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- 저자 : Ivan Kovač (검색결과 3 건)
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Ivan Kovač,Marko Šrajbek,Lado Kranjčević,Nikolina Novotni-Horčička 한국지질과학협의회 2020 Geosciences Journal Vol.24 No.5
The aim of this paper is to analyse the influence of a groundwater pumping rate on nitrate concentrations at the Bartolovec wellfield, which is part of a water supply system of the town of Varaždin, Croatia. Over the past 16 years both the pumping rate and nitrate concentrations have increased at the wellfield. The nonlinear models that describe the pumping rate to nitrate concentration levels were developed on the basis of Logistic, Gompertz, and Richards growth functions. For each function, three different types were established regarding the initial lower contamination limit parameter. The conditions that models have to meet were defined and their reliability was established. The models were implemented on the experimental data collected during the period under consideration. The models were validated and mutually compared using Akaike’s Information Criteria (AICc), while the data fitting was estimated by using a coefficient of determination. After the results were obtained by using different models, they were compared to the maximum allowable nitrate concentrations (MAC) in water for human consumption. The dependence of nitrate concentrations on a pumping rate was confirmed and the reliable model for nitrate concentration on pumping rate was created. The model was calibrated and tested on the experimental data. The model exhibits asymptotic behavior and result shows that with the further increase in the pumping rate of groundwater drainage at the Bartolovec wellfield, nitrate concentrations will not exceed the MAC value providing there are no new sources of contamination in the zone of a pollutant influence.
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The Relationship between Autonomic Regulation of Cardiovascular Function and Body Composition
Tomislav Smoljo,Ivan Stanić,Sara Sila,Uroš Kovačić,Luka Crnošija,Anamari Junaković,Ivan Adamec,Iva Hojsak,Magdalena Krbot Skorić,Mario Habek 대한비만학회 2020 The Korean journal of obesity Vol.29 No.3
Background: We investigated whether the results of autonomic function tests correlate with body composition and shape in healthy young people. Methods: We conducted cardiovascular reflex tests (heart rate [HR] and blood pressure [BP] responses to the Valsalva maneuver and HR response to deep breathing) and the tilt table test with 32 subjects (19 males; mean age, 22.1±1.9 years). Participants also completed an anthropometric measurement sequence (weight; height; upper arm, hips, and waist circumference; triceps and subscapular skinfold), bioelectric impedance testing, and hand grip strength measurements. Results: Markers of obesity, other anthropometric measures, functional measures, and the basal metabolic rate (BMR) were significantly positively correlated with systolic BP (SBP) and diastolic BP (DBP) in both the supine and tilted positions. There was a positive correlation between the difference in HR (ΔHR) between the tilt and supine body positions and markers of obesity, the functional marker of dominant handgrip strength, and BMR. Participants with a body mass index (BMI) <25 kg/m2 had significantly lower median values of ΔHR, DBP in the tilt-test, SBP at rest, and SBP in the tilt-test than participants who had a BMI ≥25 kg/m2 (10.55 vs. 21.95 bpm, P=0.003; 77.55 vs. 90.05 mmHg, P=0.045; 113.45 vs. 140.55 mmHg, P=0.013; 117.00 vs. 135.25 mmHg, P=0.006, respectively). Body fat percentage was identified as an independent positive predictor (β=0.993; 95% confidence interval [CI], 0.070 to 1.916; P=0.036) and body water percentage was an independent negative predictor of tilted SBP (β=–1.370; 95% CI, –2.634 to 0.106; P=0.035). Conclusion: High sympathetic activity, as evaluated by cardiovascular regulation, correlates with a high share of adipose tissue in young healthy persons.
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Carbonization of oriented poly(vinyl alcohol) fibers impregnated with potassium bisulfate
Petkieva Diana,Ozerin Alexander,Kurkin Tikhon,Golubev Eugenii,Ivan’kova Elena,Zelenetskii Alexander 한국탄소학회 2020 Carbon Letters Vol.30 No.6
The structural transformationss of oriented poly(vinyl alcohol) (PVA) fbers impregnated with potassium bisulfate (PBS) were studied in detail on the way from PVA precursor fbers till carbonized at a temperature of 1000 °C fbers. It has been shown that the impregnation of PVA fbers with a sulfur-containing compound (PBS) is an efcient technique to decrease the thermoplasticity of PVA fbers during heat treatment at high temperatures in air and argon and contributes to a high yield of coke residue after heat treatment up to 1000 °C. TMA, TGA, DSC, mass spectrometry, FTIR, Raman spectros�copy, SEM, WAXS and SAXS were used to study the structural transformations of oriented PVA fbers impregnated with PBS at the stages of their preliminary thermal stabilization (215 °C), thermal stabilization (215–400 °C) and carbonization (400–1000 °C). A reaction scheme has been proposed that fully describes carbonization chemistry in the entire studied temperature range. The processing temperature of 215 °C was found to be optimal for preliminary thermal stabilization of PVA fbers impregnated with PBS. The heat treatment in an inert medium can be recommended as the optimal for thermal stabilization of fbers impregnated with PBS. The characteristics of the carbonized PVA fbers, such as strength, modulus and electrical conductivity, were close to the characteristics of commercial cellulose-based carbon fbers yarns.
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