具阶段偏食的Beddington-DeAngelis反应食物链模型分析

讨论了一类三种群Beddington-DeAngelis反应食物链模型,其中第一个种群具有两阶段结构,且第二个种群对第一个种群有阶段偏食现象,得到了系统的一致持久性,进一步证明了在适当条件下,周期解及概周期解的存在性和全局渐近稳定性.     

Anomalous Scaling of Surface Growth Equations with Spatially and Temporally Correlated Noise

Based on the scaling idea of local slopes by Lopez et al. [Phys. Rev. Lett. 94 （2005） 166103], we investigate anomalous dynamic scaling of （d ＋ 1）-dimensional surface growth equations with spatially and temporally correlated noise. The growth equations studied include the Kardar-Parisi-Zhang （KPZ）, Sun-Guo-Grant （SGG）, and Lai-Das Sarma-Villain （LDV） equations. The anomalous scaling exponents in both the weak- and strong-coupling regions are obtained, respectively.     

科学家破解“落叶”之谜

美国康奈尔大学科学家证实，他们成功破解了一个半世纪以来一直使物理学家和数学家感到困惑的“落叶”问题。从高空中抛落的纸片会具有最不可预知的特性，时而向上升起，时而翻转，时而又在无风情况下改变自己的方向。因此，在平静无风的秋天落叶不仅覆盖树木底下的区域，而且还落到离开树木几米远的地方。早在1853年苏格兰物理学家J．C．麦克斯韦就开始研究”落叶”效应现象，但是由于没有进行复杂模拟的计算机和编程全套仪器，麦克斯韦始终没有破解这一问题。     

MAGNETOMECHANICAL BEHAVIORS OF GIANT MAGNETOSTRICTIVE MATERIALS

The Laves phase alloy Tb-Dy-Fe, commercially known as Terfenol-D, exhibits the giant room-temperature magnetostriction at moderate field strength of a few kOe due to its combination of high magnetostriction and low magnetocrystalline anisotropic energy. Thus, this pseudobinary rare earth iron compound has found quite a number of applications such as in magnetomechanical transducers, actuators and adaptive vibration control systems. The simultaneous measurements of magnetostriction and magnetization at various fixed compressive pre-stresses applied in the axial direction for Tb0.3Dy0.7Fe1.95 samples are presented. The results show that the magnetostriction increases with increasing compressive stress until it reaches 1742 ×10^6 under 25 MPa, so does the coercive magnetic field. And the hysteresis loop area for magnetization and magnetostriction also increases with the increment of applied compressive stresses. But the maximum magnetic susceptibility χ（dM/dH） is obtained under zero stress field and the strain derivative dλ/dH increases to the highest amplitude of 0.039×10^-6 A^-1m at a stress level of 5 MPa. In the strain versus magnetization intensity curve, the initial fiat stage mainly consisting of a 180° domain wall motion becomes shorter with increasing stress. It means more initial domains are driven to the transversal direction under the compressive stress before magnetization, which is consistent with the improvement of the magnetostriction.     

通断电自感综合演示实验

高三物理教材中的自感现象,大多是通过J2425型变压器原理说明器进行演示。有的学校可能没有,而且同用一件仪器,两次分别演示通电自感现象和断电自感现象,课堂上存在着操作麻烦的严重弊端,同时也不能给学生一个通断电自感的完整印象。为此,我对原演示实验进行了一些改进,不但能使通、断电自感现象一次完成,达到使用方便、印象完整的目的,而且还可观察断电后瞬时感生电流(电动势)的方向,有助于验证教材中所述“自感电动势总是阻碍导体中原来电流的变化的”这个结论。实验电路如图所示。     

Photochemical degradation of environmentally persistent perfluorooctanoic acid （PFOA） in the presence of Fe（Ⅲ）

Environmentally persistent and bioaccumulative perfluorooctanic acid （PFOA） was difficult to be decomposed under the irradiation of 254 nm UV light. However, in the presence of 80μmol/L Fe（Ⅲ）, 80% of PFOA with initial concentration of 48μmol/L （20 mg/L） was effectively degraded and 47.8% of fluorine atoms in PFOA molecule were transformed into inorganic fluoride ion after 4 h reaction. Shorter chain perfluorocarboxylic acids bearing C3-C7 and fluoride ion were detected and identified by LC/MS and IC as the degradation products in the aqueous solution. It was proposed that complexes of PFOA with Fe（Ⅲ） initiated degradation of PFOA irradiated with 254 nm UV light.     

新的压电薄膜——Ta2O5

据报道,日本Yasuhiko Nakagawa和Yasuo Gomi用磁控反应直流二极管溅射法将Ta_2O_5,沉积在石英基片上,得到了单晶薄膜,并且首次观察到了这种薄膜的压电现象.用叉指换能器在Ta_2O_5薄膜上成功地激发了声表面波.在Ta_2O_5/熔石英基片上,当薄膜厚度h在hk(=2πh/λ)=1.0时,其机电耦合系数k~2=0.5％,它可与熔石英基片上ZnO薄膜的机电耦合系数相比拟. 利用Ta_2O_5单晶的X射线衍射数据,推断出Ta_2O_5     

数据缺失机制不明确时的分布函数估计

研究了在数据缺失机制不明确时如何估计随机变量Y的分布函数FY(y),该问题不同于可以用参数模型刻画数据缺失机制时的情形,考虑到此时可能出现不可识别现象,获取一些辅助信息是必要的.借助一个可以完全观察到的随机变量X提供必须的辅助信息,构造了随机变量Y的分布函数Fy(y)的估计量,并研究了它的大样本性质.     

超导及其应用专题编者按

1911年荷兰科学家Heike Kamerlingh Onnes首次在金属汞中发现超导现象以来,超导作为人类发现的第一个宏观量子现象已经有百余年的研究历史.在这百余年的时间里,人们对传统的低温超导材料的认识及应用已经取得了巨大的成就,尤其是关于其超导机理的BCS理论的建立极大地推动了凝聚态物理的发展.在铜氧化物高温超导体发现后的近三十余年里,源于对其机理的研究开辟了基础物理新的领域,也为超导体的应用带来了新的技术.然而,非常规高温超导机理的研究和高临界参数的新超导体的探索仍面临许多挑战.