The time dependence of scintillation intensity in aromatic materials

A description is given of the kinetics of the prompt and delayed luminescence components from aromatic materials excited by ionizing radiation. A theoretical model has been developed to describe the origin of the delayed scintillation component. From initial assumptions of molecular triplet state diffusion and triplet-triplet annihilation to form delayed singlet states, equations are obtained defining the intensity of the delayed component with time. These equations are shown to agree well with existing experimental results. From the comparison the following parameters for triplet excitations in anthracene and stilbene crystals have been calculated: diffusion constant, 6 x 10 -6 cm 2 s -1 (anthracene) and 3 x 10 -6 cm 2 s -1 (stilbene); triplet-triplet interaction rate constant, 1·3 x 10 -11 cm 3 s -1 (anthracene) and 7·5 x 10 -12 cm 3 s -1 (stilbene); and diffusion length, 3·5 x 10 -4 cm (anthracene).

Download Full-text

KINETICS OF THE OXIDATION OF TITANIUM

Canadian Journal of Research ◽

10.1139/cjr50b-011 ◽

1950 ◽

Vol 28b (2) ◽

pp. 60-72 ◽

Cited By ~ 3

Author(s):

L. M. Pidgeon ◽

W. A. Alexander

Keyword(s):

Low Temperatures ◽

Oxidation Process ◽

Film Formation ◽

Surface Film ◽

Diffusion Constant ◽

Initial Oxidation ◽

Temperature Range ◽

Logarithmic Equation ◽

Kinetics Of ◽

And Diffusion

The rates of oxidation of titanium powder and sintered bar have been investigated in the temperature range 25° to 550 °C. at pressures of 2 and 20 cm. oxygen maintained constant throughout each experiment. It has been shown that the oxidation process can be divided into two mechanisms, viz., the formation of a thin surface film and diffusion of oxide into the metal. The surface film formation at low temperatures follows the logarithmic equation:[Formula: see text]on vacuum annealed metal surface. The diffusion process at higher temperatures is described by the equation:[Formula: see text]after the initial oxidation. This equation leads to preliminary values of the diffusion constant of the order of 10 × 10−8 cm2. per min. in the temperature range 463° to 565 °C.

Download Full-text

A theory for the simultaneous determination of the minority carrier lifetime, diffusion length and diffusion constant in a semiconducting medium using a modulated light beam

Solar Cells ◽

10.1016/0379-6787(87)90003-2 ◽

1987 ◽

Vol 20 (4) ◽

pp. 279-287 ◽

Cited By ~ 4

Author(s):

Ravdeep Kaur ◽

Suresh Garg ◽

Feroz Ahmed

Keyword(s):

Light Beam ◽

Simultaneous Determination ◽

Carrier Lifetime ◽

Minority Carrier ◽

Diffusion Length ◽

Diffusion Constant ◽

Minority Carrier Lifetime ◽

Modulated Light ◽

And Diffusion

Download Full-text

On the removal of organic vehicle from moulded ceramic bodies

Proceedings of the Royal Society of London. Series A: Mathematical and Physical Sciences ◽

10.1098/rspa.1991.0020 ◽

1991 ◽

Vol 432 (1885) ◽

pp. 321-340 ◽

Cited By ~ 50

Keyword(s):

Degradation Products ◽

Ceramic Body ◽

Infinite Cylinder ◽

Unsteady State ◽

Free Volume Theory ◽

Organic Vehicle ◽

State Diffusion ◽

Kinetics Of ◽

And Diffusion ◽

Nonlinear Numerical Model

The origin of defects in moulded ceramic bodies during pyrolytic removal of the organic vehicle is predicted. The kinetics of thermal degradation of the polymer are combined with a nonlinear, numerical model for the unsteady-state diffusion of degradation products in solution in the parent polymer. The resulting centre concentration of monomer in an infinite cylinder is used to predict the incidence of boiling which results in the formation of internal defects in the ceramic body. The calculation, which incorporates the concentration dependence of the diffusion coefficient based on free volume theory, reveals the outcome of the competition between degradation and diffusion and thus allows the influence of material, geometric and process variables to be explored.

Download Full-text

The effect of preparation conditions and the ionizing radiation on the kinetics of cupric oxide reduction by hydrogen

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19771266 ◽

1977 ◽

Vol 42 (4) ◽

pp. 1266-1277 ◽

Cited By ~ 9

Author(s):

M. Pospíšil ◽

P. Taras

Keyword(s):

Ionizing Radiation ◽

Cupric Oxide ◽

Oxide Reduction ◽

Preparation Conditions ◽

Kinetics Of

Download Full-text

Effect of ionizing radiation on the kinetics of hydrogenation on the Ni-MgO mixed catalyst

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19821780 ◽

1982 ◽

Vol 47 (7) ◽

pp. 1780-1786 ◽

Cited By ~ 2

Author(s):

Rostislav Kudláček ◽

Jan Lokoč

Keyword(s):

Experimental Data ◽

Activation Energy ◽

Liquid Phase ◽

Ionizing Radiation ◽

Oxide Catalyst ◽

Absorbed Dose ◽

Hydrogenation Rate ◽

Solution Composition ◽

Mixed Catalyst ◽

Kinetics Of

The effect of gamma pre-irradiation of the mixed nickel-magnesium oxide catalyst on the kinetics of hydrogenation of maleic acid in the liquid phase has been studied. The changes of the hydrogenation rate are compared with the changes of the adsorbed amount of the acid and with the changes of the solution composition, activation energy, and absorbed dose of the ionizing radiation. From this comparison and from the interpretation of the experimental data it can be deduced that two types of centers can be distinguished on the surface of the catalyst under study, namely the sorption centres for the acid and hydrogen and the reaction centres.

Download Full-text

Water and Deuterium Oxide Permeability through Aquaporin 1: MD Predictions and Experimental Verification

The Journal of General Physiology ◽

10.1085/jgp.200709810 ◽

2007 ◽

Vol 130 (1) ◽

pp. 111-116 ◽

Cited By ~ 31

Author(s):

Artem B. Mamonov ◽

Rob D. Coalson ◽

Mark L. Zeidel ◽

John C. Mathai

Keyword(s):

Deuterium Oxide ◽

Diffusion Constant ◽

Structural Data ◽

Md Simulations ◽

Water Model ◽

Aquaporin 1 ◽

Self Diffusion ◽

Osmotic Permeability ◽

Protein Channels ◽

And Diffusion

Determining the mechanisms of flux through protein channels requires a combination of structural data, permeability measurement, and molecular dynamics (MD) simulations. To further clarify the mechanism of flux through aquaporin 1 (AQP1), osmotic pf (cm3/s/pore) and diffusion pd (cm3/s/pore) permeability coefficients per pore of H2O and D2O in AQP1 were calculated using MD simulations. We then compared the simulation results with experimental measurements of the osmotic AQP1 permeabilities of H2O and D2O. In this manner we evaluated the ability of MD simulations to predict actual flux results. For the MD simulations, the force field parameters of the D2O model were reparameterized from the TIP3P water model to reproduce the experimentally observed difference in the bulk self diffusion constants of H2O vs. D2O. Two MD systems (one for each solvent) were constructed, each containing explicit palmitoyl-oleoyl-phosphatidyl-ethanolamine (POPE) phospholipid molecules, solvent, and AQP1. It was found that the calculated value of pf for D2O is ∼15% smaller than for H2O. Bovine AQP1 was reconstituted into palmitoyl-oleoyl-phosphatidylcholine (POPC) liposomes, and it was found that the measured macroscopic osmotic permeability coefficient Pf (cm/s) of D2O is ∼21% lower than for H2O. The combined computational and experimental results suggest that deuterium oxide permeability through AQP1 is similar to that of water. The slightly lower observed osmotic permeability of D2O compared to H2O in AQP1 is most likely due to the lower self diffusion constant of D2O.

Download Full-text

Biosorption and Diffusion Modeling of Pb(II) by Malt Bagasse

International Journal of Chemical Engineering ◽

10.1155/2016/4210561 ◽

2016 ◽

Vol 2016 ◽

pp. 1-11 ◽

Cited By ~ 4

Author(s):

Klaiani B. Fontana ◽

Giane Gonçalves Lenzi ◽

Erica R. L. R. Watanabe ◽

Ervin Kaminski Lenzi ◽

Juliana A. M. T. Pietrobelli ◽

...

Keyword(s):

Sorption Process ◽

Isotherm Models ◽

Diffusion Modeling ◽

Biosorption Capacity ◽

Kinetic And Thermodynamic Parameters ◽

Pseudo Second Order ◽

Ph Optimization ◽

Kinetics Of ◽

And Diffusion

The removal of Pb(II) from water by biosorption processes onto malt bagasse was investigated and the kinetic and thermodynamic parameters were obtained; additionally a diffusion modeling was proposed. The characterization of malt bagasse was performed by FTIR and SEM/EDS. The experiments were conducted in batch system and an experimental design based response surface methodology was applied for agitation speed and pH optimization. The kinetics of biosorption followed pseudo-second-order model and the temperature of the process affected the biosorption capacity. Isotherm models of Langmuir, Freundlich, and Elovich were applied and the Langmuir model showed better fit and the estimated biosorption capacity was 29.1 mg g−1. The negative values obtained for ΔG° and positive values of ΔH° confirm, respectively, the spontaneous and endothermic nature of the process. The diffusion modeling was performed based on experiments in the absence of agitation to investigate the influence of the biosorbent on the sorption process of Pb(II) ions.

Download Full-text