Transient Hydrogen Research Articles

Direct proton-transfer reaction via a transient hydrogen bond-bridged allyl anion system on the models of cycloheptatrienes and propene

Un deplacement intramoleculaire direct de proton 1,3 est observe dans les derives du cycloheptatriene; ce deplacement s'effectuant via un carbanion ponte par une liaison hydrogene 1,3 qui est un etat de transition plutot qu'un intermediaire

The relationship between hydrogen metabolism, sulfate reduction and nitrogen fixation in sulfate reducers

Hydrogenase and nitrogenase activities of sulfate-reducing bacteria allow their adaptation to different nutritional habits even under adverse conditions. These exceptional capabilities of adaptation are important factors in the understanding of their predominant role in problems related to anaerobic metal corrosion. Although the D2−H+ exchange reaction indicated thatDesulfovibrio desulfuricans strain Berre-Sol andDesulfovibrio gigas hydrogenases were reversible, the predominant activity in vivo was hydrogen uptake. Hydrogen production was restricted to some particular conditions such as sulfate or nitrogen starvation. Under diazotrophic conditions, a transient hydrogen evolution was followed by uptake when dinitrogen was effectively fixed. In contrast, hydrogen evolution proceeded when acetylene was substituted as the nitrogenase substrate. Hydrogen can thus serve as an electron donor in sulfate reduction and nitrogen metabolism.

Influence of the oropharyngeal microflora on the measurement of exhaled breath hydrogen

We investigated the possible contribution made by oropharyngeal microfloral fermentation of ingested carbohydrate to the generation of the early, transient exhaled breath hydrogen rise seen after carbohydrate ingestion. Ten subjects ate or were sham fed carbohydrate-containing meals with and without prior chlorhexidine mouthwash during serial collection of exhaled breath and mouth hydrogen samples. Meal ingestion and sham feeding both induced significant (p < 0.01) elevations of breath and mouth hydrogen that were virtually abolished by prior chlorhexidine mouthwash. In 7 subjects, delivery of the meal directly into the stomach via an orogastric tube did not cause a breath or mouth hydrogen rise. Oral contents incubated anaerobically in vitro with carbohydrate generated hydrogen that was again inhibited by chlorhexidine. These studies indicate that fermentation of ingested carbohydrate by oropharyngeal bacteria can contribute significantly to measured breath hydrogen values soon after meal ingestion, and may introduce avoidable error into the interpretation of serial breath hydrogen data.

Mathematical Description of Measuring Results of the Tritium and Hydrogen Permeation Through Surface Oxidized Alloys

Steady state as well as transient hydrogen permeation models have been calculated. Especially a complex pressure dependence for bright as well as oxidized alloys could be derived and compared with the various experimental findings confirming the observed transitions between square root and linear pressure dependence in the different pressure ranges. A diffusion limited transport model with linear boundary conditions has been used to describe time dependent permeation. Thereby the oxide has been treated as a heterogeneous two phase system, where the ''good'' phase mainly determines its effectiveness in permeation reduction which is more or less lessened by the ''bad'' phase.

Mathematical description of measuring results of the tritium and hydrogen permeation through surface oxidized alloys

Steady state as well as transient hydrogen permeation models have been calculated. Especially a complex pressure dependence for bright as well as oxidized alloys could be derived and compared with the various experimental findings confirming the observed transitions between square root and linear pressure dependence in the different pressure ranges. A diffusion limited transport model with linear boundary conditions has been used to describe time dependent permeation. Thereby the oxide has been treated as a heterogeneous two phase system, where the ''good'' phase mainly determines its effectiveness in permeation reduction which is more or less lessened by the ''bad'' phase.

Comparative studies of methanogenesis in thermophilic and mesophilic anaerobic digesters using membrane inlet mass spectrometry

Membrane inlet mass spectrometry was used to monitor liquid phase hydrogen and methane concentrations in samples from laboratory mesophilic (37°C) and thermophilic (55°C) anaerobic digesters supplied with a glucose based medium. The Ks obtained for H2 utilisation for the mesophilic system was 5.5 μM compared with 90 μM for the thermophilic system. Under overload situations of fatty acids or glucose, hydrogen became more apparent in the mesophilic system in contrast to the thermophilic system in which even gross overload gave only transient detectable hydrogen production.

Experimental study of the transient hydrogen jet using a fast response probe

This paper presents a fundamental study on the mixing process of the transient hydrogen jet, such as a jet of hydrogen injection engine. We improved a fast response concentration probe with a response time of less than 200 μs. Hydrogen gas was injected into quiescent atmospheric air through a single shot device or through an injection nozzle developed for a hydrogen diesel engine. A discussion on the mixing process of the jet was carried out with time and space resolved concentration distribution measured with the fast response probe and with the behaviour of jet visualized by a schlieren method and of the entrained surrounding air by the jet.

Influence of hydrogen chemisorption kinetics on the interpretation of hydrogen transport through iron membranes

The influence of a specific surface reaction on the transport of gas-phase hydrogen through iron membranes has been investigated on the basis of model calculations. The surface reaction involves an adsorbed molecular hydrogen precursor between the gas phase and the dissociated chemisorbed state. The calculations demonstrate that the surface reaction for the H2/Fe system makes significant contributions to the time delay associated with the transient hydrogen transport through iron membranes, even under conditions where the steady-state hydrogen transport is independent of the surface reaction. These contributions to the time delay are interpreted in terms of an effective diffusivity, which is a function of the pressure on the entrance side and the thickness of the membrane.

The effect of sulphur content in hydrogen induced cracking of steel weldment

This paper describes a numerical analysis which relates the sulphur content of structural steel and hydrogen induced cracking in welded-joints. Transient hydrogen concentration and hydrostatic pressure at the joint were calculated based on a mathematical model.

Effects of ionization and counterion binding on the surface areas of phosphatidic acids in monolayers.

At 24-26 degrees C, force-area isotherms show that unionized dipalmitoyl phosphatidic acid forms a solid-condensed film while unionized egg and dioleoyl phosphatidic acids form liquid-expanded films. Surface area is a characteristic feature of a specific phosphatidic acid and the purity of a phosphatidic acid preparation can be established by the surface area of the unionized phosphatidic acid (acid subphase) at 17 dynes/cm (castor oil piston). Ionized dipalmitoyl phosphatidic acid desorbs from a monolayer at a measurable rate while ionized egg and dioleoyl phosphatidic acids desorb too slowly for rate studies. The apparent surface pK(2) for dipalmitoyl phosphatidic acid, calculated from desorption rates, is 9.4. Surface areas of the phosphatidic acids expand with ionization. Solid dipalmitoyl phosphatidic acid films expand only in the pK(2) region, showing one inflection point which indicates that the K(1)/K(2) ratio is less than 100 and that, as a consequence of this ratio, the apparent surface pK(1) is greater than 7.4. Liquid egg and dioleoyl phosphatidic acid films have two inflection points, expanding in both the pK(1) and pK(2) regions. The apparent surface pK(1) and pK(2) values, calculated from inflection points in surface area data, are 3.5 and 8.0, respectively. Film expansion with phosphatidate anions is less than anticipated, showing the presence of weak transient hydrogen bonds. Expanded phosphatidate anion films are condensed by alkaline earth cations. The Ca(2+) and Ba(2+) salts of completely ionized phosphatidic acids collapse from monolayers, showing that the phosphatidate anion may function as an ionophore for the transport of alkaline earth ions.-Patil, G. S., N. J. Dorman, and D. G. Cornwell. Effects of ionization and counterion binding on the surface areas of phosphatidic acids in monolayers.

Hydrogen diffusion in palladium by galvanostatic charging

The diffusion of hydrogen in α-palladium at ambient temperature has been studied by a galvanostatic technique. Single transient and multiple transient hydrogen charging experiments were conducted on specimens over a range of charging currents and specimen thicknesses. The mathematical description of multiple transient charging is developed for the galvanostatic technique from the general solution for diffusion. The diffusion coefficient at 23°C for hydrogen in α-palladium was determined to be (3.4 ± 0.2) × 10 −7 cm 2/ s in excellent agreement with results from Gorsky-effect measurements. The results demonstrate that bulk hydrogen diffusion is the rate controlling process, and the hydrogen flux boundary conditions assumed in the mathematical analyses were satisfied by the galvanostatic technique.

Theory of lipid monolayer and bilayer phase transitions: effect of headgroup interactions.

Headgroup and soft core interactions are added to a lipid monolayer-bilayer model and the surface pressure-area phase diagrams are calculated. The results show that quite small headgroup interactions can have biologically significant effects on the transition temperature and the phase diagram. In particular, the difference in transition temperatures of lecithins and phosphatidyl ethanolamines is easy to reproduce in the model. The phosphatidic acid systems seem to require weak transient hydrogen bonding which is also conjectured to play a role in most of the lipid systems. By a simple surface free energy argument it is shown that monolayers under a surface pressure of 50 dynes/cm should behave as bilayers, in agreement with experiment. Although the headgroup interactions are biologically very significant, in fundamental studies of the main phase transition in lipids they are secondary in importance to the hydrocarbon chain interactions (including the excluded volume interaction, the rotational isomerism, and the attractive van der Waals interaction).

Pulse radiolysis of aqueous cyanide solutions. Kinetics of the transient hydroxyl radical and hydrogen atom adducts and subsequent rearrangements

Pulse radiolysis of aqueous cyanide solutions. Kinetics of the transient hydroxyl radical and hydrogen atom adducts and subsequent rearrangements

Population Densities and Ionization Coefficients of Fast Transient Hydrogen Plasmas

Abstract Population densities and ionization coefficients of transient hydrogen plasmas have been calculated for typical ionization and recombination conditions. The results have been obtained by solving a system of differential equations by means of the Runge-Kutta method. Each equation describes the temporal evolution of a quantum state belonging to the plasma. Two initial conditions have been studied: i) The number density populations of the excited states are in Saha equilibrium with the electrons ii) the densities of excited states are equal to zero, whereas the initial condition for the ground state density is caracterized by a non-equilibrium parameter b1(t = 0) =n1/n1E &gt; which has been varied from 106 to 10-2. Typical results for electron number densities ne ranging from 108 to 2.5 · 1013 p/cm3 and electron temperatures ranging from T = 8000 to 16000 °K are presented and discussed.

Electron spin polarization effects in a study of transient hydrogen atoms in acidic ices under electron irradiation

Electron spin polarization effects in a study of transient hydrogen atoms in acidic ices under electron irradiation

Dynamic Nuclear Polarization in Phosphorus Compounds with Perchlorotriphenylmethyl and Other Radicals

Dynamic nuclear polarization has been examined in liquid solutions containing the radical perchlorotriphenylmethyl and 14 different phosphorus compounds. In addition, the radicals bisdiphenylenephenylallyl, tri-t-butylphenoxyl, and diphenylpicrylhydrazyl have been examined with five phosphorus compounds. The chlorocarbon radical shows on the average the least scalar coupling of the four. This is in accord with the well-shielded spin distribution on this radical and the great chemical stability of aromatic chlorocarbons. PCTM is found to be almost completely inert, both electronically and chemically, toward phosphines and phosphites. Exceptional cases of high coupling were observed with PCTM and dimethylphosphite, triphenylphosphine oxide, and hexamethylphosphoramide. The first case appears to be due to a transient hydrogen bond Cl···H–P, the second due to an exposed polarizable orbital system, and the last due to an obscure chemical complexation tendency. Exceptional cases with the other radicals serve to illustrate further stereospecific molecular couplings between sites of active chemical or electronic attraction for each other.

Investigation of the Plasma Produced by a Normal Ionizing Shock Wave Using Polychromator Techniques

Measurements of the electron density of a transient hydrogen plasma have been made by a study of the Stark broadening of the emitted Hfl radiation. The plasma is formed by the passage of a strong ionizing shock wave through a neutral gas in the pressure range 100 .;;; p .;;; 400 mtorr. The instantaneous Stark� broadened line profiles have been constructed by simultaneously sampling the light intensities at a number of wavelengths within the Hflline by the use of an eight. channel poly. chromator.

Experimental studies of the continuum emission of hydrogen

The absolute intensity of continuum radiation emitted from a transient hydrogen plasma was measured for the wavelength range 3000–8000 Å, and found to agree closely with that theoretically predicted by considering all the significant radiating processes. The various particle densities and the temperatures needed for the comparison were spectroscopically obtained from the line radiation and independently of the continuum; the necessary assumption of local thermal equilibrium is discussed in the paper. The plasma was produced in an electrically driven shock tube, and observed close behind the shock front where impurity radiation was found to be unimportant. The measured electron densities were in the range 3 × 10 16−1·1 × 10 17 cm −3, and temperatures 11,000–18,000°K. Under some conditions both the atomic and negative ion free-bound and free-free spectra were important, while the experimental accuracy was insufficient to distinguish any contribution due to H 2 + formation.