Anisotropy of losses in amorphous ribbons

The soft magnetic properties of amorphous ribbons are expected to be anistropic because of the shear deformation during the melt spinning procedure. In this paper the losses of an Fe₈₀B₁₄Si₆ amorphous ribbon were measured on stripes which were cut either parallel or perpendicular to the ribbon axis. The dependence of the losses as a function of peak induction and frequency suggests that there is an easy axis of magnetization parallel to the ribbon axis. After stress relief annealing this anisotropy is reduced. That is why this anisotropy is assumed to be due to internal stress introduced upon quenching.     

Origin of counter-examples to Michel's conjecture

A general specification is given of all possible symmetry breaking patterns of the most general Higgs potential with one irreducible representation of a compact Lie group G. The common origin of all counter-examples to Michel's conjecture is pointed out.     

Threshold of F-center formation of alkali halide crystals by two-photon absorption

Thresholds of F-center formations for various alkali halide crystals with accuracy better than 5 meV are first reported by two-photon absorption process of a tunable dye laser.     

Non-volatile multi-state magnetic domain transformation in a Hall balance

High performance of the generation, stabilization and manipulation of magnetic skyrmions prompts the application of topological multilayers in spintronic devices. Skyrmions in synthetic antiferromagnets (SAF) have been considered as a promising alternative to overcome the limitations of ferromagnetic skyrmions, such as the skyrmion Hall effect and stray magnetic field. Here, by using the Lorentz transmission electron microscopy, the interconversion between the single domain, labyrinth domain and skyrmion state can be observed by the combined manipulation of electric current and magnetic field in a Hall balance (a SAF with the core structure of [Co/Pt]₄/NiO/[Co/Pt]₄ showing perpendicular magnetic anisotropy). Furthermore, high-density room temperature skyrmions can be stabilized at zero field while the external stimulus is removed and the skyrmion density is tunable. The generation and manipulation method of skyrmions in Hall balance in this study opens up a promising way to engineer SAF-skyrmion-based memory devices.     

Asymmetric hydrolysis,esterfication catalyzed by esterases from porcine pancreas in the synthesis of both enantiomers of cyclopentanoid building blocks

The asymmetric synthesis of the cyclopentanoid building blocks 5 and ent-5 from the easily accessible meso-diacetates 4 and meso-diols 7, respectively by crude PPL and a carboxyl esterase from crude PPL is described. Enzymatic esterfication of 8 by crude PPL gave the cyclohexanoid monoacetate 9, whereas by hydrolysis of 10 the cyclobutenoid monoacetate 11 was obtained.     

Fabrication of broadband poly(vinylidene difluoride-trifluroethylene) line-focus ultrasonic transducers for surface acoustic wave measurements of anisotropy of a (1 0 0) silicon wafer

This paper investigates a new method for fabrication of broadband line-focus ultrasonic transducers by sol–gel spin-coating the poly(vinylidene difluoride-trifluroethylene) [P(VDF-TrFE)] copolymer film on a concave fine-polished beryllium copper backing. The ferroelectric hysteresis loops of the P(VDF-TrFE) films spin-coated from different molar ratios of VDF/TrFE, 77/23 and 55/45, were measured to select the better mixture. Owing to the better acoustic matching to water, compared with lead zirconate titanate (PZT), the fabricated transducers show relatively wide bandwidth of approximately 50 MHz with high central frequency of 60 MHz obtained at the focal plane when a fused-quartz acts as a reflecting target. Each one of the two finished transducers has a focal length of 5 mm and a full aperture angle of 90°. After applying the specially developed digital signal processing algorithm to the defocusing experiment data, which is called V(f,z) analysis method based on two-dimensional fast Fourier transform (2-D FFT), the operating frequency can extend from several MHz to over 90 MHz. Surface acoustic wave (SAW) velocities of a typical (1 0 0) silicon wafer was measured along various directions between [1 0 0] and [0 1 0] to represent the anisotropic features.     

脉冲时滞抛物型方程解的振动准则

本文研究含脉冲的时滞抛物型方程解的振动性,在两类不同边界条件下得到了若干解的振动准则．     

非弹性中子散射在稀土钙钛矿研究中的应用

中子散射技术在科学研究中应用的重要性、独特性源自于中子本身的一些基本物理特点：带自旋、不带电荷、与原子核直接发生强相互作用、恰当的质量使其色散关系与一般物质内部的原子振动和磁性振动的元激发相当,以及可用于无损探测的强穿透性等。这些特点决定了中子散射探测技术在科学研究中无可替代的重要地位。经过多年发展,中子散射技术已经成为研究凝聚态物理中材料晶体结构以及磁结构的主要手段。此外由于中子的能量与物质中的元激发,如声子,磁振子等能量相当,中子散射也是研究物质动力学性质不可替代的关键技术。对于磁性材料来说,非弹性中子散射不仅可以研究对称性破缺下磁有序相的自旋波激发,而且可以直接探测无对称性破缺情况下的自旋关联。这对于研究磁阻挫等量子磁体中新奇的量子化自旋激发尤其重要。文章将主要介绍两种常用的非弹性散射谱仪,并结合最近在稀土钙钛矿结构体系中的具体应用,尤其是低维稀土自旋链中的分数化自旋子的激发,重点介绍非弹性散射技术的特色。     

Remote double stereodiffrentiation in macrocylizations of α-alkoxyallylstannanes

The homochiral epoxy stannane aldehyde 13 affords a 2.3:1 mixture of cis-Z and cis-E cyclization products 14 and 15 upon treatment with BF₃ · Et₂O at - 78°C whereas the diastereomeric epoxy stannane aldehyde 16 gives the cis-Z product 17 with only a trace of the cis-E isomer 18.