Effective fields in magnetic colloids and features of their magnetization kinetics

We present results of magnetization and magnetic susceptibility dependence investigations performed for undecane-based ferrofluids with dominant of Brownian relaxation for particles. A robust and effective method of fine particle size characterization is presented. It is based on the core–shell model and the analysis of the dependence of saturation magnetization on particle concentration. A novel advantage method has been used as a straightforward way to determine the concentration dependence of the effective field related to particle interaction that was calculated from the experimentally obtained concentration dependence of low field susceptibility. The computed relationship is compared with the concentration dependences of effective fields derived from several well-known theoretical models. We present some peculiarities of the real part of dynamic magnetic susceptibility on temperature. Investigated features are defined both by the magnetic state of fine particles and by crystallization of carrier at the liquid to a solid phase transition. For the first time, the dependence of the magnetization relaxation time on the colloidal particle concentration and the magnitude of bias DC magnetic field was investigated experimentally. Results are in good agreement with theoretical predictions for moderate concentration and significantly differs for concentration greater 7 vol%. It is concluded that this effect can be related either to the enhanced particle interaction or to the transition of some particles from superparamagnetic to a ferromagnetic state. These predictions are verified through the calculation in terms of Cole–Cole diagrams methods

Simultaneous surgical correction of atrial fibrillation and aortic valve replacement: immediate results after surgery

Aim — To assess the results of simultaneous surgical correction of atrial fibrillation and aortic valve replacement. Materials and Methods — The retrospective analysis was held for the period of 2009-2016 of patients with atrial fibrillation (AF) and pathology of the aortic valve after combined operations. 68 patients were included in the study, the average age was 56 (51; 64) years; men 53%, women 47%. All patients were in III-IV functional class by NYHA classification. The duration of AF was 34 (24; 58) months. AF: persistent in 70,6%, paroxysmal in 29,4%. Calculated risks comprised: Euro Score II – 3,8 (2,4; 5,6), the risk of in-hospital mortality and the risk of total mortality by Ambler - 5,5 (3; 7,3) and 8 (6; 9), respectively. Results ― The average number of simultaneous procedures per one patient was – 4 (4; 4), minimum – 3, maximum – 5. In 100% cases was performed aortic valve and mitral valve correction and Maze IIIB procedure. CABG was performed in 20,6% of cases and tricuspid valve repair was performed in 67,6%. The total duration of operations was 6.3 ± 1.4 hours, the time of CPB: 208 (168; 224) min, aortic clamping time: 126 (119; 151) min. In-hospital mortality was 4.4%. The main non-lethal complications in the early postoperative period were heart failure, respiratory and renal insufficience, hemorrhage and transient neurological disorder. Conclusions ― There are few data demonstrating experience in performing of such complex surgical cases due to the severity of patients and small number of institutions having such experience. In our series of hospital mortality observations correlated with the calculated and accounted for 4.4%, which is an acceptable result in this group of patients