Spectral bifurcations in dispersive wave turbulence

Dispersive wave turbulence is studied numerically for a class of one-dimensional nonlinear wave equations. Both deterministic and random (white noise in time) forcings are studied. Four distinct stable spectra are observed—the direct and inverse cascades of weak turbulence (WT) theory, thermal equilibrium, and a fourth spectrum (MMT; Majda, McLaughlin, Tabak). Each spectrum can describe long-time behavior, and each can be only metastable (with quite diverse lifetimes)—depending on details of nonlinearity, forcing, and dissipation. Cases of a long-live MMT transient state dcaying to a state with WT spectra, and vice-versa, are displayed. In the case of freely decaying turbulence, without forcing, both cascades of weak turbulence are observed. These WT states constitute the clearest and most striking numerical observations of WT spectra to date—over four decades of energy, and three decades of spatial, scales. Numerical experiments that study details of the composition, coexistence, and transition between spectra are then discussed, including: (i) for deterministic forcing, sharp distinctions between focusing and defocusing nonlinearities, including the role of long wavelength instabilities, localized coherent structures, and chaotic behavior; (ii) the role of energy growth in time to monitor the selection of MMT or WT spectra; (iii) a second manifestation of the MMT spectrum as it describes a self-similar evolution of the wave, without temporal averaging; (iv) coherent structures and the evolution of the direct and inverse cascades; and (v) nonlocality (in k-space) in the transferral process.

Excitations in Bose-Einstein condensates: collective modes, quantum turbulence and matter wave statistics

In this thesis, we present the generation and studies of a 87Rb Bose-Einstein condensate (BEC) perturbed by an oscillatory excitation. The atoms are trapped in a harmonic magnetic trap where, after an evaporative cooling process, we produce the BEC. In order to study the effect caused by oscillatory excitations, a quadrupole magnetic field time oscillatory is superimposed to the trapping potential. Through this perturbation, collective modes were observed. The dipole mode is excited even for low excitation amplitudes. However, a minimum excitation energy is needed to excite the condensate quadrupole mode. Observing the excited cloud in TOF expansion, we note that for excitation amplitude in which the quadrupole mode is excited, the cloud expands without invert its aspect ratio. By looking these clouds, after long time-of-flight, it was possible to see vortices and, sometimes, a turbulent state in the condensed cloud. We calculated the momentum distribution of the perturbed BECs and a power law behavior, like the law to Kolmogorov turbulence, was observed. Furthermore, we show that using the method that we have developed to calculate the momentum distribution, the distribution curve (including the power law exponent) exhibits a dependence on the quadrupole mode oscillation of the cloud. The randomness distribution of peaks and depletions in density distribution image of an expanded turbulent BEC, remind us to the intensity profile of a speckle light beam. The analogy between matter-wave speckle and light speckle is justified by showing the similarities in the spatial propagation (or time expansion) of the waves. In addition, the second order correlation function is evaluated and the same dependence with distance was observed for the both waves. This creates the possibility to understand the properties of quantum matter in a disordered state. The propagation of a three-dimensional speckle field (as the matter-wave speckle described here) creates an opportunity to investigate the speckle phenomenon existing in dimensions higher than 2D (the case of light speckle).

Turbulence ahead: disputes within the Russian ruling elite are gathering force. OSW Commentary No. 91, 2012-09-27

The last month has seen a public confrontation between Igor Sechin, the president of Rosneft, and Arkady Dvorkovich, the deputy prime minister, concerning the consolidation of the energy sector. This is the latest in a series of disputes between the Kremlin & businessmen from Putin’s inner circle on one side, and the government & Prime Minister Medvedev on the other. These disputes have been wide-ranging in nature, concerning economic policy, the scope of competency of individual members of the elite, but also the ‘tough line’ adopted by the Kremlin since Vladimir Putin’s return to the presidency. The Kremlin, which is still the main decision-making centre in Russia, has been effectively forcing its opinions through in its short-term disputes with the government. However, a new element in the ongoing conflicts, which is unfavourable to President Putin, is their exceptional strength, their much more public nature, and their wide range (which has included criticism of the president himself) and ever-changing context, especially the worsening socio-economic situation. These conflicts have been overlapping with signs of dissent among Putin’s business supporters, and their declining political willingness to support the leader unconditionally. The Kremlin’s response to the unrest consists of intensifying efforts to discipline the elite and weakening those groups in which Vladimir Putin has limited confidence. The elite’s support is crucial to the stability of his government; to maintain this support, the Kremlin is ready to introduce restrictive and repressive actions against both parliamentarians and government officials. In the short term, such a policy will force the Kremlin’s supporters back into obedience, but fears of a further increase in repression are also starting to be expressed on the sidelines.

Commentary on interstellar matter associated with 18 open clusters /

"September 1989"--Cover.

SUPERDUCK marine meteorological experiment data summary : mean values and turbulence parameters /

"August 1988."

Sediment suspension and turbulence in an oscillating flume /

"April 1977."

Technical report on the spectrum of turbulence in an exothermal gas flow,

"TR63-217F."

Technical report on intensification of turbulence by chemical heat release. Contract no. DA-04-495-ORD-3567(Z) Hypervelocity Range Research Program, a part of project "Defender."

"This research was supported by the Advanced Research Projects Agency, Department of defense, and was monitored by the U.S. Army Missile Command, Redstone Arsenal, Alabama."

Plasma turbulence.

"Prepared for the United States Atomic Energy Commission, under AEC Contract AT (04-3)-321, Plasma Turbulence Research."

Thermal agitation and turbulence.

"Prepared for the United States Atomic Energy Commission under AEC Contract AT(04-3)-321, Plasma Turbulence Research."

Formulation of the theory of turbulence in an incompressible fluid.

"This report was prepared in connection with Space Technology Laboratories Program of General Research."

Application of Doppler weather radar to turbulence measurements which affect aircraft /

Bibliography: p. 28-29.

Simulation of the effects of winds and turbulence upon longitudinal motions of an aircraft flying at low altitude and high speed.

Mode of access: Internet.