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1.
The coercivity of NdFeB magnets is determined by the coercivity of individual grains and the interaction between the grains composed of the magnets. The coercivity of individual grains and the intergrain interaction depend on the degree of the grain alignment, “tanθ type” Gaussian function is applied to describing the degree of the grain alignment. According to different coercivity mechanisms, there are different formula on the coercivity and the angular dependence of coercivity. The interaction between grains can be classified as the long-range magnetostatic interaction and the exchange-coupling interaction of neighboring grains. For the sintered magnet, the grain size is large and the grain boundaries are mostly separated by the non-magnetic phase. So, the long-range magnetostatic interaction is much stronger than the exchange coupling interaction and it makes the coercivity of the magnet composed of misaligned grains be bigger than that of the magnet composed of ideally aligned grains. The effects of coercivity of individual grains and the intergrain interactions are taken into account, and the starting field theory is in agreement with the experimental result for the coercivity of sintered NdFeB magnets. 相似文献
2.
The effect of small amount of Co and Dy addition on the magnetic properties of HDDR isotropic Nd-Dy-Fe-Co-B bonded magnets
was investigated. The experimental results show that the intrinsic coercivity Hcj and the reversible temperature coefficient of remanence of (Nd0.65 Dy0.35)12.5-(Fe0.9Co0.1)81B6.5 magnet were 1.53 MA·m-1(19.3 kOe) and -0.059%/°C (25–155°C), respectively. The high coercivity and low temperature coefficient of the magnet are
due to the enhanced anisotropy field, increased Curie temperature and improved microstructure by Dy and Co addition. 相似文献
3.
The changes in the flow properties under the action of electromagnetic body forces are investigated numerically for ferrofluid flow past a circular cylinder. Ferrofluid is modeled as both a Newtonian and a non-Newtonian Power-Law fluid. Magnetic forces are applied by placing magnets at different locations on the surface of the cylinder. The magnetostatic effects on the structure of the wake region, on drag reduction and on vortex formation length and frequency are shown and compared in terms of Reynolds number, interaction parameter, Power-Law index and magnet location. It is shown that the increase in the interaction parameter reduces drag for both Newtonian and non-Newtonian model. This decrease is observed to be higher for shear thinning and lower for shear thickening fluid compared to Newtonian case. It is also shown that vortex street formation in the wake region behind the cylinder may be delayed under high magnetic effects. The Strouhal number is higher for shear thinning case at both low and high Reynolds numbers, and lower for shear thickening case at high Reynolds numbers, compared to Newtonian fluid. The vortex formation frequency also decreases under the action of the magnetic field in all cases, however the vortex formation length increases. Placing the magnet towards the front region of the cylinder increases considerably the drag coefficient for both Newtonian and non-Newtonian model. This increase in drag coefficient is higher in the shear thinning fluid and lower in the shear thickening fluid compared to the Newtonian case. 相似文献
4.
E. Sh. Gutshabash 《Journal of Mathematical Sciences》2008,151(2):2865-2879
Three integrable models: the deformed Heisenberg, Landau-Lifschits, and Ishimori magnets are written in terms of the stereographic
projection. The Hamiltonians of these models are obtained and certain problems related to the existence of exact solutions
are studied. In particular, stability of solitions is studied for the Heisenberg marnet, simplest stationary solutions are
obtained for the Landau-Lifschits magnet, and Hamiltonians and topological charges are calculated for several known solutions
of the Ishimori model. Bibliography: 33 titles.
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Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 347, 2007, pp. 117–143. 相似文献
5.
Jürgen Grtner 《Mathematische Nachrichten》1988,137(1):197-248
For a system of diffusions in a domain of Rd with long-range weak interaction the behavior of the associated empirical process is studied. Under mild growth and smoothness assumptions on the drift and diffusion coefficients such as coercivity and monotonicity conditions the law of large numbers and the propagation of chaos are proved. Existence and uniqueness of the weak solution to the McKean - Vlasov equation and the associated non-linear martingale problem are investigated. 相似文献
6.
7.
We construct a relativistic potential quark model of D, Ds, B, and Bs mesons in which the light quark motion is described by the Dirac equation with a scalar-vector interaction and the heavy
quark is considered a local source of the gluon field. The effective interquark interaction is described by a combination
of the perturbative one-gluon exchange potential VCoul(r) and the long-range Lorentz-scalar and Lorentz-vector linear potentials Sl.r.(r) and Vl.r.(r). In the semiclassical approximation, we obtain simple asymptotic formulas for the energy and mass spectra and for the
mean radii of D, Ds, B, and Bs mesons, which ensure a high accuracy of calculations even for states with the radial quantum number nr ∼ 1. We show that the fine structure of P-wave states in heavy-light mesons is primarily sensitive to the choice of two parameters:
the strong-coupling constant αs and the coefficient λ of mixing of the long-range scalar and vector potentials Sl.r.(r) and Vl.r.(r).
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Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 155, No. 3, pp. 371–397, June, 2008. 相似文献
8.
N. V. Novikov A. L. Maystrenko V. I. Kushch S. A. Ivanov 《Mechanics of Composite Materials》2006,42(3):253-262
The efficiency of hot-pressed diamond-containing composite materials (DCM) for various tool applications is greatly affected
by microdefects, namely, the residual porosity of the metal matrix, damaged diamond grains, and imperfect diamond-matrix interfaces.
An instrumental evaluation of these microdefects, predetermining the quality of a tool equipped with DCM, is rather difficult
due to the small size, the nonstandard shape, and the strong heterogeneity of specimens. Proposed here is an alternative,
nondestructive technique of DCM quality rating, which includes the measurement of electric resistance and thermal conductivity
of diamond-containing composites and processing the obtained data by the methods of composite mechanics. It exploits the fact
that diamond, being a dielectric, possesses an extremely high thermal conductivity, which allows estimating the residual porosity
of a sintered metal matrix from the ratio of specific electric resistances, one being measured and another predicted by a
theory. These data, in turn, are utilized to predict the thermal conductivity ofDCMwith an imperfect matrix. Matching with
experiments, after solving the inverse problem gives the thermal resistance of diamond-matrix interface, which, within the
frame work of the given model, simulates the damage of both the diamond grains and their bonds with the matrix. Thus, the
numerical rating of quality is given in terms of two dimensionless parameters. The first one, 0 < K < 1, reflects the quality of the sintered metal matrix, whereas the second one, 0 < R <1, is an aggregate measure of the integrity of diamond grains and the perfection degree of composite interfaces. The quite
satisfactory agreement observed between the theory and experiment confirms the efficiency of the technique and the reliability
of the data obtained.
Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 42, No. 3, pp. 361–374, May–June, 2006. 相似文献
9.
V. V. Dyakin V. Ya. Raevskii O. V. Umergalina 《Computational Mathematics and Mathematical Physics》2009,49(1):172-182
A direct magnetostatic problem for magnets with a finite-size inclusion is considered in an integrodifferential form. An approach is used that, under certain conditions, reduces the problem to a single integral equation on a two-dimensional manifold-the inclusion surface. As an important illustrative example, finite formulas are derived to compute the resulting field of a magnetic half-space with a spherical cavity in an arbitrary external field. 相似文献
10.
W. I. Skrypnik 《Ukrainian Mathematical Journal》2006,58(10):1597-1615
The existence of the ferromagnetic long-range order is proved for equilibrium quantum lattice systems of linear oscillators
whose potential energy contains a strong ferromagnetic nearest-neighbor (nn) pair interaction term and a weak nonferromagnetic
term under a special condition on a superstability bound. It is shown that the long-range order is possible if the mass of
a quantum oscillator and the strength of the ferromagnetic nn interaction exceed special values. A generalized Peierls argument
and a contour bound, proved with the help of a new superstability bound for correlation functions, are our main tools.
Published in Ukrains’kyi Matematychnyi Zhurnal, Vol. 58, No. 10, pp. 1407–1424, October, 2006. 相似文献
11.
T. H. Fay L. Mead 《International Journal of Mathematical Education in Science & Technology》2013,44(3):321-329
The paper discusses an elementary spring model representing the motion of a magnet suspended from the ceiling at one end of a vertical spring which is held directly above a second magnet fixed on the floor. There are two cases depending upon the north–south pole orientation of the two magnets. The attraction or repelling force induced by the magnets follow an inverse quartic law and thus we are led to a nonlinear model suitable for discussion in a beginning differential equations course. Spring models are common fare in such courses, but usually only linear models with simple sinusoidal forcing are considered. The resultant model is autonomous and thus an energy approach permits a full phase portrait of the resultant motions in the phase plane. These phase portraits show interesting behaviour of the system, reinforcing one's natural physical intuition. The computer algebra system Mathematica is employed here, although almost any other system would suffice. Such a system permits almost effortless calculations and can generate the graphics needed to thoroughly investigate the model. 相似文献
12.
CHEN Hesheng 《中国科学A辑(英文版)》2000,43(9):996-1008
Alpha magnetic spectrometer (AMS) is the first large magndtic spectrometer in space. Its precursor flioht was completed successfully
in June 1998. The key part of AMS is the permanent magnet system, which was built by the lnstitute of Electric Engineering,
the institute of High Energy Physics and the Chinese Academy of Launch Vehicle Technology. This system includes a permanent
magnet made of high grade NdFeB and a support structure. The unique design of the permanent magnet based on the magic ring
fulfills the severe requirements on the magnetic field leakage and the dipole moment for space experiments. The permanent
magnet weighs about 2 tons, and provides a geometric acceptance of 0.6 m2 · sr and an analyzing powerBL
2 of 0.135 T · m2. It works up to 40°C without demagnetization. The main structure is a thin double shell, which undergoes the strong magnetic
force and torque of the permanent magnet, as well as the large load during launching and landing. The permanent magnet system
fulfills the requirements from AMS, and satisfies the strict safety standards of NASA. 相似文献
13.
A very general magnetostatic problem involving inhomogeneousanisotropic materials filling irregular regions and with mixedboundary conditions is formulated in terms of magnetic vectorpotential. Some restrictions inherent to the introduction ofa vector potential become apparent and additional conditionsfor the uniqueness of the vector potential naturally arise.The modelling of permanent magnets is introduced in both thevector potential and the field formulations by weakening theregularity requirements on the source term. The vector potentialformulation is also shown to be equivalent to a penalized formulationwidely used in numerical applications. 相似文献
14.
A magnet is a pair u, v of adjacent vertices such that the proper neighbours of u are completely linked to the proper neighbours of v. It has been shown that one can reduce the graph by removing the two vertices u, v of a magnet and introducing a new vertex linked to all common neighbours of u and v without changing the stability number. We prove that all graphs containing no chordless cycle C
k
(k ≥ 5) and none of eleven forbidden subgraphs can be reduced to a stable set by repeated use of magnets. For such graphs a
polynomial algorithm is given to determine the stability number. 相似文献
15.
A notion of the positive spatial association is introduced in this paper to analyze spatial dependence of Boolean models with the focus on estimating the long-range spatial dependence. The explicit tail estimates for probabilities of simultaneous damage to two distant spatial regions are obtained using the regular variation method, and the long-range spatial covariance for the Boolean models with heavy-tailed grains is shown to decay at the power-law rate that is smaller than the tail decay rate of grains. Examples and applications to spatial reliability modeling are also discussed. 相似文献
16.
V. I. Skrypnik 《Ukrainian Mathematical Journal》1997,49(5):770-778
Quantum systems of particles interacting via an effective electromagnetic potential with zero electrostatic component are
considered (magnetic interaction). It is assumed that the j th component of the effective potential for n particles equals the partial derivative with respect to the coordinate of the jth particle of “magnetic potential energy” of n particles almost everywhere. The reduced density matrices for small values of the activity are computed in the thermodynamic
limit for d-dimensional systems with short-range pair magnetic potentials and for one-dimensional systems with long-range pair magnetic
interaction, which is an analog of the interaction of three-dimensional Chern-Simons electrodynamics (“magnetic potential
energy” coincides with the one-dimensional Coulomb (electrostatic) potential energy).
Institute of Mathematics, Ukrainian Academy of Sciences, Kiev. Published in Ukrainskii Matematicheskii Zhurnal, Vol. 49, No.
5, pp. 691–698, May 1997. 相似文献
17.
Yuu Hariya 《Probability Theory and Related Fields》2006,136(1):157-170
We study 1-dimensional continuum fields of Ginzburg-Landau type under the presence of an external and a long-range pair interaction
potentials. The corresponding Gibbs states are formulated as Gibbs measures relative to Brownian motion [17]. In this context
we prove the existence of Gibbs measures for a wide class of potentials including a singular external potential as hard-wall
ones, as well as a non-convex interaction. Our basic methods are: (i) to derive moment estimates via integration by parts;
and (ii) in its finite-volume construction, to represent the hard-wall Gibbs measure on C(ℝ;ℝ+) in terms of a certain rotationally invariant Gibbs measure on C(ℝ;ℝ3). 相似文献
18.
Oksana Ozhoga-Maslovskaja Holm Altenbach Konstantin Naumenko Oleksandr Prygorniev 《PAMM》2012,12(1):145-146
A polycrystalline material is investigated under creep conditions within the framework of continuum micromechanics. Geometrical 3D model of a polycrystalline microstructure is represented as a unit cell with grains of random crystallographical orientation and shape. Thickness of the plains, separating neighboring grains in the unit cell, can have non-zero value. Obtained geometry assigns a special zone in the vicinity of grain boundaries, possessing unordered crystalline structure. A mechanical behavior of this zone should allow sliding of the adjacent grains. Within the grain interior crystalline structure is ordered, what prescribes cubic symmetry of a material. The anisotropic material model with the orthotropic symmetry is implemented in ABAQUS and used to assign elastic and creep behavior of both the grain interior and grain boundary material. Appropriate parameters set allows transition from the orthotropy to the cubic symmetry for the grain interior. Material parameters for the grain interior are identified from creep tests for single crystal copper. Model parameters for the grain boundary are set from the physical considerations and numerical model validation according to the experimental data of the grain boundary sliding in a polycrystalline copper [2]. As the result of analysis representative number of grains and grain boundary thickness in the unit cell are recommended. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
19.
The article reviews two-dimensional magnetic solitons in a classical weakly-anisotropic Heisenberg magnets. Topological classification, structure, dynamical properties and thermodynamical contribution of 2D solitons to response functions of the magnet are discussed. Based on effective equations of motion we calculated the soliton contribution to the dynamical structure factor of ferromagnets and antiferromagnets both for localized topological solitons and magnetic vortices. 相似文献
20.
DALLON JOHN; SHERRATT JONATHAN; MAINI PHILIP; FERGUSON MARK 《IMA Journal of Mathematical Control and Information》2000,17(4):379-393
We deveiop a novel mathematical model for collagen depositionand alignment during dermal wound healing. We focus on the interactionsbetween fibroblasts, modelled as discrete entities, and a continuousextracellular matrix composed of collagen and a fibrin basedblood clot. There are four basic interactions assumed in themodel: fibroblasts orient the collagen matrix, fibroblasts produceand degrade collagen and fibrin and the matrix directs the fibroblastsand determines the speed of the cells. Several factors whichinfluence the alignment of collagen are examined and relatedto current anti-scarring therapies using transforming growthfactor ß. The most influential of these factors arecell speed and, more importantly for wound healing, the influxof fibroblasts from surrounding tissue. 相似文献