Low O2 Concentrations Research Articles

Decomposition of key minerals in coal gangues during combustion in O2/N2 and O2/CO2 atmospheres

Thermal decomposition characteristics of kaolinite and dolomite during combustion of coal gangues in different O2/N2 and O2/CO2 mixtures, simulating normal air and oxy-fuel combustion atmospheres, were examined using thermogravimetric analysis (TGA), with a focus on the effect of O2 and CO2 concentrations. A kaolinite-rich coal gangue and a dolomite-rich coal gangue were studied along with their low-temperature ashes prepared by oxidising the organic matter in an oxygen plasma asher thus leaving the minerals in their original form. The TGA experiments were carried out in O2/N2 and O2/CO2 atmospheres with varying O2 concentration and from room temperature to 950 °C at a heating rate of 10 °C min−1. The thermogravimetric (TG) and differential thermogravimetric (DTG) curves of these samples were examined and compared so as to reveal key thermal events and the on-set temperatures of their occurrence. The results showed that in both pyrolysis and O2/N2 atmospheres, the mass loss of the kaolinite-rich coal gangue occurred in the temperature range of 300–600 °C in one single stage, but the mass loss of the dolomite-rich coal gangue occurred at 300–730 °C in two distinct stages. In the O2/CO2 atmospheres, the mass loss of the kaolinite-rich coal gangue retained the one stage behaviour, however, the dolomite-rich coal gangue featured a three-stage mass loss event. Compared to their low-temperature ashes, the temperature range of mass loss of the kaolinite-rich coal gangue was consistent with that of its low-temperature ash in N2, O2/N2 and O2/CO2 atmospheres. The temperature range of mass loss of the dolomite-rich coal gangue in the second stage corresponded to that of the low-temperature ash in N2 and O2/N2 atmospheres and the temperature range of mass losses in the second and third stages corresponded to that of the low-temperature ash in O2/CO2 atmospheres. These observations indicate that kaolinite decomposed concurrently with the host coal gangue combustion while dolomite decomposed after the combustion. In addition, the decomposition of dolomite changed from a one-step reaction to a two-step reaction while kaolinite decomposition remained unchanged as the gas environment was changed from O2/N2 atmospheres to O2/CO2 atmospheres. When oxygen concentration increased from 2% to 21% in the O2/N2 atmosphere and 20% to 80% in the O2/CO2 atmosphere, the mass loss curves of the two coal gangues moved towards lower temperatures and the ignition temperature decreased. However, the mass loss of the kaolinite-rich coal gangue always showed a single peak characteristic regardless of the oxygen concentration while the mass loss of the dolomite-rich coal gangue was affected significantly by decreasing the O2 concentration in O2/N2 atmospheres and increasing the CO2 concentration in O2/CO2 atmospheres. This was attributed to the partial overlap of carbon combustion and dolomite decomposition in the O2/N2 atmosphere with low O2 concentrations and the suppression of dolomite decomposition in the O2/CO2 atmosphere.

Paddy rice stored under hermetic conditions: The effect of relative humidity, temperature and storage time in suppressing Sitophilus zeamais and impact on rice quality

The aim of this study was to analyse the effect of relative humidity in suppressing Sitophilus zeamais, in paddy rice stored under hermetic conditions, during four and seven months, at different average temperatures, as well as the impact on rice quality.Hermetic bags, GrainPro® SuperGrainbag® Farm™, were used to store two rice varieties under three different relative humidities: 67%, 75% and 85% RH, and average temperatures of 14 °C, 17 °C and 24 °C, both monitored by Hobo® Data loggers, with the probe placed inside the bags. CheckpointII Portable O2 and CO2 Gas Analyzer was used to assess gas contents on the top and bottom of each bag. At the end of the trials, paddy samples were collected to estimate water activity (aw). The rheology behaviour of rice pastes prepared with race flour obtained from the different treatments was also evaluated, using a controlled stress rheometer.The results showed that the response of the stored-product insects changes with environmental conditions, O2 and CO2 contents. Other parameters were considered; aw increased with relative humidity and temperature, but decreased with storage time. The relative humidity played an important role, together with the increase of temperature, in suppressing insect populations. A modified atmosphere was naturally produced inside the hermetic bag, under 85% RH, with low O2 and high CO2 contents, at different average temperatures, 14 °C and 17 °C. These results demonstrated that S. zeamais can survive, but has no progeny. Under the same conditions, but at the higher average temperature of 24 °C, S. zeamais attained 100% mortality before producing progeny.The increase on respiration rate, registered by CO2 increase and O2 decrease, for higher RH values, reduced the viscoelastic functions and changed the starch gelatinization point of Indica and Japonica rice.The results obtained showed that storing paddy hermetically, at low relative humidity, did not change atmospheric content and maintained the viscoelastic functions of the rice pastes.

Differentiation between O2 and NO2 impact on PtOx formation in a diesel oxidation catalyst

NO oxidation activity of platinum-based catalysts undergoes reversible changes during operation in oxidative atmosphere typical for Diesel engine exhaust gas due to platinum oxides (PtOx) formation and reduction. In recent years, these changes were studied mostly with the mixtures containing both O2 and NO2 so that it was difficult to quantify individual impacts of the oxidants on PtOx formation. In this paper, Pt/Al2O3 catalyst deactivation and PtOx formation with O2 and NO2 was examined separately by the means of transient isothermal experiments at 150, 175 and 200 °C with alternating deactivation and probe periods. The largest extent of deactivation was detected at 175 °C where the NO conversion in the isothermal experiment dropped from 85% (reduced catalyst) down to 10% (steady-state PtOx level) over 4 h. The experimental data were then utilized for parameter evaluation in global kinetic model of NO oxidation on a diesel oxidation catalyst extended by the reactions describing PtOx formation and reduction. Though the rate coefficient for PtOx formation with NO2 is higher than with O2, the overall PtOx formation rate and the steady-state PtOx level are higher with O2 at typical component concentrations (8% O2 or 250 ppm NO2). Similar activation energies were observed for both PtOx formation reactions. Validity of the model was verified also at lower O2 and NO2 concentrations (4% O2 or 125 ppm NO2). The developed model is thus capable of sufficiently precise prediction of catalyst deactivation at various O2 and NO2 concentrations relevant to diesel exhaust gas.

Metabolomic study of bioactive compounds in strawberries preserved under controlled atmosphere based on GC-MS and DI-ESI-QqQ-TOF-MS.

The storage of the vegetables products in a controlled atmosphere (CA) with low O2 and high CO2 concentrations, reduces respiration rates and delays the ripening process, and in some cases, improves their quality and organoleptic properties. To obtain deep insight into strawberry fruit metabolic changes caused by these CA treatments. Freshly harvested strawberries were preserved under different atmospheres enriched with 10%, 20% and 30% of CO2 , for 2days at 0°C, containing in all the cases 5% of O2 and were subjected to a metabolomic analysis based on gas chromatography-mass spectrometry (GC-MS) and direct-infusion with electrospray ionisation source equipped with triple quadrupole coupled to time of flight mass spectrometry (DI-ESI-QqQ-TOF-MS). Partial least square discriminant analysis (PLS-DA) was employed to compare the control and treated samples for the identification of altered metabolites. Several metabolites related to CA treatment could be identified by databases and literature, which are mainly sugars, organic acids and phenolic compounds (bioactive compounds). Good correlation coefficients were obtained between discriminant metabolites and fruit quality parameters. These results suggest that treated strawberries under CA could be considered as bioactive healthy compounds, suggesting that treated strawberries under CA could be used as raw material for the preparation and formulation of food supplements and nutraceutical products.

Evaluation of Oxygen Reduction System (ORS) in Large-scale Fire Tests

An oxygen reduction system (ORS) is a fire prevention system that uses a low-oxygen environment to reduce, if not eliminate, the potential for ignition and fire propagation in a protected space. The key parameter for ORS design is the limiting oxygen concentration (LOC), defined as the lowest O2 concentration that can support combustion for a given fuel. The present work examines LOCs of solid fuels at large scale in a configuration representative of a rack-storage and discusses the results in relation to the design concentration for ORS.To simulate ORS applications in engineering practice, a two-tier fuel array of standard commodities in rack storage configuration was set up in an enclosure. A constant N2/Air mixture flow was supplied to the enclosure at a desired oxygen concentration. The oxygen concentration was varied from 9% up to 17%. A premixed flame with a constant heat release rate was used as the ignition source to maintain repeatable test conditions. This premixed flame ignitor represents potential heat sources such as electric arc and hot work that are not sensitive to oxygen level. The tested materials included five standard commodities: Class 3, Cartoned Unexpanded Plastic (CUP), Cartoned Expanded Plastic (CEP), Uncartoned Unexpanded Plastic (UUP) and Uncartoned Expanded Plastic (UEP). This paper reports detailed test results at different oxygen levels only for Class 3. The impact of the test conditions on fire propagation was examined and the results showed that the oxygen concentration was the major parameter to control fire propagation. When successful flame spread is initiated by the igniter, the fire size tends to be larger as the igniter is sustained for a longer time. The results of fire propagation success were obtained for the five standard commodities under different oxygen concentrations with a sustained igniter (hard limits) and without a sustained igniter (soft limits). The LOC was defined as an oxygen concentration at 0.05 probability of flame spread by using statistical analysis. The resulting LOC values measured for different commodities in a two-tier rack storage are:• Cartoned (Class 3, CUP and CEP) – hard limit 11.1%,• Uncartoned (UUP and UEP) – hard limit 13.0%,• Cartoned (Class 3, CUP and CEP) – soft limit 13.8%,• Uncartoned (UUP and UEP) – soft limit 14.7%.These LOCs are generally lower than the oxygen design concentrations recommended by existing standards including VdS 3527 and EN 16750 due to different test conditions. The hard limits resemble fundamental LOC for gases and vapors and do not depend significantly on the ignition duration and array size, while the soft limits vary significantly with the size and configuration of the fuel array and ignition duration. It is concluded that the hard limits are more suitable for ORS design purposes.

Investigation on the RONS and bactericidal effects induced by He + O2 cold plasma jets: In open air and in an airtight chamber

He + O2 plasma jets in open air and in an airtight chamber are comparatively studied, with respect to their production of gaseous/aqueous reactive species and their antibacterial effects. Under the same discharge power, the plasma jet in open air has higher densities of gaseous reactive species and a higher concentration of aqueous H2O2 but lower concentrations of aqueous OH and O2-. In addition, the increase in the O2 ratio in He in both plasma jets causes a linear decrease in the population of gaseous reactive species, except for O(3p5P) when a small amount of O2 is added to the working gas. The concentrations of aqueous reactive species for OH and H2O2 also drop monotonically with the increase in additive O2, while the aqueous O2- first increases and then decreases. Moreover, it is interesting that the bactericidal inactivation in the airtight chamber condition is much greater than that in the open air condition regardless of the presence or absence of additive O2 in the He plasma jet. The concentration trends of O2- for both the plasma jets are similar to their antibacterial effects, and little antibacterial effect is achieved when a scavenger of O2- is used, indicating that O2- should be a main antibacterial agent. Moreover, it should not be O2- alone to achieve the antibacterial effect, and some reactive nitrogen species such as ONOO- and O2NOO- might also play an important role.

The disuse effect on canal network structure and oxygen supply in the cortical bones of rats.

In this study, based on the measurements of intracortical vascular canal structure, we investigated the disuse effect on local O2 supply in the cortical bones of growing rats. Hindlimb disuse was produced by unilateral sciatic neurectomy (SN) at 4weeks age. The canal network structures within tibial cortical bone were evaluated in 8- and 12-week-old rats undergoing SN or no treatment (control) by synchrotron radiation micro-CT. Additionally, we developed an intracortical network model by combining the imaged-based canal network with a bone matrix containing theoretical lacunar-canalicular network, and determined the distribution of O2 concentration in bone tissue numerically. In the control bone, canal network was reduced with growth, resulting in decreased blood flow and averaged O2 concentration and increased spatial heterogeneity in tissue O2 concentration. Disuse reduced the canal network, leading to a lower flow rate, lower average O2 concentration and higher heterogeneity of O2 concentrations. However, the rarefaction of the canal network with growth was smaller under the disuse condition, and accordingly, the flow rate, the average O2 concentration and the heterogeneity of O2 concentrations remained stable. In particular, although the fraction of the canal volume was smaller, the densities of canal segments and bifurcation points under disuse condition tended to be higher than those of the control bone. The heterogeneity of O2 concentration was lower. Our results indicated that the disuse may lead to more uniformity in the canal network structure and thereby uniform O2, possibly contributing to O2 supply efficiency.

Hermetic storage of dry soybean (Glycine max): creating an effective modified atmosphere using soaked grain as O 2 depletor: Poster

Hermetic storage of grains and oilseed has been proposed as a solution for reducing food losses in developing countries. However, to obtain full benefit of the hermetic storage it is required to achieve a low O2 concentration (below 2%) or high CO2 concentration (above 20%). The gas concentration inside the hermetic container is the result of the balance between the respiration and gas exchange rates with the outside (permeability and leakage). When the grain is dry, an insufficient modification in the internal atmosphere is achieved (exchange rate higher than respiration rate), allowing insect development and, hence, grain losses. This study focuses in creating an effective modified atmosphere during the hermetic storage of dry soybean using soaked grain as O2 depletor. Three big bags with internal polyethylene liners of 70 µm thickness were filled with 590 kg of soybean (Glycine max, with 12.5% m.c.) and sealed. Gas concentration evolution was measured during 15 days (basal condition). Later, four plastic perforated bottles filled with of 4.3 kg of soaked soybean (44% m.c.) were inserted in each bag. The bags were re-sealed and gas concentration was measured during 45 days. Results indicated that the soaked soybean acted as an O2 depletor, reducing the gas concentration to 1% in only 8 days, and maintained below 1% during 45 days. This research indicated that a small portion of soaked grain (0.4% dry matter (d.m.)) can be used to generate an effective modified atmosphere to prevent biological activity in the entire grain mass. This is a simple and inexpensive approach to reduce food losses under low cost hermetic storage.

Stored Grain Protection: cases studies in Portugal:

Considering the edibility of insects’ species associated with storage ecosystem, chemical control methods can be easily replaced by environmental and economically sustainable alternatives. Use of biogenerated atmospheres is an inexpensive method that tolerates insect presence. In Portugal, during one year, hermetic bags were used to store paddy under 65-75-85% relative humidity (RH) and 14-17-24oC temperatures. Brown rice infested with Sitophilus zeamais adults was placed inside the hermetic bags. Biogenerated atmosphere was naturally produced inside the hermetic bag, at 85% RH, with low O2 and high CO2 contents, showing that S. zeamais can survive but has no progeny at 14o-17oC, or attained 100% mortality before producing progeny at 24oC. The most abundant fungi isolated were Alternaria alternata and Epicoccum nigrum. The results showed the importance of the RH on changes in atmospheric gas content of paddy, due to biological agents’ activity. Analysing the edibility of insects species associated with stored grain, preliminary studies were carried out to evaluate the nutritional value of immatures stages of Tribolium castaneum. Larvae of T. castaneum had a content of 21.4% protein, 9.1% lipids, 8.8% fiber, and a relevant content of eight essential amino acids and also manganese and copper. The edibility of insects must be consider given their high nutritional value, low emissions of Green House Gases (GHGs), low requirements for land, and by reducing and mitigating the need for chemical control.

Methylation of the N-terminal histidine protects a lytic polysaccharide monooxygenase from auto-oxidative inactivation.

The catalytically crucial N-terminal histidine (His1) of fungal lytic polysaccharide monooxygenases (LPMOs) is post-translationally modified to carry a methylation. The functional role of this methylation remains unknown. We have carried out an in-depth functional comparison of two variants of a family AA9 LPMO from Thermoascus aurantiacus (TaLPMO9A), one with, and one without the methylation on His1. Various activity assays showed that the two enzyme variants are identical in terms of substrate preferences, cleavage specificities and the ability to activate molecular oxygen. During the course of this work, new functional features of TaLPMO9A were discovered, in particular the ability to cleave xyloglucan, and these features were identical for both variants. Using a variety of techniques, we further found that methylation has minimal effects on the pKa of His1, the affinity for copper and the redox potential of bound copper. The two LPMOs did, however, show clear differences in their resistance against oxidative damage. Studies with added hydrogen peroxide confirmed recent claims that low concentrations of H2 O2 boost LPMO activity, whereas excess H2 O2 leads to LPMO inactivation. The methylated variant of TaLPMO9A, produced in Aspergillus oryzae, was more resistant to excess H2 O2 and showed better process performance when using conditions that promote generation of reactive-oxygen species. LPMOs need to protect themselves from reactive oxygen species generated in their active sites and this study shows that methylation of the fully conserved N-terminal histidine provides such protection.

Effect of different oxidative stress degrees generated by hydrogen peroxide on motility and DNA fragmentation of zebrafish (Danio rerio) spermatozoa.

An increase in reactive oxygen species (ROS) or decrease in antioxidant barriers can provoke lipid peroxidation of the membranes or DNA damage of the spermatozoa. The aim of this work is to study the effect of the different degrees of oxidative stress generated by H2 O2 incubation on total motility, kinetics, and DNA fragmentation of zebrafish (Danio rerio) spermatozoa. For this process, experimental groups were incubated in 50µM (Low; L) and 200µM (High; H) H2 O2 , respectively, for 20min at 4ºC. Sperm motility parameters were obtained with a computer-assisted sperm analysis (CASA) system. Sperm DNA fragmentation (SDF) was assessed using the sperm chromatin dispersion test. Both low and high H2 O2 concentration groups showed lower motility than control groups. Progressive motility of spermatozoa incubated in the H group dropped rapidly in comparison with other groups. Regarding SDF, the control and L groups had significantly lower values than the H group (25.0% and 31.6% vs. 48.1% fragmented sperm for C, L, and H groups, respectively; p<0.05). Sperm motility, mostly progressive motility, decreased as H2 O2 concentration increased, mainly when time after sperm activation increased. SDF increased as the H2 O2 concentration increased. However, measurements of the halo area did not agree with the subjective SDF rate.

Observations of Variable Ammonia Oxidation and Nitrous Oxide Flux in a Eutrophic Estuary

Accurate global forecasting of marine nitrous oxide (N2O) emissions requires a better understanding of atmospheric N2O fluxes from coastal systems, particularly the mechanisms controlling the net balance between N2O production and consumption. The objective of this study was to examine how physical and biological processes in the eutrophic Chesapeake Bay estuary influence the temporal and spatial variability of N2O using a combination of gas measurements (N2O and N2/Ar) and stable isotope tracer incubations. Observed concentrations of N2O varied considerably in both space and time with the highest concentrations (up to 20.9 nM) across the pycnocline. Ammonia oxidation rates ranged from 14.3 to 108.9 nM h−1 and were highest following wind events that mixed oxygenated surface water below the pycnocline into ammonium-rich bottom waters, resulting in nitrite (NO2−) accumulations of up to 13 μM. During periods of weak vertical mixing, both N2O concentrations and ammonia oxidation rates were lower, while lower O2 concentrations also allowed N2O consumption by denitrification. A three-layer box model provided estimates of N2O production at the surface and across the pycnocline of 4 μmol m−2 day−1 and 21 μmol m−2 day−1, respectively, and an estimate of N2O consumption below the pycnocline of approximately −3 μmol m−2 day−1. Our results demonstrate that physical processes affect the net balance between N2O production and consumption, making Chesapeake Bay a variable source and sink for N2O.

Hypoxia‑inducible factor 1α and ROCK1 regulate proliferation and collagen synthesis in hepatic stellate cells under hypoxia

Hypoxia serves a critical role in the pathogenesis of liver fibrosis. Hypoxia‑inducible factor 1α (HIF1‑α) is induced when cells are exposed to low O2 concentrations. Recently, it has been suggested that Rho‑associated coiled‑coil‑forming kinase 1 (ROCK1) may be an important HIF1‑α regulator. In the present study, it was analyzed whether crosstalk between HIF1‑α and ROCK1 regulates cell proliferation and collagen synthesis in hepatic stellate cells (HSCs) under hypoxic conditions. For this purpose, a rat hepatic HSC line (HSC‑T6) was cultured under hypoxic or normoxic conditions, and HIF1‑α and ROCK1 expression was measured at different time points. Additionally, HSC‑T6 cells were transfected with HIF1‑α small interfering RNA (siHIF1‑α), and measured protein expression and mRNA transcript levels of α‑smooth muscle actin, collagen 1A1 and ROCK1. Collagen 3A1 secretion was also measured by ELISA. Cell proliferation was assessed by the MTT assay under these hypoxic conditions. The results indicated that a specific ROCK inhibitor, Y‑27632, increased HIF1‑α and ROCK1 expression over time in HSC‑T6 cells in response to hypoxia. In addition, knockdown of HIF1‑α inhibited HSC‑T6 proliferation, suppressed collagen1A1 expression, decreased collagen 3A1 secretion and attenuated ROCK1 expression. Notably, ROCK1 inhibition caused HSC‑T6 quiescence, suppressed collagen secretion and downregulated HIF1‑α expression. Collectively, these findings indicated that the interplay between HIF1‑α and ROCK1 may be a critical factor that regulates cell proliferation and collagen synthesis in rat HSCs under hypoxia.

Effects of anoxia and hypoxia on the two-spotted spider mite, Tetranychus urticae (Acari: Tetranychidae)

We investigated the potential use of anoxic (0% O2) and hypoxic (lower O2 concentration than in the atmosphere) conditions for controlling the two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae). Adult T. urticae females were exposed to O2 concentrations of 0, 0.5, 1, 2, or 21% (control) with a constant CO2 concentration of 0.05% at 1 atm and 25 °C under continuous darkness for 24 h. The survival and fecundity at 8 days after treatment significantly decreased when the O2 concentration was lower than 0.5% and 1%, respectively; the lethal concentration at 50% survival (LC50) was 0.55%. The miticidal hypoxic condition (0.5% O2) led to physiological disorders in host plants. The degree of physiological disorders differed among the plant species tested. Although tomato seedlings died after the hypoxia treatment, in kidney bean and cucumber seedlings the primary leaves remained and lateral buds developed instead of the apical buds that ceased. Hypoxia treatment could be useful as a physical measure for controlling spider mites depending on plant species or cultivars.

Impacts of coral bleaching on pH and oxygen gradients across the coral concentration boundary layer: a microsensor study

Reef-building corals are surrounded by complex microenvironments (i.e. concentration boundary layers) that partially isolate them from the ambient seawater. Although the presence of such concentration boundary layers (CBLs) could potentially play a role in mitigating the negative impacts of climate change stressors, their role is poorly understood. Furthermore, it is largely unknown how heat stress-induced bleaching affects O2 and pH dynamics across the CBLs of coral, particularly in branching species. We experimentally exposed the common coral species Acropora aspera to heat stress for 13 d and conducted a range of physiological and daytime microsensor measurements to determine the effects of bleaching on O2 and pH gradients across the CBL. Heat stress equivalent to 24 degree heating days (3.4 degree heating weeks) resulted in visible bleaching and significant declines in photochemical efficiency, photosynthesis rates and photosynthesis to respiration (P/R) ratios, whereas dark respiration and calcification rates were not impacted. As a consequence, bleached A. aspera had significantly lower (− 13%) surface O2 concentrations during the day than healthy corals, with concentrations being lower than that of the ambient seawater, thus resulting in O2 uptake from the seawater. Furthermore, we show here that Acropora, and potentially branching corals in general, have among the lowest surface pH elevation of all corals studied to date (0.041 units), which could contribute to their higher sensitivity to ocean acidification. Additionally, bleached A. aspera no longer elevated their surface pH above ambient seawater values and, therefore, had essentially no [H+] CBL. These findings demonstrate that heat stress-induced bleaching has negative effects on pH elevation and [H+] CBL thickness, which may increase the overall susceptibility of coral to the combined impacts of ocean acidification and warming.

Pulverized coal swirl flames in oxy-fuel conditions: Effects of oxidizer O2 concentration on flow field and local gas composition

In an experimental study the effects of varied oxygen concentrations in the oxidizer gas on resulting flow fields, combustion products and general behavior of pulverized coal swirl flames under oxy-fuel conditions have been investigated. Experiments were carried out in a small scale down-fired cylindrical combustion chamber equipped with an annular swirl burner. Studied flames had a constant power output of 40 kWth and O2/CO2 oxidizer gas mixtures with O2 concentrations ranging from 23 to 33 vol%. Detailed two-dimensional flow field measurements are obtained from laser Doppler anemometry (LDA). Velocity profiles (Mean and RMS) have been obtained for all conditions investigated and serve as basis for identification of flow field characteristics. Velocity RMS values are provided as supplementary material. To complement flow field measurements, in-flame gas composition measurements were also conducted using a sampling probe combined with infrared gas absorption analysis via Fourier-transform infrared (FTIR) spectrometry. The results obtained show increased velocities, particularly along the main vortex for flames with increased oxygen contents, while lower velocities are found to occur inside the recirculation regions. The opposite occurs with lower O2 concentrations, showing significantly reduced velocities in the main vortex, but stronger recirculation than the high oxygen counterparts. This effect is attributed to a modification of the swirl level introduced by the expansion of product gases. Measured NO and CO in-flame concentrations showed significant variations under different O2 concentrations in the oxidizer.

Decrease in viscosity of partially hydrolyzed polyacrylamide solution caused by the interaction between sulfide ion and amide group

Viscosity of polymer solution is one of the key factors which, in some case, notably influence its application effect. However, it has been found that the viscosity drops significantly with sulfide ion. To better understand this phenomenon, the rheological behavior, dynamic light scattering (DLS), and 1H NMR analysis were conducted. The results show that sulfide ion significantly reduced the viscosity of HPAM solution and this reduction was further enhanced under low pH and high O2 content and, more specifically, could not be recovered by dialysis. The polymeric network structure of HPAM formed in water was apparently destroyed and the hydrodynamic radius was reduced by sulfide ion. Furthermore, 1H NMR spectra indicated that the chemical environment of some protons in the methyne group connected to amide group in HPAM was modified by sulfide ion. The interaction between sulfide ion and the amide groups in side chain intra-/inter-molecule of HPAM reduces the hydrodynamic radius and destroys the three dimensional network structure and consequently decreases the viscosity of HPAM solution. These results are helpful for investigating the mechanisms of HPAM-sulfide interaction and optimizing the usage of HPAM for enhanced oil recovery in oil reservoirs with sulfide ions produced by sulfate reducing bacteria.

Effect of O₂ Concentration on the Electrochromic Properties of NiOx Films.

Nickel oxide (NiOx) films were deposited onto ITO-coated glass at room temperature by DC magnetron sputtering in Ar/O2 mixing gas. The effect of O2 concentration on structure, morphology, electrochemical and electrochromic properties of NiOx films was systematically investigated. X-ray diffraction results showed NiOx films had the polycrystalline structure. NiOx films deposited at low O2 concentration had the preferred (200) peak. On the other hand, the films exhibited the strong (111) peak at high O2 concentration. Small roughness and grain size of NiOx film deposited at 15% O2 concentration were observed by atomic force microscope and scanning electron microscope results, and small crystallite size was obtained from the XRD data which leads to the good cyclic durability. The large transmittance modulation, high color efficiency and fast coloring/bleaching response time make NiOx films suitable to be applied as an anodic coloring material complemented with WO3 electrochromic window.

Hypoxia with Wharton\u2019s jelly mesenchymal stem cell coculture maintains stemness of umbilical cord blood-derived CD34+ cells

BackgroundThe physiological approach suggests that an environment associating mesenchymal stromal cells with low O2 concentration would be most favorable for the maintenance of hematopoietic stem/progenitor cells (HSPCs). To test this hypothesis, we performed a coculture of cord blood CD34+ cells with Wharton’s jelly mesenchymal stem cells (WJ-MSCs) under different O2 concentration to simulate the growth of HSPCs in vivo, and assessed the impacts on stemness maintenance and proliferation of cord blood HSPCs in vitro.MethodsCD34+ cells derived from cord blood were isolated and cocultured under 1%, 3%, or 20% O2 concentrations with irradiated WJ-MSCs without adding exogenous cytokines for 7 days. The cultured cells were harvested and analyzed for phenotype and functionality, including total nuclear cells (TNC), CD34+Lin− cells, colony forming unit (CFU) for committed progenitors, and long-term culture initiating cells (LTC-ICs) for HSPCs. The cytokine levels in the medium were detected with Luminex liquid chips, and the mRNA expression of hypoxia inducible factor (HIF) genes and stem cell signal pathway (Notch, Hedgehog, and Wnt/β-catenin) downstream genes in cord blood HSPCs were confirmed by quantitative real-time polymerase chain reaction (qRT-PCR).ResultsOur results showed that the number of TNC cells, CD34+Lin− cells, and CFU were higher or similar with 20% O2 (normoxia) in coculture and compared with 1% O2 (hypoxia). Interestingly, a 1% O2 concentration ensured better percentages of CD34+Lin− cells and LTC-IC cells. The hypoxia tension (1% O2) significantly increased vascular endothelial growth factor (VEGF) secretion and decreased interleukin (IL)-6, IL-7, stem cell factor (SCF), and thrombopoietin (TPO) secretion of WJ-MSCs, and selectively activated the Notch, Wnt/β-catenin, and Hedgehog signaling pathway of cord blood HSPCs by HIF-related factors, which may play an important role in stemness preservation and for sustaining HSPC quiescence.ConclusionsOur data demonstrate that cord blood HSPCs maintain stemness better under hypoxia than normoxia with WJ-MSC coculture, partially due to the increased secretion of VEGF, decreased secretion of IL-6 by WJ-MSCs, and selective activation of stem cell signal pathways in HSPCs. This suggests that the oxygenation may not only be a physiological regulatory factor but also a cell engineering tool in HSPC research, and this may have important translational and clinical implications.

Exploring the Atmosphere of Neoproterozoic Earth: The Effect of O2 on Haze Formation and Composition

Abstract Previous studies of haze formation in the atmosphere of the early Earth have focused on N2/CO2/CH4 atmospheres. Here, we experimentally investigate the effect of O2 on the formation and composition of aerosols to improve our understanding of haze formation on the Neoproterozoic Earth. We obtained in situ size, particle density, and composition measurements of aerosol particles produced from N2/CO2/CH4/O2 gas mixtures subjected to FUV radiation (115–400 nm) for a range of initial CO2/CH4/O2 mixing ratios (O2 ranging from 2 ppm to 0.2%). At the lowest O2 concentration (2 ppm), the addition increased particle production for all but one gas mixture. At higher oxygen concentrations (20 ppm and greater), particles are still produced, but the addition of O2 decreases the production rate. Both the particle size and number density decrease with increasing O2, indicating that O2 affects particle nucleation and growth. The particle density increases with increasing O2. The addition of CO2 and O2 not only increases the amount of oxygen in the aerosol, but it also increases the degree of nitrogen incorporation. In particular, the addition of O2 results in the formation of nitrate-bearing molecules. The fact that the presence of oxygen-bearing molecules increases the efficiency of nitrogen fixation has implications for the role of haze as a source of molecules required for the origin and evolution of life. The composition changes also likely affect the absorption and scattering behavior of these particles but optical property measurements are required to fully understand the implications for the effect on the planetary radiative energy balance and climate.