Bound entangled states of four qubits in the tomographic-probability representation

We discuss the entanglement phenomenon on the example of the Smolin state of four qubits. This state is known as the bound entangled state and its spin tomogram is found in an explicit form. We apply the qubit-portrait method for investigating the violation of the Bell inequalities, since this approach provides another tool to prove the entanglement properties of the four-qubit state under consideration.     

Amplification of wind waves in reservoirs of finite depth

A method for predicting the generation and amplification of waves from the zone of generation to large fetches, where infragravity waves occur in water of finite depth, is developed from a physical model of interaction between a horizontal air flow and a water surface caused by periodic formation of vortices in the viscous air layer. The model describes the origination of multiple frequencies, and the displacement of wave energy to low-frequency region over a fetch.     

Microcrack dynamics in a polymer composite material during friction

The dynamics of microcracks in the surface layers of a polymer and a polymer composite during friction is studied by triboluminescence (TL). The samples are prepared from poly(phenylene sulfide) (PPS) and a composite consisting of PPS reinforced by carbon fibers. An analysis of the spectra shows that TL appears during the relaxation of the electron excitation of the free radicals that form upon the breakage of chemical bonds in carbon fibers and PPS molecules. TL consists of bursts corresponding to microcrack nucleation, and the burst intensity corresponds to the microcrack surface area. Microcracks form in time intervals of several tens of microseconds rather than continuously. Within these intervals, microcracks form in series sequentially, one by one, at a time step of 3?C4 ??s. Each series consists of several (up to 30) microcracks that also form sequentially, in 20-ns intervals. The sequential nucleation of microcracks and microcrack series is explained by stress redistribution in fracture zones in PPS and the composite.     

On the theory of pulsed foil bolometers

We present simple formulas for estimating the temperatures attained during absorption of radiation in a foil. The method proposed for selecting materials for bolometers makes it possible to substantially improve the temporal resolution of the instrument.     

Existence of positive solution for a sixth–order differential system with variable parameters

This paper investigates the existence of positive solutions for a sixth-order differential system with three variable parameters. Using a fixed point theorem and an operator spectral theorem we give some new existence results.