A small-amplitude study of solitons near critical plasma compositions

The properties of small-amplitude solitons are established near critical plasma compositions in a generalized fluid plasma with an arbitrary number of species. The study is conducted via a Taylor series expansion of the Sagdeev potential. It is shown that there are two types of critical compositions, namely rich critical and poor critical compositions. The coexistence of positive and negative polarity solitons is shown to arise at rich critical compositions and near rich critical compositions. At poor critical compositions, no small-amplitude solitons exist, while weak double layers arise near poor critical compositions. A novel analytical expression is obtained for a small-amplitude acoustic speed soliton solution near rich critical compositions. These solitons have a Lorentzian shape with much fatter tails than regular solitons. A case study is also performed for a simple fluid model consisting of cold ions and two Boltzmann electron species. Exact agreement is obtained between the Sagdeev analysis and reductive perturbation theory. For the first time, we derive the same Lorentzian acoustic speed soliton from reductive perturbation theory.

The Influence of Dimensional Static and Dynamic Charge on the Spectral Parameters and Active Dynamic Conductivity of Resonanse Tunnelling Structures with Constant Electric Field

In the model of effective masses and rectangular potentials obtained self-consistent solution of Poisson and Schrödinger equations for different concentrations of electrons. It has been calculated spectral parameters and active dynamic conductivity for three-well nanostructure as active band of experimental quantum cascade laser. It has been established, that space charge deforms shape dependence of transmission factor of electron energy from Lorentzian shape to quasi-Lorentzian, shifting their maximum value to the high energy region and increasing the lifetimes of electronic quasistationary states. It was shown, that with increasing concentration of electrons energy of laser radiation in quantum transitions and decreases, and the total value of active dynamic conductivity increases so, that it increases the partial contribution component of conductivity, determined by electron flux, directed opposite to the exit of nanostructure.

Growth of Few Layers Graphene on Silicon Carbide from Nickel Silicide Supersaturated with Carbon

Few Layers Graphene (FLG) films were grown on the carbon-terminated surface of 4H-SiC from nickel silicide supersaturated with carbon. The process was realised by annealing of thin Ni films deposited on silicon carbide followed by wet processing to remove the nickel silicide. To identify and characterize the fabricated FLG films, micro-Raman scattering spectroscopy, AFM and optical microscopy have been used. The films grown on samples with initially deposited nickel thinner than 20 nm show clear graphene footprints in micro-Raman scattering spectra, namely a single component, Lorentzian shape 2D band with FWHM remarkably lower than that of the 2D peak of graphite.

Artificially Induced Perturbations in Chirped Magneto-Optical Bragg Gratings

We report on theoretical analysis of magneto-optically induced longitudinal perturbations in chirped magneto-optical Bragg gratings. The induced perturbations considered are of Lorentzian shape, with a spatial extent considerably larger than the spatial grating period but at least an order of magnitude less than the geometrical length of the grating. In the numerical simulation of the proposed device, we show on a high polarization state selectivity in the region of the perturbation, with resonance peaks of transmission for circularly polarized orthogonal components possessing a full width at half maximum as narrow as 0.18 nm, meanwhile being separated by 0.6 nm.

Crystallite-size distributions and diffraction line profiles near the peak maximum

The effect of crystallite-size distribution on the shape of X-ray diffraction peaks from powder samples is investigated focusing the attention on the region within the top half of intensity. It is shown that, unlike profile tails, this central region can markedly depart from the Lorentzian shape for crystallite-size distributions that are quite acceptable from the physical point of view. Goal of this paper is to correlate the well-known m parameter in the Pearson VII function or the η weight in the pseudo-Voigt function with a number of different distributions of crystallite dimensions ranging from the δ function of all-equal-sized crystals to a very broad distribution. The suitably normalized curvature at the peak is a possible new parameter; its correlation with m and η is shown. Also, a procedure is suggested to derive the volume-average crystal thickness 〈Tw〉 from the FWHM and the knowledge of either m or η.

On the Analysis of Raman Spectra by Curve Resolution

Raman spectra obtained during studies of solution equilibria are subjected to analysis using a combination of a small, manually controlled, digital minicomputer and a large digital computer. The shape-function of the bands is regarded as an empirical parameter, and the majority of bands are found to have Lorentzian shape. Simultaneous determination of shape-function and curved baseline is shown to be unsatisfactory. The possibility that components of a multiplet have different shape-functions is considered, and a probable example of such a case is given. Finally, it is shown that the ν3 region of the Raman spectrum of sodium nitrate in liquid ammonia probably contains three component bands, but uncertainty regarding shape-function introduces large uncertainty into the areas and positions of the bands.