热强子质量的有效手征拉氏量近似

从再现QCD标度反常的线性化手征拉氏量出发,使用热场动力学理论,计算了单圈近似下强子的热质量,并发现组分夸克质量和标量场质量在单圈近似下比在平均场近似下随温度的增加更快地下降,而在手征极限下,π介子在所有温度保持无质量.     

Novel massive ground states of spin chains in a magnetic field

Novel massive quantum states appearing in spin chains under a strong magnetic field are discussed. These states lead to plateaus in magnetization curves. When the systems are axially symmetric and the field is applied parallel to the symmetry-axis, the phenomena are analogous to metal-insulator transitions. Striking features of the plateau phenomena - exactness and rationality - are explained as consequences the commensurability condition to the underlying lattice. The effects of the planar anisotropy are also discussed in detail. Received: 16 February 1998 / Revised: 20 April 1998 / Accepted: 30 April 1998     

利用地磁场综合模型CM4分析中国大陆地区地磁场变化

第四代地磁场综合模型CM4是迄今为止将地磁场的内源场和外源场分离得最为彻底的数学模型.利用该模型结合Taylor多项式模型,基于1960—2000年期间中国大陆地区的实测数据,计算并分析了以10a为间隔的内源场和外源场的变化情况,通过将1960—1990年的所有磁异常点归算至2000年以分析地壳磁异常场的总体分布趋势.结果显示:地磁北向分量X的内源场强度总体呈逐年减弱的趋势,从1960年到2000年共下降了约750nT,外源场强度总体呈先增强后减弱的趋势,共下降了约32nT;地磁东向分量Y的内源场强度总体呈先减弱后增强的趋势,1960—2000年期间共上升了约40nT,外源场强度总体呈先减弱后增强再减弱的趋势,共上升了约3.8nT;地磁垂直分量Z的内源场变化趋势与Y分量类似,共上升了约600nT,外源场总体呈先减弱后增强的趋势,共上升了约4.6nT.对于地壳磁异常场,X分量、Z分量、地磁总强度F和地磁水平分量H在中国大陆地区都为负异常分布,X分量和H分量的负异常强度随经度增加而减弱,Z分量和F分量则相反;Y分量和磁偏角D的分布较为类似,在中国的中西部大部分地区为正异常,强度随经度增加而减弱,磁倾角I主要以负异常为主,负异常强度随经度增加而增强.     

Causality principle and nuclear dispersion anomaly in the elastic scattering for α+12C system

The optical model analysis of the alpha particle elastic scattering on a carbon target was performed on the basis of the dispersion relation between the real and imaginary parts of the calculated volume integrals. A nuclear dispersion anomaly in an α+12C system was observed and interpreted clearly.     

Parity anomaly in a \mathcal{P}\mathcal{T}-symmetric quartic Hamiltonian

In this paper, two independent methods are used to show that the non-Hermitian -symmetric wrong-sign quartic Hamiltonian H = (1/2m)p ² − gx ⁴ is exactly equivalent to the conventional Hermitian Hamiltonian . First, this equivalence is demonstrated by using elementary differential-equation techniques and second, it is demonstrated by using functional-integration methods. As the linear term in the Hermitian Hamiltonian is proportional to ℏ, this term is anomalous; that is, the linear term in the potential has no classical analog. The anomaly is a consequence of the broken parity symmetry of the original non-Hermitian -symmetric Hamiltonian. The anomaly term in remains unchanged if an x ² term is introduced into H. When such a quadratic term is present in H, this Hamiltonian possesses bound states. The corresponding bound states in are a direct physical measure of the anomaly. If there were no anomaly term, there would be no bound states.     

Magnetic phase evolution in Fe substituted GdBaCo2O5.5

Magnetization and magneto-resistance experiments have been carried out on well characterized samples of the GdBaCo_2−xFe_xO_5.5 series. Zero field cooled magnetization measurements in the low concentration Fe samples suggest, that the low temperature anti-ferromagnetic phase transforms sequentially to several ferromagnetic phases, before transforming to a paramagnetic state with increase in temperature. The anti-ferromagnetic to the first ferromagnetic phase transition is associated with a large negative magneto-resistance for Fe fractions upto x=0.075. Isothermal magnetization measurements in the ferromagnetic like region of the samples, suggests the presence of mixtures of two ferromagnetic phases. Similar measurements performed at low temperatures where anti-ferromagnetic-like phase is stabilised suggest the presence of a mixture of anti-ferromagnetic and ferromagnetic phases. Magnetization and magneto-resistance are seen to collapse for Fe fractions, x>0.1. Based on these studies a plausible scenario of the evolution of magnetism with Fe substitution in GdBaCo₂O_5.5, is suggested.     

Magnetization reversal of microsized Fe elliptic rings

We report on the magnetization reversal of elliptic ring patterns lithographically prepared from Fe films. The elliptic rings in four different arrays are all of the same size , but their geometry is disturbed by introducing an increasing number of slits into the rings. The magnetization reversal is studied by regular longitudinal vector magneto-optical Kerr effect in specular geometry as well as in Bragg geometry, using the diffraction spots from the grating for hysteresis measurements. The measurements are compared with the results of micromagnetic simulation, which allow a detailed interpretation of the experimental data. We find that the remagnetization process in an external magnetic field is characterized by single-step switching or double switching depending on the geometry of the structure.     

Structural and magnetic properties in Bi1−xRxFeO3 (x=0-1, R=La, Nd, Sm, Eu and Tb) polycrystalline ceramics

A series of rare-earth doped BiFeO₃ samples, Bi_1−xR_xFeO₃ (x=0-1, R=La, Nd, Sm, Eu and Tb), were prepared in this work. X-ray diffraction analysis showed that the structure of rare-earth doped BiFeO₃ was transformed from rhombohedral lattice to orthorhombic one by increasing x. The lattice constants and unit-cell volume decreased with the increasing of the doping content, while both the Néel temperature and magnetization were enhanced. A magnetic phase transition was observed at about 35 K for BiFeO₃. The variation of the magnetization with temperature depended on applied field strength and magnetizing history, which was explained according to the antiferromagnetic exchange interaction between Fe and R sites in Bi_1−xR_xFeO₃(x>0). The magnetocrystalline anisotropy contributed by Fe sublattice gave rise to a large coercivity in Bi_xNd_1−xFeO₃ with an orthorhombic structure.     

The influence of wire width on the charge distribution of transverse domain walls and their stray field interactions

We present here a numerical study of the magnetostatic charge distribution of transverse Néel type domain wall in permalloy nanowires. The calculations indicate that not only is the distribution highly non-uniform within a given transverse wall but it also varies dramatically with respect to the wire width. The implications of this for magnetostatic domain wall pinning are analyzed by considering the stray field interaction between a wall and another extended magnetic body for a particular domain wall chirality, where two distinct depinning mechanisms are observed depending on the wire width.