Conditions Of Oxygen Starvation Research Articles

Sensitivity of the thermohaline circulation during the Messinian: Toward constraining the dynamics of Mediterranean deoxygenation

During the Messinian, the sensitivity of the Mediterranean Basin to ecosystem perturbation was enhanced in response to the progressive restriction of water exchange with the Atlantic Ocean. The widespread deposition of organic-rich layers (i.e. sapropel) during the Messinian testifies the perturbation of the carbon and oxygen cycles; indeed, these sediments were deposited under conditions of oxygen starvation, presumably in response to a periodic deterioration of the thermohaline circulation strength. Disentangling the causes, the effect and magnitude of the thermohaline circulation weakening during the geological past is crucial for better constraining present and near-future deoxygenation dynamics in the Mediterranean region under the current climate warming. For this purpose, we investigate a Messinian sapropel-bearing succession cropping out at Monte dei Corvi (Ancona, central Italy) with mineralogical, petrographic, micropaleontological and stable Carbon and Oxygen isotopic analyses. We show that sapropel layers were deposited in response to an increase of the sea surface buoyancy, which hampered the thermohaline circulation and thus the oxygenation of bottom water, in turn affecting the bioturbating organisms. Within the lithological cycle, the recovery of an efficient thermohaline circulation is recorded by thin packstone layers underlying the marly limestone/marlstone, which record intense bottom currents. The marly limestone/marlstone accumulated during periods of intense primary productivity and organic carbon export to the sea bottom, which promoted bottom hypoxia but not organic matter preservation. We infer that these lithological changes resulted from variations in the Adriatic Deep Water formation system, controlled by precession-driven climatic and oceanographic changes.By integrating previously published Sea Surface Temperature (SST) with new isotopic and mineralogical data, we show that variations in Sea Surface Salinity (SSS) were the leading factor controlling sapropel deposition, minimizing the role of primary productivity. The SSTs characterizing the sapropel deposits are close to the range of those projected in the Eastern Mediterranean at the end of this century under climate warming. In this scenario, future warming will be coupled with SSS increase, which will counteract the density loss provided by temperature, making the bottom deoxygenation in the Eastern Mediterranean abysses unlikely. However, additional forcing, such as winter heat waves and eutrophication, could contribute to negatively affecting the Mediterranean oxygen balance and should be considered in model-based projections.

Experimental and modelling results of the QUENCH-18 bundle experiment on air ingress, cladding melting and aerosol release

The primary aims of the QUENCH-18 bundle test were to examine the oxidation of M5® claddings in air/steam mixture following a limited pre-oxidation in steam, and to achieve a long period of oxygen and steam starvations to promote interaction with the nitrogen. Additionally, the QUENCH-18 experiment investigated the effects of the presence of two Ag-In-Cd control rods, and two pressurized unheated rod simulators (6 MPa, He). The twenty low-pressurized heater rods (0.23 MPa, similar to the system pressure) were Kr-filled. In a first transient, the bundle was heated in an atmosphere of flowing argon and superheated steam by electrical power increase to the peak cladding temperature of 1400 K. During this heat-up, claddings of the two pressurized rods were burst at temperature of 1045 K. The attainment of 1400 K marked the start of the pre-oxidation stage to achieve a maximum cladding oxide layer thickness of about 80 µm. In the air ingress stage, the steam and argon flows were reduced, and air was injected. The first Ag-In-Cd aerosol release was registered at 1350 K and was dominated by Cd bearing aerosols. Later in the transient, a significant release of Ag was observed. A strong temperature escalation started in the middle of the air ingress stage. During the air ingress stage, a period of oxygen starvation occurred, which was followed by almost complete steam consumption and partial consumption of the nitrogen indicating formation of zirconium nitrides under oxygen starvation conditions. The temperatures continued to increase and stabilized at the melting temperature of Zr bearing materials until water injection. Almost immediately after the start of reflood there was a temperature excursion, leading to maximum measured temperatures of about 2430 K. Final quench was achieved after about 800 s. A significant quantity of hydrogen was generated during the reflood (238 g). Nitrogen release (>54 g) due to re-oxidation of nitrides was also registered. Residual zirconium nitrides were observed in the bundle middle. The metallographic investigations of the bundle show strong cladding oxidation and Zr melt formation. The Zr melt relocated downwards to the lower bundle part was strongly oxidized. Partially oxidized Zr-bearing melt was found down to elevation 160 mm; this elevation was the lowest with evidence of relocated pellet material. At the bundle bottom, only frozen metallic melt containing Zr, Ag, In and Cd was observed between several rods. The experiment exhibited a multiplicity of phenomena for which the data will be invaluable for code assessment and for indicating the direction of model improvements. Example of code application with SCDAPSim is given at the end of this paper.

Measurements of the impact of carbon monoxide on the performance of passive autocatalytic recombiners at containment-typical conditions in the THAI facility

Passive autocatalytic recombiners (PARs) have become one of the primary measures to mitigate the hydrogen risk for severe accidents in current and advanced water-cooled nuclear power plants (NPPs). The pgm (platinum group metals) coating of the catalyst inside the PAR is capable to oxidize hydrogen into water vapor as well as to convert carbon monoxide into carbon dioxide. The optimal efficiency of conversion requires a significant surplus of oxygen compared to the stoichiometric oxidization.A test series under containment typical boundary conditions was performed in the THAI facility (Thermal-hydraulics, Hydrogen, Aerosols and Iodine) to investigate the PAR performance under the presence of carbon monoxide. Ratios of injection mass flow rates of hydrogen and carbon monoxide into the test facility are investigated between 4:1 and 7:1, based on hypothetical release of CO by the molten core concrete interaction (MCCI). The findings are related to database on PAR performance carried out in previous OECD/NEA projects, THAI (2007–2009), THAI-2 (2011–2014), and THAI-3 (2016–2019). Special emphasis is placed on the investigation of the PAR under conditions of oxygen starvation, taking also into account a potential PAR poisoning by carbon monoxide, and under potential PAR induced ignitions at elevated hydrogen and carbon monoxide concentrations.

PATHOGENIC ASPECTS OF FUNCTIONAL DISORDERS OF THE URINARY SYSTEM IN TERM NEONATES WITH PATHOLOGY OF EARLY NEONATAL PERIOD

Introduction. Formation of the majority of disease conditions in childhood and adulthood is associated with prolongation of pathological processes occurring in the periods of antenatal development and neonatal period. The main damaging factor in the development of disadaptation syndrome in neonates is hypoxia. Increase of knowledge concerning pathogenic links of post-hypoxic damage of the kidneys in the context of the body integrity is rather topical. Objective: to determine pathogenic links promoting formation of functional disorders of the urinary system condition in term neonates with pathology of early neonatal period. Materials and methods. Clinical-paraclinical examination of 80 term neonates has been carried out. The infants divided into four groups depending on the severity degree of disorders of the somatic and neurologic status and renal dysfunction. We used factor analysis of correlation dependences between the main markers of renal dysfunction was applied using the method of principal components in case of a turn of the primary varimax row by means of Statistica Program. Laboratory methods of examination included detection of the levels of creatinine, urea, potassium, sodium in the blood serum and urine; the level of cystatin C in the blood serum with calculation of glomerular filtration rate by creatinine and cystatin C; neutrophil gelatinase-associated lipocalin, total protein, albumin, immunoglobulin G, α1-microglobulin, β2- microglobulin in urine. Examination of infants included also detection of indices of the pro-oxidant system (intensity of oxidative modification of proteins in the blood, malonic dialdehyde in erythrocytes and urine), and antioxidant defense system (ceruloplasmin, HS-groups in plasma, catalase, glucose-S-transferase and γ-glutamyl trasnferase in plasma, glutathione reductase and glucose-6-phosphate dehydrogenase in erythrocytes. Activity of enzymes in urine was investigated and their ratio to the level of creatinine in urine (cholinesterase, aspartate aminopeptidase, alanine aminopeptidase, alkaline phosphatase, lactate dehydrogenase, γ-glutamyl transpeptidase. Results and discussion. By means of Kettel method with detection of «Screen plot» criterion it determined six major factors which are important in understanding the character of correlation dependences between the indices involving 63.3% of general dispersion. Complex interrelated mechanisms of equilibrium disorders between stress-induced and stress-limited systems were found to be in the basis of formation of renal dysfunction in term neonates with disadaptation syndrome. At the same time, under conditions of moderate oxygen starvation activation of defense mechanisms of the body is detected, their action is directed to stabilization of hemodynamic and neuro-endocrine mechanisms, activation of metabolic processes promoting maintenance of the stability of the major vital functions including those of the urinary system. Severe hypoxia is associated with deep metabolic disorders with exhaustion of energy and plastic cellular pool and development of pathologic oxidative stress resulting in to destruction of anatomical integrity of the glomerular and tubular renal apparatus, damage of the cellular structures of the kidney epithelium. Considering the conception of the body «integrity» considerable disorders of the functional state of the main excretory organ are associated with further development of endogenous intoxication syndrome and accumulation of final metabolic products, which intensifies the consequences of porthypoxia lesion with the formation of syndrome of multiple organ failure. Conclusions. Conditions of oxygen starvation together with initiation of reaction of pathologic delivery oxidative stress result in deep disorders of interrelations between pro-oxidant and anti-oxidant components, imbalance of ionic homeostasis, changes of metabolic equilibrium with disorders of energy and plastic supply of the cellular functions, further initiation of the processes of apoptosis and/or necrosis. These stipulate organic changes of the renal structural elements and loss of their functional activity with disorders of the mechanisms of glomerular filtration, tubular reabsorption and secretion against the ground of pathological changes of the renal hemodynamics and imbalance of hormonal homeostasis. Understanding of the main pathogenic links of renal dysfunction formation in neonates of the first week of their life can enable to improve the ways of therapeutic correction directed to the elimination of pathological signs and prevention of complications in future.

A discrete Fourier transform-based fuel concentration and permeation sensing scheme for low temperature fuel cells

Due to the fuel permeation phenomenon, fuel cells of low temperature suffer limitations in power density and energy density. It is especially crucial to a direct methanol fuel cell. Controlling the fuel concentration within an appropriate range thus becomes significant. This paper proposes a practical sensing scheme to estimate the methanol concentration and permeation fluxes. It can also serve as a gas sensor to measure the oxygen concentration as well. By acquiring the transient response of the open-circuit voltage under oxygen starvation conditions, a measurement index is derived via the Discrete Fourier Transform (DFT) and thereby performs the estimation. The approach takes only 3s to sample the transient open-circuit voltages, while a root mean square error of the estimated methanol concentration is 1.4% relative to the maximum measurement magnitude of 2.5M. It is also validated for a wide range of oxygen concentration in the illustrative examples. There is no strict requirement for the data acquisition unit. A sampling frequency of 5Hz is enough, and this enhances its feasibility and reduces its cost. Based on the pre-established data, it makes the estimation of methanol permeation fluxes portable without carrying delicate equipments. Finally, an area-oriented index deduced from the zero-frequency term of the DFT serves as an alternative measurement basis that provides more pathways to evaluate the sensing results. The notion proposed in this paper is not only suggested for small portable fuel cells. It possesses potential for developing other kinds of electrochemical sensors as well.

The protective role of a hypothalamic proline-rich peptide during acute intoxication of rats by carbon dioxide in combination with oxygen starvation

We measured the contents of NADPH oxidases (Nox) in the membranes of erythrocytes, spleen cells, bone marrow cells, nuclei from spleen cells, and blood serum of rats that were subjected to action of carbon dioxide under conditions of oxygen starvation. We found that some increase in Nox content during intoxication with CO2 correlates with an increase in the superoxide-producing activity of Nox. Intraperitoneal administration of the synthetic analogue of the proline-rich peptide, which was previously extracted from neurosecretory granules of the hypothalamus and is referred to as galarmin, 1 hour before the treatment with CO2 resulted in a further increase in the content and superoxide-producing activity of Nox. The methemoglobin-reducing activity of Nox, which was decreased due to CO2 intoxication, increased in the presence of galarmin. We also found that considerable changes in the activities of superoxide dismutase and catalase in the cytosol of erythrocytes and the cells of rat spleen, which were induced by CO2, were reverted by galarmin, which returned these activities almost to their norm. The data we obtained suggest that galarmin may have a protective effect during CO2 intoxication under conditions of oxygen starvation.

Isolation of male strains of the aquatic Phycomycete Allomyces macrogynus

Treatment of gametophytic or sporophytic thalli of the aquatic Phycomycete Allomyces macrogynus with acridine compounds (acriflavin, acriflavin hydrochloride, ethidium bromide, acridine orange) results in gametophytic thalli which are predominantly male in phenotype (95–99% male). When the male gametes of these acridine-treated strains are crossed to wild-type female gametes or the reciprocal cross is made, using female gametes from the predominantly male strains, there is no segregation of the predominantly male phenotype among the F1 gametophytes. The acridine-induced male strains are able to grow and differentiate under conditions of oxygen starvation. It is suggested that the extreme male phenotype of acridine-treated strains mimic the wild-type male by an induced mitochondrial disfunction through the specific action of the dyes used.

The Escherichia coli yhjA gene, encoding a predicted cytochrome c peroxidase, is regulated by FNR and OxyR

The Escherichia coli FNR protein is an oxygen-responsive global transcription factor, and OxyR is a key regulator of the peroxide stress response. Here both FNR and OxyR are shown to regulate expression of the E. coli yhjA gene. The yhjA gene encodes a predicted cytochrome c peroxidase, a bacterial haem-containing protein involved in the peroxide stress response through its ability to convert hydrogen peroxide to water. It is shown that the yhjA gene of E. coli possesses a class II FNR site and an OxyR site upstream of the yhjA transcript start. Expression of yhjA was found to be dependent on this unusual combination of FNR and OxyR under conditions of oxygen starvation. Phenotypic analysis of the yhjA mutant revealed increased sensitivity to exogenous hydrogen peroxide and organic peroxides during growth under anaerobic conditions, consistent with the observed regulation and predicted function of the yhjA gene product.

Confirming the pinking mechanism of PVC profiles in mild climatic conditions

AbstractPinking of TiO2‐pigmented PVC can be observed for profiles exposed to the mild environmental conditions of northern European countries. In a previous paper, the pinking phenomenon was accounted for at the molecular level by the formation of polyene sequences, which are not completely photooxidatively bleached in conditions of oxygen starvation. This causation has been confirmed by exposing to visible light in a SEPAP 12.24 apparatus profiles in which pinking was produced during 4 year‐weathering in N.W. France. The fast phototransformations in visible light of chloropolyenes in trans‐configurations leading to α‐chloropolyenes in cis‐configurations accounts for the conversion of pinking into limited graying. It appears that the first and more intense graying observed after the initial exposure to UV and visible light of profiles in the SEPAP 12.24 can be essentially attributed to the photoreduction products of lead stabilizers. Graying could be bleached through thermooxidation at 65°C, could not be converted into pinking, and has no environmental relevance.

Growth and structure control of HfO2−x films with cubic and tetragonal structures obtained by ion beam assisted deposition

Hafnium oxide films were grown by ion beam assisted deposition on water-cooled Si (100) substrates, under conditions of oxygen starvation, using hafnium vapor and an oxygen ion beam. The transport ratio (TR), i.e., the ratio between the arrival rate of hafnium to that of oxygen, was varied between 0.5 and 10, and ion energy was varied between 1 and 20 keV. The films were analyzed using x-ray diffraction and x-ray photoelectron spectroscopy. Films having the CaF2 cubic structure with a lattice parameter of about 0.512 nm were repeatedly obtained. In addition, at 20 keV ion energy and TR values of 4 and above, films with a tetragonal structure were obtained. The latter structure, believed to be a distortion of the cubic structure, has a c/a ratio of 1.01 and its space group is considered to be different from the high temperature tetragonal HfO2 structure. The new tetragonal structure also presents high Knoop hardness, with values between 15 and 25 GPa. Substrate rotation speed was found to affect the structure and the orientation of the films. All films exhibit a stoichiometry in the vicinity of HfO1.6, with the tetragonal films apparently being Hf2O3. These structures are attributed to a very fast cooling rate during film formation. Films deposited without substrate water cooling, or with substrate heating up to 500 °C contain a large component of the monoclinic phase. The new cubic and tetragonal structures are stable at room temperature and upon annealing up to 450 °C in vacuum, but convert to the monoclinic structure upon annealing at 500 °C in air, indicating that their low oxygen content is a key factor for their stability.

Towards the prediction of pinking of PVC profiles in mild climatic conditions

AbstractPinking of TiO2‐pigmented PVC can be observed for profiles exposed to the mild environmental conditions of Northern European countries. In this paper, the pinking phenomenon is accounted for at the molecular level by the formation of polyene sequences which are not completely photooxidatively bleached under conditions of oxygen starvation. Photoreduction of TiO2 to give Ti(III) species accounts for greying which cannot be converted into pinking under mild thermooxidative conditions (65°C). The polyenic sequences which account for an initial greying after brief exposure in the SEPAP 12.24 apparatus can be converted into shorter, modified polyene sequences which explain the pinking. From the basic understanding gained, a predictive test has been designed and validated by comparison with results obtained under natural exposure conditions.

Cytochrome o (cyoABCDE) and d (cydAB) oxidase gene expression in Escherichia coli is regulated by oxygen, pH, and the fnr gene product

The aerobic respiratory chain of Escherichia coli contains two terminal oxidases that catalyze the oxidation of ubiquinol-8 and the reduction of oxygen to water. They are the cytochrome o oxidase complex encoded by cyoABCDE and the cytochrome d oxidase complex encoded by cydAB. To determine how these genes are regulated in response to a variety of environmental stimuli, including oxygen, we examined their expression by using lacZ protein fusions in wild-type and fnr mutant strains of E. coli. Anaerobic growth resulted in a 140-fold repression of cyoA'-'lacZ expression relative to aerobic growth and a 3-fold increase in cydA'-'lacZ expression. Anaerobic repression of both fusions was mediated in part by the fnr gene product, as evidenced by a 30-fold derepression of cyoA'-'lacZ expression and a 4-fold derepression of cydA'-'lacZ expression in an fnr deletion strain. Supplying wild-type fnr in trans restored wild-type repression for both fusions. Fnr thus functions as an anaerobic repressor of both cyoABCDE and cydAB expression. Reduced-minus-oxidized difference spectrum analyses of cell membranes confirmed the effect of the fnr gene product on the production of cytochrome d oxidase in the cell. Based on the pattern of anaerobic cydAB expression observed, we propose the existence of a second, as yet unidentified, regulatory element that must function either to activate cydAB expression as oxygen becomes limiting or to repress cydAB expression aerobically. Whereas cytochrome o oxidase encoded by cyoABCDE appears to be produced only under oxygen-rich growth conditions, in keeping with its biochemical properties, cytochrome d oxidase is expressed moderately aerobically and is elevated yet further when oxygen becomes limiting so that the organism can cope better under oxygen starvation conditions. We also examined cyoABCDE and cydAB expression in response to growth on alternative carbon compounds and to changes in the culture medium pH and osmolarity.

Utilization of carbohydrates by Thermomonospora sp. Grown on glucose, cellobiose, and cellulose

AbstractThermomonospora sp. was grown on glucose, cellobiose, and in order to study its growth characteristics with different carbohydrate substrates and to assess the validity of some of the assumptions made in a previously proposed model for the cellulose fermentation with this microorganism. It was observed that the nitrogen and protein contents of the cells are essentially constant during the fermentation and independent of the carbon source when glucose or cellobiose are utilized. Under oxygen starvation conditions it was shown that unidentification organic compound(s) accumulate(s) in the culture broth. Culture fluorescence was shown to be an excellent variable for monitoring and control of the fermentation process. This microorganism showed a preference for crystalline cellulose (Avicel) as substrate although it grows readily on a more amorphous cellulose (Solka Floc). The production of extra cellular protein is shown to be growth related. Data were obtained confirming the decrease in the number of active adsorption sites as the cause for the decrease in the cellulose digestion rate. It is suggested that a future model should account for the time change of surface characteristics of the cellulose particles.

Effect of Metallic Coatings on Hydrogen Embrittlement and Corrosion Performance of High Strength Wires

An evaluation has been made of the relative efficiency of three hot-dipped metallic coatings, zinc (galvanising), aluminium, and a Zn–22Al–lMg alloy, as protection for drawn steel wires in chloride environments. The tests included corrosion tests with and without applied stress in neutral salt spray and in acidified salt spray contaminated with sulphide, and electrochemical measurements. It was found that in oxygenated chloride atmospheres, aluminium coatings gave more protection than zinc, but zinc was superior in conditions of oxygen starvation. In neutral chloride zinc and aluminium were equally protective against stress corrosion, but in sour chloride, aluminium was much superior to zinc, and the alloy superior to both. On stressed bare wires, it was found that the time to failure in sulphide-containing environments decreased with increase in the applied current density, this leading to greater hydrogen embrittlement.

Effect of Metallic Coatings on Hydrogen Embrittlement and Corrosion Performance of High Strength Wires

An evaluation has been made of the relative efficiency of three hot-dipped metallic coatings, zinc (galvanising), aluminium, and a Zn–22Al–lMg alloy, as protection for drawn steel wires in chloride environments. The tests included corrosion tests with and without applied stress in neutral salt spray and in acidified salt spray contaminated with sulphide, and electrochemical measurements. It was found that in oxygenated chloride atmospheres, aluminium coatings gave more protection than zinc, but zinc was superior in conditions of oxygen starvation. In neutral chloride zinc and aluminium were equally protective against stress corrosion, but in sour chloride, aluminium was much superior to zinc, and the alloy superior to both. On stressed bare wires, it was found that the time to failure in sulphide-containing environments decreased with increase in the applied current density, this leading to greater hydrogen embrittlement.

Induction of abnormal male gametes and androgenesis in the aquatic phycomycete Allomyces.

Induction of cleavage of the cytoplasm in the gametangium of a predominantly male strain of the aquatic PhycomyceteAllomyces under conditions of oxygen starvation, in the presence of dilute lactic acid, or dilute phosphate buffer, pH 7.0, resulted in multinucleate-multi-flagellate gametes. Under certain conditions the frequency for such abnormal gametes approached 70%. Phosphate buffer pH 7.0, at a concentration of 5 × 10−3-1×10−2 M and an incubation time of 90 minutes was found to be most effective in inducing multi-flagellate-multinucleate gametes. Nuclear fusion and multiple nuclear fusions were observed in these abnormal gametes as they developed into sporophytic thalli on dilute nutrient agar (YpSS/10). Multinuclear gamete development and nuclear fusion was analysed by electron microscopy. The reported observations reveal the occurrence of androgenesis from multinuclear male gametes inAllomyces.