Clusters of interstitial carbon atoms near the graphite surface as a possible origin of dome-like features observed by STM

Formation of clusters of interstitial carbon atoms between the surface and second atomic layers of graphite is demonstrated by means of molecular dynamics simulations. It is shown that interstitial clusters result in the dome-like surface features that may be associated with some of the hillocks observed by STM on the irradiated graphite surface.Comment: 7 pages, 7 eps figures, submitted to Surface Scienc

Transient response of photoexcited electrons: negative and oscillating current

Time-dependent current of the electrons excited in the conduction band after ultrafast interband photogeneration is studied theoretically. The transient photocurrent is calculated for the nonlinear regime of response to a stationary electric field. The response demonstrates transient absolute negative conductivity when the electrons are excited slightly below the optical phonon energy, while the periodic oscillations of the electric current appear after formation of the streaming distribution. The quenching of these peculiarities by the elastic scattering of electrons is also considered.Comment: 5 pages, 3 figure

Transient magnetoconductivity of photoexcited electrons

Transient magnetotransport of two-dimensional electrons with partially-inverted distribution excited by an ultrashort optical pulse is studied theoretically. The time-dependent photoconductivity is calculated for GaAs-based quantum wells by taking into account the relaxation of electron distribution caused by non-elastic electron-phonon interaction and the retardation of the response due to momentum relaxation and due to a finite capacitance of the sample. We predict large-amplitude transient oscillations of the current density and Hall field (Hall oscillations) with frequencies corresponding to magnetoplasmon range, which are initiated by the instability owing to the absolute negative conductivity effect.Comment: 21 pages, 6 fig

The effect of interstitial clusters and vacancies on the STM image of graphite

Making use of the tight-binding Green's function technique, we have calculated the STM images of graphite with surface and sub-surface defects, while taking into account the relaxation of the lattice due to defects. We have demonstrated that two different physical mechanisms may result in the formation of hillocks in the STM images: buckling of the graphite surface due to interstitials between the uppermost graphite layers and the enhancement of the electron density of states close to the Fermi energy on the carbon atoms in the vicinity of vacancies. Our results indicate that small hillocks may originate both from the interstitial clusters and from the vacancies. By contrast, however, large hillocks in excess of 10 \AA~ in diameter can be caused only by interstitial clusters.Comment: Submitted to Surface Scienc

Didactic potential of the electronic educational resources for increasing qualification of college teachers

Рассматриваются вопросы повышения педагогической квалификации преподавателей СПО в условиях информатизации образования с использованием потенциала сетевых адаптивных электронных образовательных ресурсовThe article deals with the issues of increasing the pedagogical qualification of the faculty members in the context of the informatization of education using the potential of adaptive electronic educational resource

MATHEMATICAL MODEL OF PORTLAND CEMENT KINETICCURING REGIMES IN SULFUR-LIMY SOLUTION

The article covers the chemical method of concrete mixes modifying by setting themin sulfur-limy solution. Mathematical models of concrete curing dynamics are found, depending on concentration of sulfur in the solution, namely:- steady curing rate is observedinthe solution with low content of chemical additives (concentration of Scommon = 0,5-2,5 g/l); - obviously unsteady curing rate is observed in the solution with sulfur concentration at the range of3 to 180 g/l;- steadily high curing rate is observed in the solution ofcorresponding saturation (up to 220 g/l).

Adaptation of content in online electronic educational resources

The article is devoted to the problems of adaptation of content in networked electronic educational resources to individual user featuresОбсуждаются проблемы адаптации контента (содержания) в сетевых электронных образовательных ресурсах под индивидуальные особенности пользователе

Flow and interferometry in 3+1 dimensional viscous hydrodynamics

The expansion of the fireball created in Au-Au collisions at 200 GeV is described in (3+1)-dimensional viscous hydrodynamics with shear and bulk viscosities. We present results for the transverse momentum spectra, the directed and elliptic flow and the interferometry radii.Comment: discussion of viscous corrections at freeze-out adde