Low Atmospheres Research Articles

Evaluation of Models for Spinach Respiratory Metabolism Under Low Oxygen Atmospheres

Anaerobic respiration is a major problem that causes the deterioration of fresh produce packaged under low O2 atmospheres. The problem becomes more severe and causes high losses in the packages handling at ambient conditions, especially in developing countries. In designing modified atmosphere packaging, the risk of anaerobic development greatly depends upon the accuracy of respiration rate prediction; therefore, the respiration rate model for a particular produce has to be identified. In this study, different atmospheric storage conditions in a closed system were realized to examine the adaptability of respiration rate models for spinach storage under low O2 at an expected ambient temperature of 25 °C. Six models were applied and it was found that, for aerobic conditions, the respiration rate could be described with a constant respiratory quotient by three models, viz., (a) Michaelis–Menten model without inhibition, (b) Michaelis–Menten model with uncompetitive inhibition, and (c) Langmuir adsorption model, whereas three other models, viz. (d) Michaelis–Menten model with competitive inhibition, (e) Michaelis–Menten model with noncompetitive inhibition, and (f) Michaelis–Menten with mixed inhibition could not be fitted. Among the three successful models, the Michaelis–Menten with uncompetitive inhibition was found to be the most suitable model for practical applications in developing countries where cold-chain systems are lacking. This model can be applied for the prediction of gas composition and optimize the packages, particularly to ensure the aerobic respiration.

Effect of low oxygen storage conditions on volatile emissions and anaerobic metabolite concentrations in two plum fruit cultivars

By harvest time, small amounts of acetaldehyde were accumulated in the flesh of plums, such as 0.31 mg/l for the cv. Stanley and 1.03 mg/l for the cv. Valjevka. This relative difference in concentrations remained constant throughout the whole period of storage in a regular atmosphere. The long-term effects of higher concentrations of CO<sub>2</sub> are the same as for very low oxygen concentrations; and significant amounts of ethanol accumulate in the tissue. Out of a total number of 42 different odour compounds identified in the juice, there were 11 alcohols, 6 aldehydes, 17 esters, 2 terpenes, 3 organic acids, and 1 lactone. Very low oxygen atmospheres slow down the production of esters and aldehydes, but have little effect on the production of lactones and terpenes. It was shown that a very low oxygen concentration, without much CO<sub>2</sub> (Fluctuating anaerobiosis treatment), does not encourage the production of significant amounts of ethanol and acetaldehyde in the fruit flesh, but does significantly slow the biosynthesis of aromatic volatiles.

HIGH HELIUM CONTROLLED ATMOSPHERE STORAGE DECREASES MICROBIAL GROWTH AND PRESERVES QUALITY ON FRESH-CUT MIZUNA BABY LEAVES

The industrial sector of fresh-cut or minimally fresh processed products is very competitive and it is forced to seek technological solutions in order to satisfy the consumer's demands, by offering new, safer, nutritious and high overall quality products. In the recent years, the market of oriental baby leaves, and among them mizuna (Brassica rapa var. nipposinica), has noticeably raised. However, the scientific information about their postharvest behaviour is still very scarce. The object of this work was to study the effect of non conventional high helium controlled atmosphere storage (He-CA) versus air and a low oxygen controlled atmosphere on natural microflora development and on changes in nutritional and sensory quality on fresh-cut mizuna baby leaves during 8 days at 5°C. After harvest, the raw material was air pre-cooled at 5°C, pre-washed with tap water at 5°C and disinfected by immersion in a solution at 5°C with 100 ppm NaClO. Subsequently, the mizuna was spin dried to eliminate water excess and it was placed inside 1.5 L gastight glass jars. Four different humidified CA were assayed: 20.9 kPa O 2 + 0.03 kPa CO 2 + 79 kPa N 2 (control); 1 kPa O 2 + 20 kPa CO 2 + 79 kPa N 2 ; 83 kPa He + 15 kPa CO 2 + 2 kPa O 2 ; 98 kPa He + 2 kPa O 2 . Both He-CA storage decreased 1 log cfu g -1 the total aerobic mesophilic load after 8 days at 5°C while control and low oxygen atmosphere exceeded the maximum recommended of 7 log cfu g -1 . However, the sensory quality was acceptable for consumption in all treatments. After shelf life, no differences among treatments were found in total antioxidant activity and phenolics content which preserved their initial values of 35 g eq ascorbic acid kg -1 fw and 850 mg eq clorogenic acid kg -1 fw, respectively. As main conclusion, when compared to air or low oxygen atmospheres, He-CA storage combined or not with moderate CO 2 , improved the overall quality of minimally processed mizuna baby leaves up to 8 days at 5°C.

Study on the mortality of the stored-grain insects adults in different concentrations of low oxygen.

During this research, adults of Liposcelis bostrychophila Badonnel, Oryzaephilus surinamensis (Linnaeus), Tribolium confusum Jacquelin du Val, two strains of Tribolium castaneum (Herbst) (from Zhongshan and Yiyang), Sitophilus oryzae (Linnaeus) and Sitophilus zeamais Motschulsky were first kept in various low oxygen atmospheres whose concentrations were 0%, 1% and 2% for different exposure times, then in the normal atmosphere. The data and trend of mortality changes accompanied by the low oxygen concentration and exposure time were gained after this research. Results indicate that there were obvious inter-specific differences among the test insects in the sensitivity to low oxygen atmosphere, and the sensitivity declined as follows: L. bostrychophila, O. surinamensis, T. confusum, T. castaneum, S. oryzae and S. zeamais . The insects of closely related species presented diverse responses to the low oxygen stress. Tribolium confusum and T. castaneum showed a very dissimilar sensitivity to the low oxygen atmosphere, but there was no obvious difference between S. oryzae and S. zeamais . A fast lethal effect on the adults of L. bostrychophila, O. surinamensis, T. confusum and T. castaneum was observed when exposed to 0% oxygen. At 1% and 2% oxygen atmosphere, the mortality level of T. castaneum exceeded 60% and 80%, respectively. The lethal effect of 2% was more efficient than 1% oxygen, which was the same as S. oryzae and S. zeamais at 2% oxygen atmospheres. The mortality of S. oryzae and S. zeamais at 1% and 2% oxygen concentration was higher than at 0%, and the mortality of these two insects might be higher under the condition of a small amount of oxygen. At 1% and 2% oxygen atmosphere, the growth trend of the cumulative mortality of T. confusum and T. castaneum generally conformed to the classical model of the logistic formula which indicated the response of insect pests when applying common insecticide. These results are useful to extend the control technology of stored-grain insects with low oxygen universally. Keywords : Low oxygen; Stored-grain insect; Mortality; Treatment duration

Effects of Temperature and Controlled Atmospheres on Codling Moth Metabolism

Abstract Although controlled atmosphere temperature treatments are effective in controlling codling moth, Cydia pomonella (L.), in fruit, the mechanism by which this combination treatment kills the larvae is unknown. Differential scanning calorimetry was used to determine the effects of elevated temperatures, low O2, and high CO2 on the metabolic heat rate of fifth-instar codling moths. Total ATP levels also were determined. Metabolic heat rates in air increased from 0 to 30°C and decreased above 30°C. Heat rates measured isothermally at 23°C under decreased O2 or increased CO2 were lower than those in air with the lowest in 1 kPa O2 and 1 kPa O2 + 15 kPa CO2, Continuous temperature scans from 23 to 44.5°C under low O2 and high CO2 atmospheres produced lower metabolic heat rates than scans under air. Low O2 atmospheres produced the lowest ATP levels, and high concentrations of CO2 produced the highest ATP levels. These results indicate that heat treatments under controlled atmospheres have a dramatic effect on codling moth metabolism, low O2 prevents ATP synthesis, and high CO2 prevents use of ATP.

Selective Oxidation and Reactive Wetting of 1.0 Pct Si-0.5 Pct Al and 1.5 Pct Si TRIP-Assisted Steels

The effect of oxygen partial pressure on the selective oxidation and reactive wetting behavior of 1.0 pct Si-0.5 pct Al and 1.5 pct Si TRIP-assisted steels was studied. The annealing atmosphere affected the surface chemistry and the oxide morphology, which in turn affected reactive wetting. Similar wetting results were observed for the two TRIP steel compositions with good wetting being observed at the two lower oxygen partial pressure atmospheres (220 K (–53 °C) or 223 K (–50 °C) dew point (dp) and 243 K (–30 °C) dp) with poor reactive wetting at the higher oxygen partial pressure atmosphere (278 K (+5 °C) dp). The differences in wetting were attributed to the oxide morphology. The predominant oxide morphology at the two low oxygen partial pressure atmospheres was larger, widely spaced oxide nodules. At the 278 K (+5 °C) dp, the predominant oxide morphology was smaller, more closely spaced oxide nodules. TEM analysis revealed that at the 243 K (–30 °C) dp, Fe2Al5 was able to form between oxide nodules promoting good reactive wetting. At the 278 K (+5 °C) dp, the more closely spaced nodules may have impeded the formation of Fe2Al5, thereby producing numerous bare spot defects in the zinc coating.

Acute myocardial infarction presumambly embolic, in a patient with a mechanical aortic valve: a rare cause of non atherosclerotic coronary arterial occlusion

Abstract We present a case of an acute myocardial infarction with ST segment elevation in a patient with a mechanical aortic valve prosthesis who had discontinued anticoagulant therapy. We performed a primary coronary intervention procedure, including thrombus aspiration as well as plain balloon angioplasty (low atmospheres), in order to restore coronary flow in left anterior descending artery as soon as possible. Review of the literature suggests that in such cases the diagnosis of the embolic origin of the acute coronary syndrome is assumed and can never been proved definitely. Thrombus aspiration must be included in the therapeutic strategy of these patients.

Mechanisms of formation of nitrogen-containing polycyclic aromatic compounds in low-temperature environments of planetary atmospheres: A theoretical study

Polycyclic aromatic hydrocarbons (PAHs) are believed to be responsible for the formation of organic haze layers in Titan's atmosphere, but the nature of PAHs on Titan and their formation and growth mechanisms are not well understood. Considering the high abundance of nitrogen in Titan's atmosphere, it is likely that the haze layers hold not only pure hydrocarbon PAHs but also their nitrogenated analogs, N-containing polycyclic aromatic compounds (N-PACs) with 'hetero' N atoms in aromatic rings. Laboratory studies of Titan's tholins also support the hypothesis that, together with pure PAHs and their cations, N-PACs may be the fundamental building blocks of microphysical tholin particles. In the present work, we carried out ab initio quantum chemical calculations of potential energy surfaces for various reaction mechanisms of incorporation of nitrogen atoms into aromatic rings of polycyclic aromatic compounds, which may lead to the formation of N-PACs under the low-temperature and low-pressure conditions of Titan's atmosphere. This includes mechanisms analogous to the Ethynyl Addition Mechanism (EAM) recently proposed by us for the growth of PAH by sequential C2H additions to benzene. We consider consecutive C2H and CN additions to C6H6, C6H6 + CN --> C6H5CN + H, C6HCN + C2H --> C6H4(CN)(C2H) + H, C6H5CN + CN --> C6H4(CN)2 + H, C6H4(CN)(C2H) + C2H --> 2-aza-4-ethynyl-1-naphthyl/2-aza-1-ethynyl-4-naphthyl, C6H4(CN)2 + C2H --> C6H4(CN)(NCCCH), and C6H4(CN)(NCCCH) + C2H --> 1,4-diethynylphthalazine. Although these reactions are found to be barrierless and exothermic and therefore feasible at low temperatures, the steps leading to the aza-ethynyl-naphthyl radicals, C6H4(CN)(NCCCH), and 1,4-diethynylphthalazine can give N-PACs as final products only upon their collisional or radiational stabilization. Alternatively, an N-PAC can be synthesized via the reaction of 2-methyleneaminobenzonitrile with C2H, producing 4-ethynyl-quinoline + H without an entrance barrier via a three-step sequence including C2H addition to C of CN, ring closure, and H elimination. 2-Methyleneaminobenzonitrile itself can be formed in the reaction of methyleneaminobenzene with cyano radical, C6H5(NCH2) + CN --> C6H5(NCH2)(CN) --> C6H4(NCH2)(CN) + H, which also does not have any entrance barrier. Methyleneaminobenzene can be produced through recombination of phenyl and methylene-amidogen radicals followed by collisional stabilization of the product, via the barrierless C6Hs + CH3N --> C6Hs(NCH3) --> C6H5(NCH2) + H reaction, or in the reaction of phenyl with methyleneimine, C6H5 + CH2NH --> C6Hs(NHCH3) --> C6H5(NCH2) + H. The latter would be slow at low-temperature conditions owing to the barriers of 4.5 and 2.8 kcal mol(-1) relative to the initial reactants, but feasible if the reactants possess sufficient internal energy to overcome these barriers. We anticipate that the presented mechanisms are viable to form N-PACs in hydrocarbon and nitrogen rich, low temperature atmospheres of planets and their moons such as Titan.

EFFECT OF LOW AND HIGH OXYGEN-CONTROLLED ATMOSPHERES ON ENZYMATIC BROWNING OF LITCHI FRUIT

Experiments were conducted to test the effect of low and high O2 concentration on enzymatic browning of harvested litchi fruits. Litchi fruits were kept in air (control), 5 or 60% O2 for up to 6 days at 28C and 90–95% relative humidity. Changes in pericarp browning and disease development were evaluated. Contents of anthocyanins and total phenols, activities of phenolic metabolism-associated enzymes, polyphenol oxidase (PPO), peroxidase (POD), phenylalanine ammonia lyase (PAL) and anthocyanase, membrane permeability, 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity and reducing power were also measured. Exposure of 5 or 60% O2 delayed significantly pericarp browning and reduced rot development. The inhibition of pericarp browning was associated with high contents of anthocyanins and total phenols and reduced activities of PPO, POD and anthocyanase, as well as low membrane permeability. Moreover, the enhanced beneficial effects were obtained when 5% O2 was used compared with 60% O2. However, application of controlled atmosphere at low and high oxygen levels activated PAL activity, which was related to accumulation of anthocyanins. In addition, there were higher levels of DPPH radical scavenging activity and reducing power in litchi fruits kept in low and high oxygen atmospheres, compared with the fruit kept in air. Thus, it appeared that 5% O2 was more potential to inhibit pericarp browning and extend shelf life of harvested litchi fruit. PRACTICAL APPLICATIONS Pericarp browning is the major cause of deterioration in postharvest litchi. Conventional controlled atmosphere with low O2 and high CO2 is effective in maintaining quality and extending shelf life of fruits and vegetables, including inhibition of tissue browning. Using nonconventional gas mixtures such as superatmospheric O2 also attract the interest of postharvest scientists. In this study, 5 and 60% O2-controlled atmosphere delayed significantly pericarp browning and reduced rot development. It could potentially be useful as a postharvest technology of litchi fruit for reducing or replacing the use of chemicals such as SO2 and fungicides, but it requires further investigation.

Conductive oxide thin films: Model systems for understanding and controlling surface plasmon resonance

Degeneratively doped conductive oxides represent a unique host for exploring the inter-relationship between the properties of charge carriers and their collective plasmonic response. These materials often lack interband transitions that obfuscate interpretation of spectral response in elemental metals, and unlike metals, the electronic transport properties of conductive oxides are easily tunable. This work explores the process-structure-property relationships that regulate surface plasmon resonance (SPR) in sputter deposited indium tin oxide (ITO) thin films. Film deposition conditions are used to regulate film microstructure and tune the electronic mobility to between 7 and 40 cm2 V−1 s−1. Postdeposition annealing in low oxygen partial pressure atmospheres is used to engineer the ITO defect equilibrium and modulate carrier concentrations to between 1020 and 1021 cm−3. These electronic transport properties are modulated with near independence enabling straightforward interpretation of their influence on the SPR response observed in the infrared reflectivity spectrum. Higher electronic mobilities favor narrower surface plasmon absorption bands, while higher carrier concentrations favor higher absorption band frequencies. A simple free electron model, having only electronic carrier density and electronic mobility as variables, can be used to describe ITO’s dielectric response. Calculations that combine this dielectric function and the Fresnel equations provide simulated reflectivity spectra that match experimental data with remarkable accuracy. Because these spectra use no fitting parameters and are calculated with well-studied material properties, it opens the opportunity for future design of plasmonic response in advanced material systems including degeneratively doped semiconductors, silicides, and nitrides.

On selection of milling atmosphere for production of Al–10%Ti powders

A mixture of aluminium and 10 wt-% titanium powders was attrition milled for 10 h under air, nitrogen and vacuum atmospheres; pure aluminium powders were also prepared in a like manner. Particle size distribution, morphology and microstructure of the powders were studied by laser diffraction, scanning electron microscopy (SEM) and X-ray diffraction (XRD); special attention was paid to the influence of the milling atmosphere. There were differences in powder particle size obtained from pure Al powders that were not observed for Ti containing powders, however the same homogeneous morphology and microstructure was attained for the different milling atmospheres. The effect of milled powder annealing on microstructure was studied by differential scanning calorimetry (DSC) and XRD. New phases and their crystallite size were characterised as a function of annealing temperature, milling atmosphere, and powder microhardness. In short, the studied milling atmospheres for the production of Al–10%Ti powders do not affect the properties of the obtained powders, and in general, low cost atmospheres could be used.

Growth and mycotoxin production by food spoilage fungi under high carbon dioxide and low oxygen atmospheres

The influence of high carbon dioxide and low oxygen concentrations on growth by the foodborne fungal species, Mucor plumbeus, Fusarium oxysporum, Byssochlamys fulva, Byssochlamys nivea, Penicillium commune, Penicillium roqueforti, Aspergillus flavus, Eurotium chevalieri and Xeromyces bisporus was investigated. Production of aflatoxin by A. flavus, patulin by B. nivea and roquefortine C by P. roqueforti was also studied. Fungal growth was evaluated under atmospheres consisting of 20, 40 and 60% CO 2 plus < 0.5% O 2, on two media, Czapek Yeast Extract agar and Potato Dextrose agar. Several methods for measuring fungal growth were used: colony diameter, ergosterol content, hyphal length and/or mycelium dry weight. Among the nine species, three groups were distinguished with respect to their growth responses under modified atmospheres: (i) species which did not grow in 20% CO 2 < 0.5% O 2 ( P. commune, E. chevalieri and X. bisporus); (ii) species which grew in 20% CO 2 < 0.5% O 2, but not 40% CO 2 < 0.5% O 2 ( P. roqueforti and A. flavus); (iii) species which grew in 20%, 40% and 60% CO 2 < 0.5% O 2 ( M. plumbeus, F. oxysporum, B. fulva and B. nivea). Facultatively anaerobic behaviour was observed in these last four species, which grew under the same conditions as the obligate anaerobe, Clostridium sporogenes. The production of aflatoxin, patulin, and roquefortine C was greatly reduced under all of the atmospheres tested.

Influence of Fast Path Diffusion on the Oxidation of Mn Strengthened IF Steels

During the in-line coating process of Mn-strengthened-Interstitial-Free-steels, selective oxidation under low dew-point atmospheres may result in surface oxides that are not wetted by the coating alloy. In the current study, we investigate the formation of external and internal oxides in the metal in order to characterize the influence of fast path diffusion. The short-time oxidation in the metal was carried out in a gold-image furnace and the resulting external and internal oxides were characterized through scanning-electron microscopy. An IF steel sample containing 1.5wt.% Mn was used and the effects of dew point (DP) ranging from –75 to –15oC on oxidation was investigated at 800oC by varying the PH2/PH2O ratio in the oxidizing gas. Simulations were carried out by considering the combined effect of diffusion and mass transfer represented by a system of partial differential equations. The model equations were solved using finite element method in a Multiphysics modeling software COMSOL. The experimental and simulated results were found to be in agreement, and showed that, for DP up to –30oC, gas phase mass transport of oxidant gas controls the oxidation which results in exclusively external oxide nodules distributed uniformly on the surface. At –15oC &gt; DP &gt; –30oC, the oxidation evolves as ridges along grain boundaries and the simulations indicate that this is due to solid state diffusion control and the controlling mechanism is fast path diffusion through the alloy. At this point, internal oxides also start to appear.

A crossed molecular beams study of the reaction of the ethynyl radical (C2H(X2Σ+)) with allene (H2CCCH2(X1A1))

The crossed beams reaction of ground state ethynyl radicals, C(2)H(X(2)Sigma(+)), with allene, H(2)CCCH(2)(X(1)A(1)), was conducted under single collision conditions at a collision energy of 22.0 +/- 0.4 kJ mol(-1). The center-of-mass functions were combined with earlier ab initio calculations and revealed that the reaction was barrier-less, proceeded via indirect reaction dynamics through an addition of the ethynyl radical to the terminal carbon atom of the allene molecule, and was terminated by atomic hydrogen emission via a tight exit transition state to form the ethynylallene product. The overall reaction was found to be exoergic by 93 +/- 15 kJ mol(-1). Since the reaction is barrier-less, exoergic, and all transition states involved are located below the energy level of the separated reactants, the formation of ethynylallene is predicted to take place in low temperature atmospheres of planets and their satellites such as Titan and also in cold molecular clouds via the neutral-neutral reaction of ethynyl radicals with allene. Implications to interstellar chemistry and a comparison with the chemistry of the isoelectronic cyano radical, CN(X(2)Sigma(+)), are also presented.

250 EFFECT OF LOW OXYGEN TENSION ATMOSPHERE AND MATURATION MEDIA ON IN VITRO-MATURED SWINE OOCYTES

The aim of this study was to evaluate the efficiency of a low oxygen tension atmosphere (5% CO2, 5% O2, and 90% N2) on swine oocyte maturation in chemically defined media or when supplemented with porcine follicular fluid (PFF). Briefly, oocytes were in vitro matured for 44 h in TCM-199 with 10% PFF or 0.1% PVA added, under a low oxygen tension atmosphere or a normal oxygen tension atmosphere (5% CO2 in air, approximate 20% O2). At 0 and 44 h of maturation, cumulus oophorus cells were removed. To evaluate the migration of cortical granules, oocytes were fixed, permeabilized, and incubated in 100 μg of FITC-PNA mL–1 for 30 min. Oocytes were then incubated in 10 μg mL–1 of Rnase for 30 min and in 10 μg mL–1 of propidium iodide for 10 min to verify nuclear maturation by confocal microscopy (Zeiss LSM 510 Meta). Heat shock protein 70 (HSP70) content was assessed as described in Kawarsky and King (2001 Zygote 9(3), 39–50) to verify oxidative stress. Data were analyzed by the SAS System for Windows (2000). The nonparametric ANOVA NPAR1WAY procedure was applied to evaluate nuclear maturation rate by comparing groups in pairs. Migration of cortical granules and HSP70 content were analyzed using PROC GLM (LSD test of means). The effects of treatment and manipulation were verified in all analyses. The significance level was 5%, and data were presented as means ± SEM. Results indicated that the percentage of metaphase II oocytes did not differ among groups after 44 h of maturation [PFF 5% O2 (89.16 ± 3.73a), PFF 20% O2 (86.59 ± 6a), PVA 5% O2 (79.62 ± 8.22a), and PVA 20% O2 (93 ± 5.17a)]. However, these groups were different from the 0-h group (0 ± 0b). Results for the percentage of cortical granule migration showed that 0-h oocytes (38.92 ± 2.75a) had lower migration rates compared with other groups. After 44 h of maturation, migration of the cortical granule rate of the PFF-supplemented group under a 5% O2 atmosphere (61.66 ± 3.21b) was different when compared with the PVA 20% O2 group (50.97 ± 3.48c). The other groups showed intermediate results, but without statistical differences [PFF 20% O2 (58.51 ± 2.5bc) and PVA 5% O2 (53.75 ± 3.14bc)] for the migration of cortical granules. Moreover, no difference at pixel quantification of HSP70 was observed among groups after 44 h of maturation [PFF 5% O2 (116.45 ± 40.94a), PFF 20% O2 (44.44 ± 12.66a), PVA 5% O2 (29.95 ± 7.95a), and PVA 20% O2 (58.49 ± 22.2a)], although these groups were different from the 0-h group (247.41 ± 38.59b). Although the HSP content decreased throughout in vitro maturation of swine oocytes under the low and high oxygen tension atmospheres, it can be concluded that a low oxygen tension atmosphere did not affect nuclear maturation and rates of cortical granule migration regardless of maturation media supplementation. Financial support: FAPESP (grant no. 05/01420-7).

Quality and shelf life of packaged fresh sliced mushrooms stored at two different temperatures

The sensory and microbiological quality of sliced mushrooms (Agaricus bisporus L.) packaged in films of perforated and non-perforated PVC and stored at 3 and 9ºC, was studied. The carbon dioxide and oxygen content inside the packages, colour, weight loss, sensory attributes, mesophiles, Pseudomonas, Enterobacteriaceae, aerobic and anaerobic spore formers were determined. The atmosphere generated with the perforated PVC film was similar to that of air atmosphere at 3 or 9ºC. T.he non-perforated PVC film generated inside the packages CO2 : O2 concentrations of 3.4% : 8.1% at 3ºC and CO2 : O2 concentrations of 4.5% : 0.15% at 9ºC. Browning of mushrooms was lower at 3 than at 9ºC. The quality of sliced mushrooms packaged in perforated PVC and stored at 3ºC was adequate after 9 days. However, at 9ºC, the slice deformation and brown blotches incidence were severe after 9 days. The atmosphere generated with non-perforated PVC inhibited aerobic microorganism growth compared to mushrooms packaged in perforated PVC. At 3ºC, the shelf life of mushrooms packaged in non perforated PVC was around 13 days. However, the extremely low O2 atmospheres generated at 9ºC was accompanied by off-odours and growth of anaerobic spore formers, although the appearance of sliced mushrooms was acceptable.;

Regulation of mitochondrial polarity in mouse and human oocytes: the influence of cumulus derived nitric oxide

Whether exogenous factors influenced the level of mitochondrial polarity (DeltaPsim) in the subplasmalemmal cytoplasm of the oocyte was investigated with denuded and cumulus-enclosed human and mouse oocytes between the germinal vesicle and metaphase II stage. Co-culture of denuded oocytes with cumulus masses or primary cumulus cell cultures demonstrated a 'proximity' effect with respect to the detectable level of DeltaPsim in the oocyte. The specificity and reversibility of this effect on subplasmalemmal mitochondria were shown by repeated repositioning between cellular and acellular regions, which sequentially down- or up-regulated DeltaPsim. Experimental studies with a nitric oxide (NO) donor and inhibitor of NO synthase indicate that NO produced by cumulus cells has a regulatory influence on DeltaPsim in the subplasmalemmal cytoplasm of the corresponding oocyte. Culture of denuded and cumulus-enclosed (intact) oocytes in low and high oxygen atmospheres suggests that competition between oxygen and NO at the mitochondrial level may regulate the level of DeltaPsim and maintain mitochondria homeostasis in the pre-ovulatory oocyte, with a shift to higher polarity occurring after ovulation. The role of exogenous influences on oocyte DeltaPsim is discussed with respect to the regulation of developmental processes in the oocyte and early embryo.

Parameters affecting TGO growth rate and the lifetime of TBC systems with MCrAlY‐bondcoats

AbstractIn the present work different parameters which affect the oxide growth on MCrAlY‐bondcoats have been studied, in an attempt to find a reliable way to define the critical oxide thickness to failure of an EB‐PVD thermal barrier coatings (TBC). It was found that the variation of selected parameters such as oxidation temperature, surface roughness, and bondcoat thickness certainly alters the thermally grown oxide (TGO) growth rate. However, simultaneously the morphology, composition, and/or microstructure of the oxide are changed, which can affect the critical TGO thickness to failure in a TBC system. In contrast, the variation of the oxygen partial pressure of the oxidizing atmosphere led to different TGO growth rates without significantly changing the oxide morphology and composition. Comparing the TGOs grown at different rates in the specimens exposed to high pO2 and low pO2 atmospheres, it was estimated that at failure the oxide scales in both specimens have reached a similar critical thickness.

A Far Ultraviolet Archival Study of Cataclysmic Variables. I.FUSEandHSTSTIS Spectra of the Exposed White Dwarf in Dwarf Nova Systems

We present a synthetic spectral analysis of Far Ultraviolet Spectroscopic Explorer (FUSE) and Hubble Space Telescope/Space Telescope Imaging Spectrograph (HST/STIS) spectra of 5 dwarf novae above and below the period gap during quiescence. We use our synthetic spectral code, including options for the treatment of the hydrogen quasi-molecular satellite lines (for low temperature stellar atmospheres), NLTE approximation (for high temperature stellar atmospheres), and for one system (RU Peg) we model the interstellar medium (ISM) molecular and atomic hydrogen lines. In all the systems presented here the FUV flux continuum is due to the WD. These spectra also exhibit some broad emission lines. In this work we confirm some of the previous FUV analysis results but we also present new results. For 4 systems we combine the FUSE and STIS spectra to cover a larger wavelength range and to improve the spectral fit. This work is part of our broader HST archival research program, in which we aim to provide accurate system parameters for cataclysmic variables above and below the period gap by combining FUSE and HST FUV spectra.

Transport model for a high temperature, mixed conducting CO 2 separation membrane

High temperature membranes for CO 2 separation could lead to more efficient energy conversion systems and more effective means of CO 2 capture in power plants. One concept for a membrane that can separate CO 2 at high temperatures from a gas mixture is described here. A theoretical model is presented to describe the steady state flux of CO 2 through a mixed conducting, dual-phase membrane consisting of solid oxide and molten carbonate phases. An analytical flux solution is derived for the case in which only ionic conduction is present. The limiting factor dominating the flux of CO 2 is the oxide ion conductivity. To take advantage of solid oxide materials with higher ionic conductivities, the additional presence of n-type electronic conductivity under low oxygen atmospheres is also investigated. Using numerical and perturbation techniques we show that the presence of electronic conduction will never be great enough to overwhelm the CO 2 separation mechanism.