IR)、差热分析(DTA)等方法对样品进行了成分和结构分析,结果表明,当热处理温度为500℃、H2浓度50%时,得到VO2(B)粉体;然后,在Ar气氛下分别经过550、600、650、700℃处理1h后,VO2由B型向M型转变,700℃处理成功制备出了VO2(M)粉体.
关键词:
无机溶胶-凝胶法
,
V2O5
,
VO2(B)
,
VO2(M)
,
晶型转变
