Nonlinear parametric instability in double-well lattices

A possibility of a nonlinear resonant instability of uniform oscillations in dynamical lattices with harmonic intersite coupling and onsite nonlinearity is predicted. Numerical simulations of a lattice with a double-well onsite anharmonic potential confirm the existence of the nonlinear instability with an anomalous value of the corresponding power index, 1.57, which is intermediate between the values 1 and 2 characterizing the linear and nonlinear (quadratic) instabilities. The anomalous power index may be a result of competition between the resonant quadratic instability and nonresonant linear instabilities. The observed instability triggers transition of the lattice into a chaotic dynamical state.Comment: A latex text file and three pdf files with figures. Physical Review E, in pres

The Growth Effects of Institutional Instability

Both institutional quality and institutional stability have been argued to stimulate economic growth. But to improve institutional quality, a country must endure a period of institutional change, which implies at least a little and possibly a lot of institutional instability. We investigate the growth effects of institutional quality and instability, using the political risk index from the ICRG in a cross-country study of 132 countries, measuring instability as the coefficient of variation. Using the aggregate index, we find evidence that institutional quality is positively linked to growth. While institutional instability is negatively related to growth in the baseline case, there are indications that the effect can be positive in rich countries, suggesting that institutional reform is not necessarily costly even during a transition period. Sensitivity analysis, e.g., decomposing the political risk index by using both its constituting components and the results of a principal components analysis, using other measures of institutional quality and excluding outliers, confirm the general results, with qualifications.Institutions; Instability; Growth; Transaction costs; Uncertainty

Screw instability of the magnetic field connecting a rotating black hole with its surrounding disk

Screw instability of the magnetic field connecting a rotating black hole (BH) with its surrounding disk is discussed based on the model of the coexistence of the Blandford-Znajek (BZ) process and the magnetic coupling (MC) process (CEBZMC). A criterion for the screw instability with the state of CEBZMC is derived based on the calculations of the poloidal and toroidal components of the magnetic field on the disk. It is shown by the criterion that the screw instability will occur, if the BH spin and the power-law index for the variation of the magnetic field on the disk are greater than some critical values. It turns out that the instability occurs outside some critical radii on the disk. It is argued that the state of CEBZMC always accompanies the screw instability. In addtition, we show that the screw instability contributes only a small fraction of magnetic extraction of energy from a rotating BH.Comment: 18 pages, 13 figures; Accepted by Ap

Transverse Instability of Periodic Traveling Waves in the Generalized Kadomtsev-Petviashvili Equation

In this paper, we investigate the spectral instability of periodic traveling wave solutions of the generalized Korteweg-de Vries equation to long wavelength transverse perturbations in the generalized Kadomtsev-Petviashvili equation. By analyzing high and low frequency limits of the appropriate periodic Evans function, we derive an orientation index which yields sufficient conditions for such an instability to occur. This index is geometric in nature and applies to arbitrary periodic traveling waves with minor smoothness and convexity assumptions on the nonlinearity. Using the integrable structure of the ordinary differential equation governing the traveling wave profiles, we are then able to calculate the resulting orientation index for the elliptic function solutions of the Korteweg-de Vries and modified Korteweg-de Vries equations.Comment: 26 pages. Sign error corrected in Lemma 3. Statement of main theorem corrected. Exposition updated and references added

STUDI EFEKTIFITAS INDIKATOR KESTABILAN TEGANGAN PADA MODEL DINAMIS SISTEM TENAGA LISTRIK

TITe pape7- presents the effectiveness of voltage stability indices for dynamic povver system modelling study in providing information about the proximity of voltage IN] collapse in power system. Four simple stability indices as Voltage Instability Predictor (VIP), Inpedance Stability Index (ISI), Line Index (L index) and Voltage Collapse Prediction hadex (V(-PI) are conapared using WS(-C9 bus testsystem. The Em comparison show the ISI and VCPI are much More reliable indicator, give the fast Ind indication and fast time computation than L index for voltage collapse in dynamics voltage collapse prediction. Kata Kunci: : Dynamics Voltage Collapse, Voltage Instability Predictor Impedance Stability Index, Line Index, Voltage Collapse Prediction Index