Comparison of Copper and Graphite Crucibles for Si Extraction from TiO2 - SiO2 System at Plasma-Arc Heating

Plasma arc recovery melting of the quartz-leucoxene concentrate is investigated. Experiments were made in laboratory DC plasma arc furnace in various crucibles. The best results are reached in a cold copper crucible. The temperature field of a pool is calculated in hot graphite and cold copper crucibles. It is shown that in a graphite crucible diameter of an anode spot is more, and density of current and material temperature in a spot is less, than in copper that is the reason of the worst refinements in a graphite crucible

Raman scattering in a two-dimensional electron gas: Boltzmann equation approach

The inelastic light scattering in a 2-d electron gas is studied theoretically using the Boltzmann equation techniques. Electron-hole excitations produce the Raman spectrum essentially different from the one predicted for the 3-d case. In the clean limit it has the form of a strong non-symmetric resonance due to the square root singularity at the electron-hole frequency $\omega = vk$ while in the opposite dirty limit the usual Lorentzian shape of the cross section is reestablished. The effects of electromagnetic field are considered self-consistently and the contribution from collective plasmon modes is found. It is shown that unlike 3-d metals where plasmon excitations are unobservable (because of very large required transfered frequencies), the two-dimensional electron system gives rise to a low-frequency ($\omega \propto k^{1/2}$) plasmon peak. A measurement of the width of this peak can provide data on the magnitude of the electron scattering rate.Comment: 4 pages, 3 figures. to appear in Phys. Rev. B 59 (1999

Extra Spin-Wave mode in Quantum Hall systems. Beyond the Skyrmion Limit

We report on the observation of a new spin mode in a quantum Hall system in the vicinity of odd electron filling factors under experimental conditions excluding the possibility of Skyrmion excitations. The new mode having presumably zero energy at odd filling factors emerges at small deviations from odd filling factors and couples to the spin-exciton. The existence of an extra spin mode assumes a nontrivial magnetic order at partial fillings of Landau levels surrounding quantum Hall ferromagnets other then the Skyrmion crystal.Comment: 9 pages, 4 figure

The Cyclotron Spin-Flip Mode as the Lowest-Energy Excitation of Unpolarized Integer Quantum Hall States

The cyclotron spin-flip modes of spin unpolarized integer quantum Hall states ($\nu =2,4$) have been studied with inelastic light scattering. The energy of these modes is significantly smaller compared to the bare cyclotron gap. Second order exchange corrections are held responsible for a negative energy contribution and render these modes the lowest energy excitations of unpolarized integer quantum Hall states.Comment: Published: Phys. Rev. B 72, 073304 (2005

Cyclotron spin-flip excitations in a \nu=1/3 quantum Hall ferromagnet

Inelastic light scattering spectroscopy around the \nu=1/3 filling discloses a novel type of cyclotron spin-flip excitation in a quantum Hall system in addition to the excitations previously studied. The excitation energy of the observed mode follows qualitatively the degree of electron spin polarization, reaching a maximum value at \nu=1/3 and thus characterizing it as a \nu=1/3 ferromagnet eigenmode. Its absolute energy substantially exceeds the theoretical prediction obtained within the renowned single-mode approximation. Double-exciton corrections neglected utilizing the single-mode approach are evaluated within the framework of the excitonic representation and are inferred to be responsible for the observed effect.Comment: 4 pages,3 figures, submitted to PR

Antiphased Cyclotron-Magnetoplasma Mode in a Quantum Hall System

An antiphased magnetoplasma (MP) mode in a two-dimensional electron gas (2DEG) has been studied by means of inelastic light scattering (ILS) spectroscopy. Unlike the cophased MP mode it is purely quantum excitation which has no classic plasma analogue. It is found that zero momentum degeneracy for the antiphased and cophased modes predicted by the first-order perturbation approach in terms of the {\it e-e} interaction is lifted. The zero momentum energy gap is determined by a negative correlation shift of the antiphased mode. This shift, observed experimentally and calculated theoretically within the second-order perturbation approach, is proportional to the effective Rydberg constant in a semiconductor material.Comment: Submitted to Phys. Rev.

Physics of Auroral Phenomena

Abstract. The nighttime region at geocentric distances ~7-10R E is ordinarily considered as the near tail region. However the results of observations including latest THEMIS mission clearly demonstrate the existence of surrounding the Earth plasma ring at these geocentric distances. The distribution of plasma pressure in the ring is near to azimuthally symmetric. Daytime compression of magnetic field lines and shift of minimal value of the magnetic field till high latitudes lead to splitting of daytime transverse currents in Z direction. As a result nighttime transverse currents in the surrounding the Earth plasma ring are concentrated near equator, daytime transverse currents are spread along compressed by solar wind field lines forming the cut ring current (CRC) which is the high latitude continuation of the ordinary ring current. CRC is supported by directed to the Earth plasma pressure gradients. The role of CRC in the development of magnetic storm and the creation of the Dst variation is analyzed. We stress that the development of partial ring current, which is one of the well-known features of magnetic storm, in the CRC region helps to eliminate paradox, appeared when it was suggested that tail current could have the considerable role in the Dst formation. The contribution CRC in the process of Dst formation during magnetic storms is evaluated for selected magnetic storms with known radial profile of plasma pressure. The magnetospheric substorm is one of the most extensively stydied magnetospheric phenomena for the most than 50 latest years. However the mechanism of observed energy explosion and localization of substorm onset continue to be widely discussed. We summarize the results of observations demonstrating the isolated substorm onset at geosentric distances smaller than 10R E . It is suggested that isolated substorm onset is localized in CRC