萝卜雄性不育系花药发育的细胞形态学研究

选用５种萝卜雄性不育系为材料，以相应保持系作对照，进行细胞形态学研究．结果表明，萝卜雄性不育系小孢子败育有两种方式；１．４７５Ａ花药发育受阻于孢原细胞分化期之前，不产生孢原细胞，也不分化形成花粉囊，接近开花期时花药已畸形．２．２６２Ａ、北京白Ａ、春红Ａ、１３４Ａ花药发育受阻于单核花粉期．绒毡层细胞具多种异常变化：①径向异常肥大、高度液泡化并侵入药室；②细胞壁解体，细胞内含物融合形成周原质团；③以上两种异常活动同时具有．随着绒毡层细胞退化解体，小抱子核质解体导致败育，药室瘪缩变形，只留下少数染色很深的细胞残留物质．不育系的维管组织有韧皮部和木质部的分化，但不及保持系发达．     

LaFeO3纳米材料电四极超精细相互作用TDPAC测量

用时间微分扰动角关联方法测量了LaFeO3纳米中的电四极超精细相互作用. 扰动角关联探针核14057La 14058Ce由139La(n,γ)140La反应产生, 实验只观察到一个La晶位的四极相互作用. 在室温下， 20和40 nm 以及晶体LaFeO3的四极相互作用频率ω0分别为 687.4 , 698.3 和742.9 Mrad/s , 频率分布宽度系数σ分别为 0.014, 0.009和0.001, 电场梯度不对称系数η=0. 实验数据表明, 电场梯度主轴与晶轴方向一致; 样品具有菱方结构, 晶体到纳米发生菱方向正交结构转变, 纳米尺度越小, 越趋于正交结构; 由于邻近核的扰动, 随纳米颗粒增大, 四极相互作用频率分布宽度系数σ变小, 晶体时最小. The quadrupole interactions in the nano and crystalline LaFeO3 perovskites have been investigated by TDPAC. The TDPAC probing nuclei 14057La 14058Ce were produced through the nuclear reaction 139La(n.γ)140La at the CIAE heavy water experimental reactor. One electric quadrupole interaction was detected for each material, which is assigned to the La site. The quadrupole interaction frequencies of 687.4, 698.3 and 742.9 Mrad/s with a distribution coefficient of 0.014, 0.009 and 0.001 were observed at room temperature for the 20 and 40 nm nano LaFeO3 and crystalline LaFeO3, respectively. The fitting yielded the EFG asymmetry parameter η=0, which indicates that the principal axes of the EFG is aligned with the crystallographic axes. The experimental results show that the structure of crystalline LaFeO3 is rhombohedral, the changing of the structure towards the orthorhombic structure takes place from the crystalline LaFeO3 to the nano LaFeO3, and the smaller the nano grain size, the larger the change. The frequency distribution is caused by the perturbation of the neighboring atoms, and thus, the distribution coefficient increases with decreasing the nano grain size and the crystalline LaFeO3 arrives at its maximum.     

利用压力方法获得高2223相含量的Bi系超导材料

为制备高２２２３相含量的Ｂｉ系超导块材，提出退火处理施以６ＧＰａ高压冷处理的工艺。利用这种方法，可使２２２３相的形成速度得到大加快。从２２１２相出发，经分别为２０小时的退火和缓冷后，样品接近单２２２３相。考察了２２１２相样品退火各阶段的相结构，并粗略地分析２２２３相的生成过程，初步解释了压力处理促进２２２３相生成的相理。基于以上讨论，提出一个制备较高质量Ｂｉ系超导块的方法，其复现率很好。     

Spin transfer nano-oscillator based on synthetic antiferromagnetic skyrmion pair assisted by perpendicular fixed magnetic field

As a microwave generator, spin transfer nano-oscillator (STNO) based on skyrmion promises to become one of the next-generation spintronic devices. However, there still exist a few limitations to the practical applications. In this paper, we propose a new STNO based on synthetic antiferromagnetic (SAF) skyrmion pair assisted by a perpendicular fixed magnetic field. It is found that the oscillation frequency of this kind of STNO can reach up to 5.0 GHz, and the multiple oscillation peak with higher frequency can be realized under a fixed out-of-plane magnetic field. Further investigation shows that the skyrmion stability is improved by bilayer antiferromagnetic coupling, which guarantees the stability process of skyrmion under higher spin-polarized current density. Our results provide the alternative possibilities for designing new skyrmion-based STNO to further improve the oscillation frequency, and realize the output of multiple frequency microwave signal.     

女贞叶中总黄酮含量的测定及抗氧化活性

以70％乙醇为溶剂超声提取女贞叶中总黄酮,以表儿茶素为对照品,分光光度法测定其含量;用清除DPPH来评价女贞叶总黄酮抗氧化活性.在510nm处表儿茶素浓度在0.005-0.03mg/mL范围内线性关系良好(r=0.9994).女贞叶中总黄酮含量为39.5mg/g,平均加标回收率为101.63％ (RSD=1.96％),精密度高(RSD=0.78％),重现性好(RSD=1.96％),可作为测定女贞叶中总黄酮含量的一种好方法.抗氧化实验结果表明,女贞叶总黄酮具有较强的清除DPPH自由基的能力,其清除效果在一定范围内随着总黄酮质量浓度的增加而增强.     

对一个跃迁矩阵元的讨论

指出在计算Landau体系的光致跃迁概率时,计算矩阵元xm,k,ym,k的积分变量应是dτ=dxdy,,而不是dτ=dxdydpy,同时还指出,应将矩阵元ym,k表示为ympy,kp0     

近距离牛顿反平方定律实验检验进展

为了统一描述自然界的四种基本相互作用,科学家提出了很多理论模型,其中很多理论认为牛顿反平方定律在近距离下会发生偏离,或存在其他的非牛顿引力作用,而理论的正确与否需要高精度的实验检验.国际上很多研究组在不同间距下采用不同的技术对反平方定律进行了高精度的实验检验,本文重点介绍华中科技大学引力中心采用密度调制法分别在亚毫米与微米范围进行的实验研究进展.在亚毫米范围采用精密扭秤技术,在对牛顿引力进行双补偿、抑制电磁干扰后,结合零实验与非零实验结果,在作用程为70—300μm区间对Yukawa形式的破缺给出国际上精度最高的限制.在微米范围采用悬臂梁作为弱力传感器,通过测量金球和密度调制吸引质量间水平力的变化来检验非牛顿引力是否存在,实验结果不需进行Casimir力和静电力背景扣除,是此间距下不依赖于Casimir力和静电力理论计算模型的两个结果之一.     

Plastic Deformation of Fine-Grained Al-Cu-Fe-（B） Icosahedral Poly-Quasicrystals at Elevated Temperature

Fine-grained Al-Cu-Fe-（B） icosahedral poly-quasicrystals （1QCs） as the main materials and fine-grained Al- Pd-Mn IQCs as the supplements, both prepared by powder metallurgy, are uniaxially deformed at vaNous temperatures and strain rates. The systematic study shows the dependences of curves of the true stress versus true strain on several parameters, such as temperature, strain rate and grain size. For Al-Cu-Fe IQCs with grain sizes of about 10-30μm, QC-specific intra-granular softening drop appears in the deformation curves at lower temperatures and/or faster strain rates, but disappears in those curves at higher temperatures and/or slower strain rates, which suggests that the inter-granular effects such as grain-boundary sliding should be taken into account to interpret the continuous hardening, similarly to conventional poly-crystals. For Al-Cu-Fe-B IQCs with smaller grain sizes of about 1 μm and fine-grained AI-Pd-Mn IQCs with grain sizes of about 10μm, QC- specific intra-granular softening drop is absent for all the deformation curves at the possible lowest temperature and fastest strain rate. This implies that the sma/ler the grain size, the more the inter-granular contribution. At the same time, due to the rapid recovery caused by intense diffusion in small-sized grains, the intra-granular quasicrystal lattice reorders rapidly from disordering, which also inhibits the intra-granular softening drop to some extent.     

单层Nb2SiTe4基化合物的带隙异常变化

传统硫族化合物中阳离子相同时,随着阴离子原子序数的增加,价带顶逐渐升高,带隙呈减小趋势.在A₂BX₄基(A=V,Nb,Ta;B=Si,Ge,Sn;X=S,Se,Te)化合物中,观察到随着阴离子原子序数增加,其带隙呈现反常增大的现象.为了探究其带隙异常变化的原因,基于第一性原理计算,对A₂BX₄基化合物的电子结构展开系统地研究,包括能带结构、带边相对位置、轨道间耦合作用以及能带宽度等影响.研究发现,Nb2SiX4基化合物中Nb原子4d轨道能量明显高于阴离子p轨道,其价带顶和导带底主要由Nb原子4d轨道相互作用组成,其带宽主要影响带隙大小.Nb₂SiX₄基化合物的带隙大小通过Nb—Nb和Nb—X键共同作用于Nb原子4d轨道的宽度来控制.当阴离子序数增加时,Nb—Nb键长增加,其相互作用减弱,由Nb原子4d轨道主导的能带变宽,带隙减小;另一方面,Nb—X键长增加又使Nb原子4d带宽变窄,带隙增加,并且Nb—X键长增长占主导,所以带隙最终呈现异常增加的趋势.     

小尺寸传热面对磁性液体的强化自然对流换热

1引言磁性液体（MagneticFlu问是将超细的纳米级铁磁微粒稳定弥散于水、煤油、氟里昂等不同基液中而制成的胶体溶液．不同材料的超微粒子有着广泛的技术应用，如军用飞行器的隐身材料、固体火箭的高能添加剂、新型高效催化剂和高性能磁性材料等等．而用其制成的磁液在工业上有着更为广泛的应用，因而日、美、俄、英等国均已投入巨资，在这一领域进行竞争，其成果已经投入工业应用。根据1992年的统计，有关磁液的公开技术报告和论文已达到5000余篇，专利超过2100项l‘，‘］，有关产业的年产值已超过一亿美元K‘］磁液的应用非常广泛，归纳…