1,721,216 research outputs found
A new model for rate-independent hysteresis in permanent magnets
No full textA one-dimensional memory-based model of magnetic materials exhibiting hysteresis loops is proposed here. Mainly, we suggest a modification of the Duhem model investigated by Coleman & Hodgdon in connection with isoperms in order to better fit their real behaviour. Many properties fulfilled by the original model are preserved here. For instance, the presence of the major loop, bounding all hysteresis pathes, the existence and uniqueness of asymptotically stable periodic solutions (primitive loops), the existence of a "universal" demagnetization process (a suitable alternating magnetic field, with slowly decreasing amplitude, reproducing the "virgin state"). On the other hand, a few mathematical features are common to the Preisach model and allow the corresponding hysteretic functional to avoid effects, like self-magnetization, which are typical of the Duhem modelization but physically unsound. In particular, equilibrium states are stable with respect to noises of small amplitude (static vibro-stability)
HKT MANIFOLDS: HODGE THEORY, FORMALITY AND BALANCED METRICS
No full textLet be a compact HKT manifold, and let us denote with the conjugate Dolbeault operator with respect to I, \partial_J:=J<^>{-1}\overline\partial J, \partial<^>\Lambda:=[\partial,\Lambda], where Lambda is the adjoint of . Under suitable assumptions, we study Hodge theory for the complexes (A<^>{\bullet,0},\partial,\partial_J) and (A<^>{\bullet,0},\partial,\partial<^>\Lambda) showing a similar behavior to Kahler manifolds. In particular, several relations among the Laplacians, the spaces of harmonic forms and the associated cohomology groups, together with Hard Lefschetz properties, are proved. Moreover, we show that for a compact HKT -manifold, the differential graded algebra (A<^>{\bullet,0},\partial) is formal and this will lead to an obstruction for the existence of an HKT structure on a compact complex manifold (M, I). Finally, balanced HKT structures on solvmanifolds are studied
Thermodynamic properties and stability for the heat flux equation with linear memory
No full textWithin the linearized theory of heat conduction with fading memory, some restrictions on the constitutive equations are found as a direct consequence of thermodynamical principles. Such restrictions allow us to obtain existence, uniqueness and stability results for the solution to the heat flux equation. Both problems, which respectively occur when the instantaneous conductivity ko is positive or vanishes, are considered
Some quasi-static problems with elastic and viscous boundary conditions in linear viscoelasticity
No full textWe study the quasi-static behaviour of a linearly viscoelastic body which is subject to boundary forces respectively of elastic type and of viscous type. The ensuing problems exhibit dynamic boundary conditions. We impose on the memory kernel only those restrictions deriving from thermodynamics and, making use of the Fourier transform method, we show existence and uniqueness of the solution to each problem
Dual-frequency patch antennas
No full textDual-frequency patch antennas may provide an alternative to large-bandwidth planar antennas, in applications in which large bandwidth is really needed for operating at two separate transmit-receive bands. When the two operating frequencies are far apart, a dual-frequency patch structure can be conceived to avoid the use of separate antennas. In this paper, a critical overview of possible solutions for dual-frequency patch antennas is presented, and future perspectives are outlined
Stopband singlet: A novel structure implementing resonating couplings
No full textIn this letter a new type of singlet is introduced, called stopband singlet. The new singlet is implemented in rectangular waveguide, exploiting TE301 as resonating mode and TE10 mode as nonresonating bypass coupling. Unlike the previously introduced singlets [which produce one transmission zero (TZ) and one reflection zero (RZ)], the stopband singlet generates one TZ alone (the RZ is pushed to infinity). The novel structure allows designing filters with resonating couplings introducing TZs very close to the passband (difficult to implement with other resonating waveguide discontinuities). A prototype two-pole filter with one TZ has been designed and fabricated to validate experimentally the novel singlet configuration
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