Journal of Physics-Condensed Matter
We study the lasing action due to nonlinear interactions of photons with boson elementary excitation, such as phonons and excitons, and point out the distinct features from the conventional laser model described by the two-level model. External feedback by means of cavity mirrors is unnecessary fdr the lasing action as well as for the increasing absorption optical bistability. It is shown that the Landau theory of the second-order phase transition is applicable to the threshold behaviour of the present mirrorless laser model.
关键词:
transition
Chinese Physics Letters
A novel compound Fe-Ta-S crystal has been obtained using iodine vapor transport technology. At low temperature this compound is in a strong diamagnetic state, which is similar to a superconductor. The dependence of the diamagnetic phase transition temperature on the magnetic field could be expressed as T-c = T-c0 + gamma H-2/5 due to a strong coupling between electrons and the magnetic field.
关键词:
transition
Physical Chemistry Chemical Physics
Charge, orbital, and spin ordering of multiferroic BiMn(2)O(5) are investigated by the full-potential linearized augmented plane-wave (FPLAPW) method as implemented in the WIEN2K package. Both the generalized gradient approximation (GGA) as well as GGA plus the one-site Coulomb interaction (GGA+U) methods are considered for the exchange-correlation energy functional. The obtained results show that BiMn(2)O(5) is found stable in ferrimagnetic state with band gap about 1.23 eV. The results suggest that BiMn(2)O(5) contains two kinds of manganese: the ionicity of Mn1 (Mn(4+)) is + 3.6 with magnetic moment of 2.40 mu B and the ionicity of Mn2 (Mn(3+)) is + 3.4 with magnetic moment of 3.22 mu B. While charge disproportion between Mn1 and Mn2 is small, the difference between e(g) minority occupancies of Mn(3+) and Mn(4+) cations is large. Both these two properties give direct evidence of charge ordering. The analysis of the Born effective charge reveals that the partial ferroelectric polarization (P(ele)) originates from the charge ordering, which is in agreement with a recent work by Brink and Khomskii [J. Phys.: Condens. Matter, 2008, 20, 434217].
关键词:
transition
Journal of Applied Physics
In this paper, we investigate the influence of high temperature and high pressure (hot pressure) on the magnetic and transport properties of polycrystalline CrO(2) samples compacted under high pressure and high temperature of up to 5 GPa and 600 degrees C, respectively. The magnetic moment increases with compacting temperature, and a metal-semiconductor transition is observed in hot-pressed samples, different from the cold-pressed samples. These results indicate that the formation of Cr(2)O(3) at the grain boundaries of CrO(2) is suppressed by hot pressure. The magnitude of low field magnetoresistance of up to 1 T at 5 K is enhanced first with the increase of compacting temperature and then decreased under higher compacting temperature. This result can be well explained by the change of spin-dependent tunneling at the modulated grain boundaries of CrO(2) due to the transformation from Cr(2)O(3) to CrO(2) under hot pressure. (c) 2007 American Institute of Physics.
关键词:
transition
Shuxian CHEN
材料科学技术（英）
The flow and heat transfer of molten GaAs under the interaction of buoyancy, Marangoni and crystal rotation in the Czochralski configuration are numerically studied by using a time-dependent and three-dimensional turbulent flow model for the first time. The transition from axisymmetric flow to non-axisymmetric flow and then returning to axisymmetric flow again with increasing centrifugal and coriolis forces by increasing the crystal rotation rate was numerically observed. The origin of the transition to non-axisymmetric flow has been proved to be baroclinic instability. Several important characteristics of baroclinic instability in the CZ GaAs melt have been predicted. These characteristics are found to be in agreement with experimental observations.
关键词:
Flow transition
,
transition
,
baroclinic
,
instability
Chinese Physics Letters
Measurements of the Hall coefficient (R(H)) were carried out for a polycrystalline YBa2Cu3O7-y film, a well oriented YBa2Cu3O7-y film and an oriented GdBa2Cu3O7-y film. Sign change of R(H) was observed for the two YBa2Cu3O7-y films near T(c), but not for the GdBa2Cu3O7-y film which contains partly the component of (110) orientation. The R(H) anisotropy model proposed previously turns out to be incorrect. Why the YBa2Cu3O7-y films experience sign change of R(H) while the GdBa2Cu3O7-y film does not is tentatively investigated.
关键词:
transition
Journal of Physics-Condensed Matter
In this paper we establish the high-order perturbation formulas of zero-held splittings D and E and g factors g(x), g(y) and g(z) for 3d(3) ions in rhombic symmetry by using a two-spin-orbit (SO) coupling parameter model, in which not only the contribution due to the SO coupling of the central 3d(3) ion but also that of the ligands are included. Based on these formulas, all five EPR parameters for the Cr3+ ion at the rhombic defect site in the cubic AgCl crystal are satisfactorily explained by considering suitable defect-induced lattice distortion. The relative importance among the various contributions to the EPR parameters from the SO couplings of the central 3d(3) ion, the ligand ions and the mixed ones is discussed. It can be seen that for the 3d(3) ions in crystals with ligands having large SO coupling parameter, the contribution due to the SO coupling of ligands cannot be neglected and we should apply the two-SO parameter model in studies of EPR parameters.
关键词:
transition
G.Q. Liu
,
Y.Y. Meng
,
S.H. Liu
,
Y.H. Hu
金属学报(英文版)
DNA takes on multi-different conformations such as A-, B-, C-, D- and Z-form. These conformations can transit to one another when DNA deposited in some metal ions solutions or when changing the concentrations of the same metal ions. Here, several major conformational transitions of DNA induced by metal ions under different environment were introduced and the mechanism of the interaction of metal ions with DNA was discuss in detail.
关键词:
DNA
,
null
,
null
周婷婷
,
马书懿
,
毛雷鸣
,
丁继军
,
史新福
功能材料
采用射频磁控溅射在玻璃衬底上制备了不同掺杂量的Fe-ZnO薄膜,分析不同掺杂量对薄膜光学性能的影响.利用X射线衍射仪(XRD)和原子力显微镜(AFM)研究Fe-ZnO薄膜的微观结构和形貌结构.Fe-ZnO薄膜光致发光(PL)性质的研究发现,发光峰主要有蓝光发射和绿光发射,蓝光发射主要是由于电子从导带向锌空位形成的浅受主能级上的跃迁;绿光发射是由于电子从氧空位到锌空位的能级跃迁及导带底到氧错位缺陷能级的跃迁.由透射谱和吸收谱分析,Fe-ZnO薄膜在可见光区的平均透过率为66%,掺杂量为2%Fe的薄膜的禁带宽度最接近于ZnO的禁带宽度.
关键词:
掺杂
,
光致发光
,
跃迁
,
透射
林立
,
任静
,
蒋洪德
工程热物理学报
燃气轮机内部通流冷却叶片的流动传热特性对于燃机的整体效率有着重要的影响,而叶片表面的转捩流场一直是阻碍对叶片冷却性能进行精确分析的主要因素.本文采用SST湍流模型及γ-Re_θ转捩模型对MARK Ⅱ叶型进行数值模拟,通过分析叶栅通道内传热特性以考察该转捩模型的适应性,肯定了该转捩模型对于湍流边界层发生位置判断的正确性,以及对转捩发生点上游叶片表面温度变化趋势的预测的正确性.同时本文指出γ-Re_θ转捩模型与湍流模型结合时可能存在对湍动能过渡抑制的问题,有待进一步研究.
关键词:
转捩
,
燃气轮机
,
耦合传热
,
内部通流冷却
,
数值模拟
