Non-Breaking Undular Hydraulic Jump

The discusser performed a large number of experiments on undular hydraulic jumps (CHANSON 1993, 1995a). Most results were reported in CHANSON and MONTES (1995) and CHANSON (1995b, 1995c). The discusser wishes to stress several aspects of undular jump flows and he will show that the work of REINAUER and HAGER did not bring really new information

Flow Resistance in Skimming Flows and its Modelling

Dams and weirs must be equipped with adequate flood release facilities for a safe dissipation of the kinetic energy of the flow. With stepped spillway design, it is essential to predict accurately the flow resistance associated with the steps. The authors investigate the flow resistance of skimming flows and associated form losses. Recent experiments were systematically performed with channel slopes ranging from 5.7 degrees up to 55 degrees. The results provide a better understanding of the basic flow patterns and flow resistance mechanisms. They emphasise that form loss is dominant. Simple analytical models provide a reasonable order of magnitude of the pseudo-boundary shear stress and of the cavity ejection mechanism. Altogether more than 38 model studies and 4 prototype investigations (totalising more than 700 data points) are re-analysed

Hydraulic Condition for Undular Jump Formations. (Discussion)

An undular hydraulic jump is characterised a series of steady, stationary free-surface undulations developing downstream of the jump toe. During their classical experiments in the Canal de Bourgogne, Pont-aqueduc de Roquefavour and Pont-aqueduc de Crau, DARCY and BAZIN (1865) observed undular jumps with marked undulations extending over lengths of up to 150 m. While there might be recreational applications, design engineers tend to avoid undular hydraulic jump formation in natural channels because of higher required embankment heights to prevent overtopping and because of the risks of bed scour and large bed form formation (CHANSON 1995, 2000). The propagation of freesurface undulations and waves may impose additional impact loads, perturbations and vibrations on downstream canal structures : e.g., gates, locks, weirs. In one case, the occurrence of an undular jump immediately upstream of the intake perturbed the pump operation. Similarly undular tidal bores are well-known navigation disturbances. It is therefore essential to predict accurately the limiting conditions for free-surface undulations, and the writers' contribution is important

ROSA/LSTF Tests and RELAP5 Posttest Analyses for PWR Safety System Using Steam Generator Secondary-Side Depressurization against Effects of Release of Nitrogen Gas Dissolved in Accumulator Water

Two tests related to a new safety system for a pressurized water reactor were performed with the ROSA/LSTF (rig of safety assessment/large scale test facility). The tests simulated cold leg small-break loss-of-coolant accidents with 2-inch diameter break using an early steam generator (SG) secondary-side depressurization with or without release of nitrogen gas dissolved in accumulator (ACC) water. The SG depressurization was initiated by fully opening the depressurization valves in both SGs immediately after a safety injection signal. The pressure difference between the primary and SG secondary sides after the actuation of ACC system was larger in the test with the dissolved gas release than that in the test without the dissolved gas release. No core uncovery and heatup took place because of the ACC coolant injection and two-phase natural circulation. Long-term core cooling was ensured by the actuation of low-pressure injection system. The RELAP5 code predicted most of the overall trends of the major thermal-hydraulic responses after adjusting a break discharge coefficient for two-phase discharge flow under the assumption of releasing all the dissolved gas at the vessel upper plenum

Heterologous and High Production of Ergothioneine in Escherichia coli

Ergothioneine (ERG) is a histidine-derived thiol compound suggested to function as an antioxidant and cytoprotectant in humans. Therefore, experimental trials have been conducted applying ERG from mushrooms in dietary supplements and as a cosmetic additive. However, this method of producing ERG is expensive; therefore, alternative methods for ERG supply are required. Five Mycobacterium smegmatis genes, egtABCDE, have been confirmed to be responsible for ERG biosynthesis. This enabled us to develop practical fermentative ERG production by microorganisms. In this study, we carried out heterologous and high-level production of ERG in Escherichia coli using the egt genes from M. smegmatis. By high production of each of the Egt enzymes and elimination of bottlenecks in the substrate supply, we succeeded in constructing a production system that yielded 24 mg/L (104 μM) secreted ERG

Similitude and scale effects of air entrainment in hydraulic jumps

A hydraulic jump is characterised by some strong turbulence and air entrainment in the roller. New measurements were performed in two channels in which similar experiments with identical inflow Froude numbers and relative channel widths were conducted with a geometric scaling ratio of 2:1. Void fraction distributions showed the presence of an advection/diffusion shear layer in which the data followed an analytical solution of the diffusion equation for air bubbles. The data indicated some scale effects in the small channel in terms of void fraction and bubble count rate. Void fraction distributions implied comparatively greater detrainment at low Reynolds numbers yielding to lesser overall aeration of the jump roller. Dimensionless bubble count rates were significantly lower in the smaller channel especially in the mixing layer. The study is believed to be the first systematic investigation of scale effects affecting air entrainment in hydraulic jumps using an accurate air-water measurement technique

Sulfur assimilation using gaseous carbonyl sulfideby the soil fungus Trichoderma harzianum

Fungi have the capacity to assimilate a diverse range of both inorganic and organic sulfur compounds. It has been recognized that all sulfur sources taken up by fungi are in soluble forms. In this study, we present evidence that fungi can utilize gaseous carbonyl sulfide(COS) for the assimilation of a sulfur compound. We found that the filamentousfungus Trichoderma harzianum strain THIF08, which has constitutively high COS-degrading activity, was able to grow with COS as the sole sulfur source. Cultivation with 34S-labeled COS revealed that sulfur atom from COS was incorporated into intracellular metabolites such as glutathione and ergothioneine. COS degradation by strain THIF08, in which as much of the moisture derived from the agar medium as possible was removed, indicated that gaseous COS was taken up directly into the cell. Escherichia coli transformed with a COS hydrolase (COSase) gene, which is clade D of the β-class carbonic anhydrase subfamily enzyme with high specificity for COS but low activity for CO2 hydration, showed that the COSase is involved in COS assimilation. Comparison of sulfur metabolites of strain THIF08 revealed a higher relative abundance of reduced sulfur compounds under the COS-supplemented condition than the sulfate-supplemented condition, suggesting that sulfur assimilation is more energetically efficient with COS than with sulfate because there is no redox change of sulfur. Phylogenetic analysis of the genes encoding COSase, which are distributed in a wide range of fungal taxa, suggests that the common ancestor of Ascomycota, Basidiomycota, and Mucoromycota acquired COSase at about 790-670 Ma. © 2024 Iizuka et al

Development of high-throughput quantitative analytical method for l-cysteine-containing dipeptides by LC–MS/MS toward its fermentative production

l-Cysteine (Cys) is metabolically fundamental sulfur compound and important components in various cellular fac-tors. Interestingly, free-form Cys itself as a simple monomeric amino acid was recently shown to function in a novel antioxidative system (cysteine/cystine shuttle system) in Escherichia coli. However, as for Cys-containing dipeptides, the biological functions, effects, and even contents have still remained largely elusive. The potential functions should be a part of cellular redox system and important in basic and applied biology. For its progress, establishment of reli-able quantitation method is the first. However, such accurate analysis is unexpectedly difficult even in Cys, because thiol compounds convert through disulfide-exchange and air oxidation during sample preparation. Addressing this problem, in this study, thiol molecules like Cys-containing dipeptides were derivatized by using monobromobimane (thiol-specific alkylating reagent) and detected as S-bimanyl derivatives by liquid chromatography coupled to tandem mass spectrometry (LC–MS/MS). Sample separation was processed with a C18 column (2.1 mm × 150 mm, 1.7 μm) and with water-acetonitrile gradient mobile phase containing 0.1% (v/v) formic acid at flow rate of 0.25 ml/min. The mass spectrometer was operated in the multiple reaction monitoring in positive/negative mode with electrospray ionization. The derivatization could indeed avoid the unfavorable reactions, namely, developed the method reflecting their correct contents on sampling. Furthermore, the method was successfully applied to monitoring Cys-containing dipeptides in E. coli Cys producer overexpressing bacD gene. This is the first report of the quantitative analysis of Cys-containing dipeptides, which should be useful for further study of fermentative production of Cys-containing dipeptides

Gram-scale fermentative production of ergothioneine driven by overproduction of cysteine in Escherichia coli

Ergothioneine (ERG), a unique thiol compound, is suggested to function as an antioxidant and cytoprotectant. Despite several recent attempts to produce ERG using various organisms, its yield was still very low and the costs remained high. Since the level of ERG produced depends strictly on the availability of three distinct precursor amino acids (l-cysteine (Cys), l-histidine, and l-methionine (Met)), metabolic engineering for enhancement of the flux toward ERG biosynthesis is required. Herein, we took advantage of a high-Cys production system using Escherichia coli cells, in which Cys biosynthesis and excretion were activated, and applied it to the fermentative production of ERG from glucose. The Cys overproduction in E. coli cells carrying the egtBCDE genes from Mycobacterium smegmatis was effective for ERG production. Furthermore, coexpression of the egtA gene, which encodes γ-glutamylcysteine synthetase that synthesizes the γ-glutamylcysteine used as a sulfur source of ERG biosynthesis, enhanced ERG production even though E. coli intrinsically has γ-glutamylcysteine synthetase. Additionally, disruption of the metJ gene that encodes the transcriptional repressor involved in Met metabolism was effective in further increasing the production of ERG. Finally, we succeeded in the high-level production of 1.31 g/L ERG in a fed-batch culture process using a jar fermenter

Characterization of sulfur-compound metabolism underlying wax-ester fermentation in Euglena gracilis

Euglena gracilis is a microalga, which has been used as a model organism for decades. Recent technological advances have enabled mass cultivation of this species for industrial applications such as feedstock in nutritional foods and cosmetics. E. gracilis degrades its storage polysaccharide (paramylon) under hypoxic conditions for energy acquisition by an oxygen-independent process and accumulates high amount of wax-ester as a by-product. Using this sequence of reactions referred to as wax-ester fermentation, E. gracilis is studied for its application in biofuel production. Although the wax-ester production pathway is well characterized, little is known regarding the biochemical reactions underlying the main metabolic route, especially, the existence of an unknown sulfur-compound metabolism implied by the nasty odor generation accompanying the wax-ester fermentation. In this study, we show sulfur-metabolomics of E. gracilis in aerobic and hypoxic conditions, to reveal the biochemical reactions that occur during wax-ester synthesis. Our results helped us in identifying hydrogen sulfide (H2S) as the nasty odor-producing component in wax-ester fermentation. In addition, the results indicate that glutathione and protein degrades during hypoxia, whereas cysteine, methionine, and their metabolites increase in the cells. This indicates that this shift of abundance in sulfur compounds is the cause of H2S synthesis