The Experts below are selected from a list of 246 Experts worldwide ranked by ideXlab platform

Hyungu Jeong - One of the best experts on this subject based on the ideXlab platform.

  • alkali silica Reaction kinetics of chemistry of pore solution and calcium hydroxide content in cementitious system
    Cement and Concrete Research, 2015
    Co-Authors: Jan Olek, Hyungu Jeong
    Abstract:

    Abstract This paper presents the results of the investigations on the chemistry of pore solutions, the contents of calcium hydroxide, and the expansions in mortars containing both reactive and non-reactive aggregates. In order to examine the effect of the temperature, experiments were performed at three different temperatures (23 °C, 38 °C and 55 °C). The compositions of the pore solution were measured at short time intervals for a period of up to 130 days in order to capture the kinetics of the chemistry of pore solution. The results showed that the changes in the concentrations of alkali ions can be best explained by the first order Reaction. In addition, the proposed rate equation could reasonably simulate the changes in the actual concentrations of alkalis. Finally, the results in this paper suggest that the rate of the alkali–silica Reaction in cementitious system containing highly reactive aggregate can be also expressed as the first order Reaction.

  • Alkali–silica Reaction: Kinetics of chemistry of pore solution and calcium hydroxide content in cementitious system
    Cement and Concrete Research, 2015
    Co-Authors: Jan Olek, Hyungu Jeong
    Abstract:

    Abstract This paper presents the results of the investigations on the chemistry of pore solutions, the contents of calcium hydroxide, and the expansions in mortars containing both reactive and non-reactive aggregates. In order to examine the effect of the temperature, experiments were performed at three different temperatures (23 °C, 38 °C and 55 °C). The compositions of the pore solution were measured at short time intervals for a period of up to 130 days in order to capture the kinetics of the chemistry of pore solution. The results showed that the changes in the concentrations of alkali ions can be best explained by the first order Reaction. In addition, the proposed rate equation could reasonably simulate the changes in the actual concentrations of alkalis. Finally, the results in this paper suggest that the rate of the alkali–silica Reaction in cementitious system containing highly reactive aggregate can be also expressed as the first order Reaction.

Mark W. Dewhirst - One of the best experts on this subject based on the ideXlab platform.

  • Analytic Solution to Steady-State Radial Diffusion of a Substrate with First-Order Reaction Kinetics in the Tissue of a Krogh's Cylinder
    Radiation research, 2008
    Co-Authors: John P. Kirkpatrick, Mark W. Dewhirst
    Abstract:

    It is often useful to calculate the concentration profile for a substrate undergoing Reaction in the tissue surrounding a capillary. In this paper, we consider a model geometry consisting of a long straight cylinder of tissue surrounding a capillary. Substrate diffuses radially out of the capillary through the tissue, with consumption of substrate in the tissue directly proportional to substrate concentration (i.e., First-Order Reaction kinetics). The model is extended to include the case where a cylinder of necrotic tissue surrounds a metabolically active inner tissue cylinder. A simple analytic solution is derived, and concentration profiles are generated for various combinations of parameters. Compared to the case where substrate consumption is independent of concentration, this model predicts much more rapid depletion of substrate near the capillary interface. This can have significant implications for the calculation of the hypoxic fraction (e.g., tissue with pO(2)

Xiaoxi Zeng - One of the best experts on this subject based on the ideXlab platform.

  • Thermokinetic Research Method for Faster First-Order Reaction. Double-parameter method
    Journal of Thermal Analysis and Calorimetry, 2001
    Co-Authors: S.-q. Cheng, Zhong Huang, Xiang-guang Meng, Xiaoxi Zeng
    Abstract:

    This paper presents a novel data processing method for thermokinetics of faster First-Order Reaction on the basis of the double-parameter theoretical model of a conduction calorimeter, in which the rate constant of a First-Order Reaction can be calculated from only four peak height data from the same thermoanalytical curve without using any peak-area. The saponifications of ethyl acetate and methyl acetate in aqueous solution and ethyl benzoate in aqueous alcohol have been studied to test the validity of this method. The rate constants calculated with this method are in fair agreement with those in literature; hence the validity of this method is demonstrated.

  • Time-parameter method for studying kinetics of consecutive First-Order Reactions in calorimeter
    Journal of Thermal Analysis and Calorimetry, 2001
    Co-Authors: Younan Chen, Xiaoxi Zeng
    Abstract:

    In order to enrich the thermokinetic research methods and enlarge the applicable range of the thermokinetic time-parameter method, the integral and differential thermokinetic equations of consecutive First-Order Reaction have been deduced, and the mathematical models of the time-parameter method for consecutive First-Order Reactions have been proposed in this paper. The rate constants of two steps can be calculated from the same thermoanalytical curve measured in a batch conduction calorimeter simultaneously with this method. The thermokinetics of saponifications of diester in aqueous ethanol solvent has been studied. The experimental results indicate that the time-parameter method for the consecutive First-Order Reaction is correct.

Jan Olek - One of the best experts on this subject based on the ideXlab platform.

  • alkali silica Reaction kinetics of chemistry of pore solution and calcium hydroxide content in cementitious system
    Cement and Concrete Research, 2015
    Co-Authors: Jan Olek, Hyungu Jeong
    Abstract:

    Abstract This paper presents the results of the investigations on the chemistry of pore solutions, the contents of calcium hydroxide, and the expansions in mortars containing both reactive and non-reactive aggregates. In order to examine the effect of the temperature, experiments were performed at three different temperatures (23 °C, 38 °C and 55 °C). The compositions of the pore solution were measured at short time intervals for a period of up to 130 days in order to capture the kinetics of the chemistry of pore solution. The results showed that the changes in the concentrations of alkali ions can be best explained by the first order Reaction. In addition, the proposed rate equation could reasonably simulate the changes in the actual concentrations of alkalis. Finally, the results in this paper suggest that the rate of the alkali–silica Reaction in cementitious system containing highly reactive aggregate can be also expressed as the first order Reaction.

  • Alkali–silica Reaction: Kinetics of chemistry of pore solution and calcium hydroxide content in cementitious system
    Cement and Concrete Research, 2015
    Co-Authors: Jan Olek, Hyungu Jeong
    Abstract:

    Abstract This paper presents the results of the investigations on the chemistry of pore solutions, the contents of calcium hydroxide, and the expansions in mortars containing both reactive and non-reactive aggregates. In order to examine the effect of the temperature, experiments were performed at three different temperatures (23 °C, 38 °C and 55 °C). The compositions of the pore solution were measured at short time intervals for a period of up to 130 days in order to capture the kinetics of the chemistry of pore solution. The results showed that the changes in the concentrations of alkali ions can be best explained by the first order Reaction. In addition, the proposed rate equation could reasonably simulate the changes in the actual concentrations of alkalis. Finally, the results in this paper suggest that the rate of the alkali–silica Reaction in cementitious system containing highly reactive aggregate can be also expressed as the first order Reaction.

Scott K. Hansen - One of the best experts on this subject based on the ideXlab platform.

  • A Practical Modeling Framework for Non-Fickian Transport and Multi-Species Sequential First-Order Reaction.
    Ground water, 2018
    Co-Authors: Daniel K. Burnell, Scott K. Hansen, Lawrence S. Sims, Charles R. Faust
    Abstract:

    Many studies indicate that small-scale heterogeneity and/or mobile-immobile mass exchange produce transient non-Fickian plume behavior that is not well captured by the use of the standard, deterministic advection-dispersion equation (ADE). An extended ADE modeling framework is presented here that is based on continuous time random walk theory. It can be used to characterize non-Fickian transport coupled with simultaneous sequential First-Order Reactions (e.g., biodegradation or radioactive decay) for multiple degrading contaminants such as chlorinated solvents, royal demolition explosive, pesticides, and radionuclides. To demonstrate this modeling framework, new transient analytical solutions are derived and are inverted in Laplace space. Closed-form, steady-state, multi-species analytical solutions are also derived for non-Fickian transport in highly heterogeneous aquifers with linear sorption-desorption and matrix diffusion for use in spreadsheets. The solutions are general enough to allow different degradation rates for the mobile and immobile zones. The transient solutions for multi-species transport are applied to examine the effects of source remediation on the natural attenuation of downgradient plumes of both parent and degradation products in highly heterogeneous aquifers. Results for representative settings show that the use of the standard, deterministic ADE can over-estimate cleanup rates and under-predict the cleanup timeframe in comparison to the extended ADE analytical model. The modeling framework and calculations introduced here are also applied for a 30 year groundwater cleanup program at a site in Palm Bay, Florida. The simulated plume concentrations using the extended ADE exhibited agreement with observed long concentration tails of trichloroethene, cis 1,2 DCE, and VC that remained above cleanup goals.

  • Transient modeling of non-Fickian transport and First-Order Reaction using continuous time random walk
    Advances in Water Resources, 2017
    Co-Authors: Daniel K. Burnell, Scott K. Hansen
    Abstract:

    Abstract Contaminants in groundwater may experience a broad spectrum of velocities and multiple rates of mass transfer between mobile and immobile zones during transport. These conditions may lead to non-Fickian plume evolution which is not well described by the advection–dispersion equation (ADE). Simultaneously, many groundwater contaminants are degraded by processes that may be modeled as First-Order decay. It is now known that non-Fickian transport and Reaction are intimately coupled, with Reaction affecting the transport operator. However, closed-form solutions for these important scenarios have not been published for use in applications. In this paper, we present four new Green's function analytic solutions in the uncoupled, uncorrelated continuous time random walk (CTRW) framework for reactive non-Fickian transport, corresponding to the quartet of conservative tracer solutions presented by Kreft and Zuber (1978) for Fickian transport. These consider pulse injection for both resident and flux concentration combined with detection in both resident and flux concentration. A pair of solutions for resident concentration temporal pulses with detection in both flux and resident concentration is also presented. We also derive the relationship between flux and resident concentration for non-Fickian transport with First-Order Reaction for this CTRW formulation. An explicit discussion of employment of the new solutions to model transport with arbitrary upgradient boundary conditions as well as mobile–immobile mass transfer is then presented. Using the new solutions, we show that First-Order Reaction has no effect on the anomalous spatial spreading rate of concentration profiles, but produces breakthrough curves at fixed locations that appear to have been generated by Fickian transport. Under the assumption of a Pareto CTRW transition distribution, we present a variety of numerical simulations including results showing coherence of our analytic solutions and CTRW particle tracking.