High Levels Of Hydrogen Research Articles

High rates of photobiological H2 production by a cyanobacterium under aerobic conditions

Among the emerging renewable and green energy sources, biohydrogen stands out as an appealing choice. Hydrogen can be produced by certain groups of microorganisms that possess functional nitrogenase and/or bidirectional hydrogenases. In particular, the potential of photobiological hydrogen production by oxygenic photosynthetic microbes has attracted significant interest. However, nitrogenase and hydrogenase are generally oxygen sensitive, and require protective mechanisms to function in an aerobic extracellular environment. Here, we describe Cyanothece sp. ATCC 51142, a unicellular, diazotrophic cyanobacterium with the capacity to generate high levels of hydrogen under aerobic conditions. Wild-type Cyanothece 51142 can produce hydrogen at rates as high as 465 μmol per mg of chlorophyll per hour in the presence of glycerol. Hydrogen production in this strain is mediated by an efficient nitrogenase system, which can be manipulated to convert solar energy into hydrogen at rates that are several fold higher, compared with any previously described wild-type hydrogen-producing photosynthetic microbe.

Hydrogen Peroxide-sensitive Cysteines in the Sty1 MAPK Regulate the Transcriptional Response to Oxidative Stress

MAPK are activated by and orchestrate responses to multiple, diverse stimuli. Although these responses involve the increased phosphorylation of substrate effector proteins, e.g. transcription factors, the mechanisms by which responses are tailored to particular stimuli are unclear. In the fission yeast Schizosaccharomyces pombe, the Sty1 MAPK is crucial for changes in gene expression that allow adaptation to many forms of environmental stress. Here, we have identified two cysteine residues in Sty1, Cys-153 and Cys-158, that are important for hydrogen peroxide-induced gene expression and oxidative stress resistance but not for other functions of Sty1. Many Sty1-dependent changes in gene expression are mediated by the Atf1 transcription factor. In response to stress, Sty1 increases Atf1 levels by (i) promoting increases in atf1 mRNA and by (ii) directly phosphorylating and stabilizing Atf1 protein. Although dispensable for phosphorylation and stabilization of Atf1 protein, we find that both Cys-153 and Cys-158 are required for increases in atf1 mRNA levels and Atf1-dependent gene expression in response to hydrogen peroxide but not osmotic stress. Indeed, our data indicate that oxidation of Sty1, by formation of a disulfide bond between Cys-153 and Cys-158, is important for maintaining atf1 mRNA stability at high concentrations of hydrogen peroxide. Together, these data reveal that redox regulation of cysteine thiols in Sty1 is involved in a stress-specific mechanism regulating transcriptional responses to oxidative stress. Intriguingly, the conservation of these cysteine residues in other MAPK raises the possibility that similar mechanisms may ensure appropriate responses to hydrogen peroxide in other eukaryotes.

Multiscale Modeling of Irradiation Induced Hardening in a-Fe, Fe-Cr and Fe-Ni Systems

AbstractStructural materials in the new Generation IV reactors will operate in harsh radiation conditions coupled with high levels of hydrogen and helium production, thus experiencing severe degradation of mechanical properties. The development of structural materials for use in such a hostile environment is predicated on understanding the underlying physical mechanisms responsible for microstructural evolution along with corresponding dimensional instabilities and mechanical property changes. As the phenomena involved are very complex and span in several length scales, a multiscale approach is necessary in order to fully understand the degradation of materials in irradiated environments. The purpose of this work is to study the behavior of Fe systems (namely a-Fe, Fe-Cr and Fe-Ni) under irradiation using both Molecular Dynamics (MD) and Dislocation Dynamics (DD) simulations. Critical information is passed from the atomistic (MD) to the microscopic scale (DD) in order to study the degradation of the material under examination. In particular, information pertaining to the dislocation-defects (such as voids, helium bubbles and prismatic loops) interactions is obtained from MD simulations. Then this information is used by DD to simulate large systems with high dislocation and defect densities.

Elastic moduli of single crystal palladium hydride near the tri-critical point.

Palladium has long been studied as a model metal hydride system because of the high absorption rates and levels of hydrogen. Even moderately high pressures and temperatures can result in almost one to one hydrogen to palladium atom ratios. Depending on the ambient temperature and hydrogen pressure, the structural phase of hydrogen atoms in the palladium lattice can have three different forms: alpha, beta, and a mixed phase (alpha + beta). There exists a triple point in the pressure versus temperature phase diagram near 290° C and 400 psi. A recent model for absorption/desorption hysteresis in metal hydride systems predicts a sharp drop in the shear modulus near this triple point. Results from recent elastic constants and acoustic attenuation measurements as a function of both temperature and pressure near the triple point will be shown [R. B. Schwarz and A. G. Khachaturyan, Acta Mater. 54, 313 (2006)]. The experimental procedures for resonant ultrasound spectroscopy measurements at high temperatures and pressures will be also discussed.

Kinetic model of hydrogen generation by Rhodobacter sphaeroides in the presence of NH4+ ions

To examine the effects of ammonium ion concentration and illumination intensity on the effectivness of the hydrogen generation process of Rhodobacter sphaeroides. In all experiments the amount of evolved hydrogen, biomass growth, concentration of ammonium ions, pH and chemical oxygen demand were measured. A nonstructural kinetic model was applied in description of biomass growth, the amount of evolved hydrogen and consumption of organic compounds and ammonium ions. An increase of ammonium ions concentration resulted in a decrease of maximal specific hydrogen potential production. At higher ammonium ion concentrations, no hydrogen evolution was observed. The efficiency of malic acid conversion into hydrogen and the PHB content in the biomass were the highest with lower concentrations of nitrogen compounds. The presence of ammonium ions inhibits hydrogen photogeneration. A good agreement between the experimental data and model simulations were obtained. In all cases, hydrogen evolution started after an exhaustion of ammonium ions and the increase was proportional to the C/N ratio in the medium. The accumulation of PHB competes with the hydrogen evolution process while the conversion of acids into biomass was limited at higher levels of hydrogen generation. Confirmation of the suitability of the selected model for kinetic studies of hydrogen photoevolution.

Iron carburization in CO‐H2‐He gases, Part I: Experiment

AbstractCarburization of iron was studied at atmospheric pressure over the temperature range 850°C to 1150°C in gaseous mixtures of CO, H2, and He. The resistance relaxation method was applied to measure the carburization rates. Experimental results show that for carburization in CO‐He mixtures, the carburization rate increased proportionally with CO partial pressure with a reaction order of unity. The overall rate also increased with temperature up to approximately 960°C and subsequently decreased with further increases in temperature. For carburization in CO‐H2‐He mixtures, the carburization rate increased with both the CO and H2 partial pressures under most conditions and was considerably faster than the rate in mixtures without hydrogen. Up to approximately 960°C, the rate was nearly independent of temperature with H2 present, but decreased with a further increase in temperature. The decrease in reaction rate for mixtures with and without H2 at 960°C coincides closely with the change in phase of iron from α to γ. Experiments at 925°C with constant P and PCO indicate that CO dissociation on the iron surface is faster than oxygen removal from the surface except at high ratios of P/PCO, and therefore oxygen removal was generally the rate‐limiting step. The rate of oxygen removal from the surface by H2 was found to be of the same order as that by CO. At high hydrogen levels, the rate of oxygen removal exceeds dissociative absorption of CO and the latter becomes rate controlling. The present results are used to establish a numerical model for the carburization of iron, which is described in a companion paper. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 327–336, 2009

Nano-cavities observed in a 316SS PWR flux thimble tube irradiated to 33 and 70 dpa

The radiation-induced microstructure of a cold-worked 316SS flux thimble tube from an operating pressurized water reactor (PWR) was examined. Two irradiated conditions, 33 dpa at 290 °C and 70 dpa at 315 °C were examined by transmission electron microscopy. The original dislocation network had completely disappeared and was replaced by fine dispersions of Frank loops and small nano-cavities at high densities. The latter appear to be bubbles containing high levels of helium and hydrogen. An enhanced distribution of these nano-cavities was found at grain boundaries and may play a role in the increased susceptibility of the irradiated 316SS to intergranular failure of specimens from this tube during post-irradiation slow strain rate testing in PWR water conditions.

Light‐toned salty soils and coexisting Si‐rich species discovered by the Mars Exploration Rover Spirit in Columbia Hills

Light‐toned soils were exposed, through serendipitous excavations by Spirit Rover wheels, at eight locations in the Columbia Hills. Their occurrences were grouped into four types on the basis of geomorphic settings. At three major exposures, the light‐toned soils are hydrous and sulfate‐rich. The spatial distributions of distinct types of salty soils vary substantially: with centimeter‐scaled heterogeneities at Paso Robles, Dead Sea, Shredded, and Champagne‐Penny, a well‐mixed nature for light‐toned soils occurring near and at the summit of Husband Hill, and relatively homogeneous distributions in the two layers at the Tyrone site. Aeolian, fumarolic, and hydrothermal fluid processes are suggested to be responsible for the deposition, transportation, and accumulation of these light‐toned soils. In addition, a change in Pancam spectra of Tyrone yellowish soils was observed after being exposed to current Martian surface conditions for 175 sols. This change is interpreted to be caused by the dehydration of ferric sulfates on the basis of laboratory simulations and suggests a relative humidity gradient beneath the surface. Si‐rich nodules and soils were observed near the major exposures of S‐rich soils. They possess a characteristic feature in Pancam visible near‐infrared (Vis‐NIR) spectra that may be diagnostic of hydrated species, and this spectral feature can be used to search for additional Si‐rich species. The exposures of hydrated salty soils within various geomorphic settings imply the potential existence of hydrous minerals in similar settings over a much wider area. Hydrous sulfates represent one of the candidates that may contribute the high level of water equivalent hydrogen in equatorial regions detected by the Neutron Spectrometer on Mars Odyssey.

A chemical kinetic study of n-butanol oxidation at elevated pressure in a jet stirred reactor

Biofuels are attractive alternatives to petroleum derived transportation fuels. n-Butanol, or biobutanol, is one alternative biofuel that can replace gasoline and diesel in transportation applications. Similar to ethanol, n-butanol can be produced via the fermentation of sugars, starches, and lignocelluloses obtained from agricultural feedstocks. n-Butanol has several advantages over ethanol, but the detailed combustion characteristics are not well understood. This paper studies the oxidation of n-butanol in a jet stirred reactor at 10atm and a range of equivalence ratios. The profiles for CO, CO2, H2O, H2, C1–C4 hydrocarbons, and C1–C4 oxygenated compounds are presented herein. High levels of carbon monoxide, carbon dioxide, water, hydrogen, methane, formaldehyde, ethylene, and propene are detected. The experimental data are used to validate a novel detailed chemical kinetic mechanism for n-butanol oxidation. The proposed mechanism well predicts the concentration of major product species at all temperatures and equivalence ratios studied. Insights into the prediction of other species are presented herein. The proposed mechanism indicates that n-butanol consumption is dominated by H-atom abstraction from the α, β, and γ carbon atoms. A sensitivity analysis is also presented to show the effects of reaction kinetics on the concentration of several poorly predicted species.

Biological compost stability influences odor molecules production measured by electronic nose during food-waste high-rate composting

Composting is a technique that is used to convert organic waste into agriculturally useful products. Composting is an aerobic, solid-state biological process, which typically can be divided into two phases, a high-rate composting phase and a curing phase. High-rate composting plays an important role during the composting process, owing to the high microbial activity occurring during this phase. It requires an accurate plant design to prevent the formation of anaerobic conditions and odors. The formation of anaerobic conditions mainly depends on the rate of O 2 consumption needed to degrade the substrate, i.e., the biological stability of the substrate. In this study, we investigated the relationship between the biological activity, measured by the dynamic respiration index (DRI) and the odor molecules production, measured by an electronic nose (EN) during two food-waste high-rate composting processes. Although the O 2 concentration in the biomass free air space (FAS) was kept optimal (O 2 > 140 ml l − 1 , v/v) during composting, strong anaerobic conditions developed. This was indicated by the high levels of sulfur compounds, methane, and hydrogen in the outlet air stream. Both the high level of O 2 consumption, needed to degrade the high-degradable water-soluble organic matter and the low water O 2 solubility, caused by high temperature reached in this stage (up to 60 °C), led to the anaerobic conditions observed in the biofilm-particle level. The application of the partial least square (PLS) analysis demonstrated a good regression between the DRI and the odor molecules produced that was detected by the EN ( R 2 = 0.991; R 2 CV = 0.990), signifying the usefulness of the DRI as a parameter to estimate the potential production of odor molecules of the biomass.

Photochemical production of molecular hydrogen in lake water and coastal seawater

Samples of lake water and coastal seawater from Nova Scotia, Canada, were irradiated with natural or artificial sunlight to investigate the potential for photochemical hydrogen production. Hydrogen photo-production was observed in all natural water samples. Rates of hydrogen formation were highest in coloured lake water (range: 98–163 pmol L − 1 h − 1 ) and lower in seawater (range: 19–45 pmol L − 1 h − 1 ). Dilutions of the most highly coloured lake sample (Kejimkujik Lake) showed a positive linear relationship between H 2 production rates and CDOM concentration. Photo-production rates normalised to UV absorption coefficients at 350 nm indicated that the photochemical efficiency of hydrogen formation varied between samples, perhaps due to differences in the CDOM composition. Photochemical hydrogen formation was also seen in solutions of syringic acid and acetaldehyde: two low-molecular-weight carbonyl compounds found in natural waters. Photochemistry may therefore offer least a partial explanation for the persistently high levels of hydrogen observed in the low-latitude surface ocean.

Hydrogen atom in strong magnetic field: A high accurate calculation in spheroidal coordinates

A B-spline-type basis set method for the calculation of hydrogen atom in strong magnetic fields in the frame of spheroidal coordinates has been introduced. High accurate energy levels of hydrogen in the magnetic field, with strength ranging from 0 to 1000 a.u., have been obtained. For the ground state, 1s0, energies with at least 11 significant digits have been obtained. For the low-lying excited state, 2p−1, energies with at least 9 significant digits are obtained. The method has also been applied to the calculation of hydrogen Rydberg states in laboratory magnetic fields. Energy spectra with at least 10 significant digits are presented. A comparison with other results in the literatures has been performed. Our results are comparable to the most accurate one up to date. A possible extension to the cases of parallel and crossed electric and magnetic fields have been discussed.

Susceptibility of Low Strength Rutile Flux-Cored Weld Metal to Hydrogen Assisted Cold Cracking

This paper presents the results of an investigation into hydrogen assisted cold cracking (HACC) susceptibility of seamless and seamed low strength rutile flux cored wires, with nominal diffusible hydrogen (HD) levels of 5 and 10 ml/100 g, respectively. The objective was to assess the influence of key welding parameters on susceptibility of weld metal to cold cracking. Parameters investigated were the welding current, the contact-tip to work-piece distance (CTWD), the shielding gas and the preheat temperature. The gapped bead-on-plate (G-BOP) test was used to examine the effects of these parameters on the extent of weld metal transverse cracking at a range of preheat temperatures. The overall results indicate that the weld metal susceptibility to cold cracking correlates with diffusible hydrogen content, HD. It was found that, without preheat, the seamless wire weld deposits ( 5 ml/100 g) exhibited cold cracking. Weld metal deposited using 75Ar-25CO2 shielding gas resulted in a higher HD levels than for CO2 shielding gas and, consequently, a higher susceptibility to cold cracking for no or low temperature preheat conditions. Preheating was found to have a strong effect on crack susceptibility, substantially decreasing the amount of cold cracking in the seamed wire welds.

Hydrogen and methane gases are frequently detected in the stomach

To investigate the incidence of bacterial overgrowth in the stomach by using a new endoscopic method in which intragastric hydrogen and methane gases are collected and analyzed. Studies were performed in 490 consecutive patients undergoing esophagogastroscopy. At endoscopy, we intubated the stomach without inflation by air, and 20 mL of intragastric gas was collected through the biopsy channel using a 30 mL syringe. Intragastric hydrogen and methane concentrations were immediately measured by gaschromatography. H pylori infection was also determined by serology. Most of intragastric hydrogen and methane levels were less than 15 ppm (parts per million). The median hydrogen and methane values (interquartile range) were 3 (1-8) ppm and 2 (1-5) ppm, respectively. The high hydrogen and methane levels for indication of fermentation were decided if the patient had the values more than 90 percentile range in each sample. When a patient had a high level of hydrogen or methane in one or more samples, the patient was considered to have fermentation. The overall incidence of intragastric fermentation was 15.4% (73/473). Intragastric methane levels were higher in the postoperative group than in other groups. None of the mean hydrogen or methane values was related to H pylori infection. Hydrogen and methane gases are more frequently detected in the stomach than expected, regardless of the presence of abdominal symptoms. Previous gastric surgery influences on the growth of methane-producing bacteria in the fasting stomach.

Metabolic engineering of Clostridium acetobutylicum for the industrial production of 1,3-propanediol from glycerol

Clostridium butyricum is to our knowledge the best natural 1,3-propanediol producer from glycerol and the only microorganism identified so far to use a coenzyme B 12-independent glycerol dehydratase. However, to develop an economical process of 1,3-propanediol production, it would be necessary to improve the strain by a metabolic engineering approach. Unfortunately, no genetic tools are currently available for C. butyricum and all our efforts to develop them have been so far unsuccessful. To obtain a better “vitamin B 12-free” biological process, we developed a metabolic engineering strategy with Clostridium acetobutylicum. The 1,3-propanediol pathway from C. butyricum was introduced on a plasmid in several mutants of C. acetobutylicum altered in product formation. The DG1(pSPD5) recombinant strain was the most efficient strain and was further characterized from a physiological and biotechnological point of view. Chemostat cultures of this strain grown on glucose alone produced only acids (acetate, butyrate and lactate) and a high level of hydrogen. In contrast, when glycerol was metabolized in chemostat culture, 1,3-propanediol became the major product, the specific rate of acid formation decreased and a very low level of hydrogen was observed. In a fed-batch culture, the DG1(pSPD5) strain was able to produce 1,3-propanediol at a higher concentration (1104 mM) and productivity than the natural producer C. butyricum VPI 3266. Furthermore, this strain was also successfully used for very long term continuous production of 1,3-propanediol at high volumetric productivity (3 g L −1 h −1) and titer (788 mM).

Recombination dynamics of primordial hydrogen and helium (He I) in the universe

We calculated the ionization fraction for hydrogen and helium (He I) as a function of the redshift z by including the two-photon decays of high hydrogen and parahelium levels and the radiative transfer in the helium 23P1 ↔ 11S0 intercombination line. We show that this yields corrections of no more than a few percent to the ionization fraction for hydrogen and speeds up significantly the recombination for helium compared to the recent works by Seager et al. (1999, 2000), in which these effects were disregarded.

Hydrogen Embrittlement Susceptibility of Conventional and Reduced Activation 9Cr-Steels

Hydrogen embrittlement behaviour of the reduced activation ferritic/martensitic steels, Eurofer’97 and VS3104, has been compared to that of the conventional alloy T91, by means of constant extension rate tests run under dynamic electrochemical charging. Charged versus uncharged reduction of specimen area ratios at rupture were taken as the most suitable ductility indexes for material discrimination in terms of hydrogen damage resistance. Fractographic analysis indicated that hydrogen content as low as 1.6 wppm caused rupture of al investigated steels, but to different degree, by promoting grain boundary decohesion. Higher hydrogen levels stimulated failure by the combined effect of bond strength weakening and stress intensification from dislocation blocking at interfaces. The better performances of T91 as well as the variability of Eurofer tensile responses were ascribed to the different chemistry and density of key microstructural factors, already suspected from metallurgical examination and further supported by hydrogen thermal extraction results.

Amperometric sensor for selective and stable hydrogen measurement

Amperometric gas sensors in a three-electrode configuration were investigated for hydrogen measurements in atmospheres containing carbon monoxide. The hydrogen-sensing working electrode was based on a platinum black electrode deposited on a porous Teflon ® substrate. To achieve selectivity, an FEP membrane was mounted at the gas inlet of the sensor. Hydrogen readily diffused through the FEP membrane and was detected on the Pt working electrode. The cross-sensitivity to gases such as carbon monoxide, ammonia and hydrogen sulfide was eliminated with nearly 100% efficiency in the short term. In addition, the poisoning effect of the carbon monoxide was virtually eliminated. Sensor stability to high levels of hydrogen was improved by the development of a hydrogen-insensitive reference electrode.

Characterization for Fusion Candidate Vanadium Alloys

This paper summarizes recent achievements in the characterization of candidate vanadium alloys obtained for fusion in the framework of the Japan-China Core University Program. National Institute for Fusion Science (NIFS) has a program of fabricating high-purity V-4Cr-4Ti alloys. The resulting products (NIFS-HEAT-1,2), were characterized by various research groups in the world including Chinese partners. South Western Institute of Physics (SWIP) fabricated a new V-4Cr-4Ti alloy (SWIP-Heat), and carried out a comparative evaluation of hydrogen embrittlement of NIFS-HEATs and SWIP-Heat. The tensile test of hydrogen-doped alloys showed that the NIFS-HEAT maintained the ductility to relatively high hydrogen levels. The comparison of the data with those of previous studies suggested that the reduced oxygen level in the NIFS-HEATs should be responsible for the increased resistance to hydrogen embrittlement. Based on the chemical analysis data of NIFS-HEATs and SWIP-Heats, neutron-induced activation was analyzed in Institute of Plasma Physics (IPP-CAS) as a function of cooling time after the use in the fusion first wall. The results showed that the low level of Co dominates the activity up to 50 years followed by a domination of Nb or Nb and Al in the respective alloys. It was suggested that reduction of Co and Nb, both of which are thought to have been introduced via cross-contamination into the alloys from the molds used should be crucial for reducing further the activation.

A Kinetic Monte Carlo Model for Helium Diffusion and Clustering in Fusion Environments

Structural materials in fusion reactors will operate in harsh radiation conditions including high displacement rates from 14 MeV neutrons with accompanying high levels of hydrogen and helium production and will experience severe property degradation. Predicting their in-service performance requires a detailed understanding of the mechanisms of defect accumulation and microstructure evolution. The physical processes involved in radiation damage are inherently multiscale, spanning more than 15 orders of magnitude in length and 24 orders of magnitude in time. Here, we describe a kinetic Monte Carlo (KMC) model to simulate the migration and clustering of transmutant helium gas atoms and ultimately determine the role of helium in mediating the long term aging of primary defects (vacancies, self-interstitial atoms and their clusters) produced in displacement cascades. The results illustrate the mechanisms responsible for the formation of vacancy-He clusters, in particular the high mobility of small vacancy-He clusters, which often lead to cluster growth through cluster–cluster coalescence events.