Twisted electrostatic waves in a self‐gravitating dusty plasma

A generalized response (dielectric) function for twisted electrostatic waves is derived for an un‐magnetized self‐gravitating thermal dusty plasma, whose constituents are the Boltzmann‐distributed electrons and positive ions in the presence of negatively charged micrometre‐sized massive dust particulates. For this purpose, a set of Vlasov–Poisson coupled equations is solved along with the perturbed Laguerre–Gauss distribution function, as well as the electrostatic and gravitational potentials in the limit of paraxial approximation. For plane wave solution, the wavefronts of the dust‐acoustic (DA ) wave are assumed to have a constant phase with electric and gravitational field lines propagating straight along the propagation axis. On the other hand, non‐planar wave solutions show helical (twisted) wavefronts, in which field lines spiral around the propagation axis owing to the azimuthal velocity component to account for the finite orbital angular momentum (OAM ) states. The dispersion relation and damping rate for twisted DA waves are studied both analytically and numerically. It is shown that finite OAM states, the dust to electron temperature ratio, and dust self‐gravitation effects significantly affect the linear dispersion and Landau damping frequencies. In particular, the phase speed of twisted DA waves is reduced with the variation of the twist parameter η (= k /lq_ϕ ), dust concentration δ (= n_{d 0}/n_{i 0}), and dust self‐gravitation α (= ω_Jd /ω_pd ). The relevance of our findings to interstellar dust clouds is also discussed for micrometre‐sized massive dust grains.     

Nonplanar Electrostatic Solitary Waves in a Relativistic Degenerate Dense Plasma

By employing the reductive perturbation technique, the propagation of cylindrical and spherical ion acoustic solitary waves is studied in an unmagnetized dense relativistic plasma, consisting of relativistically degenerate electrons and cold fluid ions. A modified Korteweg-de-Vries equation is derived and its numerical solutions have been analyzed to identify the basic features of electrostatic solitary structures that may form in such a degenerate Fermi plasma. Different degrees of relativistic electron degeneracy are discussed and compared. It is found that increasing number density leads to decrease the amplitude the width of the ion acoustic solitary wave in both the cylindrical and spherical geometries. The relevance of the work to the compact astrophysical objects, particularly white dwarfs is pointed out.     

Optical transmission through an interface between subwavelength slits

This paper studies optical transmission through an interface between two slits with different widths in a sheet composed of an ideal conductor. Such a structure is of potential use in fabricating optical diode and may be the simplest one compared to other designs. Our calculations show that there is a critical wavelength. When the light wavelength is below the critical wavelength, the transmissivity is unidirectional. The expression of the stable transmissivity as a function of the ratio of the widths of the two slits was obtained analytically. Particularly, at the critical wavelength, the transmissivities are zero. This phenomenon has great potential for application in the manufacture of wavelength blockers.     

Dressed ion acoustic solitary waves in quantum plasmas with two polarity ions and relativistic electron beams

A theory for dressed quantum ion acoustic waves (QIAWs), which includes higher-order corrections when QIAWs are investigated by the reductive perturbation method, is presented for unmagnetized plasmas containing positive and negative ions and weakly relativistic electron beams. The properties of the QIAWs are investigated using a quantum hydrodynamic model, from which a Korteweg–de Vries equation is derived using the reductive perturbation method. An equation including higher-order dispersion and nonlinearity corrections is also derived, and the physical parameter space is discussed for the importance of these corrections.     

Current-driven electron drift solitons

The soliton formation by the current-driven drift-like wave is investigated for heavier ion (such as barium) plasma experiments planned to be performed in future. It is pointed out that the sheared flow of electrons can give rise to short scale solitary structures in the presence of stationary heavier ions. The nonlinearity appears due to convective term in the parallel equation of motion and not because of temperature gradient unlike the case of low frequency usual drift wave soliton. This higher frequency drift-like wave requires sheared flow of electrons and not the density gradient to exist.     

Extension of the range of resonator scanning spectrometer into submillimeter band and some perspectives of its further developments

Extension of the working frequency of modern resonator spectrometers into submillimeter wave range is described. Experimental record of atmospheric absorption spectrum covering 45-370 GHz range is demonstrated for the first time, and measured water vapor J′_{ka′, kc′}-J_{ka, kc} = 5_1,5-4_2,2 at 325 GHz line parameters are presented. For the first time pressure lineshift for the 325-GHz water vapor line is measured. Further extension of working range is discussed. New estimations of physical limits of time needed for measurements of absorption in the whole Backward Wave Oscillator (BWO) range are given for phase continuous synthesizer regime. Basic schemes of fast broadband continuous phase synthesized sources are discussed. Verification of the previous measurements of water vapor 3_1,3-2_2,0 at 183 GHz line parameters is presented. Comparisons with ringdown resonator spectrometers are given.     

套管井水泥环空间介质波阻抗与厚度反演方法

针对实际反射式超声波测井,把套管与地层环空间单层介质的波阻抗和厚度作为两个待反演参数,分别将相移正切函数及反正切函数形式下的方程作为目标函数,提出了对波阻抗和厚度反演的线性化最小二乘法.通过对两种反演方程误差函数的数值考察和对合成数据反演结果的分析,发现相移反正切函数形式下方程的线性化最小二乘法是较为稳定有效的方法,能够完全消除多极值的缺点,反演结果对波阻抗和厚度初值不敏感.     

Solitary waves in the Madelung's fluid: Connection between the nonlinear Schrödinger equation and the Korteweg-de Vries equation

An investigation to deepen the connection between the family of nonlinear Schr?dinger equations and the one of Korteweg-de Vries equations is carried out within the context of the Madelung's fluid picture. In particular, under suitable hypothesis for the current velocity, it is proven that the cubic nonlinear Schr?dinger equation, whose solution is a complex wave function, can be put in correspondence with the standard Korteweg-de Vries equation, is such a way that the soliton solutions of the latter are the squared modulus of the envelope soliton solution of the former. Under suitable physical hypothesis for the current velocity, this correspondence allows us to find envelope soliton solutions of the cubic nonlinear Schr?dinger equation, starting from the soliton solutions of the associated Korteweg-de Vries equation. In particular, in the case of constant current velocities, the solitary waves have the amplitude independent of the envelope velocity (which coincides with the constant current velocity). They are bright or dark envelope solitons and have a phase linearly depending both on space and on time coordinates. In the case of an arbitrarily large stationary-profile perturbation of the current velocity, envelope solitons are grey or dark and they relate the velocity u₀ with the amplitude; in fact, they exist for a limited range of velocities and have a phase nonlinearly depending on the combined variable x-u_{0 s} (s being a time-like variable). This novel method in solving the nonlinear Schr?dinger equation starting from the Korteweg-de Vries equation give new insights and represents an alternative key of reading of the dark/grey envelope solitons based on the fluid language. Moreover, a comparison between the solutions found in the present paper and the ones already known in literature is also presented. Received 20 February 2002 and Received in final form 22 April 2002 Published online 6 June 2002     

On the Purely Longitudinal Space Charge Wave of an Extended Electromagnetic Theory

An extended electromagnetic theory has earlier been developed, as being based on the hypothesis of a nonzero electric field divergence in vacuo and the requirement of Lorentz invariance. This basis is supported by the commonly accepted fact that the vacuum is not merely an empty space, but has a ground state of nonzero energy and can become electrically polarized. The vacuum is thereby considered as electrically polarizable in the sense of being capable of supporting charge motion in the form of, e.g., space-charge waves. One result of the dynamic states of the present theory is the prediction of a purely longitudinal electric space-charge wave (S-wave) having no induced magnetic field. The behaviour of this wave type is demonstrated for a number of geometrical configurations. Some preliminary proposals are finally made for generation and detection of S waves. These waves are expected to have features which differ from those of the conventional transverse electromagnetic waves. If the S wave would come out to be physically realizable, it may thus form the basis of a new principle for telecommunication without or with very small magnetic induction effects.     

Magnetic properties of the Cr(0 0 1) surface studied by spin-polarized scanning tunneling spectroscopy

The magnetic properties of the Cr(0 0 1) surface have been studied by spin-polarized scanning tunneling spectroscopy (SP-STS). Spatially resolved mapping of the spectroscopic dI/dU signal at an energy close to the spin-polarized Cr(0 0 1) surface state allows the confirmation of the topological antiferromagnetic order of the Cr(0 0 1) surface. It is shown that the presence of screw dislocations leads to the formation of domain walls which exhibit a width of 120–170 nm. A long-period modulation of the SP-STS signal was not observed indicating that the bulk spin-density wave is modified at the surface due to symmetry breaking.