Causes of recurrences of mitral stenosis

The authors present an analysis of the late results of closed mitral commissurotomy in 364 patients (maximum terms of observation--17 years). Main causes of recurrent mitral stenosis were recognized: activation of a rheumatic process (50%), nonspecific scarring processes (27%), inadequate commissurotomies (11.1%) and others (11.1%). The routine antirheumatic therapy (bicillin+salicylates) was found to be ineffective in prophylaxis against mitral restenoses. Recurrent mitral stenosis proved to occur more frequently in patients operated upon in young age (under 30).     

Unequal cross-over is involved in human alpha satellite DNA rearrangements on a border of the satellite domain

It can be invoked from the theory of tandem repeat homogenization that DNA on a satellite/non-satellite border may carry sequence marks of molecular processes basic to satellite evolution. We have sequenced a continuous 17-kb alpha satellite fragment bordering the non-satellite in human chromosome 21, which is devoid of higher-order repeated structure, contains multiple rearrangements, and exhibits higher divergence of monomers towards the border, indicating the lack of efficient homogenization. Remarkably, monomers have been found with mutually supplementary deletions matching each other as reciprocal products of unequal recombination, which provide evidence for unequal cross-over as a mechanism generating deletions in satellite DNA.     

Crack propagation in a pipe steel subjected to cyclic loading after long-term operation

The mechanical properties (under static and cyclic loading) and damage of a product pipeline made of 3G steel have been studied after its long-term operation. The ultrasound velocity in a damaged steel and the fatigue crack length on the sample surface are determined at various stages of macrocrack initiation. At the stage of main-crack initiation, the cumulative curves of fatigue microcrack distribution are well described by both exponential and power functions, with their exponents decreasing with increasing stress amplitude. The majority of fatigue microcracks have a length close to the average grain size.