Search results for "Instability"
showing 10 items of 724 documents
Influence of Rotor Suspension Anisotropy on Oil Film Instability
2018
A crucial problem of turbomachinery is the oil film instability on increasing the angular speed, which is correlated with the asymmetry of the bearing stiffness matrix and resembles the hysteretic instability somehow. As a beneficial effect is exerted on the latter by the anisotropy of the support stiffness, some favorable effects have been recently found by the author also for the former, whence a systematic analysis has been undertaken. The instability thresholds may be detected by the usual conventional methods, but a detailed analysis may be carried out by closed-form procedures in the hypothesis of symmetry of the rotor-shaft-support system, which condition approaches the real working …
Lattice Instability and Competing Spin Structures in the Double Perovskite InsulatorSr2FeOsO6
2013
The semiconductor Sr2FeOsO6, depending on temperature, adopts two types of spin structures that differ in the spin sequence of ferrimagnetic iron-osmium layers along the tetragonal c axis. Neutron powder diffraction experiments, 57Fe Mossbauer spectra, and density functional theory calculations suggest that this behavior arises because a lattice instability resulting in alternating iron-osmium distances fine-tunes the balance of competing exchange interactions. Thus, Sr2FeOsO6 is an example of a double perovskite, in which the electronic phases are controlled by the interplay of spin, orbital, and lattice degrees of freedom.
Modulational instability processes in optical isotropic fibers under dual-frequency pumping
2001
Experiments are presented showing that under dual-frequency, circular polarization pumping, a host modulational instability processes can be generated in a single isotropic fiber, by carefully tuning the frequency spacing between the pumps.
Very low instability threshold in a three-level laser model with incoherent optical pumping
1997
Abstract The stability properties of a laser model based on a closed three-level atomic scheme with incoherent optical pumping are studied. Unexpectedly, the instability threshold can be very low approaching the lasing threshold for large unsaturated gain values.
Limits of stability in supported graphene nanoribbons subject to bending
2016
Graphene nanoribbons are prone to in-plane bending even when supported on flat substrates. However, the amount of bending that ribbons can stably withstand remains poorly known. Here, by using molecular dynamics simulations, we study the stability limits of 0.5-1.9 nm wide armchair and zigzag graphene nanoribbons subject to bending. We observe that the limits for maximum stable curvatures are below ~10 deg/nm, in case the bending is externally forced and the limit is caused by buckling instability. Furthermore, it turns out that the limits for maximum stable curvatures are also below ~10 deg/nm, in case the bending is not forced and the limit arises only from the corrugated potential energy…
Turing pattern formation in the Brusselator system with nonlinear diffusion.
2013
In this work we investigate the effect of density dependent nonlinear diffusion on pattern formation in the Brusselator system. Through linear stability analysis of the basic solution we determine the Turing and the oscillatory instability boundaries. A comparison with the classical linear diffusion shows how nonlinear diffusion favors the occurrence of Turing pattern formation. We study the process of pattern formation both in 1D and 2D spatial domains. Through a weakly nonlinear multiple scales analysis we derive the equations for the amplitude of the stationary patterns. The analysis of the amplitude equations shows the occurrence of a number of different phenomena, including stable supe…
Convergence in critical fuel moisture and fire weather thresholds associated with fire activity in the pyroregions of Mediterranean Europe
2021
Wildfires are becoming an increasing threat to many communities worldwide. There has been substantial progress towards understanding the proximal causes of increased fire activity in recent years at regional and national scales. However, subcontinental scale examinations of the commonalities and differences in the drivers of fire activity across different regions are rare in the Mediterranean zone of the European Union (EUMed). Here, we first develop a new classification of EUMed pyroregions, based on grouping different ecoregions with similar seasonal patterns of burned area. We then examine the thresholds associated with fire activity in response to different drivers related to fuel moist…
Relationship of Weather Types on the Seasonal and Spatial Variability of Rainfall, Runoff, and Sediment Yield in the Western Mediterranean Basin
2020
Producción Científica
Flux-flow instability and heating effects in Bi2Sr2CaCu2O8 and YBa2Cu3O7 thin films
2000
Abstract We investigated current–voltage curves of Bi 2 Sr 2 CaCu 2 O 8 and YBa 2 Cu 3 O 7 thin films. Voltage jumps due to flux-flow instabilities at high vortex-velocities were found and interpreted in the framework of the theory of Larkin and Ovchinnikov. The extensions introduced by Bezuglyj et al. account for quasiparticle heating during the measurement. While in Bi 2 Sr 2 CaCu 2 O 8 the instability is found in the vortex-liquid phase, in YBa 2 Cu 3 O 7 we observed it in the vortex-glass phase. Moreover, we studied the temporal behavior of the instability in current–voltage curves with a time resolution in the microsecond range.
Polarization Modulation Instability in All-Normal Dispersion Microstructured Optical Fibers With Quasi-Continuous Pump
2019
We report the experimental observation of the polarization modulation instability (PMI) effect in all-normal dispersion (ANDi) microstructured optical fibers (MOFs) with quasi-continuous pumping. The small unintentional birefringence (~10-5), that any realistic non-polarization maintaining MOF exhibits, contributes to this nonlinear effect. PMI can produce two sidebands whose polarization state is orthogonal to the polarization of the pump. In this work, only one type of PMI process is observed, i.e., when the pump is polarized along the slow axis of the fiber and sidebands are generated in the fast axis mode. This PMI process was studied experimentally in two ANDi fibers with different dis…