Demagnetizing factors for cylinders

Fluxmetric (ballistic) and magnetometric demagnetizing factors N_f and N_m for cylinders as functions of susceptibility χ and the ratio γ of length to diameter have been evaluated. Using a one-dimensional model when γ⩾10, N_f was calculated for -1⩽χ<∞ and N_m was calculated for χ→∞. Using a two-dimensional model when 0.01⩽γ⩽50, an important range for magnetometer measurements, N_m and N_f were calculated for -1⩽χ<∞. Demagnetizing factors for χ<0 are applicable to superconductors. For χ=0, suitable for weakly magnetic or saturated ferromagnetic materials, N_f and N_m were computed exactly using inductance formulas     

Demagnetizing factors for square bars

Using a finite-element method, we have calculated fluxmetric and magnetometric demagnetizing factors N/sub f/ and N/sub m/ for square cross-section bars as functions of susceptibility /spl chi/ and length-to-width ratio c/a over the range /spl chi/=-1 to /spl infin/ and c/a=0.01 to 100. We present the results in figures and tables and compare them with those for cylinders. We give an approximate conjugate relation for N/sub m/(/spl chi/) of a cube.     

Demagnetizing factors for rectangular prisms

For rectangular prisms of dimensions 2a/spl times/2b/spl times/2c with constant material susceptibility /spl chi/, we have calculated and tabulated the fluxmetric and magnetometric demagnetizing factors N/sub f/ and N/sub m/, defined along the 2c dimension as functions of c/(ab)/sup 1/2/(=1/spl sim/500), a/b(=1/spl sim/256), and /spl chi/(=0/spl sim/10/sup 9/). We introduce an interpolation technique for obtaining N/sub f,m/ with arbitrary values of c/(ab)/sup 1/2/, a/b, and /spl chi/.     

Enhanced Voidage Correlations for Packed Beds of Various Particle Shapes and Sizes

Mean voidage in packed beds of spherical, cylindrical, and nonconventional cylindrical particles has been accurately measured, and the data obtained were employed to develop predictive mean voidage correlations that were not only simpler to use and more accurate than existing correlations, but also helped in developing a single general voidage correlation incorporating a particle shape factor applicable to a variety of particle shapes. Such mean voidage correlations are highly sought in packed bed design for a multitude of applications and can also assist in minimizing pressure drop in such packed beds by guiding particle shape selection.     

The Structure of Fraunhofer Diffraction Patterns of Apertures with N-fold Rotational Symmetry

The moment theorem is used to show that the innermost part of the Fraunhofer diffraction pattern of any real aperture with higher than two-fold rotational symmetry is rotationally invariant. Then a formalism is presented in which aperture transmission-functions are represented by series of Zernike circle polynomials and diffracted field-amplitudes by series of Bessel functions, from which it is easily shown that the diffraction patterns of such apertures consist of regions, contained between well-defined values of the radius, whose rotational symmetries are integral multiples of that of the aperture. The central region, extending from = 0 to , N ( measures the diffraction angle, and N is the degree of rotational symmetry of the aperture) is rotationally invariant, and successive circumjacent regions have progressively higher rotational symmetries. The diffraction patterns of sectoral apertures and of rings of pinholes are derived and shown to exemplify these general conclusions. Finally it is shown how the diffraction patterns of some apertures (‘chiral apertures’) with rotational symmetries but no mirror symmetry can be deduced from the diffraction pattern of a related aperture with mirror symmetries, to which a chiral perturbation is applied.     

Collisions between Liquid Drops of Various Shapes in a Gas Flow

Technical Physics Letters - We have experimentally studied the interaction between water drops of various surface configurations moving in a gas medium. Results of high-speed video monitoring...     

Fabrication of a Stable New Polymorph Gold Nanowire with Sixfold Rotational Symmetry

Gold is known as the most noblest metal with only face‐centered cubic (fcc) structure in ambient conditions. Here, stable hexagonal non‐close‐packed (ncp) gold nanowires (NWs), having a diameter of about 50 nm and aspect ratios of well over 400, are reported. Au NWs are grown in the confined system of nanotubular TiO₂ arrays via photoelectrochemical reduction of HAuCl₄ precursors. Some of the resulting Au NWs are proved to have sixfold rotational symmetry, observed by transmission electron microscopy tilting experiments. This new polymorph is identified as a hexagonal ncp‐structure with lattice parameters of a = 2.884 Å and c = 7.150 Å, showing quite a large interplanar spacing (c/a ≈ 2.48). That is, Au atoms are close‐packed along the ab plane, but each plane is not closely stacked along the c axis like in graphite. The structure is usually expected to be unstable, but the present ncp‐2H gold is stable under ambient conditions and intense electron beam irradiation, and shows thermal stability up to 400 °C. Moreover, the resulting physical properties as a result of the corresponding change in electronic structures are investigated by comparing the optical properties of fcc and ncp‐2H Au NWs.     

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)     

Magnetometric diagnostics of ferritin in living matter

Investigations in a broad sample set of living matter, including plants and silty soil fractions from various climate and soil zones, microorganisms, and muscle tissues of birds and mammals (a total of about 200 samples) show that iron in native substances occurs in the form of nanodimensional particles of hydroxide (ferrihydrite). Based on the data of Mössbauer spectroscopy and magnetic measurements, these nanoparticles can be identified as nuclei of the globular protein ferritin. Most measurements were performed at 290 K (i.e., without using cryogenic techniques).     

Magnetometric determination of the angular position of an object

A method is described for finding the angular position of an object by measuring at two selected points in space the components of an alternating magnetic field set up by two sources. The angular position of the object and its coordinates can be measured even if the object is moved or rotated about any axis through 0 to 360° in the presence of magnetic interference. Translated from Izmeritel'naya Tekhnika, No. 12, pp. 34–37, December, 1996.     

Magnetometric study of gadolinium solubility in magnetite nanocrystals

Gadolinium ions have been demonstrated experimentally to be incorporated into magnetite nanoparticles. Increasing the percentage of gadolinium considerably reduces the magnetic moment of the magnetite nanoparticles (by two orders of magnitude). This effect is discussed in terms of known models for the effect of nanocrystal size (the number of dopant atoms) on the dopant solubility in nanocrystals. Experimental data obtained for a system of gadolinium-doped iron oxide nanoparticles by magnetometry are in qualitative agreement with the models.     

边界元应力函数法解旋转体的扭转问题

本文考虑旋转体在端部受有扭矩作用的弹性扭转问题。由调和函数φ/(r~2)sin 2θ(其中φ为应力函数,r、θ、z 为圆柱坐标)出发,根据格林公式建立边界积分方程。在该方程中场变量为φ和1/(r~2)(бφ)/(бn),在侧面上φ为常数,且与施加的扭矩有关,而后者恰为所需求的在旋转体侧面上的合剪应力。文末给出三个计算实例。     

旋转黏度计转子修正系数的校准与测量能力(CMC)

按标准黏度液测量范围分段,对旋转黏度计转子修正系数测量值的校准与测量能力进行了评定。讨论了影响校准与测量能力(CMC)的主要因素。     

Precise Magnetometric Diagnostics of Critical-Current Inhomogeneities in High-Temperature Semiconductor Tapes

Technical Physics Letters - We present a new precise method of contactless magnetometric determination of the local critical current in high-temperature superconductor (HTS) tapes, which involves...     

Experimental Investigation of Symmetry Reduction and Electron—Molecular Vibration Coupling in Various RbC60 Phases

In the monomer, dimer and polymer phase of RbC₆₀ the principal infrared modes exhibit significant shifts and splittings. We compare the positions of the main components of the four T_1μ modes of C₆₀ in these three phases. Hie frequency shifts are determined by two competing effects: lattice hardening due to the formation—of chemical bonds between the balls, and softening induced by electron-molecular vibration (EMV) coupling. The behavior of the individual modes correlates with their sensitivity to pressure and their EMV coupling constants.     

Geometries With the Demagnetizing Energy Independent of the Direction of Magnetization

We have studied single-domain particles of nonellipsoidal shape and of uniform magnetization and have found that the demagnetizing energy is independent of the direction of magnetization in bodies with certain symmetries. Our study used several symmetries containing rotation or rotoinversion in the calculation of demagnetizing energies in various directions of axis     

Effect of Various Operating Factors on Wet Stirred Mill Performance

In this study, the effects of various operating factors, such as initial particle size, feed quantity, filling volume of the ball, and ball size distribution on fine grinding of calcite powders (CaCO₃) were studied using a laboratory stirred mill under wet conditions. A series of laboratory experiments using 2⁴ full factorial designs was conducted to determine the optimum grinding parameters. The main and interaction effects on the specific surface area (m²/g) of the ground product were evaluated using Yates' analysis. The test results showed that the main factors that influence the mill grinding performance are the feed quantity and the ball size distribution.     

Optimum Patch Repair Shapes for Cracked Members

In the present paper the problem of finding the optimal patch repair shape in a cracked structural component with respect to a given objective function, is investigated by using a biological-based procedure known as Genetic Algorithm (GA) in conjunction with a penalty constraint. The search for an optimal patch shape, which can be regarded also as an optimal topology problem, is obtained by determining the corresponding patch’s continuous material’s density distribution: the design optimisation considered in the present study takes into account the minimisation of some mechanical desired performance of the structure’s while keeping constant the total available patched area (optimal constrained problem). The proposed optimisation model is implemented in a F.E. code and some numerical simulations are performed in order to assess its reliability in optimal topology design of patch repairs, applied to mode I cracked members, with respect to some expected performances. For the considered problems, the optimisation algorithm allows a quite important improvement (in reducing the stress intensity factor) with respect to cracked components repaired with simple shape (i.e. rectangular) bonded patches.     

不同因素对Pd-Fe合金共沉积规律的影响

以FeSO4·7H2O、Pd(NH3)2Cl2、磺基水杨酸(SSCS)和(NH4)2SO4所组成的溶液体系为研究对象,采用循环伏安法分析了镀液中Pd:Fe配比、电极转速、扫描速度、溶液pH值、pH调整剂和导电盐等因素对Pd-Fe合金共沉积电位的影响规律.结果表明,Pd-Fe合金的共沉积电位介于Fe2 和Pd2 的沉积电位之间.溶液中Fe2 浓度增加使其共沉积峰位略有负移,且阳极峰值电流逐渐增大;电极转速或扫描速度增大均使共沉积峰位发生负移,使峰值电流增加;溶液pH值减小使共沉积峰位正移,且pH值小于4时几乎无沉积峰;由乙二胺调节溶液pH值比由氨水调节后Pd-Fe合金的共沉积峰位负移;导电盐的存在使共沉积峰位正移,且峰值电流增大.     

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.