Higher harmonics in the output spectrum of a generator with turbulent electron beam

Formation of electron bunches in turbulent electron beams is numerically simulated and experimentally studied. A prototype of a laboratory generator is proposed, and control parameters (in particular, electron spread with respect to longitudinal velocities and additional deceleration of electron beam by electrostatic field of collector) that affect the characteristics of electron bunches and provide an increase in the number and amplitude of higher harmonics in the output spectrum are determined.     

Stretching in a model of a turbulent flow

Using a multi-scaled, chaotic flow known as the KS model of turbulence [J.C.H. Fung, J.C.R. Hunt, A. Malik, R.J. Perkins, Kinematic simulation of homogeneous turbulence by unsteady random fourier modes, J. Fluid Mech. 236 (1992) 281-318], we investigate the dependence of Lyapunov exponents on various characteristics of the flow. We show that the KS model yields a power law relation between the Reynolds number and the maximum Lyapunov exponent, which is similar to that for a turbulent flow with the same energy spectrum. Our results show that the Lyapunov exponents are sensitive to the advection of small eddies by large eddies, which can be explained by considering the Lagrangian correlation time of the smallest scales. We also relate the number of stagnation points within a flow to the maximum Lyapunov exponent, and suggest a linear dependence between the two characteristics.     

Particular features of higher harmonics generation in nanocluster-containing plasmas using single- and two-color pumps

The wavelength conversion of femtosecond laser pulses in laser plasmas containing clusters of different nature and dimension (fullerenes, metal nanoparticles) is studied. Pulses of a titanium-sapphire laser are used in combination with orthogonally polarized second-harmonic pulses as radiation to be converted. Variations in the generation efficiency of higher harmonics are analyzed under conditions of phase-modulated pulses. It is shown that the optimization of components of a nonlinear optical plasma medium, of plasma excitation conditions by single- and two-color pumps, and of phase and spectral parameters of radiation to be converted leads to a considerable increase in the generation efficiency of higher harmonics.     

On the possibility of coherent Doppler determination of the aerosol-size spectrum in a turbulent flow

The development of laser Doppler measurement of velocity (LDMV) raises the question of the possibility of working out new remote, contactless methods of determining the spectrum of aerosol particle sizes in a turbulent medium. The fact that particles of different sizes show differing lags in response to velocity pulsations of the medium [1] can be made the foundation of such methods.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 21, No. 11, pp. 1703–1706, November, 1978.     

The Shuttle Potential and return electron experiment (SPREE)

Summary The Shuttle Potential and Return Electron Experiment (SPREE) was designed and fabricated for flight as part of the joint NASA/Agenzia Spaziale Italiana Tethered Satellite System (TSS-1) mission. The SPREE is a complex instrument package designed to measure ion and electron particle flux and wave-particle interactions. The SPREE flight hardware consists of two multiangular electrostatic analyzer units, two rotary tables, a data processing unit, a particle correlator experiment, and two data recording units. The electrostatic analyzers measure both electrons and ions, in an energy range from 10 eV to 10 keV and simultaneously over an angular fan of (100×10) degrees. These units are mounted on the rotary tables to provide a 2π steradian field of view out of the Orbiter's payload bay. To assess negative charging of the Orbiter with respect to the ambient plasma, ion data from the analyzers are processed real time by an on-board algorithm operating within the data processing unit. The particle correlator experiment determines wave-particle interactions in the frequency range 0–10 MHz for electrons and from 0–10 kHz for ions. SPREE operated successfully throughout the TSS-1 mission. Examples of the data returned by the SPREE are shown.     

The output of a quartz transducer oscillating in its fundamental and higher harmonics

The output from a quartz crystal oscillating in three liquids, at its fundamental, 3rd harmonic and 5th harmonic have been measured by the calorimetric method keeping the crystal amplitude the same. The output is found to be much less than that one can expect from theoretical considerations.     

Behavioral model of macromolecules in a turbulent flow and its analytical consequences

A mathematical dependence relating physicochemical properties of diluted solutions of high-molecular polymers to the increment of the bulk velocity of the turbulent solution flow in comparison with pure solvent is derived. Based on the obtained dependence, boundary conditions of the Toms effect manifestation are deduced.     

On the validity criteria of the phenomenological theory of electron absorption and amplification of sound in semiconductors

By using the kinetic equation for the electron distribution function in the acoustic wave field, the criteria are established for the validity of the phenomenological (“hydrodynamic”) theory of electron absorption and amplification of sound (acoustic waves) in the semiconductors. It is shown that the upper frequency limit of the validity of this theory lies, generally speaking, in the region of considerably lower (maybe by orders of magnitude) frequencies than it follows from the usually accepted criterion ql ? 1.     

FANSY 1.0: a phenomenological model for simulation of coplanar particle generation in superhigh-energy hadron interactions

Simulations show that a phenomenon of coplanarity of most energetic subcores of γ-ray–hadron families found in mountain-based and stratospheric X-ray–emulsion chamber experiments requires to introduce a coplanar particle generation with large transverse momenta in hadron interactions at superhigh energies. Some physical mechanisms are considered. A phenomenological model, which makes it possible to simulate the coplanar particle generation, is presented. Different versions of this model are considered, their features are described and compared with those of models applied by the CORSIKA package. Cosmic-ray experimental data and simulated results are compared. Conclusion on features of hadron interactions at superhigh energies and some predictions with respect to LHC experiments are made.     

The possibility of cyclotron echo generation in graphene on a SiC substrate

The possibility of cyclotron echo generation in graphene on a silicon carbide substrate has been predicted on the basis of the direct quasi-classical Monte Carlo simulation. The nature of this effect is the quasi-relativistic dependence of the effective mass of charge carriers on their velocity. The numerical values of the field strengths at which the effect should be most pronounced are found.     

The generation of superradiance pulses by high-current subnanosecond electron bunches moving in a periodic slow-wave system: Theory and experiment

Cherenkov superradiance observed when an electron bunch rectilinearly moves through a slow-wave periodic system is studied theoretically and experimentally. The simulation based on averaged equations and the direct numerical simulation using the PIC-code KARAT show that the peak power of the microwave pulses varies as the total number of the particles in a bunch squared. This finding is confirmed experimentally. Ultrashort (300 ps wide) high-power (up to 140 MW) pulses are generated at a frequency of 39 GHz. As an electron source, the high-current subnanosecond RADAN-303 accelerator is used. It injects 0.5-to 1.5-ns-wide electron bunches of current up to 2 kA and energy 200–300 keV. The simulation suggests that the power of the electromagnetic pulses can be increased further (up to 300 or 400 MW) by optimizing the accelerating voltage pulse shape.     

Fluxon dynamics and higher harmonics of a.c. susceptibility in HTSC

Il Nuovo Cimento D - Measurements of fundamental and higher harmonics of a.c. susceptibility on polycrystalline high-T c superconductors were carried out using a new method, involving a 2-channel...     

Mass properties of active and sterile neutrinos in a phenomenological (3 + 1 + 2) model

A generalized model involving three active neutrinos and three sterile neutrinos of different mass, one being relatively heavy [(3 + 1 + 2) model], is considered on the basis of experimental data, which admit the existence of anomalies beyond the minimally extended standard model featuring three active neutrinos of different mass. Basic properties used to describe massive active and sterile neutrinos are studied along with methods for determining the absolute scale of neutrino masses and for estimating neutrino masses on the basis of available experimental data. In the approximation of CP conservation, admissible values of the elements of the neutrino mass matrix are found from numerical calculations versus the possible values of the mass of one of the sterile neutrinos. The dependences of the mass properties of the neutrinos on the sterile-neutrino mass are constructed with allowance for possible sterile-neutrino contributions. The respective results can be used to interpret and predict results of various neutrino experiments.     

Cyclotron-resonance harmonics in the ac response of a 2D electron gas with smooth disorder

The frequency-dependent conductivity sigma(xx)(omega) of 2D electrons subjected to a transverse magnetic field and smooth disorder is calculated. The interplay of Landau quantization and disorder scattering gives rise to an oscillatory structure that survives in the high-temperature limit. The relation to recent experiments on photoconductivity by Zudov et al. and Mani et al. is discussed.     

Theoretical calculation and experiment of microwave electromagnetic property of Ni(C) nanocapsules

With the combination of the dielectric loss of the carbon layer with the magnetic loss of the ferromagnetic metal core,carbon-coated nickel Ni(C) nanoparticles are expected to be the promising microwave absorbers. Microwave electromagnetic parameters and reflection loss in a frequency range of 2 GHz–18 GHz for paraffin-Ni(C) composites are investigated.The values of relative complex permittivity and permeability, the dielectric and magnetic loss tangent of paraffin-Ni(C) composites are measured, respectively, when the weight ratios of Ni(C) nanoparticles are equal to 10 wt%, 40 wt%, 50 wt%,70 wt%, and 80 wt% in paraffin-Ni(C) composites. The results reveal that Ni(C) nanoparticles exhibit a peak of magnetic loss at about 13 GHz, suggesting that magnetic loss and a natural resonance could be found at that frequency. Based on the measured complex permittivity and permeability, the reflection losses of paraffin-Ni(C) composites with different weight ratios of Ni(C) nanoparticles and coating thickness values are simulated according to the transmission line theory. An excellent microwave absorption is obtained. To be proved by the experimental results, the reflection loss of composite with a coating thickness of 2 mm is measured by the Arch method. The results indicate that the maximum reflection loss reaches-26.73 d B at 12.7 GHz, and below-10 d B, the bandwidth is about 4 GHz. The fact that the measured absorption position is consistent with the calculated results suggests that a good electromagnetic match and a strong microwave absorption can be established in Ni(C) nanoparticles. The excellent Ni(C) microwave absorber is prepared by choosing an optimum layer number and the weight ratio of Ni(C) nanoparticles in paraffin-Ni(C) composites.     

Raman amplification and optical short pulse generation in a waveguide with periodic gain

In this paper a new configuration of amplification is proposed for Raman amplification. In this new configuration a spatial periodic Raman gain is used to amplify a CW Raman seed that generates a short optical pulse taking into account the SPM, XPM, walk-off and pulse depletion. The amplification process is accomplished by using an intense pump pulse where its energy is transferred through SRS effect. A CW weak seed is used to represent the signal to be amplified and for pump is used a Gaussian pulse. We discuss the advantages to this configuration. First, this scheme means that the Raman-gain coefficient assumes a periodic characteristic and like a modulation process, it gives possibility to control the energy transfer from the pump to Raman seed. Second, the efficient use of the parameters of the periodic Raman coefficient function, like amplitude and frequency of the modulation, can result in a more efficient control of the signal amplification. This new configuration provides some very interesting features in the Raman amplification process when compared to the standard procedure. A complete discussion of this configuration is presented.