Bidirectional Ray Tracing for the Integration of Illumination by the Quasi-Monte Carlo Method

Algorithms used to generate physically accurate images are usually based on the Monte Carlo methods for the forward and backward ray tracing. These methods are used to numerically solve the light energy transport equation (the rendering equation). Stochastic methods are used because the integration is performed in a high-dimensional space, and the convergence rate of the Monte Carlo methods is independent of the dimension. Nevertheless, modern studies are focused on quasi-random samples that depend on the dimension of the integration space and make it possible to achieve, under certain conditions, a high rate of convergence, which is necessary for interactive applications. In this paper, an approach to the development of an algorithm for the bidirectional ray tracing is suggested that reduces the overheads of the quasi-Monte Carlo integration caused by the high effective dimension and discontinuity of the integrand in the rendering equation. The pseudorandom and quasi-random integration methods are compared using the rendering equations that have analytical solutions.     

Interaction of propagating discrete breathers with a vacancy in a two-dimensional crystal

The interaction of discrete breathers (DBs) propagating along a close-packed atomic row with a vacancy situated in the same row has been studied by molecular dynamics in a two-dimensional monoatomic crystal with the Morse interatomic potential. It is established that DBs moving at a velocity below a certain threshold exhibit elastic repulsion from the vacancy, while DBs with velocities above this threshold are scattered on the vacancy. The interaction of DBs with a vacancy decreases the energy barrier for vacancy migration in the crystal.     

Eddy-current measuring system for analysis of alloy defects and weld seams

A measuring system based on an eddy-current transformer permits the detection of defects in plates of duralumin and aluminum–magnesium alloys.     

Modelling the Sliding Behaviour of Tribofilms Forming During Automotive Braking: Impact of Loading Parameters and Property Range of Constituents

The impact of pressure, sliding velocity and property variation of constituents on the sliding behaviour of a model tribofilm was studied with the method of movable cellular automata (MCA). Whereas a clear pressure dependency of the coefficient of friction (COF) was always observed and could be correlated with the structure formation in terms of varying thickness of a mechanically mixed layer, the impact of the other parameters was either negligible or rather weak. Only if a brittle-to-ductile transition of the oxide-based tribofilm was assumed, a significant decrease in the COF level was predicted. Temperature-dependent property changes can be neglected during MCA modelling, unless this transition takes place. For magnetite-based tribofilms, the transition temperature is beyond 800°C, i.e. a temperature leading to fading effects during braking anyway. Thus, it could be concluded that, except for very severe braking conditions, sliding simulations with the MCA method yield meaningful results without considering temperature-dependent mechanical properties.     

Effect of postgrowth techniques on the characteristics of triple-junction InGaP/Ga(In)As/Ge solar cells

The photoelectric characteristics of triple-junction InGaP/Ga(In)As/Ge solar cells are studied in relation to the method used to form the photocell chip. It is shown that the application of a postgrowth technique developed in the study for separating a nanoheterostructure into chips in a single process makes it possible to improve the quality of passivation of the chip edges, which diminishes the surface leakage currents and makes larger the yield of devices with improved characteristics.