Low Oxygen Environment Research Articles

Expression and distribution of erythropoietin, vascular endothelial growth factor (VEGF) and VEGF receptor 2 in small intestine of yaks at different ages.

This study aimed to detect the expression and distribution of vascular endothelial growth factor (VEGF), VEGF receptor 2 (VEGFR-2), and erythropoietin (EPO) proteins in small intestinal tissues of 50-day-old, newborn, and adult yaks. The results provide basic data for the study of the relationship between adaptability and age of plateau yak. Small intestine tissues from healthy adult, 50-day-old, and newborn yak were collected and embedded in paraffin sections. Histological features were observed by haematoxylin and eosin staining. The expression of VEGF, VEGFR-2, and EPO proteins were detected by immunohistochemical staining. Immunohistochemical results showed that of the expression VEGF, VEGFR-2, and EPO were detected in the small intestinal villi of yaks at all ages. The EPO expression level in the jejunum and duodenal villous epithelial cells of newborn yaks was significantly higher than that of 50-day-old and adult yaks. The EPO expression level in ileum villous epithelial cells of 50-day-old yaks was significantly higher than that of newborn and adult yaks. VEGF expression in newborn yak ileum and jejunum epithelial cells of the intestinal villus were significantly higher than in the 50-day-old and adult. In the 50-day-old yaks, the duodenal intestinal villus epithelial cells expression levels were higher than in the adult and newborn yaks. The expression level of VEGFR-2 in the ileum, jejunum and duodenal villous epithelial cells of 50-day-old yak was significantly higher than in that of adult and newborn yak. The expression and distribution characteristics of EPO, VEGF, and VEGFR-2 in yak intestinal tissues of different ages indicate that these proteins may be involved in the physiological regulation of yak intestines in hypoxic environments. It may be an important regulatory protein in yak adaptation to a high altitude and low oxygen environment.

Development of Fuel Cell System Using Metal Hydride and Hydrogen Peroxide in Low-Oxygen Environments

Hydrogen energy is attracting attention as a promising power system due to high energy storage density and environmentally friendly features. For these reasons, fuel cell system using hydrogen energy in unmanned underwater vehicles have been studied. However, in low-oxygen environment, fuel cell system requires an oxygen storage as well as a hydrogen storage. In this study, a fuel cell system using a metal hydride and hydrogen peroxide was designed. The metal hydride can charge and discharge hydrogen at a lower pressure than a high-pressure hydrogen tank and has a high hydrogen storage density. In this system, AB2 type metal hydride is used to store hydrogen. Hydrogen desorption reaction of the metal hydride is an endothermic reaction, and heat supply is required to maintain the temperature of the metal hydride in order to stably supply hydrogen. Therefore, in this system, hydrogen peroxide was used as an oxygen source. Hydrogen peroxide reacts with a metal catalyst to generate oxygen and water. The decomposition reaction of hydrogen peroxide is an exothermic reaction and can supply heat required for the metal hydride. In this system, hydrogen peroxide is decomposed into water and oxygen through a catalytic reaction, and the generated heat is supplied to the metal hydride. Finally, hydrogen and oxygen are supplied to the PEMFC stack to generate power. For system design, in this study, PCT characteristics of AB2 type metal hydride, thermal management method, and hydrogen peroxide decomposition catalyst were studied, and an operation strategy for non-humidified PEMFC operation was proposed. This system generated a power output of about 290 W for 97 hours, and the hydrogen utilization rate of the fuel cell was confirmed to be 92.3%.

COVID associated mucormycosis: various trends, effects of treatment and sequelae

Background: With second wave of covid-19 pandemic rapid rise in cases of covid associated mucormycosis (CAM) was detected. The primary reason that appears to be facilitating Mucorales spores to germinate in people with COVID-19 is an ideal environment of low oxygen, high blood glucose, acidic medium (metabolic acidosis, diabetic ketoacidosis [DKA], high serum iron levels. Aim of this study is to evaluate the extent of disease, its causative factors, various associations and effect of treatment. Methods: This is a prospective study done on 180 patients. Detailed history and diagnostic nasal endoscopic guided biopsies were taken and sent for histopathological and microbial examination. Computed tomography (CT) and MRI of paranasal sinus, orbit, skull base and brain were done. The data collected was entered in Microsoft excel and analyzed data was presented in form of frequency and percentage shown by bar chart and pie charts. Results: The average age of the patients was 50.53 ± 11.280 years. Majority of patients were male (73.3%). Mean duration of onset was 19.28±11.482 days. The most common presenting symptom was headache( 90%). 98.9% (N=178) patients were diabetics, 52.2% patients were known diabetics, newly diagnosed diabetics were 41.7%. 73.90% patients had history of steroid intake. 39 patients were certified dead with overall 21.7% mortality rate. Conclusions: Increase in mucormycosis in Indian context appears to be an unholy intersection of trinity of COVID-19, Diabetes mellitus and corticosteroid. High suspicion, early diagnosis and rigorous management is the key to favourable prognosis.

Partially melted powder in laser based directed energy deposition: Formation mechanism and its influence on microstructure

The powder–melt pool interaction behavior is crucial in laser-based directed energy deposition (LDED). Partially melted particles, which are formed as a result of this interaction, significantly influence on the microstructure and mechanical performance of multi-material and metal-matrix composites fabricated via LDED. However, the presence of partially melted particles is a contentious issue that has been overlooked in single-material LDED studies. Furthermore, the investigation of partially melted particles is hindered by the difficulties in direct observation. To overcome this obstacle, this study was conducted using a single-bead Ti–6Al–4V printing experiment with a relatively high oxygen content to distinguish partially melted particles directly. The formation mechanism of the partially melted particles was revealed through experimental studies combined with numerical analysis using a self-established model. Additionally, the influence of partially melted particles on the grain structure of LDED–fabricated parts was investigated in a low–oxygen environment. The partially melted particles tend to survive close to the surface of the deposited layer. As the penetration depth increased, the particle size decreased and the aspect ratio increased. The formation of partially melted particles collectively depends on the laser power, scanning velocity, powder size and powder feed speed, differing from the common conclusion that an insufficient input energy results in poor powder melting behavior. Furthermore, a Ti–6Al–4V sample with high–fraction equiaxed grains was fabricated using optimized processing conditions. The partially melted particles significantly affected the solidification behavior. In addition to the heterogeneous nucleation mechanism caused by the partially melted particles, a novel seed crystal mechanism was proposed to support the abnormal formation of equiaxed grains. This study highlights the importance of partially melted particles in LDED, and provides useful insights into in-situ microstructural control in LDED.

Reductive sorption of vanadium by green rust in seawater

Vanadium (V) is a redox-sensitive trace metal that typically exists in one of three oxidation states (+3, +4 and +5) in natural waters; a feature increasingly used in paleoredox studies of ancient marine sediments. However, our knowledge of V geochemistry in low-oxygen marine environments is still limited, especially regarding interactions of V with reduced iron minerals such as green rust. Carbonate green rusts (GRCO3) are mixed FeII/FeIII-phases found in some modern ferruginous settings, such as Lake Matano (Indonesia), and were likely abundant in ancient ferruginous marine systems where they may have played an essential role in authigenic V enrichments in sediments. Here, we present an abiotic pathway of V removal from seawater via reduction and adsorption onto amorphous GRCO3. Suspensions of the freshly precipitated GRCO3 (1 g L−1) were added to vanadate (1 mg VV L−1 initial concentration) in anoxic synthetic seawater solutions. Vanadium removal by GRCO3 was rapid and efficient, with 92 – 99% of V removed in under 20 seconds. Synchrotron-based X-ray absorption near edge structure (XANES) spectroscopy showed that VV adsorbed by GRCO3 was partially reduced to a mixture of VV and VIV, with the average oxidation state of adsorbed V increasing (+4.3 to +4.7) with increasing solution pH (7.5 to 8.5). Upon subsequent exposure to aerated seawater, V-bearing GRCO3 oxidized to lepidocrocite [γ–FeO(OH)] within 24 h, with concomitant reduction of all solid-phase VV to VIV. During oxidation, V was not released back into solution; rather, extended X-ray absorption fine structure (EXAFS) modeling revealed that VIV was structurally incorporated into lepidocrocite as octahedral vanadyl (VO2+). Our work further constrains the aqueous geochemistry of V, which has implications for understanding V cycling and removal mechanisms in both modern and ancient marine systems.

A novel oxygen-enriched method for sentry buildings on plateaus based on an attached jet

Due to the existence of windows and the weak thermal resistance of building envelopes, the sentry building is easily affected by the low-oxygen and low-temperature environment at high-altitudes, which affects the work efficiency, cognitive ability and comfort of personnel. This study proposed a novel oxygen supply method suitable for plateau sentry buildings based on attached jet theory, which can achieve coupling control of the thermal and oxygen environment. The computational fluid dynamics (CFD) method was adopted to study the effect of air supply parameters and oxygen supply concentration on environment creation. The results showed that the environmental creation method could efficiently create the local environment. In addition, a nonuniform oxygen environment is created indoors. That is, the oxygen concentration in the head area is greater than that in the non-head area. It greatly improved the utilization rate of oxygen resources. The influence of the air supply velocity on the indoor environment creation effect is greater than that of the air supply temperature. The effect of creating a local oxygen environment is proportional to the concentration of oxygen supplied. The optimal air supply parameters are an air supply velocity (V) of 3 m/s, air supply temperature (Ts) of 30 °C, and oxygen supply concentration (C) of 90%, with the highest oxygen-enriched velocity of 1.598%/min. The research conclusions will provide new ideas for local environmental control methods in sentry buildings on the plateau and expand to actual projects to solve the problem of engineering application.

Spatial distribution and water quality index of Lahore Canal, Pakistan

Abstract The Lahore Canal (LC) in Lahore city of Pakistan, with the discharge of 402 cusecs, runs along the city's centre. With rapid urbanization and population growth, the LC water is deteriorating. This study determined the water quality index and spatial distribution of pollutants. Three months of sampling from six separate locations were performed. Water quality parameters were analysed. The results indicated that pH, solids, turbidity, hardness, alkalinity, and chlorides were within guidelines, but DO BOD and nitrogen were beyond guidelines. Moderate BOD values (2.24–8.06 mg/L) and low DO values (0.13–3.56 mg/L) indicated a low oxygen environment. Heavy metal concentration was as follows: Fe > Pb > Cr > Cu. The Pearson correlation coefficient indicated ± poor to moderate (0.3–0.7) correlation. The ANOVA result supported the alternative hypothesis, i.e., the pollutants originated from the same source. Principal component analysis and cluster analysis showed three primary sources for the different pollutants based on loading of variance and Euclidean distance, respectively. The WQI of LC at all locations was above 300, indicating that LC water is not suitable for any usage. The spatial distribution of parameters indicated the effects of urbanization and commercialization (small household industries) at Location-4. The poor water quality of LC needs immediate government attention.

High temperature tribological properties of the D-gun WC-12Co coating in fluoride molten salt

Development of anti-corrosion and wear-resistant materials in FLiNaK molten salt is vital to the service safety and reliability of the various mechanical systems for the molten salt reactor. In this work, a WC-12Co coating was fabricated by detonation gun spraying technique. Its microstructure, mechanical properties and tribological behaviors in FLiNaK molten salt were studied. A ball-on-disk rotary configuration was selected for the tribological test, in which the WC-12Co coating disks slid against Al2O3, SiC, Si3N4 and steel counterface materials in FLiNaK molten salt and low-oxygen environment at 600 °C. The results showed that the WC-12Co coating displays a low porosity of 0.71%, a bonding strength of above 44 MPa and good anti-corrosion in molten salt. FLiNaK molten salt provides the good lubricity and inhibits the oxidation wear of the WC-12Co coating, contributing to the low friction coefficient of 0.097–0.17 and wear rate of (4.95–8.40) × 10−7 mm3N−1m−1.

Experimental Analysis of Heavy Metal Contaminated Electroplating Industrial Site Soil Using Tamarind Seed Biochar

Abstract: Biochar application is a promising strategy for the rehabilitation of contaminated soil while ensuring suitable waste management. Biochar is a highly porous organic material derived from wood, manure, or plant-based biomass through pyrolysis in a low-oxygen environment. Pyrolysis is a technique that produces biochar by means of the thermal decomposition of the feedstock in an oxygen-free environment. In this work, tamarind seed was pyrolyzed in a muffle furnace 500 – 700oC to prepare biochar. The soil is contaminated with the electroplating industrial effluent, which is rich in nickel (Ni), copper (Cu), and chromium (Cr) concentrations. In this study, the atomic absorption spectrophotometer (AAS) technique has been used to find the removal efficiency of heavy metals for a curing time of 7, 14 and 28 days soil samples The result obtained from the physicochemical analysis indicated that the contaminated soils recorded an acidic pH. Adding biochar to contaminated soil in different percentages (2%, 4%, 6%, 8%, and 10%) to increase the pH value and using direct shear test, the shear strength of the soil determined different percentage of biochar. The result obtained adding 8% of Biochar to get optimum Shear strength. The functional groups present in the raw biomass and pyrolyzed biochar are determined using fourier transform infrared spectroscopy (FTIR)

Mucilage secretion by aerial roots in sorghum (Sorghum bicolor): sugar profile, genetic diversity, GWAS and transcriptomic analysis.

Aerial root mucilage can enhance nitrogen fixation by providing sugar and low oxygen environment to the rhizosphere microbiome in Sierra Mixe maize. Aerial root mucilage has long been documented in sorghum (Sorghum bicolor), but little is known about the biological significance, genotypic variation, and genetic regulation of this biological process. In the present study, we found that a large variation of mucilage secretion capacity existed in a sorghum panel consisting of 146 accessions. Mucilage secretion occurred primarily in young aerial roots under adequately humid conditions but decreased or stopped in mature long aerial roots or under dry conditions. The main components of the mucilage-soluble were glucose and fructose, as revealed by sugar profiling of cultivated and wild sorghum. The mucilage secretion capacity of landrace grain sorghum was significantly higher than that of wild sorghum. Transcriptome analysis revealed that 1844 genes were upregulated and 2617 genes were downregulated in mucilage secreting roots. Amongst these 4461 differentially expressed genes, 82 genes belonged to glycosyltransferases and glucuronidation pathways. Sobic.010G120200, encoding a UDP-glycosyltransferase, was identified by both GWAS and transcriptome analysis as a candidate gene, which may be involved in the regulation of mucilage secretion in sorghum through a negative regulatory mechanism.

Patrolling the border: Billfish exploit the hypoxic boundary created by the world's largest oxygen minimum zone.

Pelagic predators must contend with low prey densities that are irregularly distributed and dynamic in space and time. Based on satellite imagery and telemetry data, many pelagic predators will concentrate horizontal movements on ephemeral surface fronts-gradients between water masses-because of enhanced local productivity and increased forage fish densities. Vertical fronts (e.g. thermoclines, oxyclines) can be spatially and temporally persistent, and aggregate lower trophic level and diel vertically migrating organisms due to sharp changes in temperature, water density or available oxygen. Thus, vertical fronts represent a stable and potentially energy rich habitat feature for diving pelagic predators but remain little explored in their capacity to enhance foraging opportunities. Here, we use a novel suite of high-resolution biologging data, including in situ derived oxygen saturation and video, to document how two top predators in the pelagic ecosystem exploit the vertical fronts created by the oxygen minimum zone of the eastern tropical Pacific. Prey search behaviour was dependent on dive shape, and significantly increased near the thermocline and hypoxic boundary for blue marlin Makaira nigricans and sailfish Istiophorus platypterus, respectively. Further, we identify a behaviour not yet reported for pelagic predators, whereby the predator repeatedly dives below the thermocline and hypoxic boundary (and by extension, below the prey). We hypothesize this behaviour is used to ambush prey concentrated at the boundaries from below. We describe how habitat fronts created by low oxygen environments can influence pelagic ecosystems, which will become increasingly important to understand in the context of global change and expanding oxygen minimum zones. We anticipate that our findings are shared among many pelagic predators where strong vertical fronts occur, and additional high-resolution tagging is warranted to confirm this.

Hypoxic response patterns in lung tissue: An integrated analysis of comparative physiological and transcriptomic studies from Neodon fuscus and Lasiopodomys brandtii

Oxygen (O2) is essential for the survival and reproduction of most species. However, in recent years, with global climate change and the increasing impact of human activities on the ecosystem, the frequency of extreme environmental events, such as heat waves, cold waves, droughts, and floods, has increased, resulting in dramatic changes in environmental oxygen concentration (hypoxic environment, etc.), threatening the survival of animals and pushing them toward extreme adaptation. In this context, how organisms, especially those with differences in original habitats, adapt to low oxygen environment is particularly important. In this study, we systematically analyzed hypoxic response patterns in lung tissues of small rodents Neodon fuscus, Lasiopodomys brandtii, and Mus musculus with different experiences of natural hypoxia tolerance through laboratory simulation of hypoxia environment, combined with hematological, histological, and transcriptomic analysis. Our results show that all three species exhibit increased antioxidant defense and damage repair ability to a certain extent under hypoxia, although the specific molecular mechanisms are not the same. L. brandtii showed better damage repair ability than the others, which is likely to be closely related to the intermittent hypoxia environment experienced in the natural environment, and genes such as Glrx5, Prdx2, Col1a1, Lama1, and Eln may play a crucial role in this process. In addition, we found that both N. fuscus and L. brandtii appropriately enhanced oxygen transport in tissues under hypoxic conditions, with a series of functional genes related to hemoglobin synthesis and vascular smooth muscle contraction were significantly up-regulated in both species of voles, such as Actg2, Ptgir, Alas2, Hba, Hbb and Bpgm. Our results, to a certain extent, reveal the differences and similarities of hypoxic response patterns in lung tissues of small rodents with different hypoxic life histories and provide a relatively perfect analytical paradigm for related studies.

Nitrogen metabolism in mycobacteria: the key genes and targeted antimicrobials.

Nitrogen metabolism is an important physiological process that affects the survival and virulence of Mycobacterium tuberculosis. M. tuberculosis's utilization of nitrogen in the environment and its adaptation to the harsh environment of acid and low oxygen in macrophages are closely related to nitrogen metabolism. In addition, the dormancy state and drug resistance of M. tuberculosis are closely related to nitrogen metabolism. Although nitrogen metabolism is so important, limited research was performed on nitrogen metabolism as compared with carbon metabolism. M. tuberculosis can use a variety of inorganic or organic nitrogen sources, including ammonium salts, nitrate, glutamine, asparagine, etc. In these metabolic pathways, some enzymes encoded by key genes, such as GlnA1, AnsP2, etc, play important regulatory roles in the pathogenesis of TB. Although various small molecule inhibitors and drugs have been developed for different nitrogen metabolism processes, however, long-term validation is needed before their practical application. Most importantly, with the emergence of multidrug-resistant strains, eradication, and control of M. tuberculosis will still be very challenging.

Pressurised combustion in hot and low-oxygen environments: Chemiluminescence imaging and modelling

Turbulent flames in a confined and pressurised jet-in-hot-coflow combustor, under a range of pressures and coflow conditions, are investigated in this study. The investigation involves both experimental and numerical analyses, with the central focus on extending the use of an atmospheric-pressure computational fluid dynamics (CFD) model to describe hot and low-oxygen combustion at elevated pressures. A series of CFD simulations are compared against experimental images, in terms of both flame structure and chemiluminescence behaviour. The imaging of OH* and CH* is performed experimentally for flames with Reynolds numbers of 10,000 and 15,000, issuing into coflows with O2 concentrations ranging from 3%–9%. The experimental results show a reduction in OH* and CH* intensity with increasing pressure under the various coflow conditions, while the CFD results display some key differences in the trends with pressure and O2. The computational analysis is complemented by a series of one-dimensional laminar flame simulations at a range of pressures and oxidant O2 concentrations. These simulations enable the changes in chemical kinetics with pressure and O2 concentration to be studied in greater detail, and several key differences in comparison with the CFD results are observed. Ultimately, the results highlight the importance of accurately predicting both the flow-field and finite-rate chemistry to reproduce the trends observed under hot and low-oxygen combustion conditions at elevated pressures.

Quantitative Proteomic Analysis of Yorkshire Pig Liver Reveals Its Response to High Altitude.

In this study, the protein profiles in the livers of Shannan Yorkshire pigs (SNY), Linzhi Yorkshire pigs (LZY), and Jiuzhaigou Yorkshire pigs (JZY) were comparatively analyzed using quantitative proteomics. A total of 6804 proteins were identified, of which 6471 were quantified and 774 differentially expressed proteins (DEPs) were screened. The higher level of energy metabolism in LZY livers was in response to the critical altitude environment compared to that in JZY, while the high-altitude environment suppressed energy output in SNY livers. Several key antioxidant enzymes were locally regulated in Yorkshire pig liver to balance antioxidant levels in a high-altitude, low-oxygen environment. In addition, ribosomal proteins were differentially expressed in Yorkshire pig livers in response to different altitudinal environments. These findings provide clues to the adaptation of the Yorkshire pig liver to the three altitudinal environments and the molecular links that exist between them.

Distributions of and environmental risks posed by Cr and Zn when co-treating solid waste in different kilns

In order to dispose solid waste reasonably and provide reference data for solid waste co-treatment in industrial kilns, coal chemical products were co-treated in a pulverized coal furnace and refuse-derived fuel was co-treated in a gasifier-coupled pulverized coal furnace system. The distribution and environmental risks of Cr and Zn in different kilns were compared and analyzed. The Cr and Zn distributions in the solid products from the pulverized coal furnace tests were similar. Fly ash contained > 80% of the Cr and Zn. In the gasifier, cyclone dust and gasification gas contained only ∼ 60% of the Cr and Zn, and gasification slag contained > 40% of the Cr and Zn. The gasification gas contained ∼ 33% of the Cr and Zn volatilized. The pulverized coal furnace temperature was > 1,500 °C. Most of the Cr and Zn volatilized and then condensed, so became enriched in the fly ash. The gasifier temperature was ∼ 750 °C, so less volatilization occurred and Cr and Zn became enriched in the gasification slag. The Cr and Zn concentrations in leachates of the solid products were lower than the limits of “GB 5085.3–2007”. However, the Cr and Zn concentrations in the gasification slag and cyclone dust leachates were close to the limits and tens to hundreds of times higher than the concentrations in the pulverized coal furnace fly ash and slag leachates. The low temperatures and low-oxygen environments of gasifiers are not conducive to heavy metals being stable in the solid products, and the environmental risks posed by heavy metals in the solid products are high. The risks to the environment are less serious for co-treating solid waste in pulverized coal furnaces than gasifiers.

Authigenic greigite in late MIS 3 sediments: Implications for the Yellow Sea Cold Water Mass and Yellow Sea Warm Current evolution

Yellow Sea current conditions during the late Marine Isotope Stage 3 (late MIS3, 40–30 ka B.P.) highstand remain unknown. Here, environmental magnetism, geochemistry, particle size, and scanning electron microscope methods are employed to analyze core YS01A with a basal age of 40 kyr from the South Yellow Sea mud deposits. Greigite formed in marine sedimentary layers with thickness >7 m during early diagenesis. Greigite formation is related to the redox state and total organic content (TOC) availability, which are controlled, respectively, by the Yellow Sea Cold Water Mass (YSCWM) and the Yellow Sea Warm Current (YSWC). In MIS1 (7–0 ka B.P.), a strong YSWC brought greater TOC, and a strong YSCWM (thickness of 48 m) resulted in a strongly reducing low-oxygen environment. This led to massive magnetite dissolution and pyrite preservation. In late MIS3 (37–31 ka B.P.), the weak Kuroshio Current and East Asian Winter Monsoon (EAWM) resulted in a low-intensity YSWC that provided less TOC. A weak YSCWM (thickness of 35 m), caused by shallow water depths and a weak EAWM, contributed to a less reducing sedimentary environment. Thus, pyritization was interrupted and greigite was preserved. Greigite content can, thus, be used to trace the development of Yellow Sea currents. During a period of slow sea level rise at 41–37 ka B.P., minor greigite formed with most magnetite being preserved, which indicates that the environment started to become reducing. This can be interpreted as due to initial formation of a thin and weak YSCWM. During the 37–31 ka B.P. highstand, the greigite content increased, which suggests more reducing conditions related to establishment of a thicker and intensified YSCWM. In addition, the greigite content decreased progressively, which may have resulted from YSWC weakening. Our results suggest that greigite can be used as a simple tool to reflect current evolution in the Yellow Sea, which can give a better understanding of continental shelf environment change.

Genesis and mineralization implications of dissolution–regrowth pyrite in the large Qukulekedong Au–Sb deposit, East Kunlun, NW China

The Qukulekedong deposit is a recently discovered large Au–Sb deposit in the western part of the East Kunlun Orogenic Belt, NW China. Pyrite with a characteristic dissolution–regrowth texture has developed in the high-grade Au ore of the deposit. In this study, information on the mineralogical properties, elements distribution, and in situ S isotopic composition of the dissolution–regrowth pyrite was used to interpret its genesis and relationship to Au concentration. The pyrite grains are composed of a core, mantle, and rim. The core consists of pyrite with δ34S values ranging from 1.02 ‰ to 1.99 ‰, indicating a neutral pH, medium-oxygen fugacity environment. The mantle consists of sphalerite, sericite, quartz, and ankerite with dissolution texture, indicating pyrite dissolution and replacement in a neutral pH, high-oxygen fugacity environment. The rim consists of pyrite with fine arsenopyrite inclusions and recovers the crystal shape of the pyrite, which have δ34S values ranging from 1.60 ‰ to 2.67 ‰. This indicates that the rim was formed via regrowth in a neutral pH, low-oxygen fugacity environment. The dissolution of the mantle and regrowth of the rim represent an oxygen fugacity increasing–decreasing process in the formation of pyrite. The increase in oxygen fugacity could remobilize Au from dissolved pyrite, forming a highly Au-concentrated hydrothermal fluid. The decrease in oxygen fugacity triggered the supersaturation and precipitation of Au, forming an Au-rich rim. Combining geological characteristics, the pyrite likely had a magmatic sulfur origin and formed via a dissolution-regrowth process caused by the depressurization–oxidation associated with rock fractures. The dissolution-regrowth pyrite can be used as a mineralogical indicator for regional Au exploration.

Characteristics of ethylene and methane combustion in a range of high temperature and low oxygen environments

New understanding of turbulent jet flames of natural gas, and blends of natural gas with ethylene (C2H4), issuing into a range of preheated coflowing oxidisers with reduced oxygen (O2) concentrations are reported. Comparisons are made for coflow O2 concentrations of 3%, 4%, 5%, 6%, 9% and 11% and coflow temperatures of 1250 K, 1315 K and 1385 K. Instantaneous and simultaneously planar imaging measurements of temperature, hydroxyl radicals (OH) and formaldehyde (CH2O) were taken at eight locations ranging from 9 mm to 75 mm downstream of the jet exit plane. The experimental data is supplemented with chemical reaction modelling. It is shown that increasing the proportion of C2H4 in the fuel supply resulted in an increase in the flame front temperature. At 3% O2, CH2O signal did not very between the three fuels containing C2H4, whilst at 9%, the signal increased with increasing C2H4. OH number density was highest for a blend of 66% NG and 33% C2H4. The fuel composition made little effect on the jet spread rate. Reaction modelling found evidence of changes in the reaction process, both in the suppression of reactions with different fuels, and in the suppression of reactions, and the locations they occur, with reducing O2 concentrations. Reaction modelling also found a significant decrease in ignition delay when C2H4 was present in the fuel mixture, and an increase in ignition delay as all four fuels transition to MILD combustion.

Environmental and microbial influence on chemistry and dolomite formation in an ancient lake, Green River Formation (Eocene), Uinta basin, Utah, U.S.A.

ABSTRACT Integrated stratigraphic, petrographic, and geochemical data allow interpretation of biogeochemical and mineralization processes in paleoenvironmental context of ancient lacustrine environments. These indicate that lake chemistry, microbial processes, and organic matter (OM) strongly influenced dolomite formation in near-surface environments throughout deposition of the Green River Formation (Eocene, Uinta basin, Utah). The lower Green River Formation consists of interbedded fluvio-deltaic siliciclastics, paleosols, carbonate mud, coated-grain carbonates, mollusk and ostracod limestones, and microbialites all landward of profundal OM-bearing illitic mudrocks. Calcite, dolomite, Fe-dolomite, and authigenic feldspars are common. Carbonate δ18O and δ13C are covariant, and positive excursions of carbonate δ13C (up to 6.9‰ VPDB) and organic-matter δ15N (up to 13.9‰ V-AIR) occur in profundal OM-bearing mudrocks. The upper Green River Formation consists mainly of laminated OM-lean and OM-rich dolomitic muds (i.e., “oil-shales”). Zoned dolomite crystals with Mg-calcite centers and Fe-dolomite rims are widespread in addition to authigenic feldspars and Na-carbonates. Carbonate δ13C-enrichment (up to 15.8‰ VPDB), and organic-matter δ15N-enrichment (up to 18.4‰ V-AIR) occur in these OM-rich dolomite muds. Organic-matter δ13C is relatively invariable (mean = –29.3‰ VPDB) and does not covary with carbonate δ13C. Trends in mineralogy, organic-matter abundance, and stable isotopes result from changing hydrologic systems, paleoclimate, lake chemistry and microbial processes coincident with the Early Eocene Climate Optimum. The lower Green River Formation paleo-lake was smaller in area and volume, heavily influenced by meteoric fluvial input, variably oxygenated, and ranged from neutral and fresh to alkaline and saline. Especially in littoral environments with abundant microbialites, dolomite formed through recrystallization of precursor carbonate involving both replacement of precursor carbonate and direct precipitation as cements and overgrowths. The upper Green River Formation paleo-lake was more expansive with widespread low-oxygen, nutrient-rich, and alkaline saline environments with increased planktic organic-matter productivity. Microbial decay of organic matter in low-oxygen environments produced alkaline lake waters through methanogenesis, possible denitrification, and bacterial sulfate reduction to a limited degree. This favored precipitation of widespread dolomite, as well as Na-carbonates, authigenic feldspars, and analcime from lake water and phreatic pore water. Extracellular polymeric substances (EPS) excreted by microbial communities provided favorable nucleation sites for Mg-carbonate, allowing kinetic barriers of low-temperature dolomite formation to be overcome. Cycling of pH due to turnover of organic matter and associated microbial processes potentially bolstered EPS generation and abiotic environmental conditions favorable to dolomite precipitation. It is likely that metastable precursor carbonate was recrystallized to ordered dolomite, but it is possible that direct precipitation occurred. Fe-dolomite overgrowths precipitated after dolomite where microbial Fe reduction occurred in stagnant, oxygen-depleted, alkaline pore waters.