Magnetization Switching With Nonstandard Dissipation

We report on our study of magnetization switching in a single-domain ellipsoidal particle. Under the assumption of uniaxial anisotropy collinear with the applied field, we derive an explicit formula for the switching time from the Landau-Lifschitz equation for a class of dissipation mechanisms that includes Gilbert's, dry friction, and others. While some dissipation is essential to finite-time switching, we show that too much of it would be detrimental, in that it would lengthen the time required to switch, no matter what mechanism is chosen in the class under study     

Stress Induced Enhancement of Magnetization Reversal Process of DyFeCo Films With Perpendicular Magnetization

A method to control magnetization reversal in magnetic films with perpendicular magnetic anisotropy was demonstrated in this study. Alloys of rare earth-transition metals (RE-TM) with their extremely large anomalous Hall coefficient and relatively large magnetostriction constants were suitable to observe the stress induced anisotropy using anomalous Hall effect. Stress applied to the RE-TM thin films significantly reduced the perpendicular coercivity and nucleation field of the film in comparison with that of the film in stress-free condition. Dy_x(Fe₉₀Co₁₀)_1-x thin films revealed large Hall voltage and remarkable change in the coercivity under the mechanical tensile stress     

Measuring the Size‐Independent Fracture Energy of Concrete

Abstract: The fracture energy of concrete is an important parameter in the analysis of the mechanical behaviour of concrete structures, so it is considered as a material property. However, the most universal test method for measuring the specific fracture energy of concrete (RILEM work‐of‐fracture) has been a subject of intense debate among researchers. The values have been found to vary with the size and shape of the test specimen. In this study, an experimental comparative analysis of the size‐independent fracture energy obtained by two main methods has been carried out. One of these is based on the local fracture energy model of Hu et al. The second is based on the curtailment of the tail of the P–δ curve by Elices et al. Therefore, the relationship between both methods is highlighted. It is shown that both methods give almost identical results.     

Magnetometric Demagnetizing Factors for Various Shapes of Rotational Symmetry

We have investigated the magnetometric demagnetizing factors of rotation-symmetrical magnetic bodies of relative permeability $mu$ placed in a uniform magnetic field parallel to the axis of rotation. The bodies we considered include a cylinder, a sphere, a bicone, and a rotating astroid. We numerically calculated the magnetometric demagnetizing factors from the surface magnetic charge densities $sigma$ obtained by the surface magnetic charge simulation method. We show that the magnetometric demagnetizing factors for various shapes of rotation-symmetrical bodies are significantly different from those of a sphere. We have determined the shape producing the largest demagnetizing field in ferromagnetic bodies with sufficiently large relative permeability $mu$ . We report the magnetometric demagnetizing factors for uniformly magnetized bodies ($mu=1$ , i.e., susceptibility $chi=0$ ) of various shapes.      

Demagnetizing field computation for dynamic simulation of themagnetization reversal process

The magnetic-field distribution for a thin magnetic film is computed using the fast Fourier transform technique. The method is quite general and accommodates any two-dimensional magnetization distribution. It allows the computation of fields both inside the film (demagnetizing fields) and outside (stray fields and leakage)     

检定电子式无功电能表的建议

指出了电子式无功电能表没有对应的检定规程,提出了检定电子式无功电能表时,判定合格与否的基本误差限,以及测定基本误差应调定的负载功率。     

Magnetization Curve of the Kagome-Strip-Lattice Antiferromagnet

We study the magnetization curve of the Heisenberg model on the quasi-one-dimensional Kagome-strip lattice that shares the same lattice structure in the inner part with the two-dimensional Kagome lattice. Our numerical calculations based on the density matrix renormalization group method reveal that the system shows several magnetization plateaus between zero magnetization and the saturated one; we find the presence of the magnetic plateaus with the n/7 height of the saturation for n=1,2,3,4,5 and 6 in the S=1/2 case, whereas we detect only the magnetic plateaus of n=1,3,5 and 6 in the S=1 case. In the cases of n=2,4 and 6 for the S=1/2 system, the Oshikawa-Yamanaka-Affleck condition suggests the occurrence of the translational symmetry breaking (TSB). We numerically confirm this non-trivial TSB in our results of local magnetizations. We have also found that the macroscopic jump appears near the saturation field irrespective of the spin amplitude as well as the two-dimensional Kagome model.     

负能量问题——超光速研究的重要方向

论述了关于负能量的多个理论预期和相关实验,阐明了超光速研究和负能量概念的关系。     

Energy Absorption and Deformation Mechanism of Lotus-type Porous Coppers in Perpendicular Direction

As metallic foams used for energy absorption in the automotive and aerospace industries, recently invented lotus-type porous metals are viewed as potential energy absorbers. Yet, solid conclusion on their eligibility as energy absorbers is still in question, particularly when compression is in the direction perpendicular to the axial orientation of cylindrical pores. In this work, the energy absorption of lotus-type porous coppers in the perpendicular direction is investigated at strain rates from 0.001 s~(-1) to~2400 s~(-1). The energy absorption capacity and the energy absorption efficiency are calculated to be4–16 k J/kg and 0.32–0.7, respectively, slightly inferior to metal foams and the same porous solid compressed in the parallel direction due to the shortened extent of the plateau stress region. The deformation mechanism is examined experimentally in conjunction with finite element modeling. Both suggest that gradual squeeze and collapse of pores are the mechanisms accommodating the energy absorption. The deformation is generally evenly distributed over pore ligaments and independent of strain rate.     

The Effect of the Demagnetizing Field on the NMR Spectra for Liquids Enclosed in a Cylinder

The NMR spectrum of a simple liquid in a cell of size L depends on D, the diffusion constant, G, the applied field gradient, and M ₀, the z-component of magnetization before tipping of the spins. For small tipping angles the shape of the spectrum depends on which of the corresponding frequency scales—ω _D = D/L ²,ω _G = γ FL, and ω _M = γ μ₀ M ₀—is the largest. We explore the evolution of the spectrum between the inhomogeneous broadening regime (ω _G ? ω _D ,ω _M ) and the regime where the spin dynamics is dominated by magnetostatic modes (ω _M ? ω _D ,ω _G )for a liquid confined in a cylinder of length 2L, both for classical liquids, and for liquids which exhibit the Leggett–Rice effect.     

热湿独立处理空调系统的分析模型

介绍了热湿独立处理空调系统的工作原理及特点;运用热力学第二定律,从[火用]流的角度分别建立了系统部件以及湿空气和溶液的炯分析模型;并对系统炯效率进行了初步分析,为系统的炯分析奠定了理论基础。     

爆破能量传播方向与边坡夹角对露天矿边坡稳定性的影响

大量爆破现场边坡破坏现象表明爆破能量传播方向与所造成损伤的差异性研究对边坡保护很重要,以往对爆破能量传播方向对露天矿边坡稳定性的研究较少,而研究这一关系对实际工程有理论和实际意义。首先对国电平庄西露天矿台阶爆破进行超声波检测试验研究,再对试验数据进行对比分析,获取该爆破场地地质条件下的角度与损伤关系,对该矿区爆破生产产生的边坡损伤进行较为准确的预测及判断。     

独立学院热能与动力工程专业基础课教学探索

分析了工程热力学与传热学研究内容,两者的侧重点不同,但在教学方法和内容上都有相似之处;研究了工程流体力学与工程热力学中某些概念和内容,其表述虽不相同但本质是一致的;对比分析边界层理论在传热学与工程流体力学中的特点,同时得出比拟法在教学中的应用价值。结合独立学院办学特点,提出今后热能与动力工程专业基础课教学内容和教学方法的改革方向。     

Binding of Two Helium Atoms in Confined Geometries

We carry out a comprehensive study of the binding of two helium atoms in unrestricted and, in particular, in restricted geometries in both two and three dimensions. Besides the well known binding of the⁴He dimer in unrestricted geometry in two and three dimensions, we also find weakly bound states of the³He-⁴He molecule and the³He dimer in 2 dimensions. Furthermore, any combination of two⁴He or³He atoms can form a molecule if their motion is sufficiently confined. Our calculations are carried out by numerically solving the Schrödinger equation as well as by constructing a suitable variational wave function.     

Alternative Polarisation Geometries in Tests of Bell Inequalities

Abstract

The unitary transformation induced by an optical element on polarisation vectors corresponds to a rotation of the associated vectors in polarisation space on the Poincaré sphere. The degree of violation of a Bell inequality, which is of central interest in discriminating between hidden variable and quantum theories, involves only scalar products in polarisation space, and so is invariant under joint transformation of the relevant polarisation vectors. Conventionally, the plane of polarisation of any analyser is switched by an angle ψ of, say, π/8. The same violation is predicted if, instead, the analyser switching is performed by adding a relative phase of 2ψ through field-dependent birefringence. As with recent optical demonstrations of the Berry phase, the doubling of the angle indicates the simplicity of a unified analysis of both types of switching in polarisation space.     

Magnetization of a two-component Stoner-Wohlfarth particle

The free energy of an arbitrary two-component Stoner-Wohlfarth particle is derived and general criteria for stable states of magnetization are established. Hysteretic properties of coaxial prolate spheroids composed of γ-Fe2O3coated iron particles are calculated numerically and the specific extension to epitaxial cobalt ferrite γ-Fe2O3particles amongst other two-component systems is indicated.     

延时叠加震源激发地震波能量的研究

根据弹性波动理论,分析了装药爆炸时冲击波转换成地震波的能量关系,对多级小药量垂向延时震源地震波能量叠加的原理进行了研究,建立了简化模型.试验结果表明,垂向延时叠加震源可在保证一定的信噪比的前提下,提高地震波的主频率,是高分辨率地震勘探的较理想的激发震源.     

铁素体纤维的损伤与磁性

在铁素体纤维提取工艺理论分析的基础上,研究了提取过程中纤维的损伤机制,提出了提高纤维磁性的工艺措施。结果表明,纤维的损伤机制为氧化反应和置换反应,纤维中的氧、铜和吸附水导致其磁性下降。当mCr/m(Fe+Cr)在13%附近时,通过采取适当的工艺措施,纤维的比饱和磁化强度MS出现极大值(159 emu/g)。     

Magnetization of Materials Used in Cryostats

We measure the magnetic susceptibility of a group of materials commonly used in the construction of low temperature cryostats. These materials are considered non-magnetic at room temperature. We use a variable temperature susceptometer to measure samples at temperatures between 2.0 K and 12.0 K and at magnetic fields between 0.25 Tesla and 4 Tesla. The samples we use include Aluminum, Beryllium Copper, fused silica, Grafoil, stainless steel, filled and unfilled epoxy, Macor, polycarbonate, aerogel, silver powder, Teflon, and Vespel. We present plots of the magnetization vs. temperature and field, and a table of the parameters to a fitting function which can be used to interpolate the data.