Inverse cascades and resonant triads in rotating and stratified turbulence

Kraichnan’s seminal ideas on inverse cascades yielded new tools to study common phenomena in geophysical turbulent flows. In the atmosphere and the oceans, rotation and stratification result in a flow that can be approximated as two-dimensional at very large scales but which requires considering three-dimensional effects to fully describe turbulent transport processes and non-linear phenomena. Motions can thus be classified into two classes: fast modes consisting of inertia-gravity waves and slow quasi-geostrophic modes for which the Coriolis force and horizontal pressure gradients are close to balance. In this paper, we review previous results on the strength of the inverse cascade in rotating and stratified flows and then present new results on the effect of varying the strength of rotation and stratification (measured by the inverse Prandtl ratio N/f, of the Coriolis frequency to the Brunt-Väisäla frequency) on the amplitude of the waves and on the flow quasi-geostrophic behavior. We show that the inverse cascade is more efficient in the range of N/f for which resonant triads do not exist, /2≤N/f≤21/2≤N/f≤2. We then use the spatio-temporal spectrum to show that in this range slow modes dominate the dynamics, while the strength of the waves (and their relevance in the flow dynamics) is weaker.Fil: Oks, D.. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; ArgentinaFil: Mininni, Pablo Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Marino, R.. Universite Lyon 2; FranciaFil: Pouquet, A.. State University of Colorado Boulder; Estados Unido

Generation of Electron Beam Plasma inside the Dielectric Tube

The results of experimental study of electron beam plasma inside the dielectric tube are presented. Beam plasma was generated by the fore-vacuum plasma electron source at (2-10) Pa in dc mode. It is shown, that the dependence of the plasma potential on gas pressure inside the tube is completely different in comparison with similar dependence without a tube. Monotonic dependence of the insulated beam col-lector potential in the tube on beam energy has two stages: slow and fast growth

Sarcoidosis presenting as Wallenberg syndrome and panuveitis

© 2018 The Authors Sarcoidosis is a multi-system disease with neurological involvement being one of the more rare manifestations. We report a case of a patient who presented with the lateral medullary syndrome and panuveitis as her initial manifestation of sarcoidosis. The patient\u27s course was further complicated by renal involvement. Lacrimal gland and renal biopsies showed noncaseating granulomas without evidence of infection, establishing the diagnosis. Intracranial vertebral artery involvement was confirmed by brain imaging. Bilateral hilar lymphadenopathy with upper lobe predominant nodules on chest imaging was consistent with asymptomatic pulmonary involvement. Systemic steroid therapy is indicated for treatment of ocular sarcoidosis, with standard stroke management indicated for the treatment of lateral medullary syndrome

The effect of parallel static and microwave electric fields on excited hydrogen atoms

Motivated by recent experiments we analyse the classical dynamics of a hydrogen atom in parallel static and microwave electric fields. Using an appropriate representation and averaging approximations we show that resonant ionisation is controlled by a separatrix, and provide necessary conditions for a dynamical resonance to affect the ionisation probability. The position of the dynamical resonance is computed using a high-order perturbation series, and estimate its radius of convergence. We show that the position of the dynamical resonance does not coincide precisely with the ionisation maxima, and that the field switch-on time can dramatically affect the ionisation signal which, for long switch times, reflects the shape of an incipient homoclinic. Similarly, the resonance ionisation time can reflect the time-scale of the separatrix motion, which is therefore longer than conventional static field Stark ionisation. We explain why these effects should be observed in the quantum dynamics. PACs: 32.80.Rm, 33.40.+f, 34.10.+x, 05.45.Ac, 05.45.MtComment: 47 pages, 20 figure

Broad, intense, quiescent beam of singly charged metal ions obtained by extraction from self-sputtering plasma far above the runaway threshold

Dense metal plasmas obtained by self-sputtering far above the runway threshold are well suited to generate intense quiescent ion beams. The dilemma of high current density and charge state purity can be solved when using target materials of low surface binding energy by utilizing non-resonant exchange reactions before ion extraction. Space-charge-limited quiescent beams of Cu+, Zn+, and Bi+ with ~;;10 mA/cm2 have been obtained through multi-aperture gridded ion extraction up to 45 kV from self-sputtering plasmas

New materials based on polylactide modified with silver and carbon ions

An integrated study of poly-L-lactide (PL) synthesis and the physicochemical properties of film surfaces, both modified by silver and carbon ion implantation and also unmodified PL surfaces, has been carried out. Surface modification was done using aMevva-5.Ru metal ion source with ion implantation doses of 1·1014, 1·1015 and 1·1016 ion/cm2. Material characterization was done using NMR, IRS, XPS and AFM. The molecular weight (MW), micro-hardness, surface resistivity, and limiting wetting angle of both un-implanted and implanted samples were measured. The results reveal that degradation of PL macromolecules occurs during ion implantation, followed by CO or CO2 removal and MW decrease. With increasing implantation dose, the glycerol wettability of the PL surface increases but the water affinity decreases (hydrophobic behavior). After silver and carbon ion implantation into the PL samples, the surface resistivity is reduced by several orders of magnitude and a tendency to micro-hardness reductionis induced

X-ray spectroscopy of super-intense laser-produced plasmas for the study of nonlinear processes. Comparison with PIC simulations

We present X-ray spectroscopic diagnostics in femto-second laser-driven experiments revealing nonlinear phenomena caused by the strong coupling of the laser radiation with the created plasma. Among those nonlinear phenomena, we found the signatures of the Two Plasmon Decay (TPD) instability in a laser-driven CO2 cluster-based plasma by analyzing the Langmuir dips in the profile of the O VIII Lyϵ line, caused by the Langmuir waves created at the high laser intensity 3 1018Wcm-2. With similar laser intensities, we reveal also the nonlinear phenomenon of the Second Harmonic Generation (SHG) of the laser frequency by analyzing the nonlinear phenomenon of satellites of Lyman δ and ϵ lines of Ar XVII. In the case of relativistic laser-plasma interaction we discovered the Parametric Decay Instability (PDI)-induced ion acoustic turbulence produced simultaneously with Langmuir waves via irradiation of thin Si foils by laser intensities of 1021Wcm-2

Observation of narrow Autler-Townes components in the resonant response of a dense atomic gas

We have experimentally studied the reflection of a weak probe beam from a dense atomic potassium vapor in the presence of a strong laser field tuned to the atomic resonance transition. We have observed an Autler-Townes doublet under hitherto unexplored conditions, namely that the Rabi frequency induced by the strong laser field is much smaller than the self-broadened width of the resonance transition of the unexcited vapor. We attribute our observation to a reduction of the atomic decoherence by the strong drive field. We present a theoretical model of nonlinear processes in a dense atomic gas to explain the observed results

In-depth study of intra-Stark spectroscopy in the x-ray range in relativistic laser-plasma interactions

Intra-Stark spectroscopy (ISS) is the spectroscopy within the quasistatic Stark profile of a spectral line. The present paper advances the ISS-based study of the relativistic laser-plasma interaction from our previous paper (Oks et al 2017 Opt. Express 25 1958). By improving the experimental conditions and the diagnostics, it provides an in-depth spectroscopic study of the simultaneous production of the Langmuir waves and of the ion acoustic turbulence at the surface of the relativistic critical density. It demonstrates a reliable reproducibility of the Langmuir-wave-induced dips at the same locations in the experimental profiles of Si XIV Ly-beta line, as well as of the deduced parameters (fields) of the Langmuir waves and ion acoustic turbulence in several individual 1 ps laser pulses and of the peak irradiances of 1-3 ×1020 W cm-2. Besides, this study employs for the first time the most rigorous condition of the dynamic resonance, on which the ISS phenomenon is based, compared to all previous studies in all kinds of plasmas in a wide range of electron densities. It shows how different interplays between the Langmuir wave field and the field of the ion acoustic turbulence lead to distinct spectral line profiles, including the disappearance of the Langmuir-wave-induced dips