A study on defect formation and magnetic properties of nitrogen-doped ZnO nanowires by the first principles

Theoretical calculation based on density functional theory (DFT) and generalized gradient approximation (GGA) has been carried out in studying defect formation energies, ionizing energies and ferromagnetism of nitrogen-doped ZnO nanowires. The result shows that N_O is deep acceptor, which make it hard to ionize. Ferromagnetic (FM) and antiferromagnetic (AFM) coupling between N atoms are also investigated. The results show that FM coupling between N atoms is more stable than AFM coupling. The FM coupling mechanism is explained by the interaction of N energy level. In addition, zinc and oxygen vacancies affecting FM coupling is also discussed. It is found that zinc and oxygen vacancies are unfavorable for stabilizing FM coupling of nitrogen-doped ZnO nanowires.     

Study on Mn-doped SrTiO3 with first principle calculation

The defect formation energies and electronic structures of Mn doped strontium titanate have been studied using CRYSTAL-09 code. The defect formation energies for Mn_Sr and Mn_Ti, under different chemical potential conditions, have been obtained to determine the way Mn prefers to occupy in the Mn doped SrTiO₃ crystal. From the electronic structures of Mn doped SrTiO₃, it is shown that Mn_Sr cannot change the band gap of SrTiO₃. However, Mn_Ti can effectively reduce the band gap of SrTiO₃ and improve the photocatalysis.     

Studies of the g factors and the local structure of the orthorhombic Ni center in KTaO3 crystal

The local structure and the g factor (g_x, g_y, and g_z) of the Ni⁺ center in KTaO₃ are theoretically studied using the perturbation formulas of the g factors for a 3d⁹ ion in orthorhombically elongated octahedra. The orthorhombic field parameters are determined from the superposition model and the local geometry of the system. In view of the covalency, the contributions from the ligand orbital and spin–orbit coupling interactions are taken into account from the cluster approach. In the calculations, the orthorhombic center is attributed to Ni⁺ occupying the host Ta⁵⁺ site, associated with the nearest-neighboring oxygen vacancy V_O along the c-axis. Furthermore, the planar Ni⁺–O²⁻ bonds are found to experience the relative variation ΔR (≈0.076 Å) along the a- and b-axis, respectively, due to the Jahn–Teller effect and the size mismatching substitution of Ta⁵⁺ by Ni⁺. Meanwhile, the effectively positive V_O can make the central Ni⁺ displace away from V_O along the c-axis by about 0.20 Å. The calculated g factors based on the above local distortions show good agreement with the experimental data.     

Compressive response of a sandwich plate containing a cracked diamond-celled lattice

The compressive strength is determined for a sandwich plate containing a centre-cracked core made from an elastic–brittle, diamond-celled lattice. It is assumed that the lattice fails when the major component of principal stress anywhere in the lattice attains the compressive or tensile strength of the solid, or when local buckling intervenes. First, analytical and numerical predictions are given for the unnotched strength of the core and for the compressive fracture toughness of the lattice K_IC. Second, finite element simulations and analytical models are reported for the fracture response of the sandwich plate with cracked core. The active failure mechanism in the cracked core is sensitive to core height, crack length, lattice geometry and material choice; this is illustrated by means of material-property charts.     

Detection of rolling bearing defects using discrete wavelet analysis

In the detection of bearing faults the so much desired objective remains the extraction of the defect vibratory signature from the measured signal in which immerses the random noise and other components of the machine. In this article a denoising method of the measured signals is presented. Based on the optimization of wavelet multiresolution analysis, it uses the kurtosis as an optimization and evaluation criterion, several parameters were then selected. The experimental results show the validity of this method within the detection of several defects simulated on ball bearings. The various configurations, in which the signals were measured, allow leading to optimum conditions of its application. The application of WMRA on filtered signals allows better results than its application on wide bands signals or a simple band pass filtering.     

A Conceptual Study of Cavity Aeroacoustics Control Using Porous Media Inserts

In this study, an integrated flow simulation and aeroacoustics prediction methodology is applied to testing a sound control technique using porous inserts in an open cavity. Large eddy simulation (LES) combined with a three-dimensional Ffowcs Williams–Hawkings (FW–H) acoustic analogy is employed to predict the flow field, the acoustic sources and the sound radiation. The Darcy pressure – velocity law is applied to conceptually mimic the effect of porous media placed on the cavity floor and/or rear wall. Consequently, flow in the cavity could locally move in or out through these porous walls, depending on the local pressure differences. LES with “standard” subgrid-scale models for compressible flow is carried out to simulate the flow field covering the sound source and near fields, and the fully three-dimensional FW–H acoustic analogy is used to predict the sound field. The numerical results show that applying the conceptual porous media on cavity floor and/or rear wall could decrease the pressure fluctuations in the cavity and the sound pressure level in the far field. The amplitudes of the dominant oscillations (Rossiter modes) are suppressed and their frequencies are slightly modified. The dominant sound source is the transverse dipole term, which is significantly reduced due to the porous walls. As a result, the sound pressure in the far field is also suppressed. The preliminary study reveals that using porous-inserts is a promising technology for flow and sound radiation control.     

光诱导纳米二氧化钛超新水薄膜SPM图像分析和氧空位浓度理论探讨

选用典型的二氧化钛纳米超亲水薄膜,用扫描探针显微镜（SPM）和电化学测试系统进行了一般性的表征。着重运用固体化学和纳米力学的原理,对SPM图像、氧空位浓度和超亲水性的机理进行理论分析;进一步解释了作者于1999年底提出的,与润湿性能有关的二氧化钛缺陷生成反应方程、普通表面物理模型、两憎（amphiphobic)表面概念和材料表面设计问题。     

光诱导纳米二氧化钛超亲水薄膜SPM图像分析和氧空位浓度理论探讨

选用典型的二氧化钛纳米超亲水薄膜 ,用扫描探针显微镜 (SPM )和电化学测试系统进行一般性的表征 .着重运用固体化学和纳米力学的原理 ,对SPM图像、氧空位浓度和超亲水性的机理进行理论分析 ;进一步解释了作者于 1999年底提出的 ,与润湿性能有关的二氧化钛缺陷生成反应方程、普适表面物理模型、两憎 (amphiphobic)表面概念和材料表面设计问题     

Self-Assembly of C-Methyl Calix[4]resorcinarene with 5,5′-Bipyrimidine

Abstract The X-ray crystal structure of the complex formed between 5,5′-bipyrimidine and C-methylresorcinarene is described. The structure (C₄₁H₄₅N₅O₁₂) is triclinic with a = 12.8610(10), b = 13.0560(10), c = 13.6068(11)?, α = 104.0730(10), β = 104.9260(10), γ = 111.6430(10)° and space group P-1. The structure reveals that the resorcinarene adopts a boat conformation and forms a three-dimensional network through hydrogen bonding to two water molecules and one dipyrimidine ligand. A single nitromethane molecule is included in the superstructure. Graphical Abstract Self-Assembly of C-Methyl Calix[4]resorcinarene with 5,5’-Bipyrimidine Charles L. Barnes(1) and Eric Bosch(2)* The X-ray crystal structure of the complex formed between 5,5′-bipyrimidine and C-methylresorcinarene is reported.      

偏轴双腔互比型腔式束流位置监测器

 提出一种利用偏轴双腔来监测电子束位置的新方法,根据谐振腔归一化分流阻抗参数分析了其工作原理和主要特性。偏心束流在偏轴谐振腔中激发出较强的偶极模TM₁₁₀信号,根据两腔输出的偶极模信号幅度比可直接测量束流的中心偏移量。偶极模信号幅度变化反映了束流的偏移方向,省去了鉴相工作,简化了前端接收电路的的设计,基模抑制问题已被解决。利用MAFIA和HFSS软件对本征模进行仿真,并分析了模式耦合特性,仿真结果验证了新结构的可行性。