Interaction between atomic hydrogen and YBa2Cu3O7

1992 ◽  
Vol 7 (11) ◽  
pp. 2908-2915 ◽  
Author(s):  
Angel L.G. Ponce ◽  
Jose J. Fripiat
Keyword(s):  
Induction Period ◽  
Atomic Hydrogen ◽  
Dissociative Chemisorption ◽  
Experimental Conditions ◽  
Reaction Proceeds ◽  
Order Of Magnitude ◽  
O Vacancy ◽  
The Creation ◽  
Approximate Limit

Atomic hydrogen obtained from dissociative chemisorption of molecular H2 on Pt particles deposited on the surface of YBa2Cu3O7 reacts with the oxide in producing O vacancies and intercalating H at 82 °C under a H2 pressure of about 400 Torr. An induction period which extends over 1 h is observed as long as the concentration in O vacancies is below 0.1. Above this approximate limit the reaction proceeds quickly until about 1 mol H2 has been consumed. It then slows down progressively, but it is not completed even after 27 h of reaction and ∼1.4 H2 consumed, under these experimental conditions. The enthalpy for the creation of the O vacancy is 143 kcal/g mol O, while the H intercalation enthalpy is −57.5 kcal/g mol H. It appears that the reaction of molecular H2 over YBa2Cu3O7 not coated with Pt proceeds similarly, but the rate is nearly one order of magnitude slower, under identical conditions. The stoichiometry of the reaction agrees with the earlier suggestion that O1 is a labile oxygen which can be replaced by intercalated H. This site and the interstitial vacant sites in the copper chains square plane would be the first ones to be occupied by intercalated H.

scholarly journals Observational manifestations of ‘cosmological dinosaurs’ at redshifts z ∼ 20

2021 ◽  
Vol 503 (2) ◽  
pp. 3081-3088
Author(s):  
V K Dubrovich ◽  
Yu N Eroshenko ◽  
S I Grachev
Keyword(s):  
Black Hole ◽  
Atomic Hydrogen ◽  
Radiation Transfer ◽  
Ring Width ◽  
High Mass ◽  
Primordial Black Hole ◽  
Array Type ◽  
Local Sources ◽  
Order Of Magnitude ◽  
Very High

ABSTRACT We consider a primordial black hole of very high mass, $10^9\!-\!10^{10}\, \mathrm{M}_\odot$, surrounded by the dark matter and bayonic halo at redshifts z ∼ 20 without any local sources of energy release. Such heavy and concentrated objects in the early Universe were previously called ‘cosmological dinosaurs’. Spectral distribution and spatial variation of the brightness in the 21-cm line of atomic hydrogen are calculated with the theory of radiation transfer. It is shown that a narrow and deep absorption arises in the form of the spherical shell around the primordial black hole at the certain radius. The parameters of this shell depend almost exclusively on the mass of the black hole. The angular diameter 18 arcsec of the absorption ring at z ∼ 20 is well within the current technical possibilities of the Square Kilometre Array type telescopes. But the observation of the ring width itself requires an order of magnitude better resolution.

scholarly journals Benthic microalgae community response to flooding in a tropical salt flat

2016 ◽  
Vol 76 (3) ◽  
pp. 577-582 ◽  
Author(s):  
L. S. M. Masuda ◽  
A. Enrich-Prast
Keyword(s):  
Sea Water ◽  
Shannon Index ◽  
Community Response ◽  
Microbial Mat ◽  
Total Density ◽  
Experimental Conditions ◽  
Effect Of Water ◽  
Salt Flat ◽  
Field Samples ◽  
Order Of Magnitude

Abstract This research evaluated the effect of flooding on the microphytobenthos community structure in a microbial mat from a tropical salt flat. Field samples were collected during four consecutive days: on the first three days the salt flat was dry, on the fourth day it was flooded by rain. In order to evaluate the community maintained in flood conditions, samples from this area were collected and kept in the laboratory for 10 days with sea water. The results of total abundance of microphytobenthos varied from 4.2 × 108 to 2.9 × 109 organisms L–1, total density increased one order of magnitude under the effect of water for both situations of precipitation in the salt flat and in experimental conditions, an increase due to the high abundance of Microcoleus spp. Shannon index (H’) was higher during the desiccation period. Our data suggest that changes in the abundance of organisms were due to the effect of water. The dominance of the most abundant taxa remained the same under conditions of desiccation and influence of water, and there is probably a consortium of microorganisms in the microbial mat that helps to maintain these dominances.

Verbalization and musical memory in string players

2017 ◽  
Vol 23 (2) ◽  
pp. 212-230
Author(s):  
Eric Timperman ◽  
Peter Miksza
Keyword(s):  
Recall Performance ◽  
Experimental Conditions ◽  
Immediate Recall ◽  
Short And Long Term ◽  
The Creation ◽  
24 Hour Recall ◽  
Associative Recall ◽  
Verbal Analysis ◽  
Musical Memory

The purpose of this study was to examine the effect of verbalization about a brief etude on collegiate string players’ short- and long-term recall of the etude in question. We examined competing hypotheses that suggest it is possible that verbalization (i.e., verbal analysis of musical features) (a) could aid in recall both by highlighting patterns and constraints that inform the music’s creation and by facilitating the creation of explicit performance cues that help to bridge gaps between associative recall chains or (b) may hinder recall by interfering with the creation of procedural and auditory memories necessary for musical performance. Participants ( N = 20) were assigned to experimental conditions in which they learned an unfamiliar etude either through repetition alone or through repetition followed by the completion of a verbalization worksheet provided by the experimenter. Recall was tested both immediately following initial practice and 24 hours later to examine the effect of verbalization on both short- and long-term retention. Findings indicated no differences between groups on immediate recall performance but significant differences at the 24-hour recall task with participants in the verbalization condition recalling more material. In addition, the patterns of errors found across groups indicated a strong primacy effect. Theoretical implications for the study of memory processes in musical contexts and practical implications regarding the preparation of memorized performance are discussed.

Untersuchung konkurrierender Reaktionen in strömenden Kohlenwasserstoff-Gemischen / Investigation of Competing Reactions in Flowing Mixtures of Hydrocarbons

1974 ◽  
Vol 29 (4) ◽  
pp. 642-649 ◽  
Author(s):  
R. Laupert ◽  
G. von Bünau
Keyword(s):  
Rate Constants ◽  
Atomic Hydrogen ◽  
Relative Rate ◽  
Experimental Conditions ◽  
Kinetic Evaluation ◽  
Alkyl Radicals ◽  
Relative Rate Constants ◽  
Flow Apparatus ◽  
Competing Reactions

The reactions of atomic hydrogen with propene, butene-2, and trimethylethylene, and with mixtures of these olefins with ethylene have been studied using flow apparatus. It was found that under the experimental conditions intermediate alkyl radicals reacted practically only with atomic hydrogen. This made possible a kinetic evaluation of the results yielding numerical values of several relative rate constants of competing intermediate reactions.

4,5-Seco-4,6-cyclosteroids. III. Observations on the course of reductive rearrangement of 6β-Bromo-4β,5-epoxy-5β-cholestan-3β-ol

1969 ◽  
Vol 22 (4) ◽  
pp. 807 ◽  
Author(s):  
DJ Collins ◽  
JJ Hobbs ◽  
RJ Rawson
Keyword(s):  
Hydrogen Bromide ◽  
High Yield ◽  
Lithium Aluminium Hydride ◽  
Experimental Conditions ◽  
Lithium Aluminium ◽  
Reaction Proceeds ◽  
Derivatives Of

It has been shown that reductive rearrangement of 6β-bromo-4β,5-epoxy- 5β-cholestan-3β-ol (I) to 4,5-seco-4,6-cycle-6β-cholestane-3β,5α-diol (IXa) with lithium aluminium hydride in tetrahydrofuran proceeds via 6β-bromo-5β-cholestane-3β,5-diol (IIa). Relevant reactions of the latter and the corresponding 3-ketone are discussed. ��� Similar conversion of the 3-epimer of (I) into 4,5-seco-4,6-cyclo- 6β-cholestane-3α,5α-diol (XIIIa) in high yield indicates that reductive rearrangement of the 6β-bromo-5β-hydroxy moiety proceeds without participation of the 3-aluminate complex. Some derivatives of (XIIIa) are described. ��� Experimental conditions required for the conversion of (I) into (IXa) are defined. ��� Combined evidence indicates that the reaction proceeds in a concerted manner by essentially base-catalysed, 1,3-elimination of hydrogen bromide from diol (IIa) with 4,5-bond migration to give the formal intermediate 3β-hydroxy-4,5-seco-4,6-cyclo-6β-cholestan-5-one (VI), further reduced to (IXa).

The mechanism of the production of atomic hydrogen by hot tungsten

1936 ◽  
Vol 32 (4) ◽  
pp. 653-656 ◽  
Author(s):  
J. K. Roberts ◽  
G. Bryce
Keyword(s):  
Temperature Variation ◽  
Atomic Hydrogen ◽  
Hydrogen Molecule ◽  
Hydrogen Pressure ◽  
The Other ◽  
Square Root ◽  
Important Process ◽  
Experimental Conditions ◽  
Tungsten Atom ◽  
Tungsten Surface

The fact that the rate of production of atomic hydrogen at a tungsten surface at a given temperature is proportional to the square root of the hydrogen pressure means either that the important process is the evaporation of atoms from an adsorbed film which over the whole range of experimental conditions is sparsely occupied, or that the production of atoms is in the main due to a process in which a hydrogen molecule strikes a bare tungsten atom in the surface, one atom being adsorbed and the other evaporating and the surface being almost completely covered over the whole range of experimental conditions. Either process leads to a temperature variation in the rate of atom production in agreement with experiment. A definite decision between the two processes cannot yet be made.

scholarly journals Hα Absorption in Transiting Exoplanet Atmospheres

2013 ◽  
Vol 8 (S299) ◽  
pp. 281-282
Author(s):  
Duncan Christie ◽  
Phil Arras ◽  
Zhi-Yun Li
Keyword(s):  
Impact Parameter ◽  
Atomic Hydrogen ◽  
State Level ◽  
Atomic Layer ◽  
Ionization Rate ◽  
Upper Atmosphere ◽  
Theoretical Understanding ◽  
Radiative Transitions ◽  
Order Of Magnitude ◽  
Specific Impact

AbstractRecent observations by Jensen et al. of Hα absorption by the upper atmosphere of HD189733b have motivated the need for a theoretical understanding of the distribution of n=2 hydrogen within hot Jupiter atmospheres. With this in mind, we model the n=2 state of atomic hydrogen in a hydrostatic atmosphere in thermal and photoionization equilibrium. Both collisional and radiative transitions are included in the calculation of the n = 2 state level population. In our model, the Hα absorption is dominated by a τ ~ 1 shell composed of metastable 2s hydrogen located within the neutral atomic layer, with the contribution coming roughly uniformly throughout the layer instead of from a specific impact parameter. An ionization rate an order of magnitude over the expected value can reproduce the observed transit depth.

scholarly journals Radical Chain Monoalkylation of Pyridines

2021 ◽  
Author(s):  
Samuel Rieder ◽  
Camilo Meléndez ◽  
Kleni Mulliri ◽  
Philippe Renaud
Keyword(s):  
Rate Constant ◽  
Iodine Atom ◽  
Radical Chain ◽  
Enol Ethers ◽  
Alkyl Radicals ◽  
Reaction Proceeds ◽  
Order Of Magnitude ◽  
Enol Esters ◽  
The One ◽  
Neutral Conditions

<p>The monoalkylation of N-methoxypyridinium salts with alkyl radicals generated from alkenes (via hydroboration with catecholborane), alkyl iodides (via iodine atom transfer) and xanthates is reported. The reaction proceeds under neutral conditions since no acid is needed to activate the heterocycle and does not require the use of an external oxidant. A rate constant for the addition of a primary radical to N-methoxylepidinium >107 M–1 s–1 was experimentally determined. This rate constant is more than one order of magnitude larger than the one measured for the addition of primary alkyl radical to protonated lepidine demonstrating the remarkable reactivity of methoxypyridinium salts towards radicals. The reaction could be extended to a three component carbopyridinylation of electron rich alkenes including enol esters, enol ethers and enamides.</p>

scholarly journals On the estimation errors of KM and V from time-course experiments using the Michaelis–Menten equation

2016 ◽  
Author(s):  
Wylie Stroberg ◽  
Santiago Schnell
Keyword(s):  
Time Course ◽  
Enzyme Concentration ◽  
Mass Action ◽  
Accurate Estimation ◽  
Estimation Errors ◽  
Experimental Conditions ◽  
Progress Curve ◽  
Steady State Kinetics ◽  
Initial Substrate ◽  
Order Of Magnitude

AbstractThe conditions under which the Michaelis–Menten equation accurately captures the steady-state kinetics of a simple enzyme-catalyzed reaction is contrasted with the conditions under which the same equation can be used to estimate parameters, KM and V, from progress curve data. Validity of the underlying assumptions leading to the Michaelis–Menten equation are shown to be necessary, but not sufficient to guarantee accurate estimation of KM and V. Detailed error analysis and numerical “experiments” show the required experimental conditions for the independent estimation of both KM and V from progress curves. A timescale, tQ, measuring the portion of the time course over which the progress curve exhibits substantial curvature provides a novel criterion for accurate estimation of KM and V from a progress curve experiment. It is found that, if the initial substrate concentration is of the same order of magnitude as KM, the estimated values of the KM and V will correspond to their true values calculated from the microscopic rate constants of the corresponding mass-action system, only so long as the initial enzyme concentration is less than KM.

Fibrin Binding of Plasminogen Coated Liposomes In Vitro

1996 ◽  
Vol 75 (01) ◽  
pp. 134-139 ◽  
Author(s):  
J L M Heeremans ◽  
P Los ◽  
R Prevost ◽  
D J A Crommelin ◽  
C Kluft
Keyword(s):  
Binding Sites ◽  
In Vitro Model ◽  
Model System ◽  
Binding Properties ◽  
Experimental Conditions ◽  
Binding Rate ◽  
Order Of Magnitude ◽  
Vitro Model

SummaryIn this study, the fibrin binding properties of liposomes containing a number of plasminogen (Pig) molecules on the outside were compared to those of free (non-liposomal) Pig in an in vitro model system. Fibrin monolayer coated 96-wells plates were used, containing fibrin monomer at a density of around 3.4 to 3.9 × 10-4 nmol/cm2. These densities are similar to liposomal Plg-densities, thus allowing multivalent interactions to occur.In the panel of experimental conditions that was chosen, binding of free Pig and liposomes with Pig showed three main differences in characteristics. Firstly, in the fibrin binding of Plg-liposomes not all Pig may be involved, but on the average 40% of the total amount of liposomal Pig. This was shown by lysing the liposomes after binding to the fibrin and estimation of truly bound Pig. With Plg-densities on the liposomes below the fibrin binding sites density, the maximal number of bound Pig molecules remains below the amount of available fibrin binding sites. Secondly, a higher binding rate by at least one order of magnitude was observed for liposomes with Pig compared to free Pig. Thirdly, liposomes with Pig exhibit a fibrin binding affinity which increases with Plg-density, because of the multivalent character of interaction. Liposomal Pig can successfully compete for fibrin binding sites with a 100 fold higher concentration of free Pig.These in vitro findings indicate that in view of avid and rapid fibrin binding, liposomes with attached plasminogen may be suitable for in vivo targeting to fibrin based thrombi.

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