The Problem of Adhesion Methods and Locomotion Mechanism Development for Wall-Climbing Robots

This review considers a problem in the development of mobile robot adhesion methods with vertical surfaces and the appropriate locomotion mechanism design. The evolution of adhesion methods for wall-climbing robots (based on friction, magnetic forces, air pressure, electrostatic adhesion, molecular forces, rheological properties of fluids and their combinations) and their locomotion principles (wheeled, tracked, walking, sliding framed and hybrid) is studied. Wall-climbing robots are classified according to the applications, adhesion methods and locomotion mechanisms. The advantages and disadvantages of various adhesion methods and locomotion mechanisms are analyzed in terms of mobility, noiselessness, autonomy and energy efficiency. Focus is placed on the physical and technical aspects of the adhesion methods and the possibility of combining adhesion and locomotion methods

Giant Magnetoresistance Oscillations Induced by Microwave Radiation and a Zero-Resistance State in a 2D Electron System with a Moderate Mobility

The effect of a microwave field in the frequency range from 54 to 140 $\mathrm{GHz}$ on the magnetotransport in a GaAs quantum well with AlAs/GaAs superlattice barriers and with an electron mobility no higher than $10^6$ $\mathrm{cm^2/Vs}$ is investigated. In the given two-dimensional system under the effect of microwave radiation, giant resistance oscillations are observed with their positions in magnetic field being determined by the ratio of the radiation frequency to the cyclotron frequency. Earlier, such oscillations had only been observed in GaAs/AlGaAs heterostructures with much higher mobilities. When the samples under study are irradiated with a 140-$\mathrm{GHz}$ microwave field, the resistance corresponding to the main oscillation minimum, which occurs near the cyclotron resonance, appears to be close to zero. The results of the study suggest that a mobility value lower than $10^6$ $\mathrm{cm^2/Vs}$ does not prevent the formation of zero-resistance states in magnetic field in a two-dimensional system under the effect of microwave radiation.Comment: 4 pages, 2 figur

Anisotropic positive magnetoresistance of a nonplanar 2D electron gas in a parallel magnetic field

We study the transport properties of a 2D electron gas in narrow GaAs quantum wells with AlAs/GaAs superlattice barriers. It is shown that the anisotropic positive magnetoresistance observed in selectively doped semiconductor structures in a parallel magnetic field is caused by the spatial modulation of the 2D electron gas.Comment: 4 pages, 3 figure

Ultrahard spectra of PeV neutrinos from supernovae in compact star clusters

Starburst regions with multiple powerful winds of young massive stars and supernova remnants are favorable sites for high-energy cosmic ray acceleration. A supernova shock colliding with a fast wind from a compact cluster of young stars allows the acceleration of protons to energies well above the standard limits of diffusive shock acceleration in an isolated SN. The proton spectrum in such a wind-supernova PeV accelerator is hard with a large flux in the high-energy-end of the spectrum producing copious gamma-rays and neutrinos in inelastic nuclear collisions. We argue that SN shocks in the Westerlund 1 cluster in the Milky Way may accelerate protons to about 40 PeV. Once accelerated, these CRs will diffuse into surrounding dense clouds and produce neutrinos with fluxes sufficient to explain a fraction of the events detected by IceCube Observatory from the inner Galaxy.Comment: 10 pages, 7 figures, MNRAS v.453, p.113-121, 201

Effect of parallel magnetic field on the Zero Differential Resistance State

The non-linear zero-differential resistance state (ZDRS) that occurs for highly mobile two-dimensional electron systems in response to a dc bias in the presence of a strong magnetic field applied perpendicular to the electron plane is suppressed and disappears gradually as the magnetic field is tilted away from the perpendicular at fixed filling factor $\nu$. Good agreement is found with a model that considers the effect of the Zeeman splitting of Landau levels enhanced by the in-plane component of the magnetic field.Comment: 4 pages, 4 figure

Non-Maxwellian electron distributions in clusters of galaxies

Thermal X-ray spectra of clusters of galaxies and other sources are commonly calculated assuming Maxwellian electron distributions. There are situations where this approximation is not valid, for instance near interfaces of hot and cold gas and near shocks. The presence of non-thermal electrons affects the X-ray spectrum. To study the role of these electrons in clusters and other environments, an efficient algorithm to calculate the X-ray spectra is needed. We approximate an arbitrary electron distribution by the sum of Maxwellian components. The decomposition is done using either a genetic algorithm or an analytical approximation. The X-ray spectrum is then evaluated using a linear combination of those Maxwellian components. Our method is fast and leads to an accurate evaluation of the spectrum. The use of Maxwellian components allows to use the standard collisional rates that are available in plasma codes such as SPEX. We give an example of a spectrum for the supra-thermal electron distribution behind a shock in a cluster of galaxies. The relative intensities of the satellite lines in such a spectrum are sensitive to the presence of the supra-thermal electrons. These lines can only be investigated with high spectral resolution. We show that the instruments on future missions like Astro-H and IXO will be able to demonstrate the presence or absence of these supra-thermal electrons.Comment: 6 pages, 4 figures, accepted for publication in Astronomy and Astrophysics, main journa