Thermal suppression of surface barrier in ultrasmall superconducting structures

In the recent experiment by Cren \textit{et al.} [Phys. Rev. Lett. \textbf{102}, 127005 (2009)], no hysteresis for vortex penetration and expulsion from the nano-island of Pb was observed. In the present paper, we argue that this effect can be associated with the thermoactivated surmounting of the surface barrier by a vortex. The typical entrance (exit) time is found analytically from the Fokker-Planck equation, written in the form suitable for the extreme vortex confinement. We show that this time is several orders of magnitude smaller than 1 second under the conditions of the experiment considered. Our results thus demonstrate a possibility for the thermal suppression of the surface barrier in nanosized low-$T_{c}$ superconductors. We also briefly discuss other recent experiments on vortices in related structures.Comment: 12 pages, 2 figure

Цифровая трансформация проектирования технологических процессов при подготовке инженеров-проектировщиков: история и перспективы

Significant advances in the implementation of information technology in the educational process cannot occur on their own. Success in this area is ensured by many years of hard work aimed at a gradual transition from the use of traditional teaching methods to automated ones. This transition on the example of implementing a computeraided design of technological processes is considered. The stages of the formation of this activity are described, starting with systems based on SM EVM (СМ ЭВМ, abbreviation of Система Малых ЭВМ – literally System of Mini Computers. It was the general name for several types of Soviet minicomputers produced in the 1970s and 1980s) operating under the control of a real-time operating system, and ending with electronic complexes for information support of design and technological design based on PDM systems.Значительные достижения в области внедрения информационных технологий в учебный процесс не могут возникнуть сами по себе. Успех в этой сфере обеспечивается многолетней и упорной работой, направленной на постепенный переход от использования традиционных методов обучения к автоматизированным. Этот переход рассматривается на примере внедрения системы автоматизированного проектирования технологических процессов. Описываются этапы становления этой деятельности, начиная с систем на базе СМ ЭВМ, работающих под управлением ОС РВ, и, заканчивая электронными комплексами для информационной поддержки конструкторско-технологического проектирования на базе PDM-систем

Unidentified aerial phenomena I. Observations of events

NASA commissioned a research team to study Unidentified Aerial Phenomena (UAP), observations of events that cannot scientifically be identified as known natural phenomena. The Main Astronomical Observatory of NAS of Ukraine conducts an independent study of UAP also. For UAP observations, we used two meteor stations. Observations were performed with colour video cameras in the daytime sky. We have developed a special observation technique, for detecting and evaluating UAP characteristics. According to our data, there are two types of UAP, which we conventionally call: (1) Cosmics, and (2) Phantoms. We note that Cosmics are luminous objects, brighter than the background of the sky. Phantoms are dark objects, with contrast from several to about 50 per cent. We observe a significant number of objects whose nature is not clear. Flights of single, group and squadrons of the ships were detected, moving at speeds from 3 to 15 degrees per second. Some bright objects exhibit regular brightness variability in the range of 10 - 20 Hz. We use colourimetry methods to determine of distance to objects and evaluate their colour characteristics. Objects RGB colours of the Adobe colour system had converted to the Johnson BVR astronomical colour system using the colour corrections. Phantom shows the colour characteristics inherent in an object with zero albedos. It is a completely black body that does not emit and absorbs all the radiation falling on it. We see an object because it shields radiation due to Rayleigh scattering. An object contrast makes it possible to estimate the distance using colourimetric methods. Phantoms are observed in the troposphere at distances up to 10 - 12 km. We estimate their size from 3 to 12 meters and speeds up to 15 km/s.Comment: 8 pages, 23 figures, Odessa Astronomical Publication

Stress induced dislocation roughening -- phase transition in 1d at finite temperature

We present an example of a generically forbidden phase transition in 1d at finite temperature -- stress induced and thermally assisted roughening of a superclimbing dislocation in a Peierls potential. We also argue that such roughening is behind the strong suppression of the superflow through solid \he4 in a narrow temperature range recently observed by Ray and Hallock (Phys.Rev. Lett. {\bf 105}, 145301 (2010)).Comment: 4 revtex pages, 5 figures. Replaced with the published versio

The role of Helium-3 impurities in the stress induced roughening of superclimbing dislocations in solid Helium-4

We analyze the stress induced and thermally assisted roughening of a forest of superclimbing dislocations in a Peierls potential in the presence of Helium-3 impurities and randomly frozen in static stresses. It is shown that the temperature of the dip $T_d$ in the flow rate observed by Ray and Hallock (Phys.Rev. Lett. {\bf 105}, 145301 (2010)) is determined by the energy of the impurity activation from dislocation core. However, it is suppressed by, essentially, the logarithm of the impurity fraction. The width of the dip is determined by inhomogeneous fluctuations of the stresses and is shown to be much smaller than $T_d$.Comment: Submitted to the LT26-conference proceeding

Thermodynamics of carrier-mediated magnetism in semiconductors

We propose a model of carrier-mediated ferromagnetism in semiconductors that accounts for the temperature dependence of the carriers. The model permits analysis of the thermodynamic stability of competing magnetic states, opening the door to the construction of magnetic phase diagrams. As an example we analyze the stability of a possible reentrant ferromagnetic semiconductor, in which increasing temperature leads to an increased carrier density, such that the enhanced exchange coupling between magnetic impurities results in the onset of ferromagnetism as temperature is raised.Comment: 4 pages, 3 figure