Numerical investigation of tunnelling contributions to electron scavenging reactions in liquids at short times

1977 ◽  
Vol 55 (11) ◽  
pp. 2124-2132 ◽  
Author(s):  
P. Robin Butler ◽  
Michael J. Pilling ◽  
Stephen A. Rice ◽  
Timothy J. Stone
Keyword(s):  
Diffusion Equation ◽  
Time Dependence ◽  
Numerical Investigation ◽  
Concentration Profile ◽  
Electron Concentration ◽  
Significant Contribution ◽  
Reaction Parameters ◽  
Sink Term ◽  
Short Time ◽  
Short Times

Fick's second diffusion equation, with an added exponential sink term, is integrated numerically to simulate the decay of electrons at short times in the presence of scavengers. The time dependence of the scavenger concentration profile, the scavenging rate constant, and the electron concentration are illustrated graphically. Using the experimental results of Buxton et al. and Jonah et al. It is shown that the Smoluchowski equation is valid within their experimental time ranges provided the cage encounter distance is replaced by Reff, where Reff can be evaluated explicitly in terms of reaction parameters. It is also shown that tunnelling from relaxed traps may make a significant contribution to ultra-short time electron scavenging.

The Effect of Structural Relaxation on the Diffusion of Au in Amorphous Pd80Si20

1992 ◽  
Vol 279 ◽  
Author(s):  
A. V. Wagner ◽  
F. Spaepen
Keyword(s):  
Time Dependence ◽  
Viscous Flow ◽  
Concentration Profile ◽  
Structural Relaxation ◽  
Rutherford Backscattering Spectrometry ◽  
New Method ◽  
Relaxation Model ◽  
Sputter Deposited ◽  
Kinetics Of ◽  
Short Times

ABSTRACTThe diffusivity of Au in sputter-deposited amorphous Pd80Si20 has been measured by Rutherford backscattering spectrometry (RBS) between 275°C and 380°C. A new method based on scaling of the evolution of the variance of the concentration profile was used to analyze the data. The diffusivity was found to be independent of the Au concentration below 3 at.%. Structural relaxation causes a time dependence that is evident at short times. The kinetics of this relaxation can be described by the bimolecular relaxation model used in the analysis of viscous flow.

scholarly journals Breeding Strategies to Improve Miscanthus as a Sustainable Source of Biomass for Bioenergy and Biorenewable Products

Agronomy ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 673 ◽  
Author(s):  
John Clifton-Brown ◽  
Kai-Uwe Schwarz ◽  
Danny Awty-Carroll ◽  
Antonella Iurato ◽  
Heike Meyer ◽  
...  
Keyword(s):  
Significant Contribution ◽  
Perennial Grass ◽  
Time Frame ◽  
Eastern Asia ◽  
Germplasm Collections ◽  
Naturally Occurring ◽  
Wide Range ◽  
Yield Quality ◽  
Short Time ◽  
Commercial Expansion

Miscanthus, a C4 perennial grass native to Eastern Asia, is being bred to provide biomass for bioenergy and biorenewable products. Commercial expansion with the clonal hybrid M. × giganteus is limited by low multiplication rates, high establishment costs and drought sensitivity. These limitations can be overcome by breeding more resilient Miscanthus hybrids propagated by seed. Naturally occurring fast growing indigenous Miscanthus species are found in diverse environments across Eastern Asia. The natural diversity provides for plant breeders, the genetic resources to improve yield, quality, and resilience for a wide range of climates and adverse abiotic stresses. The challenge for Miscanthus breeding is to harness the diversity through selections of outstanding wild types, parents, and progenies over a short time frame to deploy hybrids that make a significant contribution to a world less dependent on fossil resources. Here are described the strategies taken by the Miscanthus breeding programme at Aberystwyth, UK and its partners. The programme built up one of the largest Miscanthus germplasm collections outside Asia. We describe the initial strategies to exploit the available genetic diversity to develop varieties. We illustrate the success of combining diverse Miscanthus germplasm and the selection criteria applied across different environments to identify promising hybrids and to develop these into commercial varieties. We discuss the potential for molecular selections to streamline the breeding process.

Numerical Solution of Nonlinear Reaction–Advection–Diffusion Equation

2019 ◽  
Vol 14 (4) ◽  
Author(s):  
Anup Singh ◽  
S. Das ◽  
S. H. Ong ◽  
H. Jafari
Keyword(s):  
Finite Difference ◽  
Finite Difference Method ◽  
Diffusion Equation ◽  
Difference Method ◽  
Conservative System ◽  
Computational Time ◽  
Advection Diffusion Equation ◽  
Advection Diffusion ◽  
Nonlinear Reaction ◽  
Sink Term

In the present article, the advection–diffusion equation (ADE) having a nonlinear type source/sink term with initial and boundary conditions is solved using finite difference method (FDM). The solution of solute concentration is calculated numerically and also presented graphically for conservative and nonconservative cases. The emphasis is given for the stability analysis, which is an important aspect of the proposed mathematical model. The accuracy and efficiency of the proposed method are validated by comparing the results obtained with existing analytical solutions for a conservative system. The novelty of the article is to show the damping nature of the solution profile due to the presence of the nonlinear reaction term for different particular cases in less computational time by using the reliable and efficient finite difference method.

The kinetics of proton and deuteron transfer from 4-nitrophenylnitromethane and l-(4-nitrophenyl)-l-nitroethane to 2,7-dimethoxy-l,8-bis(dimethylamino)naphthalene in acetonitrile solvent

1981 ◽  
Vol 59 (21) ◽  
pp. 3034-3038 ◽  
Author(s):  
Kenneth T. Leffek ◽  
Przemyslaw Pruszynski
Keyword(s):  
Isotope Effect ◽  
Reaction Rate ◽  
Significant Contribution ◽  
Reaction Parameters ◽  
Deuterium Isotope Effect ◽  
First Order ◽  
Enthalpy Of Activation ◽  
Deuteron Transfer ◽  
Slow Dissociation ◽  
Kinetics Of

4-Nitrophenylnitromethane reacts with 2,7-dimethoxy-1,8-bis(dimethylamino)naphthalene in acetonitrile in a bimolecular proton transfer, which shows a primary deuterium isotope effect, kH/kD = 12.2 at 25 °C. The large isotope effect on the enthalpy of activation, (ΔHD≠ – ΔHH≠) = 4.6 ± 0.3 kcal mol−1 is consistent with a significant contribution of proton tunnelling to the reaction rate of the protium substrate.The analogous reaction of 1-(4-nitrophenyl)-1-nitroethane with the same base in acetonitrile gives contrasting kinetics and reaction parameters. The reaction is first order, showing no dependence on base concentration. While the isotope effect kH/kD = 9.3 at 25 °C, the enthalpy of activation difference (ΔHD≠ – ΔHH≠) is only 0.5 ± 0.1 kcal mol−1. It is concluded that the 1-(4-nitrophenyl)-1-nitroethane undergoes a slow dissociation, with a very small dissociation constant, followed by a fast association with the base to yield the carbanion ion-pair.

scholarly journals Extension of a short-time solution of the diffusion equation with application to micropore diffusion in a finite system

2007 ◽  
Vol 48 (4) ◽  
pp. 503-521 ◽  
Author(s):  
P. D. Haynes ◽  
S. K. Lucas
Keyword(s):  
Diffusion Equation ◽  
Error Function ◽  
Exponential Series ◽  
Laplace Domain ◽  
Function Solution ◽  
Micropore Diffusion ◽  
Time Solution ◽  
Long Time ◽  
Negative Exponential ◽  
Short Time

AbstractThe diffusion equation is used to model and analyze sorption, a process used in the purification or separation of fluids. For the diffusion inside a spherical porous solid immersed in a limited-volume and well-stirred fluid, Ruthven [5], Crank [3] and, for the analogous flow of heat, Carslaw and Jaeger [2] give an eigenfunction expansion solution to the diffusion equation that provides accurate long-time solutions when only a few terms are used. However, to obtain the same accuracy for short-time solutions the number of eigenfunction terms required increases exponentially. An alternative error function solution of Carman and Haul [1] is accurate for sufficiently short times but not for long times. Although their solution is well quoted [3, 4, 6], Carman and Haul do not provide a derivation in their paper. This paper provides a full derivation of the short-time solution of Carman and Haul that uses only the first term of a negative exponential series in the Laplace domain. It is shown that the accuracy and range of the short-time result is improved by the inclusion of additional terms of the negative exponential series. An analysis of short-time and long-time resultsis presented, together with recommendations as to their use.

Dynamic Coercivity and Thermal Decay of Magnetic Media

1998 ◽  
Vol 517 ◽  
Author(s):  
Kurt Rubin ◽  
Jason Goldberg ◽  
Hal Rosen ◽  
Ernesto Marinero ◽  
Mary Doemer ◽  
...  
Keyword(s):  
Time Dependence ◽  
Decay Rate ◽  
Experimental Technique ◽  
Linear Density ◽  
Magnetic Media ◽  
Magnetic Transitions ◽  
Thermal Decay ◽  
Thermally Induced ◽  
The Media ◽  
Short Times

AbstractThermally induced decay of longitudinally recorded magnetic transitions is measured on a spin-stand. The decay rate increases with increased linear density and decreases with increased media coercivity. A new spin-stand experimental technique has been developed which allows measurements of the time dependence of the media coercivity as a function of write times spanning short times characteristic of write times in drives to long times associated with VSM measurements. The ratio of long to short write time coercivity was larger for media which are thermally unstable.

Unsteady Viscous Flows and Stokes's First Problem

2006 ◽  
Author(s):  
Y. S. Muzychka ◽  
M. M. Yovanovich
Keyword(s):  
Correlation Method ◽  
Viscous Flows ◽  
Unsteady Boundary Layer ◽  
Unsteady Couette Flow ◽  
Long Time ◽  
Layer Flow ◽  
Short Time ◽  
Relationship Of ◽  
The Relationship ◽  
Short Times

Unsteady viscous flows and Stokes's first problem are examined. Three problems are considered: unsteady Couette flow, unsteady Poiseuille flow, and unsteady boundary layer flow. The relationship between these three fundamental unsteady flows and Stokes' first problem is illustrated. Scaling principles are used to deduce the short time and long time characteristics of these three problems. Asymptotic analysis is used to obtain exact short and long time characteristics and to show the relationship of each problem to Stokes's first problem for short times. Finally, compact robust models are developed for all values of time using the Churchill-Usagi asymptotic correlation method to combine the short and long time characteristics.

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