Features of radio wave refraction in the near-polar regions

The radio-wave refraction parameters are analyzed under the Arctic conditions. The features of the troposphere and ionosphere of this zone are taken into account. It is demonstrated that the refraction angles of near-polar regions has no substantial differences from those of other regions. Calculations are performed numerically with the use of exact formulas for refraction of electromagnetic wave. The relationship between true and total refraction angles is derived.     

Effect of a diet with an increased protein content on reparative processes in experimental ulcerous lesions of the gastric and duodenal mucosa

Experimental rats were subjected to an extreme action: 3-hour immobilization with simultaneous electrostimulation. A complete healing of erosion-ulcerous defects of the gastroduodenal mucosa was recorded in rats given diets with an increased (by 4 g) protein content (group I), on day 5. The mucosal affections in the rats receiving a standard ration still persisted. The content of creatine-phosphate in the gastric wall tissue, decreased under the extreme action, was rapidly recovered in group I rats, no changes in the proper fluorescence level of reduced NADH and flavoproteins were noted. In group II rats both parameters returned to normal only on day 5. Blood serum ceruloplasmin (CP) activity increased during first 3 days with a similar rate in both animal groups. However, in the following 2 days CP activity in group I rats became completely normal, while that in group II animals was still rising. The results of the study have shown that the diet with increased protein content stimulates epithelization of the gastroduodenal mucosa due to the improvement of the bioenergy processes in the gastroduodenal area, and to intensified adaptation potentialities of the body.     

High-vacuum cryomicrotome with a single bellows input of the sample motion and cooling

A cryomicrotome based on a heated inlet of liquid nitrogen and complex (an 8-mm-amplitude reciprocating and circular rotary about the vertical axis) motion allows one to conduct all freeze-fracturing operations under visual control (the temperatures of the object and knife are −115°C and −180°C, respectively) and to obtain high-quality replicas of the studied biological sample in the operation chamber with a volume below 1.11 under an oil-free vacuum no worse than 10⁻⁵ Pa, created by a turbo-molecular pump.     

Distribution of the Strength of the Low-Frequency Field Demodulated in the Disturbed Lower Ionosphere over the Earth Surface

The possible distribution of the field strength of the low-frequency demodulated radiation of the high-power transmitter of the HAARP station (Alaska, USA) over the Earth surface in the Earth–ionosphere waveguide has been numerically simulated. It has been shown that, owing to the extremely weak electromagnetic coupling between the ionosphere and the waveguide in the case of an ionospheric source, the strengths of the electric and magnetic fields of the waveguide waves are relatively low and are at the level of the low-frequency noise even in the immediate vicinity of the center of the distribution. It has been confirmed that, in order to detect such a signal and measure its parameters, it is necessary to use special procedures for processing data from ground-based receivers.     

On algorithms for construction of all irreducible partial covers

Lower and upper bounds on the cardinality and the number of irreducible partial covers for almost all set cover problems are obtained. These bounds allow us to prove that there is no polynomial algorithm which for almost all set cover problems constructs all irreducible partial covers, but there exists a totally polynomial algorithm which constructs all irreducible partial covers for almost all set cover problems.     

Greedy Algorithm for Set Cover in Context of Knowledge Discovery Problems

In the paper some problems connected with a process of knowledge discovery are considered. These problems are reduced to the set cover problem. It is known that under a plausible assumption on the class N P the greedy algorithm is close to best approximate polynomial algorithms for the set cover problem solving. Unfortunately, the performance ratio of this algorithm grows almost as natural logarithm on the cardinality of covered set. Instead of usual greedy algorithm we consider greedy algorithm with threshold. This algorithm constructs a partial cover, which covers at least a fixed part (for example, 90%) of the set. We prove that the cardinality of constructed partial cover is bounded from above by a linear function on the minimal cardinality of exact cover C_min. In the case of 90% -cover, for example, in the capacity of such function we can take the function 2.31,·,C_min+1. This bound is independent of the cardinality of covered set. Notice that the concept of partial cover in context of knowledge discovery problems is very close to the concept of approximate reduct.