First-principles study on the metallic antiferromagnet Co[PhPO3]·H2O

The electronic structure and the magnetic properties of transition metal phosphonate Co(PhPO₃)·H₂O have been studied by first-principles within the density-functional theory (DFT) and the full potential linearized augmented plane wave (FP-LAPW) method. The total energy, the total magnetic moment, the atomic spin magnetic moments and the density of states(DOS) of Co(PhPO₃)·H₂O were all calculated. The calculations reveal that the title compound is a metallic antiferromagnet and has a metallic ferromagnetic metastable state, which are in good agreement with the experiment. The spin magnetic moment of Co(PhPO₃)·H₂O is about 4.93 _μB${\mu }_{\mathrm{B}}$ per molecule, and it is mainly assembled at the cobalt atom, at the same time, with a little contribution from the P, O1, O2, O3.     

Entropy of Einstein—Maxwell-Dilaton—Axion Black Holes

The entropy of Einstein—Maxwell-dilaton—axion black holes is calculated by using the improved brick-wall model. Taking into account of the statistical physics, we propose not to consider the superradiant modes. The result shows that the nonsuperradiant modes do contribute exactly the area-law entropy for extreme black hole. Moreover, our cut-off which does not require an angular cut-off is independent of angle . As for the extreme black hole, we found that its entropy is zero.     

幂硬化介质中平面应力动态裂纹的尖端弹塑性场

本文采用塑性动力学方程,对幂硬化介质中平面应力动态裂纹尖端场进行了渐近分析,其结果表明:在裂纹尖端附近,应力具有的奇异性,应变具有的奇异性,其中A是一个与塑性区尺寸有关的常数因子,r是离开裂纹尖端的距离,n为硬化指数,文中给出了尖端场的控制参量D,它依赖于马赫数;并且给出了各物理量的角函数。     

The structure-tunable synthesis and magnetic properties of Fe3O4 nanocrystals

Magnetite nanocrystals with tunable crystalline structures (orthorhombic and cubic) were synthesized via a simple oxidation-coprecipitation approach basing on the reaction of FeSO₄·7H₂O with C₆H₁₂N₄. The average diameter of prepared orthorhombic Fe₃O₄ nanorods were 15 nm while their lengths were approximately 150~200 nm. As-prepared cubic counterparts were composed of 10 nm sized nanoparticles. XRD, FESEM, TEM, SAED and HRTEM were then used to characterize our samples. In addition, magnetic measurements showed the saturation magnetization of orthorhombic magnetite was lower than that of cubic ones. Mössbauer spectroscopy verified the samples possessed the nature of cubic magnetite. Finally, a possible growth mechanism for orthorhombic nanorods and cubic nanoparticles was also discussed.     

Comparative investigation of resistance and ability to trigger high voltage discharge for single and multiple femtosecond filaments in air

A comparative investigation of resistance and ability to trigger high voltage (HV) discharge for single filament (SF) and multiple filaments (MF) has been carried out. The experimental results show that the trend of the breakdown threshold of the SF exactly follows that of its resistance, but this is not the case for the MF. The MF's resistance is much smaller than SF's. However, the MF shows a bit higher HV breakdown threshold than the SF. The underlying physics is that the measured resistance of the MF is collectively contributed by every filament in the MF while the HV breakdown threshold is determined by only one single discharging path.     

碳纳米管锁模双包层光纤激光器的实验研究

本文采用双包层掺镱光纤作为增益介质,用单壁碳纳米管作为饱和吸收体,获得最高输出功率为336 mW的锁模脉冲激光.用飞秒激光诱导水击穿法直接在单模光纤上制备出D形区,通过在D形光纤上滴涂单壁碳纳米管溶液,成功制备出碳纳米管饱和吸收体,并对其饱和吸收特性进行测试,发现其调制深度为27％.利用该饱和吸收体作为锁模器件,制备出具有环形腔结构的锁模光纤激光器.当抽运功率为4W时,获得了脉宽为93.8 fs,中心波长为1083.8 nm,3 dB谱宽为8.6 nm,重复频率为5.59 MHz,平均功率为336 mW的飞秒脉冲激光输出.     

A Quantum Watermark Protocol

Quantum watermarking is the technique which embeds the invisible quantum signal such as the owner’s identification into quantum multimedia data (such as audio, video and image) for copyright protection. In this paper, a watermark strategy for quantum images is proposed based on flexible representation for quantum images (FRQI). Compared with the former strategy, which can only be used to verify the identity of the true owner of a carrier image, the proposed method can be used to find out who is the real owner, and our strategy’s capacity reaches the largest. It is impossible for anyone except the copyrighter to clear off or extract the watermark images.     

Hydrothermal synthesis of LiMnO2 microcubes for lithium ion battery application

Two kinds of LiMnO₂ microcubes were successfully synthesized by hydrothermal method using solid or hollow Mn₂O₃ microcubes as precursors. One was made up of nanoparticles varying in size and the other was made up of interlaced polygonal nanoplates with the thickness of 70 nm. Both kinds of LiMnO₂ microcubes were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Charge–discharge curves were carried out to investigate their electrochemical properties. LiMnO₂ microcubes with interlaced nanoplates showed much better capacities than the ones with nanoparticles indicating it is more suitable for application in the lithium ion batteries. The former material could deliver the capacities of 197 and 134 mAh/g at 0.1 and 1 C, respectively. And its capacity fading after 50 cycles did not exceed 7 %. The excellent electrochemical performance of the former material could be ascribed to the smaller size which could shorten the path length for lithium ion transport and increase the electrode and electrolyte contact.     

晶体相场方法研究二维六角相向正方相结构转变

应用双模PFC模型,计算二维PFC相图,模拟二维六角晶格向正方晶格的结构转变过程, 观察新相(二维正方相)的形核、长大特点,以及相结构转变的动力学特征. 结果表明:六角结构相向正方结构相的转变,正方相最易在六角相晶界处, 尤其是在三晶粒的交汇处首先生成正方相的晶核,之后是正方相逐渐通过吞噬六角相的边缘, 向六角相内部推进,并不断长大.对于结构转变生成的正方相晶粒,其晶粒取向几乎是随机的, 与原先六角相晶粒取向角没有明显的关系.正方相转变的面积分数随时间变化的动力学曲线 呈现典型的"S"形.由Avrami曲线可将相变曲线看成由两阶段组成. 计算模拟得到的Avrami曲线的第二阶段直线斜率K的范围在2.0和3.0之间, 与JMAK理论的指数n相符合. 关键词： 结构转变 晶体相场 相图 晶粒取向