flow stress
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The properties of unsteady open-channel turbulent flow were theoretically and experimentally investigated in a circular cross section channel with fixed sediment deposits. Velocity and turbulence distribution data were obtained using an ultrasonic velocity profiler (UVP). Different uniform flow conditions and triangular-shaped hydrographs were analysed. The hydrograph analysis revealed a dynamic wave behaviour, where the time lags of mean cross section velocity, friction velocity, discharge and flow depth were all evident. The bottom shear stress dynamic behaviour was estimated using four different approaches. Measurements of the velocity distribution in the inner region of the turbulent layer and of the Reynolds stress distribution in the turbulent flow provided the analysed data sets of the bottom shear stress. Furthermore, based on the Saint Venant equation, the bottom shear stress time behaviour was studied using both the kinematic and the dynamic flow principles. The dynamic values of the bottom shear stress were compared with those for the steady flow conditions. It is evident that bottom shear stress varies along the generated flood hydrograph and its variation is the function of the flow unsteadiness. Moreover, the kinematic flow principle is not an adequate type of approximation for presented flow conditions.
Cyanobacteria are prokaryotic organisms characterised by their complex structures and a wide range of pigments. With their ability to fix CO2, cyanobacteria are interesting for white biotechnology as cell factories to produce various high-value metabolites such as polyhydroxyalkanoates, pigments, or proteins. White biotechnology is the industrial production and processing of chemicals, materials, and energy using microorganisms. It is known that exposing cyanobacteria to low levels of stressors can induce the production of secondary metabolites. Understanding of this phenomenon, known as hormesis, can involve the strategic application of controlled stressors to enhance the production of specific metabolites. Consequently, precise measurement of cyanobacterial viability becomes crucial for process control. However, there is no established reliable and quick viability assay protocol for cyanobacteria since the task is challenging due to strong interferences of autofluorescence signals of intercellular pigments and fluorescent viability probes when flow cytometry is used. We performed the screening of selected fluorescent viability probes used frequently in bacteria viability assays. The results of our investigation demonstrated the efficacy and reliability of three widely utilised types of viability probes for the assessment of the viability of Synechocystis strains. The developed technique can be possibly utilised for the evaluation of the importance of polyhydroxyalkanoates for cyanobacterial cultures with respect to selected stressor-repeated freezing and thawing. The results indicated that the presence of polyhydroxyalkanoate granules in cyanobacterial cells could hypothetically contribute to the survival of repeated freezing and thawing.
- Klíčová slova
- Biotechnology, Cyanobacteria, Flow cytometry, Fluorescent viability probes, Stress resistance, Viability assessment,
- MeSH
- fluorescenční barviva * MeSH
- fyziologický stres * MeSH
- mikrobiální viabilita * MeSH
- polyhydroxyalkanoáty metabolismus MeSH
- průtoková cytometrie * metody MeSH
- sinice * fyziologie MeSH
- Synechocystis * fyziologie MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- fluorescenční barviva * MeSH
- polyhydroxyalkanoáty MeSH
Background Several recent studies have reported the opportunity to diagnose significant narrowing of the coronary arteries without stress testing using local flow acceleration. Purpose To define how often patients with increased coronary flow velocities at rest (≥ 0.70 m/s) have a positive exercise echocardiography test. Material and Methods A total of 150 patients scheduled for exercise echocardiography were studied using transthoracic Doppler echocardiography in order to assess coronary artery flow velocity before exercise. Pulsed wave Doppler registered blood flow velocity placed on the color signal. The maximal diastolic velocity of coronary flow was measured. Results Of participants, 16% had a velocity of more than 0.70 m/s in the left main/proximal left anterior/proximal left circumflex arteries (LM/pLAD). A significant correlation was observed between the value of the maximal velocity in LM/pLAD and the ejection fraction at the peak of exercise ( r ≈ -0.39, P < 0.0001); between the value of the maximal velocity in LM/pLAD and index of wall motion abnormalities (IWMA) at the peak of exercise ( r ≈ 0.44, P < 0.0001); and between the value of the maximal velocity in LM/pLAD and dIWMA ( r ≈ 0.41, P < 0.0001). Afterwards, severe ischemia in stress echocardiography tests was observed in this group. The average IWMA of these tests was found to be 2.3. Sixty-two angiograms were available for comparison with Doppler data. Conclusion There is a significant correlation between the value of the maximal velocity in LM/pLAD/pLCx at rest and the severity of wall motion abnormalities during exercise tests.
- Klíčová slova
- Doppler flow aliasing, Transthoracic echocardiography, coronary artery Doppler, exercise stress echo,
- MeSH
- dopplerovská echokardiografie * MeSH
- hodnocení rizik MeSH
- koronární cirkulace * MeSH
- lidé středního věku MeSH
- lidé MeSH
- odpočinek MeSH
- prediktivní hodnota testů MeSH
- zátěžová echokardiografie * MeSH
- zátěžový test * MeSH
- Check Tag
- lidé středního věku MeSH
- lidé MeSH
- mužské pohlaví MeSH
- ženské pohlaví MeSH
- Publikační typ
- časopisecké články MeSH
Considering the fact that hemodynamics plays an important role in the patency and overall performance of implanted bypass grafts, this work presents a numerical investigation of pulsatile non-Newtonian blood flow in three different patient-specific aorto-coronary bypasses. The three bypass models are distinguished from each other by the number of distal side-to-side and end-to-side anastomoses and denoted as single, double and triple bypasses. The mathematical model in the form of time-dependent nonlinear system of incompressible Navier-Stokes equations is coupled with the Carreau-Yasuda model describing the shear-thinning property of human blood and numerically solved using the principle of the SIMPLE algorithm and cell-centred finite volume method formulated for hybrid unstructured tetrahedral grids. The numerical results computed for non-Newtonian and Newtonian blood flow in the three aorto-coronary bypasses are compared and analysed with emphasis placed on the distribution of cycle-averaged wall shear stress and oscillatory shear index. As shown in this study, the non-Newtonian blood flow in all of the considered bypass models does not significantly differ from the Newtonian one. Our observations further suggest that, especially in the case of sequential grafts, the resulting flow field and shear stimulation are strongly influenced by the diameter of the vessels involved in the bypassing.
- Klíčová slova
- Carreau-Yasuda model, SIMPLE algorithm, finite volume method, hybrid grid system, patient-specific aorto-coronary bypass, pulsatile blood flow,
- MeSH
- algoritmy MeSH
- hemodynamika fyziologie MeSH
- koronární bypass metody MeSH
- koronární cévy chirurgie MeSH
- lidé MeSH
- mechanický stres MeSH
- rychlost toku krve fyziologie MeSH
- teoretické modely MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
In the presented research, conventional hot processing maps superimposed over the flow stress maps or activation energy maps are utilized to study a correlation among the efficiency of power dissipation, flow stress, and activation energy evolution in the case of Cr-Mo low-alloyed steel. All maps have been assembled on the basis of two flow curve datasets. The experimental one is the result of series of uniaxial hot compression tests. The predicted one has been calculated on the basis of the subsequent approximation procedure via a well-adapted artificial neural network. It was found that both flow stress and activation energy evolution are capable of expressing changes in the studied steel caused by the hot compression deformation. A direct association with the course of power dissipation efficiency is then evident in the case of both. The connection of the presence of instability districts to the activation energy evolution, flow stress course, and power dissipation efficiency was discussed further. Based on the obtained findings it can be stated that the activation energy processing maps represent another tool for the finding of appropriate forming conditions and can be utilized as a support feature for the conventionally-used processing maps to extend their informative ability.
- Klíčová slova
- activation energy maps, artificial neural networks, flow stress maps, processing maps,
- Publikační typ
- časopisecké články MeSH
Increasing crop productivity under optimal conditions and mitigating yield losses under stressful conditions is a major challenge in contemporary agriculture. We have recently identified an effective anti-senescence compound (MTU, [1-(2-methoxyethyl)-3-(1,2,3-thiadiazol-5yl)urea]) in in vitro studies. Here, we show that MTU delayed both age- and stress-induced senescence of wheat plants (Triticum aestivum L.) by enhancing the abundance of PSI supercomplex with LHCa antennae (PSI-LHCa) and promoting the cyclic electron flow (CEF) around PSI. We suppose that this rarely-observed phenomenon blocks the disintegration of photosynthetic apparatus and maintains its activity as was reflected by the faster growth rate of wheat in optimal conditions and under drought and heat stress. Our multiyear field trial analysis further shows that the treatment with 0.4 g ha-1 of MTU enhanced average grain yields of field-grown wheat and barley (Hordeum vulgare L.) by 5-8%. Interestingly, the analysis of gene expression and hormone profiling confirms that MTU acts without the involvement of cytokinins or other phytohormones. Moreover, MTU appears to be the only chemical reported to date to affect PSI stability and activity. Our results indicate a central role of PSI and CEF in the onset of senescence with implications in yield management at least for cereal species.
- Klíčová slova
- 1-(2-methoxyethyl)-3-(1,2,3-thiadiazol-5yl)urea, MTU, cyclic electron flow, drought stress, heat stress, photosystem I, stress tolerance, wheat,
- Publikační typ
- časopisecké články MeSH
During metastasis, cancer cells navigate through harsh conditions, including various mechanical forces in the bloodstream, highlighting the need to understand the impact of mechanical and shear stresses on cancer cells. To overcome the current methodological limitations of such research, here we present a new device that replicates similar conditions by applying shear stress on cultured cells. The device provides a less complex, easily accessible alternative to traditional fluidics while generating fluid shear stress values comparable to those in human veins and capillaries. The device allows analyses of large cell numbers in standard cell culture flasks and incubators. Using this device to explore the shear stress-induced responses of various human cell lines, we discovered a previously unknown, reversible pre-cytokinetic block occurring in cells that lose anchorage during mitosis and are kept under constant shear stress. Notably, some cancer cell lines appear to bypass this unorthodox cell-cycle block, suggesting its role as a safety checkpoint to restrict the proliferation of cancer cells in the bloodstream and their overall spreading potential. These findings provide new insights into the diverse responses of normal and cancer cells to shear stress and highlight the potential of our technology for research on circulating tumor cells and metastatic spread.
- Klíčová slova
- Circulating tumor cells, Fluid shear stress, Fluidic systems, Metastasis, Mitosis,
- MeSH
- lidé MeSH
- mechanický stres * MeSH
- mitóza * MeSH
- nádorové buněčné linie MeSH
- nádory * patologie MeSH
- pevnost ve smyku MeSH
- proliferace buněk MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
During environmental stress, the vegetative cells of the facultative pathogenic amoeba Acanthamoeba castellanii reversibly differentiate into resistant dormant stages, namely, cysts or pseudocysts. The type of resistant stage depends on the nature and duration of the stressor. Cell differentiation is accompanied by changes in morphology and cellular metabolism. Moreover, cell differentiation is also expected to be closely linked to the regulation of the cell cycle and, thus, to cellular DNA content. While the existence of the resistant stages in A. castellanii is well known, there is no consensus regarding the relationship between differentiation and cell cycle progression. In the present work, we used flow cytometry analysis to explore the changes in the DNA content during Acanthamoeba encystation and pseudocyst formation. Our results strongly indicate that A. castellanii enters encystation from the G2 phase of the cell cycle. In contrast, differentiation into pseudocysts can begin in the G1 and G2 phases. In addition, we present a phylogenetic analysis and classification of the main cell cycle regulators, namely, cyclin-dependent kinases and cyclins that are found in the genome of A. castellanii.
- Klíčová slova
- Acanthamoeba, Cell cycle, Cyclin-dependent kinase, Cysts, Pseudocysts, Synchronization,
- MeSH
- Acanthamoeba castellanii klasifikace genetika MeSH
- buněčná diferenciace genetika MeSH
- fylogeneze MeSH
- fyziologický stres genetika MeSH
- proteiny buněčného cyklu genetika MeSH
- protozoální DNA analýza MeSH
- průtoková cytometrie MeSH
- stadia vývoje genetika MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- proteiny buněčného cyklu MeSH
- protozoální DNA MeSH
This paper introduces a general concept of Eulerian reformulation of Langrangian particle tracking methods in evaluation of platelet damage and activation. It is applied to formulation of a new multistage algorithm describing the delayed activation of platelets due to excessive exposure to supra-critical stress. This new class of multistage Eulerian activation models allows for numerous extensions and generalizations, while preserving its simplicity and flexibility.
- Klíčová slova
- Activation, Blood flow, Platelet, Stress,
- MeSH
- aktivace trombocytů fyziologie MeSH
- lidé MeSH
- mechanický stres * MeSH
- modely kardiovaskulární * MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
Twenty-nine men with chronic stable angina pectoris were investigated using stress electrocardiography (ECG) and stress transthoracic echocardiography by means of transoesophageal stimulation of the left atrium. At rest and after each stimulated frequency, ECG and 2-dimensional echocardiography combined with Doppler were performed simultaneously. Fourteen patients without ischaemia at stress ECG and two patients who were subjected only to two different frequencies of stimulation were excluded from our study. Thirteen patients with ischaemic electrocardiographic response at stress, who were subjected to at least three stimulated frequencies, were evaluated. Their deceleration time of early transmitral filling was prolonged from 171 +/- 15.4 ms to 178.1 +/- 14.4 ms (P = ns) after the first stimulated frequency, to 172.8 +/- 15.1 ms after the second stimulated frequency (P = ns) and was shortened to 143.6 +/- 7.9 ms (P < 0.05) after the fastest stimulated frequency. The ratio of peak transmitral flow velocity in early diastole (E) to that during atrial contraction (A) decreased from 0.93 +/- 0.07 at rest to 0.85 +/- 0.07 (P < 0.05) after the first stimulated frequency, to 0.87 +/- 0.07 (P = ns) after the second stimulated frequency and increased to 1.13 +/- 0.08 (P < 0.05) after the fastest stimulated frequency. In patients with angina pectoris and myocardial ischaemia, the changes in the E/A ratio and deceleration time during stress are not linear and their direction depends on the moment of their evaluation. Their use for the quantitative evaluation of the diastolic function of the left ventricle is problematic.
- MeSH
- angina pectoris diagnostické zobrazování patofyziologie MeSH
- dopplerovská echokardiografie * MeSH
- dospělí MeSH
- echokardiografie * MeSH
- elektrokardiografie MeSH
- hemodynamika fyziologie MeSH
- infarkt myokardu diagnostické zobrazování patofyziologie MeSH
- ischemická choroba srdeční diagnostické zobrazování patofyziologie MeSH
- kardiostimulace umělá MeSH
- lidé středního věku MeSH
- lidé MeSH
- mitrální chlopeň diagnostické zobrazování patofyziologie MeSH
- rychlost toku krve fyziologie MeSH
- senioři MeSH
- srdeční blokáda diagnostické zobrazování patofyziologie MeSH
- Check Tag
- dospělí MeSH
- lidé středního věku MeSH
- lidé MeSH
- mužské pohlaví MeSH
- senioři MeSH
- Publikační typ
- časopisecké články MeSH
