Measurement of the electric fluctuation spectrum of magnetohydrodynamic turbulence

Magnetohydrodynamic (MHD) turbulence in the solar wind is observed to show the spectral behavior of classical Kolmogorov fluid turbulence over an inertial subrange and departures from this at short wavelengths, where energy should be dissipated. Here we present the first measurements of the electric field fluctuation spectrum over the inertial and dissipative wave number ranges in a Beta > or approximately = 1 plasma. The k(-5/3) inertial subrange is observed and agrees strikingly with the magnetic fluctuation spectrum; the wave phase speed in this regime is shown to be consistent with the Alfvén speed. At smaller wavelengths krho(i) > or = 1 the electric spectrum is enhanced and is consistent with the expected dispersion relation of short-wavelength kinetic Alfvén waves. Kinetic Alfvén waves damp on the solar wind ions and electrons and may act to isotropize them. This effect may explain the fluidlike nature of the solar wind.     

Theoretical analysis of electron acoustic shock waves in magnetized superthermal plasma with electron beam

We have analysed the small-amplitude non-linear electron acoustic shock waves by taking into account the effects of electron beam in magnetized plasma. Satellite observations in different regions of the Earth's magnetosphere have shown that the electrostatic solitary waves are generally associated with electron or/and ion beams. The nonlinear Korteweg-de-Vries Burgers (KdVB) equation has been derived by considering the basic fluid equations and dissipation effects. The nonlinear coefficient of KdVB equation comes out to be negative. Only dip-shaped potential structures are reported here. For the parameters discussed in this paper, we did not find positive polarity shocks. This could be due to the restrictions on the plasma parameters since we are using the fixed densities of the cold, hot, and beam electrons as observed by the Viking satellite in the auroral region. In this paper, the importance of the cold electron to hot electron temperature in conjunction with the beam speed is pointed out. Increase in beam density, kinematic viscosity, and magnetic field results in increase in the amplitude while the increase in hot electron concentration and superthermality leads to decrease in potential. The numerical analysis is presented for the parameters corresponding to the observation of burst b event by Viking satellite in the dayside auroral zone of the earth's magnetosphere.     

Electron acceleration and type II radio emission at quasi-parallel shock waves

Solar type II radio bursts are interpreted as the radio signature of shock waves travelling through the solar corona. Some of these shock waves are able to enter into the interplanetary medium and are observed as interplanetary type II bursts. The nonthermal radio emission of these bursts indicates that electrons are accelerated up to superthermal and/or relativistic velocities at the corresponding shocks. Plasma wave measurements at interplanetary shock waves support the assumption that the fundamental type II radio emission is generated by wave-wave interactions of electron plasma waves and ion acoustic waves and that the source region is located near the transition region of the shock. Therefore, the instantaneous bandwidth of type II bursts should reflect the density jump across the shock. Comparing the theoretically predicted density jump of coronal shock waves (Rankine-Hugoniot relations) and the measured instantaneous bandwidth of solar type II radio bursts it is appropriate to assume that these bursts are generated by weak supercritical quasi-parallel shock waves. Two different mechanisms for the accelaration of electrons at this kind of shock waves are investigated in the form of test particle calculations in given magnetic and electric fields. These fields have been extracted from in-situ measurements at the quasi-parallel region at Earth’s bow shock, which showed large amplitude magnetic field fluctuations (so-called SLAMS: Short Large Amplitude Magnetic Field Structures) as constituent parts. The first mechanism treats these structures as strong magnetic mirrors, at which charged particles are reflected and accelerated. Thus, thermal electrons gain energy due to multiple reflections between two approaching SLAMS. The second mechanism shows that it is possible to accelerate electrons inside a single SLAMS due to a noncoplanar component of the magnetic field in these structures. Both mechanism are described in the form of test particle calculations, which are supplemented by calculations according to adiabatic theory. The results are discussed for circumstances in the solar corona and in interplanetary space. Astrophysikalisches Institut, Observatorium für solare Radioastronomie, Potsdam, Germany. Published from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 1, pp. 84–104, January, 1998.     

Electron acceleration and type II radio emission at quasi-parallel shock waves

Solar type II radio bursts are interpreted as the radio signature of shock waves travelling through the solar corona. Some of these shock waves are able to enter into the interplanetary medium and are observed as interplanetary type II bursts. The nonthermal radio emission of these bursts indicates that electrons are accelerated up to superthermal and/or relativistic velocities at the corresponding shocks. Plasma wave measurements at interplanetary shock waves support the assumption that the fundamental type II radio emission is generated by wave-wave interactions of electron plasma waves and ion acoustic waves and that the source region is located near the transition region of the shock. Therefore, the instantaneous bandwidth of type II bursts should reflect the density jump across the shock. Comparing the theoretically predicted density jump of coronal shock waves (Rankine-Hugoniot relations) and the measured instantaneous bandwidth of solar type II radio bursts it is appropriate to assume that these bursts are generated by weak supercritical quasi-parallel shock waves. Two different mechanisms for the accelaration of electrons at this kind of shock waves are investigated in the form of test particle calculations in given magnetic and electric fields. These fields have been extracted from in-situ measurements at the quasi-parallel region at Earth’s bow shock, which showed large amplitude magnetic field fluctuations (so-called SLAMS: Short Large Amplitude Magnetic Field Structures) as constituent parts. The first mechanism treats these structures as strong magnetic mirrors, at which charged particles are reflected and accelerated. Thus, thermal electrons gain energy due to multiple reflections between two approaching SLAMS. The second mechanism shows that it is possible to accelerate electrons inside a single SLAMS due to a noncoplanar component of the magnetic field in these structures. Both mechanism are described in the form of test particle calculations, which are supplemented by calculations according to adiabatic theory. The results are discussed for circumstances in the solar corona and in interplanetary space.     

Enhancement of fringe visibility in a fibre interferometer

A simple method for increasing fringe visibility of an interference pattern in a Mach-Zehnder type fibre interferometer is presented. In order to obtain high visibility, two elliptically polarized waves emitted from fibres with birefringence are transformed into two linearly polarized waves of equal amplitude and with parallel planes of polarization by using ordinary optical components. Instability of fringe patterns due to temperature fluctuation of the air surrounding the fibres is also discussed.     

Observations of distortions of optical features in the UV auroraldistribution

Observations made by the Viking satellite have for the first time shown the development of multiple large-scale surge features. The longer time scale of the features is contrasted with smaller-scale vortex streets found along the poleward edge of the evening oval, which are generally observed to exist for less than 2 min. The ratio of wavelength-to-diameter of these features is shown to decrease with increasing wavelength. These observations support the view that the origin of the larger surge features are of the Kelvin-Helmholtz instability type, originating further out in the magnetosphere than their vortex-street counterparts. Observations of spiral features have been made at all local times and the spirals always have a counterclockwise sense (viewed in the direction of the magnetic field in the northern hemisphere). One interpretation of these events is that they are the result of an exponential growth along a field line of an initial upward field-aligned current perturbation     

南海北部海域内波环境下声传播损失起伏统计特性

浅海内波会引起声传播能量随时间的起伏变化,进而影响水声设备的工作性能.本文利用2015年南海北部一次浅海声场起伏实验数据,对比分析了浅海线性内波和孤立子内波条件下的声传播损失统计特性.在孤立子内波条件下,声传播损失起伏明显加剧,可达11 dB,且分布明显展宽,相对于线性内波的环境,声传播损失起伏可增加5 dB.从简正波...     

Information (no-energy) waves described by global potentials

The case where the magnetic flux inside an electronic loop varies with time is considered for an experiment in which the Aharonov-Bohm effect is observed. The electromagnetic field and potentials of a solenoid with an alternating current are studied. It is shown that the vector potential outside the solenoid contains a term corresponding to a zero electromagnetic field at the same point of space. This part of the potential (global potential) describes standing waves whose properties differ from those of ordinary electromagnetic waves and which can be conventionally called information potential waves. A method of detecting information waves is proposed involving an effect similar to the Aharonov-Bohm effect (quasi-Aharonov-Bohm effect). Unlike ordinary electromagnetic waves, these information waves are not involved in any energy interactions but they can carry information.     

Nonlinear oblique propagation of magnetohydrodynamic waves in the solar wind

Summary Oblique propagating magnetohydrodynamic waves with various wave forms and amplitudes are observed both at the Earth's foreshock and at comets. The possibility of interpreting some observational results in terms of nonlinear evolution of one- and two-dimensional hydromagnetic waves is investigated. For this purpose both analytical and numerical techniques are employed. It is found that an initial monochromatic wave changes its polarization giving origin to magnetosonic shocks and rotational discontinuities; the time evolution of density-magnetic-field correlation is studied, as a function of the plasma parameters and of the propagation angle. In the two-dimensional case both a transverse instability and a self-focusing effect may take place. Moreover, a two-dimensional magnetosonic solution is found, in which the density fluctuations are driven by the total pressure fluctuation as in a one-dimensional simple wave. These theoretical predictions compare well with the features observed in the solar-wind waves. Paper presented at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990.     

On the problem of polarization characteristics of radio waves in a randomly inhomogeneous magnetoactive plasma

Expressions for the Stokes parameters when radio waves propagate in a turbulent magnetoactive plasma have been obtained using a refractive scattering method. The problem of the spatial coherence of polarized radiation is considered. Expressions for the correlation functions and fluctuation dispersions of the Stokes parameters are found in the case of saturated wave field fluctuation. It is shown that the fluctuation of the circular polarized component will be observed in the received radiation even if the circular polarization is absent in the radiation that is incident on the magnetoactive plasma slab. A method is proposed to define the preference orientation of the magnetic field in the inhomogeneous layer of space plasma, which is biased on the simultaneous measurement of the space correlation functions of the I, V Stokes parameter fluctuation and Faraday rotation of the radiation polarization plane from the source with known polarization characteristics.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 39, No. 8, pp. 1007–1013, August, 1996.This work was supported in part by the Russian Foundation for Fundamental Research under Project No. 96-02-18632.     

Ultrasonic beam focusing characteristics of shear-vertical waves for contact-type linear phased array in solid

We investigate the beam focusing technology of shear-vertical(SV) waves for a contact-type linear phased array to overcome the shortcomings of conventional wedge transducer arrays. The numerical simulation reveals the transient excitation and propagation characteristics of SV waves. It is found that the element size plays an important role in determining the transient radiation directivity of SV waves. The transient beam focusing characteristics of SV waves for various array parameters are deeply studied. It is particularly interesting to see that smaller element width will provide the focused beam of SV waves with higher quality, while larger element width may result in erratic fluctuation of focusing energy around the focal point. There exists a specific range of inter-element spacing for optimum focusing performance. Moreover, good beam focusing performance of SV waves can be achieved only at high steering angles.     

Random generation of coherent solitary waves from incoherent waves

The random generation of coherent solitary waves from incoherent waves in a medium with an instantaneous nonlinearity has been observed. One excites a propagating incoherent spin wave packet in a magnetic film strip and observes the random appearance of solitary wave pulses. These pulses are as coherent as traditional solitary waves, but with random timing and a random peak amplitude.     

On polarized neutron scattering from magnetized samples and the spin echo effect

The scattering of polarized neutrons from magnetized samples is considered in the general case of arbitrary orientation between the incident polarization, the magnetic field of the sample and the polarization of the scattered neutrons. Including both nuclear and magnetic scattering the general expressions for the cross section and the polarization of the scattered beam are derived in the case of small-angle scattering. It is shown that under certain experimental conditions an effect analogous to the Neutron Spin Echo should be observed, which could be used to measure small energy transfers. The contribution arising from the scattering by spin waves is examined in detail.     

Single-Frequency Laser Using a 100-μm Thick Nd:YVO4 Crystal in a 50-mm Long Cavity

A new type of single-frequency solid state laser for achieving a highly stable second-harmonic generation in a simple configuration was developed using a quite thin laser medium. A 100-μm thick Nd:YVO4 crystal with one side coated for high reflection in a 50-mm long cavity which serves as automatic gain discriminator was end-pumped by a laser diode. Single-frequency output powers of 100 mW and 17 mW were obtained for fundamental and second-harmonic waves respectively by 1-W excitation. No chaotic fluctuation was observed with the frequency-doubled output.     

Zur Frequenz- und Temperaturabhängigkeit der Koerzitivkraft dünner polykristalliner Nickelschichten bei Wechselfeldmagnetisierung

The magnetoresistance is used for measuring the coercivityH _c of nickel thin films, which have been condensed onto glass substrates at temperatures of 200°C and 400°C. TheH _c -data obtained at various measuring temperatures using an alternating magnetic field in the frequency range from 40 cps to 10 kc permit an extra-polation to the results obtained with a Wheatstone bridge and galvanometer (i.e. with a nearly “static” method). With decreasing film thickness or reduction of the average grain size of the samples an increased influence of time effects is directly observed. This may essentially be attributed to thermal fluctuation effects. Thus the decrease of coercivity in the thickness range below about 100 Å, as it has been found at the type of films used in this investigation, may mainly be explained.     

On some electromagnetic phenomena in the tether magnetoplasma cloud

Summary The tethered satellite system (TSS) will be accompanied by a variety of electromagnetic phenomena. An independent interconnected formation, a ?tethered magnetoplasma cloud? (TMC), moving in space along the orbit of TSS, at an altitude of about 300 km, will be created. This time-dependent cloud will be a very complicated inhomogeneous formation including electromagnetic oscillations and waves of different type. Some of these waves will be observed on the Earth's surface. Rarefiel regions of the magnetoplasma behind, and dense regions in front of the shuttle orbiter (SO) and the subsatellite (SS) will arise. The neutral nitrogen beam ejected by the thruster becomes an ion beam on the day-light part of the orbit. Its energy is much greater than the local thermal energy. Instabilities of different kind as well as diffusion and recombination effects are expected to accompany the interaction of these beams with the surrounding plasma. The electron beams will produce other types of instabilities. By the electrons precessing along the magnetic-field lines, a current (5·10³V, 0.5 A) should be induced in the 20th km length conducting tether. It will be closed at the bottom of the ionosphere. This huge magnetic loop, so-called ?phantom loop? (PL), should accompany the tether system along its orbit. The length of this ?tether electromagnetic tail? (TEMT) is about 200 km, its magnetic moment will be about 10¹³ A·cm². Alfvén waves and nonlinear effects of heating type may be produced by this loop along the magnetic-field lines. ?Strings? of hot plasma may accompany the tether system.     

Noise in a coupling electromagnetic detecting system for high frequency gravitational waves

This paper discusses the basic categories of noise in detecting high frequency gravitational waves in the microwave band (～0.1--10 GHz), which contain shot noise from the laser and the thermal radiation photons, thermal noise from statistical fluctuation of the thermal photons and fluctuation of the temperature, radiation press noise on the fractal membrane, the noise caused by the scattering of the Gaussian Beam (GB) in the detecting tube and noise in the microwave radiometers. The analysis shows that a reasonable signal-to-noise ratio may be achieved for a detecting device with the fixed power of GB (10⁵ W), only when the temperature of the environment is no more than T=1 K, and the optimal length of the microwave radiometers is about 0.3 m.     

Giant magnetic moments in metals as thermodynamic fluctuations

The nucleation of giant magnetic moments in certain dilute alloys is interpreted in terms of a Landau-Ginsburg type fluctuation theory. Beyond a certain threshold value of the coupling energy of the bare impurity spin to the spin density of the host a characteristic fluctuation localized around the impurity spontaneously acquires a non-zero, autonomous value. As observed, the magnitude of the giant moment decreases with increasing impurity concentration, at least at low concentrations.     

Wavelength dependence of intensity fluctuations in laser speckle patterns from biological specimens

Speckle patterns obtained when botanical specimens are illuminated with laser light are observed to fluctuate at a rate which depends on the wavelength of the light used. It is suggested that this wavelength dependence may be of value as an additional degree of freedom in some applications of intensity fluctuation spectroscopy.     

Localized axion photon states in a strong magnetic field

We consider the axion field and electromagnetic waves with rapid time dependence, coupled to a strong time independent, asymptotically approaching a constant at infinity “mean” magnetic field, which takes into account the back reaction from the axion field and electromagnetic waves with rapid time dependence in a time averaged way. The direction of the self consistent mean field is orthogonal to the common direction of propagation of the axion and electromagnetic waves with rapid time dependence and parallel to the polarization of these electromagnetic waves. Then, there is an effective U(1) symmetry mixing axions and photons. Using the natural complex variables that this U(1) symmetry suggests we find localized planar soliton solutions. These solutions appear to be stable since they produce a different magnetic flux than the state with only a constant magnetic field, which we take as our “ground state”. The solitons also have non-trivial U(1) charge defined before, different from the uncharged vacuum. These solitons represent a new, non-gravitational mechanism, of trapping light. They could also affect the vacuum structure in models of the QCD vacuum that incorporate a magnetic condensate, introducing may be gluon axion solitons.