Kinetics Of Adjustment Research Articles

Small-Scale Phenomena in Reactive Bubbly Flows: Experiments, Numerical Modeling, and Applications.

Improving the yield and selectivity of chemical reactions is one of the challenging tasks in paving the way for a more sustainable and climate-friendly economy. For the industrially highly relevant gas-liquid reactions, this can be achieved by tailoring the timescales of mixing to the requirements of the reaction. Although this has long been known for idealized reactors and time- and space-averaged processes, considerable progress has been made recently on the influence of local mixing processes. This progress has become possible through joint research between chemists, mathematicians, and engineers. We present the reaction systems with adjustable kinetics that have been developed, which are easy to handle and analyze. We show examples of how the selectivity of competitive-consecutive reactions can be controlled via local bubble wake structures. This is demonstrated for Taylor bubbles and bubbly flows under technical conditions. Highly resolvednumerical simulations confirm the importance of the bubble wake structure for the performance of a particular chemical reaction and indicate tremendous potential for future process improvements.

Determination of shelf life of gilthead seabream (Sparus aurata) with time temperature indicators

Gilthead seabream was stored in a refrigerator at 3.8 °C (group C), iced (IO), or iced and covered with paper (IFT) for 18 days, and sensory attributes, chemical (TVB-N value, TMA-N value, Ammonia content, and TBA value) and microbial quality (mesophiles and psychrophiles) was measured. Time–temperature indicators (TTI) with adjustable kinetics were stored with the samples. The sensory shelf-life was measured as 12 days for IO and IFT treatments, and less than 9 days for group C. Mesophilic and psychrophilic counts exceeded permitted limits at day 6 for group C, 9 for groups IO and IFT. TTI activated for 11–15 s correctly predicted the end-of-shelf life based on quality indices. It was revealed that TTIs was a useful and practice tool to detect the quality assurance especially for the consumers. Practical applications TTIs can be used to monitor the changes in quality parameters of fish samples by the consumers in daily life. The study revealed that TTIs could be attached into packaging material, so they give the knowledge on the remaining shelf life of highly perishable fish material easily.

Разработка специальных тампонажных составов с регулируемой кинетикой расширения

Разработка специальных тампонажных составов с регулируемой кинетикой расширения

Adjustable kinetics in heterogeneous photocatalysis demonstrating the relevance of electrostatic interactions

The performance of a photocatalyst depends on a complicated correlation of a multitude of parameters including extrinsic ones. Among, the pH value is probably the most important parameter. Gaining a detailed knowledge of the underlying processes still represents a major challenge but is required to optimize known or to develop efficient novel photocatalysts. Here, we present a favorable model system comprising nano-β-SnWO4 as the photocatalyst and azo-dyes in different charge states. Disentangling parameters, we demonstrate that the reaction order of our exemplary photocatalytic degradation reaction can be fully tuned from first over zero- to mixed-order by simply adjusting the pH. Thereby we elucidate the importance of electrostatic interactions which are of significance to various aspects including: the decomposition of non-charged persistent pollutants, the inactivation of bacteria as well as the influence of electrolyte containing media, the polarity of the solvent or of specific crystal facets. Based on our results, we suggest taking the electric double layer on the photocatalyst into account. This multi-component view reconciles reported contradictions and allows interpreting results that have been intriguing or misunderstood so far.

Progressive recruitment of muscle fibers is not necessary for the slow component of V̇o2kinetics

The "slow component" of O2 uptake (VO2) kinetics during constant-load heavy-intensity exercise is traditionally thought to derive from a progressive recruitment of muscle fibers. In this study, which represents a reanalysis of data taken from a previous study by our group (Grassi B, Hogan MC, Greenhaff PL, Hamann JJ, Kelley KM, Aschenbach WG, Constantin-Teodosiu D, Gladden LB. J Physiol 538: 195-207, 2002) we evaluated the presence of a slow component-like response in the isolated dog gastrocnemius in situ (n=6) during 4 min of contractions at approximately 60-70% of peak VO2. In this preparation all muscle fibers are maximally activated by electrical stimulation from the beginning of the contraction period, and no progressive recruitment of fibers is possible. Muscle VO2 was calculated as blood flow multiplied by arteriovenous O2 content difference. The muscle fatigued (force decreased by approximately 20-25%) during contractions. Kinetics of adjustment were evaluated for 1) VO2, uncorrected for force development; 2) VO2 normalized for peak force; 3) VO2 normalized for force-time integral. A slow component-like response, described in only one muscle out of six when uncorrected VO2 was considered, was observed in all muscles when VO2/peak force and VO2/force-time were considered. The amplitude of the slow component-like response, expressed as a fraction of the total response, was higher for VO2/peak force (0.18+/-0.06, means+/-SE) and for VO2/force-time (0.22+/-0.05) compared with uncorrected VO2 (0.04+/-0.04). A progressive recruitment of muscle fibers may not be necessary for the development of the slow component of VO2 kinetics, which may be caused by the metabolic factors that induce muscle fatigue and, as a consequence, reduce the efficiency of muscle contractions.

Comparison of oxygen uptake kinetics during knee extension and cycle exercise

The knee extension exercise (KE) model engenders different muscle and fiber recruitment patterns, blood flow, and energetic responses compared with conventional cycle ergometry (CE). This investigation had two aims: 1) to test the hypothesis that upright two-leg KE and CE in the same subjects would yield fundamentally different pulmonary O(2) uptake (pVo(2)) kinetics and 2) to characterize the muscle blood flow, muscle Vo(2) (mVo(2)), and pVo(2) kinetics during KE to investigate the rate-limiting factor(s) of pVo(2) on kinetics and muscle energetics and their mechanistic bases after the onset of heavy exercise. Six subjects performed KE and CE transitions from unloaded to moderate [< ventilatory threshold (VT)] and heavy (>VT) exercise. In addition to pVo(2) during CE and KE, simultaneous pulsed and echo Doppler methods, combined with blood sampling from the femoral vein, were used to quantify the precise temporal profiles of femoral artery blood flow (LBF) and mVo(2) at the onset of KE. First, the gain (amplitude/work rate) of the primary component of pVo(2) for both moderate and heavy exercise was higher during KE ( approximately 12 ml.W(-1).min(-1)) compared with CE ( approximately 10), but the time constants for the primary component did not differ. Furthermore, the mean response time (MRT) and the contribution of the slow component to the overall response for heavy KE were significantly greater than for CE. Second, the time constant for the primary component of mVo(2) during heavy KE [25.8 +/- 9.0 s (SD)] was not significantly different from that of the phase II pVo(2). Moreover, the slow component of pVo(2) evident for the heavy KE reflected the gradual increase in mVo(2). The initial LBF kinetics after onset of KE were significantly faster than the phase II pVo(2) kinetics (moderate: time constant LBF = 8.0 +/- 3.5 s, pVo(2) = 32.7 +/- 5.6 s, P < 0.05; heavy: LBF = 9.7 +/- 2.0 s, pVo(2) = 29.9 +/- 7.9 s, P < 0.05). The MRT of LBF was also significantly faster than that of pVo(2). These data demonstrate that the energetics (as gain) for KE are greater than for CE, but the kinetics of adjustment (as time constant for the primary component) are similar. Furthermore, the kinetics of muscle blood flow during KE are faster than those of pVo(2), consistent with an intramuscular limitation to Vo(2) kinetics, i.e., a microvascular O(2) delivery-to-O(2) requirement mismatch or oxidative enzyme inertia.

Catalytic Enzyme Activity Concentration in Plasma of Man, Sheep, Dog, Cat, Rabbit, Guinea Pig, Rat and Mouse. Approach to a Quantitative Diagnostic Enzymology. I. Communication

For the most convenient laboratory animals in experimental medicine such as the sheep, dog, cat, rabbit, guinea pig, rat and mouse, the catalytic concentrations of seventeen enzymes and the protein and albumin concentrations in plasma were determined. The corresponding data for man were taken from the literature. The experimental conditions were selected so as to minimize the influence on catalytic activity, variance and statistical distribution pattern of such factors as handling procedures, the choice of blood drawing technique, the choice of anaesthetic agent for distinct species and the preparation procedure of plasma from the blood specimen. Because these considerations have been largely neglected to date in experimental enzymology, normal values for most enzymes require revision and were in some instances established for the first time in certain species. Our use of assay conditions, which were identical for all animal species, satisfies current requirements in clinical chemistry with respect to standardization and optimization of enzyme catalytic activity concentration measurement, and allowed comparison of these enzymes. The catalytic activities established this way will be the basis for a later comparative study of their kinetics of adjustment in plasma.