多值数据的自适应脉冲宽度调制预加重方法

信号受长距离同轴电缆的趋肤效应、介电损耗等因素的影响, 高频衰减严重, 产生码间干扰, 使接收端很难恢复信号, 限制信号传输速度. 脉冲宽度调制(PWM)预加重技术, 是通过时域信息处理来增加信号的传输速度, 在二进制信号中已经得到很好运用. 自适应PWM预加重方法则是进一步针对数据相关性抖动, 对不同数据序列进行或强或弱的预加重, 动态补偿多进制数据的传输损耗, 提高信号完整性, 眼图结果表明该方法改善了信号传输质量.     

Electronic transport properties of metallic single-walled carbon nanotubes

We have calculated the differential conductance of metallic carbon nanotubes by the scatter matrix methon.It is found that the differential conductance of metallic nanotube-based devices oscillates as a function of the bias voltage between the two leads and the gate voltage.Oscillation period T is directly proportional to the reciprocal of nanotube length.In addition,we found that electronic transport properties are sensitive to variation of the length of the nanotube.     

Codoping of Potassium and Bromine in Carbon Nanotubes： A Density Functional Theory Study

We investigate the co-doping of potassium and bromine in single-walled carbon nanotubes （SWCNTs） and doublewalled carbon nanotubes （DWCNTs） based on density functional theory. In the co-doped （6,0） SWCNTs, the 4s electron of potassium is transferred to nanotube and Br, leading to the n-type feature of SWCNTs. When potassium is intercalated into inner tube and bromine is put on outer tube, the positive and negative charges reside on the outer and inner tubes of the （7,0）@（16,0） DWCNT, respectively. It is expected that DWCNTs would be an ideal candidate for p-n junction and diode applications.     

Electronic Transport in Nanostructures Consisting of Magnetic—Electric Barriers

We present a theoretical investigation on the transport properties of the nanostructures consisting of magneticelectric barriers produced by the deposition,on the top of a heterostructure,of metallic ferromagnetic stripe with an applied voltage.Both the transmission probability and the conductance are found to be greatly dependent upon the applied voltage.When a positive voltage is applied to the stripe,both the transmission probability and the conductance shift towards low-energy region and increase.Conversely,they move towards high-energy direction and reduce for an applied negative voltage.     

阻尼作用下一维非线性单原子链中的孤子

利用多重尺度法,研究了弱阻尼作用下一维非线性单原子链中的波动行为,发现在O(ε)级阻尼作用下其格波幅度减小,群速变慢.在晶格动力学中导出了参数耗散型非线性Schr?dinger方程,对方程进行解析求解.结果表明:在O(ε)级阻尼作用下一维非线性单原子链中的格孤波为传播的包络孤子;在O(ε²)级阻尼作用下,格孤波为钟状或扭结的孤子.     

硼或氮掺杂的锯齿型石墨烯纳米带的非共线磁序与电子输运性质

基于非共线磁序密度泛函/非平衡格林函数方法,研究了硼或氮掺杂的锯齿型石墨烯纳米带的非共线磁序与电子透射系数.未掺杂的石墨烯纳米带的计算结果表明磁化分布主要遵循类似于Neel磁畴壁的螺旋式磁化分布.相比于未掺杂的情况,硼/氮掺杂的石墨烯纳米带的磁化分布出现了双区域的特征,即杂质原子附近的磁化较小,杂质原子左(右)侧区域的磁化分布更接近于左(右)电极的磁化方向,这为通过掺杂手段在石墨烯纳米带边缘上构建不同磁畴壁提供了可能性.与未掺杂的透射系数不同的是,硼/氮掺杂的石墨烯纳米带的透射系数在费米面附近随着磁化偏转角增大而减小,表明非共线磁序引起的自旋翻转散射占据主导地位.而在E=±0.65 eV处,出现了一个较宽的dip结构,投影电子态密度的分析表明其来源于杂质原子形成的束缚态所引起的背散射.我们的研究结果对于理解石墨烯纳米带中的非共线磁序与杂质散射以及器件设计具有一定的意义.     

管长和管径对单壁碳纳米管电导的影响

基于紧束缚模型，发展转移矩阵方法研究了单壁碳纳米管的导电性质.研究表明，由于卷曲效应，锯齿型(3k,0)管(k为整数)出现窄的电导沟，其大小与能隙一致.在费米能附近，电子输运不仅与管径和管长紧密相关，而且电子在不同能量下可能出现弹道的、扩散的和经典的三种不同输运特征. 关键词： 碳纳米管 转移矩阵 电导     

Lattice Dynamics of Potassium－Doped Single－Walled Carbon Nanotubes

We calculate the vibrational properties of potassium-doped single-walled carbon nanotubes within lattice dynamical theory. The results show that the frequency of high-frequency Raman mode E29 for K5C40 downshifts to 1553cm^-1, which is in agreement with the value for highly doped samples with effective composition KC8.Moreover, the specific heat curves have a turnover at 22 K, originating from the saturation of K atoms vibrational modes at low energy.     

二元凝聚体中亮-亮孤子的振荡-局域转变行为

考虑时间相关的种间相互吸引作用,研究了局限于谐振外部势阱中的二元玻色-爱因斯坦凝聚体中亮-亮孤子的传播特性.结果表明,当种内和种间相互吸引作用都不变时,亮-亮孤子呈现出周期性的振荡;如果种内相互吸引作用仍保持不变,而种间相互吸引作用随时间指数增加时,发现凝聚体中产生振荡-局域转变行为,且这种振荡-局域的转变行为可通过调节谐振势阱的横向囚禁频率来控制.此外,还设计了实验方案来观察孤子的这种振荡-局域转变行为.