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61.
62.
M. Fukuyama 《Journal of statistical physics》2000,98(5-6):1049-1061
Georgii's theorem ensures that, restricted to two-dimensional planes, a single ocean (i.e., infinite connected component) of a ground state and islands (i.e., finite connected components) are observed in lattice spin systems at sufficiently low temperature. This paper extends his results for higher dimensional hyperplanes. Our proof is mainly based on a kind of Peierls argument and is different from Georgii's, which relies on the percolation method. 相似文献
63.
Catherine Kealley Margaret Elcombe Arie Van Riessen 《Journal of synchrotron radiation》2008,15(1):86-90
Synchrotron radiation diffraction data were collected from hydroxyapatite–carbon nanotube bioceramic composites to determine the crystallite size and to measure changes in non‐uniform strain. Estimates of crystallite size and strain were determined by line‐profile fitting of discrete peaks and these were compared with a Rietveld whole‐pattern analysis. Overall the two analysis methods produced very similar numbers. In the commercial hydroxyapatite material, one reflection in particular, (0 2 3), has higher crystallite size and lower strain values in comparison with laboratory‐synthesized material. This could indicate preferential crystal growth in the [0 2 3] direction in the commercial material. From the measured strains in the pure material and the composite, there was a degree of bonding between the matrix and strengthening fibres. However, increasing the amount of carbon nanotubes in the composite has increased the strain in the material, which is undesirable for biomedical implant applications. 相似文献
64.
65.
A new type of crisis is shown to exist in a broad class of systems (including the Lorenz model) which leads to an anomalous band splitting or to a symmetry-breaking bifurcation of the strange attractor, depending on the actual values of the control parameters. A piecewise linear model is used to understand the mechanism of this crisis and to obtain exact results. 相似文献
66.
67.
Bernhard Schweizer 《Nonlinear dynamics》2009,57(4):509-532
High-speed rotors are often supported in floating ring bearings because of their good damping behavior. In contrast to conventional
hydrodynamic bearings with a single oil film, full-floating ring bearings consist of two oil films: An inner and an outer
oil film. As single oil-film bearings, full-floating ring bearings also show the typical fluid-film-induced instabilities
(self-excited vibrations). Both inner and outer oil films can become unstable and exhibit oil whirl/whip instabilities.
The paper at hand considers a Laval (Jeffcott) rotor, which is symmetrically supported in full-floating ring bearings, and
investigates the occurring oil whirl/whip effects by means of run-up simulations. It is shown that the inner oil film, which usually becomes unstable first, gives
rise to a limit-cycle oscillation with an exactly circular rotor orbit, if gravity and imbalance are neglected. Interesting
is the instability generated by the outer oil film. The calculations demonstrate that instability in the outer oil film does
not lead to a simple circular limit-cycle orbit. Whirl/whip-induced limit-cycle oscillations generated by the outer oil film are more complex and entail a coupled circumferential and
radial motion, although the mechanical problem is radially symmetric, if gravity and imbalance are neglected. Thus, whirl/whip instability in the outer fluid film may be interpreted as symmetry breaking.
Finally, a further kind of bifurcation/instability occurring in rotors supported in full-floating ring bearings—called Total Instability in this paper—is analyzed. It is shown that Total Instability is caused by synchronization of two limit cycles, namely synchronization of the inner and outer oil whirl/whip. Total Instability is of practical interest and observed in real technical rotor systems, and frequently leads to complete rotor damage. 相似文献
68.
We introduce a model motivated by studies of Bose-Einstein condensates (BECs) trapped in double-well potentials. We assume that a mixture of two hyperfine states of the same atomic species is loaded in such a trap. The analysis is focused on symmetry-breaking bifurcations in the system, starting at the linear limit and gradually increasing the nonlinearity. Depending on values of the chemical potentials of the two species, we find numerous states, as well as symmetry-breaking bifurcations, in addition to those known in the single-component setting. These branches, which include all relevant stationary solutions of the problem, are predicted analytically by means of a two-mode approximation, and confirmed numerically. For unstable branches, outcomes of the instability development are explored in direct simulations. 相似文献
69.
It is conjectured that flavor mixing furnishes a universal mechanism for the spontaneous breaking of supersymmetry. The conjecture is proved explicitly for the mixing of two chiral N=1 supermultiplets and arguments for its general validity are given. That is an instance of the O?Raifeartaigh Lagrangian for which there is no tree-level nor perturbative breaking. Nonetheless, the dynamical breaking occurs due to the vacuum condensate, a mixing-induced nonperturbative effect that lifts the zero point energy. 相似文献
70.
Considered herein is a modified periodic Camassa–Holm equation with cubic nonlinearity which is called the modified μ-Camassa–Holm equation. The proposed equation is shown to be formally integrable with the Lax pair and bi-Hamiltonian structure. Local well-posedness of the initial-value problem to the modified μ-Camassa–Holm equation in the Besov space is established. Existence of peaked traveling-wave solutions and formation of singularities of solutions for the equation are then investigated. It is shown that the equation admits a single peaked soliton and multi-peakon solutions with a similar character of the μ-Camassa–Holm equation. Singularities of the solutions can occur only in the form of wave-breaking, and several wave-breaking mechanisms for solutions with certain initial profiles are described in detail. 相似文献