Search results for "PLASMA"

Even harmonics generation of high frequency radiation in current-carrying plasmas

2005

Generation of high frequency radiation harmonics in a current-carrying plasma is studied. The physical mechanism responsible for harmonics generation is provided by electron-ion collisions. The current in the plasma is sustained by a constant electric field. It is shown that the electron distribution function anisotropy due to the static field yields generation of even harmonics. As a result, the radiation spectrum emitted by the current-carrying plasma contains both even and odd harmonics, the latter being attributed to currentless plasma. For a broad range of plasma and high frequency radiation parameters, a detailed analysis of the even harmonics properties is reported.

2000

We report on lifetime measurements of the 3d(5)(S-6)4s4p(P-3)y P-6 degrees states of Fe II using time-resolved vacuum ultraviolet (VUV) laser spectroscopy. A laser-produced plasma has been used as the source of free Fe+ ions. The tunable VUV radiation was obtained employing resonantly enhanced sum-difference four-wave-mixing of short laser pulses. We obtained tau((6)P(3/2)degrees) = 3.90(20) ns, tau((6)P(5/2)degrees) = 3.80(20) ns and tau((6)P(7/2)degrees) = 3.65(20) ns.

Hidden Oscillations in Electromechanical Systems

2016

In this paper an electromechanical system with two different types of motor is considered. It is shown that during the spin-up, the system with DC motor may experience unwanted vibration—the Sommerfeld effect. This is a well-known effect when the motor of electromechanical system gets stuck near the resonance zone instead of reaching its nominal power. The absence of this effect is demonstrated in the system with synchronous motor. Nowadays, there are many works devoted to the study of this effect in various systems. Here we discuss the Sommerfeld effect from the point of view of localization of the so-called hidden oscillations.

Temporal evolution of neoclassical tearing modes in the frequently interrupted regime

2010

A phenomenological method for description of temporal evolution of neoclassical tearing modes in the frequently interrupted regime (FIR) is proposed. The method makes it possible to predict the beginning and the end of the FIR regime as well as the frequency of the FIR drops. A few experimental parameters which are used in the model are commonly measured quantities. Several specific ASDEX Upgrade (http://en.wikipedia.org/wiki/ASDEX_Upgrade) FIR discharges with different heating and different FIR behavior are analyzed in detail.

Measurement of the higher-order anisotropic flow coefficients for identified hadrons in Au + Au collisions atsNN=200GeV

2016

Measurements of the anisotropic flow coefficients v2{Ψ2},v3{Ψ3},v4{Ψ4}, and v4{Ψ2} for identified particles (π±,K±, and p+p) at midrapidity, obtained relative to the event planes Ψm at forward rapidities in Au + Au collisions at sNN=200GeV, are presented as a function of collision centrality and particle transverse momenta pT. The vn coefficients show characteristic patterns consistent with hydrodynamical expansion of the matter produced in the collisions. For each harmonic n, a modified valence quark-number Nq scaling [plotting vn{Ψm}/(Nq)n/2 versus transverse kinetic energies (KET)/Nq] is observed to yield a single curve for all the measured particle species for a broad range of KET. A si…

Mixed-mode oscillation-incrementing bifurcations and a devil’s staircase from a nonautonomous, constrained Bonhoeffer-van der Pol oscillator

2018

Engineering the Success of Quantum Walk Search Using Weighted Graphs

2016

Continuous-time quantum walks are natural tools for spatial search, where one searches for a marked vertex in a graph. Sometimes, the structure of the graph causes the walker to get trapped, such that the probability of finding the marked vertex is limited. We give an example with two linked cliques, proving that the captive probability can be liberated by increasing the weights of the links. This allows the search to succeed with probability 1 without increasing the energy scaling of the algorithm. Further increasing the weights, however, slows the runtime, so the optimal search requires weights that are neither too weak nor too strong.

Faster Quantum Walk Search on a Weighted Graph

2015

A randomly walking quantum particle evolving by Schr\"odinger's equation searches for a unique marked vertex on the "simplex of complete graphs" in time $\Theta(N^{3/4})$. In this paper, we give a weighted version of this graph that preserves vertex-transitivity, and we show that the time to search on it can be reduced to nearly $\Theta(\sqrt{N})$. To prove this, we introduce two novel extensions to degenerate perturbation theory: an adjustment that distinguishes the weights of the edges, and a method to determine how precisely the jumping rate of the quantum walk must be chosen.

Dynamical Processes in Open Quantum Systems from a TDDFT Perspective: Resonances and Electron Photoemission

2015

We present a review of different computational methods to describe time-dependent phenomena in open quantum systems and their extension to a density-functional framework. We focus the discussion on electron emission processes in atoms and molecules addressing excited-state lifetimes and dissipative processes. Initially we analyze the concept of an electronic resonance, a central concept in spectroscopy associated with a metastable state from which an electron eventually escapes (electronic lifetime). Resonances play a fundamental role in many time-dependent molecular phenomena but can be rationalized from a time-independent context in terms of scattering states. We introduce the method of c…

Long-time dynamics of modulated waves in a nonlinear discrete LC transmission line.

2003

International audience; The long-time dynamics of modulated waves in a nonlinear LC transmission line is investigated. Considering the higher-order nonlinear Schrodinger equation, we define analytically the conditions leading to the instability of modulated waves. We show that two kinds of instabilities may develop in the network depending on the frequency range of the chosen carrier wave and on the magnitude of its initial amplitude, which is confirmed by our numerical simulations. The nonreproducibility of numerical experiments on modulated waves is also considered.