The effects of temperature and frequency on the magnetization switching mode in circular MI sensors

This paper presents results computed using a meshless method in a point collocation formulation to investigate the effects of temperature and frequency on the magnetization switching mode in the circular amorphous magneto-impedance sensor (element). Specifically, the solutions characterizing the MI effect are solved from a set of coupled nonlinear equations consisting of the Maxwell’s equations, the Landau-Lifshitz-Gilbert equation, and the thermal diffusion equation. This coupled nonlinear space-time model predicts the formation and propagation of dynamic domain walls in switching and it is shown how they contribute to experimentally observed temperature and frequency effects. Computed results (that agree well with reported experimental data) suggest radial domain walls may play a larger role in the MI effect than originally believed even for the realistic conditions considered here at 1 MHz or more.     

Vibrational properties of polysiloxanes: from dimer to oligomers and polymers. 1. Structural and vibrational properties of hexamethyldisiloxane (CH3)3SiOSi(CH3)3

The hexamethyldisiloxane (HMDS)(CH₃)₃SiOSi(CH₃)₃ molecule is one of the basic building blocks of silicones and polysiloxanes, as it is used for many chain terminations. Far‐infrared, mid‐infrared, and polarized Raman spectroscopic studies, combined with quantum chemical calculations and vibrational normal mode analyses, were performed for the HMDS molecule. The internal rotation of the trimethylsilyl group was calculated to be nearly free. The large‐amplitude bending motion was found very anharmonic with a barrier to linearity below 4 kJ/mol. Exhaustive assignments of observed wavenumbers have been performed on the basis of calculated potential energy distributions (PED) and atomic displacements. By isotopic ¹⁶O ¹⁸O substitution, the Si O Si symmetric and antisymmetric stretching modes shift from 521 and 1074 cm⁻¹ to 514 and 1028 cm⁻¹, respectively. This spectroscopic observation provides convincing evidence that the molecule is bent with an angle estimated at around 150°. The comparison of HMDS vibrational spectra with the vibrational spectra of some siloxane derivatives reveals strong effects of silicon substituents on the Si O Si symmetric and antisymmetric stretchings. The Si O Si siloxane bridge group plays a key role in the properties of the HMDS molecule and may also account for some important silicone polymer properties such as their very low glass transition, their high compressibility, and their low surface tension. Copyright © 2009 John Wiley & Sons, Ltd.     

Metal‐assisted regioselectivity in nucleophilic substitutions: a study by Raman spectroscopy and density functional theory calculations

A series of complexes (Fe^II, Cu^II and Ni^II) of the N,O bidentate ligand 6,7‐dichloroquinoline‐5,8‐dione in water was investigated by using Raman spectroscopy, and the experimental peaks were assigned with the help of computed spectra by density functional theory (DFT) calculations. A strong shift to lower wavenumbers was observed for the vibration of the CO group involved in chelation, depending on the type of metal ion. When each complex was used in the substitution reaction by the nucleophilic reagent piperidine, two products having the same molecular composition but showing the substituent in different regions of the molecule were obtained, and moreover their regioselective formation was in agreement with the size of the Raman shifts previously observed for the complexes. This example confirms the potential of the approach involving Raman spectroscopy combined with DFT calculations in the characterization of metal complexes as key intermediates in organic reactions, with the possibility of predicting the metal system capable to achieve the highest selectivity. Copyright © 2010 John Wiley & Sons, Ltd.     

124 W diode-side-pumped Nd:YAG laser in dynamic fundamental mode

A high power dynamic fundamental mode Nd:YAG laser is experimentally demonstrated with a stagger-pumped laser module and a V-shaped resonator. The rod is pumped symmetrically by staggered bar modules. And dynamic fundamental mode is achieved under different pump levels. The maximal continuous wave (CW) output of 124 W (M²=1.4) is achieved with a dual rod. Average output of 112 W, pulse width of 120 ns, pulse energy of 11.2 mJ and peak power of 93 kW are obtained in Q-switched operation of 10 kHz.     

New side-pump scheme for large mode area fiber lasers by wrapping polished fibers conjugate caustic removed

With the purpose of uniform gain coefficient along the axial direction in the core of gain guided and index anti-guided fiber, a new kind of side-pump scheme by wrapping particularly treated fibers around the central GGIAG fiber is reported in this paper. According to leakage mode analysis on wrapped fiber and numerical simulation on this pumping structure having ytterbium doped central fiber and conventional wrapped side fiber, we find this kind of pump scheme can improve the uniformity of gain coefficient along the fiber direction, and also, it can support multi channels of pumping sources by adding more side fibers to improve the total effective incident pumping power.     

Internal oscillation of vector solitons and necklace solitons

Internal modes and internal oscillation of vector solitons associated with photoisomerization and necklace solitons in Bessel lattices are researched. While white noise gives rise to the unsmoothness of the vector solitons, the perturbation of internal modes results in the long-distance quasi-periodic oscillation of soliton shape. Internal modes of two-dimensional necklace solitons in Bessel lattices have both real and imaginary parts, which is different with the internal modes of one-dimensional solitons which have only real part.     

Multilayer growth of BaTiO3 thin films via pulsed laser deposition: An energy-dependent kinetic Monte Carlo simulation

An energy-dependent kinetic Monte Carlo approach was proposed to simulate the multilayer growth of BaTiO₃ thin films via pulsed laser deposition, in which the four steps, such as the deposition of atoms, the diffusion of adatoms, the bonding of adatoms, and the surface migration of adatoms, were considered. Distinguishing with the traditional solid-on-solid (SOS) model, the adatom bonding and the overhanging of atoms, according to the perovskite structure, were specially adopted to describe the ferroelectric thin film growth. The activation energy was considered from the interactions between the ions, which were calculated by Born-Mayer-Huggins (BMH) potential. From the simulation the relative curves of the each layer coverage and roughness vs total coverage were obtained by varying the parameter values of the incident kinetic energy, laser repetition rate and mean deposition rate. The relationship between growth modes and the different parameters was also acquired.     

二维光子带隙结构圆波导特性的分析

利用CST微波工作室软件对二维光子带隙（PBG）结构圆波导的传播特性进行了研究。研究给出了PBG圆波导存在高次缺陷TM模的条件;证实了PBG圆波导不存在缺陷TE模,高次TEmax模有可能由于其场分布主要集中在缺陷区域而非常类似于缺陷TEml模（l〈n）,l与n之间的关系则与PBG圆波导的具体结构有关。并对本文的分析结果和计算方法进行了讨论。     

含负折射率缺陷的正负交替光子晶体的缺陷模

利用光学特征矩阵方法,研究了含负折射率缺陷的正负折射率交替一维光子晶体缺陷模的相关特性。研究表明：当缺陷层的光学厚度不变时,随着缺陷层折射率的增加,分布在禁带中心两侧的缺陷模分别向临近的禁带边缘方向移动,并与透射谱形成连续的透射带,随着折射率的增加,透射带的透射率逐渐增加,其半高宽度逐渐减小;而当缺陷层折射率不变时,随着缺陷层的光学厚度增加,缺陷模向长波方向平移,同时缺陷模的个数也随之增加,而由缺陷模和透射谱连成的透射带的带宽逐渐减小。与正折射率缺陷情形相比较,负折射率缺陷层可以获得更多的缺陷膜。     

PFMEA在SMT装配中的应用研究

SMT装配过程涉及多个设备和多道工序,工艺流程多样,为了保证SMT产品的质量与可靠性,需要采用科学的方法研究SMT装配过程。文章将PFMEA这一可靠性研究工具引入SMT装配过程,简介PFMEA的应用流程,并以单面贴装工艺漉程为例,说明应用PFMEA研究SMT装配过程的实施方法。