Dynamic Design of Systems with Semi-rigid Connections Based on Experimental Investigation of the Full Scale Structure

Semi-rigid connections in the construction permit mutual rotation of the nodes. Since such connections are quite common in constructions, especially in the precast ones, it is of interest to determine their dynamic characteristics that is the subject of this proposed paper. During our investigation full scale experiments have been carried out and experimentally determined dynamic characteristics have been compared with those obtained by use of the computational model. The real dynamic characteristics are determined and resonant frequencies of the basic modes in the horizontal and vertical directions, the forms of vibrations at these frequencies, as well as the corresponding coefficient of viscous damping. Testing has been done on the frame structure without facade walls. For the typical precast system "Minoma 1" with span of 12m, "Minoma 2" with span of 20m, and "Minoma 3" with span of 27m, dynamic characteristics: have been determined experimentally by use of forced harmonic excitation, free oscillations and ambient vibration. Experimentally and theoretically obtained values are in a relatively good agreement that is a good starting point for mathematical modeling

THE EFFECTS OF SULFUR-CONTAINING COMPOUNDS ON REDOX STATUS IN HOMOCYSTEINE-TREATED RATS

There is growing interest in the activity of sulfur-containing compounds on redox balance in physiological and pathological conditions, considering that some of these compounds have not only antioxidative but also pro-oxidative activities. Aim of this study was to assess possible differences in the effects of various sulfur-containing compounds on redox balance of cardiovascular system in its physiological state and in the early onset of hyperhomocysteinemia. This experimental study divided Wistar albino rats into two groups: saline-treated (control) and DL-homocysteine-treated (experimental group). Rats from experimental group were subjected to subchronic subcutaneous administration of DL-homocysteine at dose of 0.45 μmol/g body weight twice a day for 2 weeks. At the end of this period, rats were sacrificed, and blood samples were collected to be analysed for homocysteine concentration and systemic oxidative stress. Isolated rat hearts were excised and attached to the Langendorff apparatus. To assess the effects of acute administration of L-methionine, L-cysteine, N-acetylcysteine, and sodium hydrogen sulfide, the hearts were perfused individually with each of the mentioned substances at same single dose of 0.5 mmol/l for 5 min. In collected samples of coronary venous effluent oxidative stress biomarkers were determined using spectrophotometry. Total homocysteine level was significantly higher in the experimental group than in the control group, and the effects of applied sulfur-containing compounds were significantly different in experimental and control groups. DL-homocysteine induced considerable changes in functioning of cardiovascular system even before an increase in plasma homocysteine values, and action of sulfur-containing compounds varied depending on the presence of homocysteine

Training/detraining-induced gender specific functional adaptations of isolated rat heart

Background/Aim. Mechanisms responsible for the bene-ficial effects of aerobic exercise training on cardiovascular function are well known, but detraining effects on myo-cardial parameters have not been adequately elucidated. Therefore, the study aimed to determine the occurrence and speed of cardiac adaptation reversibility after the ces-sation of aerobic exercise and to reveal gender differences in achieved effects of training/detraining. Methods. Fe-male and male Wistar albino rats were divided into the fol-lowing groups: Control, trained, and two detrained groups. Hearts were perfused according to the Langendorff tech-nique and the following cardiodynamic parameters were determined: The maximum and minimum rate of pressure development in the left ventricle (dp/dt max and dp/dt min, respectively), systolic and diastolic left ventricular pressure (SLVP and DLVP, respectively), heart rate (HR), and coronary flow. Results. Training significantly reduced values of dp/dt max, dp/dt min, and SLVP in males and females, and coronary flow in males. Detraining caused a reversion of those changes, which was gender-specific. In females, levels of SLVP were higher after 4 weeks of de-training compred to training, and after 2 weeks of detrain-ing. Values of SLVP were lower in both detraining periods compared to training in males. Males had higher coronary flow after 2 weeks of detraining. Simultaneously, coronary flow was reduced in the 4th week of detraining in females. Conclusion. By using a model of the isolated rat heart, the present study confirmed the existence of training-induced changes in cardiac function. Cessation of training was followed by the loss of those adaptations, faster in males than females