Lagrangian chaos and the effect of drag on the enstrophy cascade in two-dimensional turbulence

We investigate the effect of drag force on the enstrophy cascade of two-dimensional Navier-Stokes turbulence. We find a power law decrease of the energy wave number (k) spectrum that is faster than the classical (no-drag) prediction of k(-3). It is shown that the enstrophy cascade with drag can be analyzed by making use of a previous theory for finite lifetime passive scalars advected by a Lagrangian chaotic fluid flow. Using this we relate the power law exponent of the energy wave number spectrum to the distribution of finite time Lyapunov exponents and the drag coefficient.     

Spin squeezing and quantum correlations

We discuss the notion of spin squeezing considering two mutually exclusive classes of spin-s states, namely, oriented and non-oriented states. Our analysis shows that the oriented states are not squeezed while non-oriented states exhibit squeezing. We also present a new scheme for construction of spin-s states using 2s spinors oriented along different axes. Taking the case of s=1, we show that the ‘non-oriented’ nature and hence squeezing arise from the intrinsic quantum correlations that exist among the spinors in the coupled state.     

Application of the Model for Thermal Transport in Tokamaks

The anomalous electron thermal transport model baaed on collisionleas plasma instabilities driven by electron temperature gradient is applied to tokamak plasma with auxiliary heating. The steady state electron equation is solved and the results ahow good agreement with experimental observations including the principle of profile consltency, various scaling laws, and even some results for detached plasmas.     

Spatio-temporal development of the filaments due to the thermal self-focusing instability near the critical surface in ionospheric plasmas

We study fully nonlinear spatio-temporal development of the thermal self-focusing instability of high-power radio waves near the critical surface of the ionosphere. These simulations improve on our earlier work by including an evolution equation for the density instead of using the assumption of constant pressure to determine the perturbed density connected with the known temperature perturbation. Using our two-dimensional nonlinear code we analyze the time scale and associated velocity for the development of the field-aligned irregularities as they spread from the critical surface both in the underdense as well as the overdense regions. The scaling of this velocity as a function of the radiated power of the heater electromagnetic wave (ERP) is determined. We also study the characteristic size of the self-focused filament as a function of ERP. Finally, the spectrum of the density and temperature fluctuations as well as modifications in the equilibrium values of these parameters for different values of ERP are presented. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 7, pp. 670–681, July 1999.     

Modulational instability in the presence of Langmuir turbulence

We investigate the effect of high frequency short wavelength Langmuir turbulence on parametrically driven modulational instabilities and find that turbulence reduces their threshold for excitation. We also find an interesting modification of the modulational stability of the Langmuir plasmons due to the presence of the pump wave.     

Sleep disturbances in highly stress reactive mice: Modeling endophenotypes of major depression

Background  

Neuronal mechanisms underlying affective disorders such as major depression (MD) are still poorly understood. By selectively breeding mice for high (HR), intermediate (IR), or low (LR) reactivity of the hypothalamic-pituitary-adrenocortical (HPA) axis, we recently established a new genetic animal model of extremes in stress reactivity (SR). Studies characterizing this SR mouse model on the behavioral, endocrine, and neurobiological levels revealed several similarities with key endophenotypes observed in MD patients. HR mice were shown to have changes in rhythmicity and sleep measures such as rapid eye movement sleep (REMS) and non-REM sleep (NREMS) as well as in slow wave activity, indicative of reduced sleep efficacy and increased REMS. In the present study we were interested in how far a detailed spectral analysis of several electroencephalogram (EEG) parameters, including relevant frequency bands, could reveal further alterations of sleep architecture in this animal model. Eight adult males of each of the three breeding lines were equipped with epidural EEG and intramuscular electromyogram (EMG) electrodes. After recovery, EEG and EMG recordings were performed for two days.     

Measurement of Hurst exponents for semiconductor laser phase dynamics

The phase dynamics of a semiconductor laser with optical feedback is studied by construction of the Hilbert phase from its experimentally measured intensity time series. The Hurst exponent is evaluated for the phase fluctuations and grows from 0.5 to approximately 0.7 (indicating fractional Brownian motion) as the feedback strength is increased. A comparison with numerical computations based on a delay-differential equation model shows excellent agreement and reveals the relative roles of spontaneous emission noise and deterministic dynamics for different feedback strengths.