纳米多晶铜中冲击波阵面的分子动力学研究

冲击波阵面反映材料在冲击压缩下的弹塑性变形行为以及屈服强度、应变率条件等宏观量, 还与冲击压缩后的强度变化联系. 本文使用分子动力学方法, 模拟研究了冲击压缩下纳米多晶铜中的动态塑性变形过程, 考察了冲击波阵面和弹塑性机理对晶界存在的依赖, 并与纳米多晶铝的冲击压缩进行了比较. 研究发现: 相比晶界对纳米多晶铝的贡献而言, 纳米多晶铜中晶界对冲击波阵面宽度的影响较小; 并且其塑性变形机理主要以不全位错的发射和传播为主, 很少观察到全位错和形变孪晶的出现. 模拟还发现纳米多晶铜的冲击波阵面宽度随着冲击应力的增加而减小, 并得到了冲击波阵面宽度与冲击应力之间的定量反比关系, 该定量关系与他人纳米多晶铜模拟结果相近, 而与粗晶铜的冲击压缩实验结果相差较大.     

A Distributed Architecture for Secure Delegated Quantum Computation

In this paper, we propose a distributed secure delegated quantum computation protocol, by which an almost classical client can delegate a (dk)-qubit quantum circuit to d quantum servers, where each server is equipped with a 2k-qubit register that is used to process only k qubits of the delegated quantum circuit. None of servers can learn any information about the input and output of the computation. The only requirement for the client is that he or she has ability to prepare four possible qubits in the state of (|0〉+eiθ|1〉)/2, where θ∈{0,π/2,π,3π/2}. The only requirement for servers is that each pair of them share some entangled states (|0〉|+〉+|1〉|−〉)/2 as ancillary qubits. Instead of assuming that all servers are interconnected directly by quantum channels, we introduce a third party in our protocol that is designed to distribute the entangled states between those servers. This would simplify the quantum network because the servers do not need to share a quantum channel. In the end, we show that our protocol can guarantee unconditional security of the computation under the situation where all servers, including the third party, are honest-but-curious and allowed to cooperate with each other.     

A broadband self-powered UV photodetector of aβ-Ga2O3/γ-CuI p–n junction

The symmetric Ti/Au bi-layer point electrodes have been successfully patterned on theβ-Ga;O;films which are prepared by metal–organic chemical vapor deposition(MOCVD)and theγ-Cu I films which are prepared by spin-coating.The fabricated heterojunction has a large open circuit voltage(Voc)of 0.69 V,desired for achieving self-powered operation of a photodetector.Irradiated by 254-nm ultraviolet(UV)light,when the bias voltage is-5 V,the dark current(Idark)of the device is 0.47 p A,the photocurrent(Iphoto)is-50.93 n A,and the photo-to-dark current ratio(Iphoto/Idark)reaches about 1.08×10;.The device has a stable and fast response speed in different wavelengths,the rise time(τr)and decay time(τd)are 0.762 s and 1.741 s under 254-nm UV light illumination,respectively.While theτr andτd are 10.709 s and7.241 s under 365-nm UV light illumination,respectively.The time-dependent(I–t)response(photocurrent in the order of10-10 A)can be clearly distinguished at a small light intensity of 1μW·cm;.The internal physical mechanism affecting the device performances is discussed by the band diagram and charge carrier transfer theory.     

High power-added-efficiency AlGaN/GaN HEMTs fabricated by atomic level controlled etching

An atomic-level controlled etching(ACE)technology is invstigated for the fabrication of recessed gate AlGaN/GaN high-electron-mobility transistors(HEMTs)with high power added efficiency.We compare the recessed gate HEMTs with conventional etching(CE)based chlorine,Cl₂-only ACE and BCl³/Cl₂ACE,respectively.The mixed radicals of BCl₃/Cl₂were used as the active reactants in the step of chemical modification.For ensuring precise and controllable etching depth and low etching damage,the kinetic energy of argon ions was accurately controlled.These argon ions were used precisely to remove the chemical modified surface atomic layer.Compared to the HEMTs with CE,the characteristics of devices fabricated by ACE are significantly improved,which benefits from significant reduction of etching damage.For BCl₃/Cl₂ACE recessed HEMTs,the load pull test at 17 GHz shows a high power added efficiency(PAE)of 59.8%with an output power density of 1.6 W/mm at Vd=10 V,and a peak PAE of 44.8%with an output power density of 3.2 W/mm at Vd=20 V in a continuous-wave mode.     

On the fractional integral of Weyl inL p

This work has been partially supported by D.G.C.Y.T., grant PS88-0115, Spain     

线性调频信号激励过阻尼双稳系统的随机共振现象研究

线性调频信号是工程中常见的一种信号, 由于其为非周期信号, 无法以频域信噪比作为衡量其是否产生随机共振的测量手段, 故鲜有文献研究以线性调频信号为激励信号的随机共振现象. 本文利用线性调频信号在最优分数阶Fourier变换域上的能量聚集性, 首次提出以最优分数阶Fourier变换域上定义的信噪比作为测量手段, 研究了线性调频信号叠加高斯白噪声激励过阻尼双稳系统的随机共振现象, 且发现了以线性调频信号为激励信号时产生的新现象, 即随着信号频率的增大, 随机共振将逐渐减弱, 并给出了合理的解释.仿真的结果与理论分析一致, 验证了本文所提出方法的有效性. 关键词： 线性调频信号 分数阶Fourier变换 随机共振     

脉冲激光沉积法制备的ZnO薄膜的低阈值电抽运紫外随机激射

分别采用直流反应溅射法和脉冲激光沉积法在硅衬底上沉积ZnO薄膜, 用X射线衍射、扫描电镜、光致发光谱等手段对两种方法沉积的ZnO薄膜的结晶状态、 表面形貌和光致发光等进行了表征. 进一步对比研究了以上述两种方法制备的ZnO薄膜作为发光层的金属-绝缘体-半导体结构器件的电抽运紫外随机激射. 结果表明, 与以溅射法制备的ZnO薄膜作为发光层的器件相比, 以脉冲激光沉积法制备的ZnO薄膜为发光层的器件具有更低的紫外光随机激射阈值电流和更高的输出光功率. 这是由于脉冲激光沉积法制备的ZnO薄膜中的缺陷更少, 从而显著地减少了紫外光在光散射过程中的光损耗. 关键词： 随机激射 ZnO薄膜 脉冲激光沉积 溅射     

Zn1-xTMxO (TM=Al,Ga, In)导电性能的模拟计算

基于密度泛函理论框架下的第一性原理平面波超软赝势方法, 构建了未掺杂与相同掺杂浓度的Zn_1-xTM_xO (TM=Al, Ga, In) 超胞模型,分别对模型进行了几何结构优化、态密度分布和能带分布的计算. 结果表明, 分别高掺杂 (Al, Ga, In) 相同原子分数3.125 at%的条件下, In掺杂对ZnO导电性能最好的结果, 计算结果和实验结果相一致. 关键词： (Al,Ga,In) 高掺ZnO 导电性能 第一性原理     

国产六面顶压机多晶种法合成宝石级金刚石单晶

对国产六面顶压机平台下使用多晶种法合成宝石级金刚石单晶进行了系统的研究. 通过合理调整温度梯度法的合成腔体组装, 采用多晶种法, 探索多晶种法金刚石合成的压力和温度区间, 在单个合成腔体内放置3–5颗金刚石晶种, 成功合成出多颗(3–5)优质Ib型宝石级金刚石单晶. 多颗晶种的引入, 单次实验合成的多个金刚石晶体晶形及品质一致; 同时, 晶体的整体生长速度也有明显的增大. 多晶种法金刚石单晶合成的研究, 可以有效地利用腔体空间、提高单次金刚石单晶合成的效率, 解决压机大型化下高温高压资源利用率低的问题; 同时, 为宝石级金刚石单晶商业化生产提供重要的依据. 关键词： 金刚石 国产六面顶 多晶种 温度梯度法     

Reduced field-of-view DTI segmentation of cervical spine tissue

The number of diffusion tensor imaging (DTI) studies regarding the human spine has considerably increased and it is challenging because of the spine’s small size and artifacts associated with the most commonly used clinical imaging method. A novel segmentation method based on the reduced field-of-view (rFOV) DTI dataset is presented in cervical spinal canal cerebrospinal fluid, spinal cord grey matter and white matter classification in both healthy volunteers and patients with neuromyelitis optica (NMO) and multiple sclerosis (MS). Due to each channel based on high resolution rFOV DTI images providing complementary information on spinal tissue segmentation, we want to choose a different contribution map from multiple channel images. Via principal component analysis (PCA) and a hybrid diffusion filter with a continuous switch applied on fourteen channel features, eigen maps can be obtained and used for tissue segmentation based on the Bayesian discrimination method. Relative to segmentation by a pair of expert readers, all of the automated segmentation results in the experiment fall in the good segmentation area and performed well, giving an average segmentation accuracy of about 0.852 for cervical spinal cord grey matter in terms of volume overlap. Furthermore, this has important applications in defining more accurate human spinal cord tissue maps when fusing structural data with diffusion data. rFOV DTI and the proposed automatic segmentation outperform traditional manual segmentation methods in classifying MR cervical spinal images and might be potentially helpful for detecting cervical spine diseases in NMO and MS.