Quantitative plane-resolved crystal growth and dissolution kinetics by coupling in situ optical microscopy and diffusion models : the case of salicylic acid in aqueous solution

The growth and dissolution kinetics of salicylic acid crystals are investigated in situ by focusing on individual microscale crystals. From a combination of optical microscopy and finite element method (FEM) modeling, it was possible to obtain a detailed quantitative picture of dissolution and growth dynamics for individual crystal faces. The approach uses real-time in situ growth and dissolution data (crystal size and shape as a function of time) to parametrize a FEM model incorporating surface kinetics and bulk to surface diffusion, from which concentration distributions and fluxes are obtained directly. It was found that the (001) face showed strong mass transport (diffusion) controlled behavior with an average surface concentration close to the solubility value during growth and dissolution over a wide range of bulk saturation levels. The (1̅10) and (110) faces exhibited mixed mass transport/surface controlled behavior, but with a strong diffusive component. As crystals became relatively large, they tended to exhibit peculiar hollow structures in the end (001) face, observed by interferometry and optical microscopy. Such features have been reported in a number of crystals, but there has not been a satisfactory explanation for their origin. The mass transport simulations indicate that there is a large difference in flux across the crystal surface, with high values at the edge of the (001) face compared to the center, and this flux has to be redistributed across the (001) surface. As the crystal grows, the redistribution process evidently can not be maintained so that the edges grow at the expense of the center, ultimately creating high index internal structures. At later times, we postulate that these high energy faces, starved of material from solution, dissolve and the extra flux of salicylic acid causes the voids to close

Carbon dioxide fluxes increase from day to night across European streams

Globally, inland waters emit over 2 Pg of carbon per year as carbon dioxide, of which the majority originates from streams and rivers. Despite the global significance of fluvial carbon dioxide emissions, little is known about their diel dynamics. Here we present a large-scale assessment of day- and night-time carbon dioxide fluxes at the water-air interface across 34 European streams. We directly measured fluxes four times between October 2016 and July 2017 using drifting chambers. Median fluxes are 1.4 and 2.1 mmol m−2 h−1 at midday and midnight, respectively, with night fluxes exceeding those during the day by 39%. We attribute diel carbon dioxide flux variability mainly to changes in the water partial pressure of carbon dioxide. However, no consistent drivers could be identified across sites. Our findings highlight widespread day-night changes in fluvial carbon dioxide fluxes and suggest that the time of day greatly influences measured carbon dioxide fluxes across European streams

Cardiac surgery - present and future. comparison European cardiac surgery register and cardiac surgical practice in university cardiac surgery - Varna

With presented study we intend to compare cardiac surgical practice in Varna - Bulgaria with data presented by First Adult Cardiac Surgery Database Report 2003 (FACSDR 2003), which is representative for European cardiac surgical practice. Ten months results of University Cardiac Surgery Department - Varna were used. Demographic profile, type of the operation, hospital stay and mortality were studied and compared. All selected parameters were comparable with those from FACSDR 2003. Major tendencies of modern cardiac surgery were summarized and extrapolated to Bulgarian population. The grounds for national cardiac surgical registry in Bulgaria were stated

Late potentials in patients with different models of left ventricular hypertrophy and isolated diastolic dysfunction after aortic valve replacement

Background: Left ventricular hypertrophy is an independent predictive factor of cardiovascular mortality. It is associated with complex ventricular arrhythmias. Patients with aortic valve stenosis have higher incidence of sudden cardiac death. The presence of late ventricular potentials (LVP) detected with signal averaged electrocardiography (SAECG) represents an arrhythmia substrate in the myocardium and is a strong predictor for malignant ventricular arrhythmias.Aim: The aim of the study was to identify factors determining the occurrence of LVP in patients after aortic valve replacement (AVR), paying particular attention to LVH pattern and LV diastolic function. Method and groups: We studied 39 patients after aortic valve replacement (27 women and 12 men; age 65.95 ±7.87 years) with normal ejection fraction and without ischemic heart disease. They were divided according to left ventricular mass index and relative wall thickness in three groups: eccentric LV hypertrophy (group 1), concentric remodeled ventricle (group 2), concentric hypertrophy (group 3).Additionally three other groups were formed according to the severity of the LV diastolic dysfunction: impaired relaxation (group A), pseudonormalization (group B) and restriction (group 3). M-mode, B-mode echocardiography, Doppler echocardiography, 24 h. Holter ECG and SAECG were performed. Late potentials were present when at least two criteria in SAECG were positive.Results: The incidence of LVP in group 1 was 33.3% and in group 3 - 30%. These were the groups with LVMI > 125 g/m2. In group 2 (LVMI < 125 g/m2), the incidence of LVP was 18.2%. We found significant differences in LAS 40 between group 1 and 2 (ð = 0.028), and between group 1 and 3 (ð = 0.026). We discovered significant negative correlations between LAS 40 and the diameter of the ascending aorta (r = -0.507, p=0.023), RMS 40 and IVRT (r =-0.470, p=0.012). There were no correlations between the components of the late ventricular potentials and preoperatively measured peak and mean transaortic pressure gradients.Conclusions: The incidence of late potentials is higher in patients with left ventricular hyper trophy and impaired LV relaxation. The concentric LVH probably carries higher SCD risk. The ventricular arrhythmias risk does not correlate with the stenos is grade but depends on the severity and the pattern of left ventricular hyper trophy