The thermal conductivity of ceramic powder packed beds was measured at temperatures below 100 °C for various powder sizes and compositions and under different gas atmospheres. Measurements at low pressures (down to 10 Pa) combined with a theoretical model allowed the elucidation of geometrical and thermal resistance parameters for the contact points between granules. The gap thickness and contact point size were found to be well correlated with the mean particle size. The thermal conductivities of all powders at low pressure were found to differ at most by a factor of two, whereas the solid‐phase conductivities of the powder materials differed by more than one order of magnitude. A theoretical model accounting for the size‐dependence of contact point conductivity is incorporated to rationalize this trend.
Vibrational motion and dynamics of two-dimensional layers composed of identical inelastic solid disks are investigated experimentally and characterized in terms of the dimensionless acceleration. Several vibrational regimes with different degrees of vibrofluidization are studied by means of the layers' videorecordings and tracking the motion of one larger disk immersed into each bed of smaller particles. It is shown that depending on the vibrational acceleration, the larger disk either ultimately rises on top of the layer or vigorously moves throughout it, thereby indicating possibilities for efficient mixing. In a certain narrow range of the vibrational acceleration the layer is observed to repack and move as a single block. This acceleration range is well described by the model of an absolutely plastic body moving above a vibrated plate. Small deviations from this acceleration range lead to a significant layer expansion and distortion of its upper surface due to transverse waves. The vibrofluidization regimes are also characterized by measuring the force acting on the vessel's bottom and the time of its contact with the layer. The propagation speed of the compression-expansion waves is estimated and found consistent with the predictions of our earlier semiempirical and analytical models.
Background. In this study the dependence of the level of cortisol on the age of the patient, the presence of disorders of fat metabolism, the dose of muscle relaxant and anesthetic propofol was revealed. Determining the level of cortisol as a component of anesthetic monitoring enables not only to assess the level of perioperative stress, but also to predict the height of the expected stress response. The aim of our study was to determine the influence of perioperative factors on cortisol levels during cardiac surgery. Material and methods. A prospective non-randomized observational study was conducted. The study involved 30 cardiac surgery patients. The age of the patients ranged from 49 to 67 (64 (59; 70)) years, the body mass index was 29.05 (25.56; 33.25) kg/m2. All the patients underwent cardiac surgery under cardiopulmonary bypass. All the patients underwent venous blood sampling to determine the level of cortisol at the following stages: stage 1 - the patient on the operating table, peripheral vein catheterization; Stage 2 - during anesthesia, before connecting to a heart-lung machine; Stage 3 - the end of the operation, suturing the skin; Stage 4 - 1-3 hours after the operation; Stage 5 - 17-20 hours after surgery. Quantitative determination of cortisol in blood serum was carried out by the immunochemical method using the Architect plus i10000sr apparatus (Abbott, USA). Results. The analysis of the obtained data showed that the level of cortisol in the early postoperative period was significantly higher in patients older than 65 (18.8 (10.3; 26.0) µg/dL). The level of cortisol at the second stage of the study was higher in patients with impaired fat metabolism (11.1 (7.1; 15.6) µg/dL). Cortisol levels were significantly lower with higher doses of pipecuronium bromide during anesthesia (5.8 (3.6; 10.5) µg/dL). A significant correlation was found between the dose of propofol at the induction stage and the level of cortisol at stage 4 (R=-0.6; р=0.007). A moderate inverse correlation was established between the level of cortisol and the total dose of fentanyl at the second stage (R=-0.43; p=0.017). Conclusion. Determining the level of cortisol should be a component of anesthetic monitoring when performing cardiac surgery under conditions of cardiopulmonary bypass.
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