Shock Tube Studies on Recombination Kinetics of Sodium Ion with Electron

The ionization kinetics of sodium diluted in argon is studied in a shock tube, in which the test gas mixture is ionized by a reflected shock wave and subsequently quenched by a strong rarefaction wave. A Langmuir electrostatic probe is used to monitor the variation of the ion number density at the reflection shock wave region. The working state of the probe is in the near fi-ee fall region and a correction for reduction of the probe current due to elastic scattering in the probe sheath is introduced. At the temperature range of 800 to 2600 K and in the ambience of argon gas, the three-body recombination rate coefficient of the sodium ion with electron is determined: 3.43 x 10(-14)T(-3.77) cm(6).s(-1).

Kinetics of Glass Transition and Crystallization in Carbon Nanotube Reinforced Mg-Cu-Gd Bulk Metallic Glass

Mg65 Cu25 Gdlo bulk metallic glass and its carbon nanotube reinforced composite were prepared. Differential scanning calorimeter (DSC) was used to investigate the kinetics of glass transition and crystallization processes. The influence of CNTs addition to the glass matrix on the glass transition and crystallization kinetics was studied. It is shown that the kinetic effect on glass transition and crystallization are preserved for both the monothetic glass and its glass composite. Adding CNTs in to the glass matrix reduces the influence of the heating rate on the crystallization process. In addition, the CNTs increase the energetic barrier for the glass transition. This results in the decrease of GFA . The mechanism of the GFA decrease was also discussed.

Effects of Surface Microtopology and Membrane Stiffness on Kinetics of Selectin/Ligand interactions by a Modified BFP

More and more evidences come out to support that the functionality of adhesion molecules are influenced by the surface microtopology of cell carrier or substrate. Adhesive molecules usually express on the microvilli of a cell, providing a well-defined spatial configuration to mediate the adhesions to the counterpart molecules on the apposed surface.

Shock Tube Studies on the Nonequlibrium Electron Affinity Kinetics of Fluorine Atom at High Temperatures

To study electron affinity kinetics, a shock tube method was applied, in which the test gas was ionized by a reflected shock wave and subsequently quenched by a strong rarefaction wave. As the quenching speed of 106 K/s was reached, a nonequilibrium ionization-recombination process occurred, which was dominated by ion recombination with electrons. A Langmuir electrostatic probe was used to monitor variation in the ion number density at the reflection shock region. The working state of the probe was analyzed...

Effects of Molecular Length, Ortientation and Amino Acid Mutation on Kinetics of Selectin/Ligand interactions

Receptor/ligand interactions are basic issues to cell adhesion, which are important to many physiological and pathological processes such as lymphocyte-mediated cytotoxicity, tumor metastasis and inflammatory reactionl. Selectin/carbohydrate ligand bindings have been found to mediate the fast rolling of leukocytes on activated endothelial monolayer. Kinetic rate and binding affinity constants are essential determinants of cell adhesion...

Kinetics of the chemical looping oxidation of H2 by a co-precipitated mixture of CuO and Al2O3

Chemical-looping combustion (CLC) has the inherent property of separating CO2 from flue gases. Instead of air, it uses an oxygen-carrier, usually in the form of a metal oxide, to provide oxygen for combustion. When used for the combustion of gaseous fuels, such as natural gas, or synthesis gas from the gasification of coal, the technique gives a stream of CO2 which, on an industrial scale, would be sufficiently pure for geological sequestration. An important issue is the form of the metal oxide, since it must retain its reactivity through many cycles of complete reduction and oxidation. Here, we report on the rates of oxidation of one constituent of synthesis gas, H2, by co-precipitated mixtures of CuO+Al2O3 using a laboratory-scale fluidised bed. To minimise the influence of external mass transfer, and also of errors in the measurement of [H2], particles sized to 355-500μm were used at low [H2], with the temperature ranging from 450 to 900°C. Under such conditions, the reaction was slow enough for meaningful measurements of the intrinsic kinetics to be made. The reaction was found to be first order with respect to H2. Above ∼800°C, the reaction of CuO was fast and conformed to the shrinking core mechanism, proceeding via the intermediate, Cu2O, in: 2CuO+H2→Cu2O+H2O, ΔH1073 K0=- 116.8 kJ/mol; Cu2O+H2→2Cu+H2O, ΔH1073 K0-80.9 kJ/mol. After oxidation of the products Cu and Cu2O back to CuO, the kinetics in subsequent cycles of chemical looping oxidation of H2 could be approximated by those in the first. Interestingly, the carrier was found to react at temperatures as low as 300°C. The influence of the number of cycles of reduction and oxidation is explored. Comparisons are drawn with previous work using reduction by CO. Finally, these results indicate that the kinetics of reaction of the oxygen carrier with gasifier synthesis gases is very much faster than rates of gasification of the original fuel. © 2010 The Institution of Chemical Engineers.

Measuring Binding Kinetics Of Surface-Bound Molecules Using The Surface Plasmon Resonance Technique

Surface plasmon resonance (SPR) technology and the Biacore biosensor have been widely used to measure the kinetics of biomolecular interactions in the fluid phase. In the past decade, the assay was further extended to measure reaction kinetics when two counterpart molecules are anchored on apposed surfaces. However, the cell binding kinetics has not been well quantified. Here we report development of a cellular kinetic model, combined with experimental procedures for cell binding kinetic measurements, to predict kinetic rates per cell. Human red blood cells coated with bovine serum albumin and anti-BSA monoclonal antibodies (mAbs) immobilized on the chip were used to conduct the measurements. Sensor-grams for BSA-coated RBC binding onto and debinding from the anti-BSA mAb-immobilized chip were obtained using a commercial Biacore 3000 biosensor, and analyzed with the cellular kinetic model developed. Not only did the model fit the data well, but it also predicted cellular on and off-rates as well as binding affinities from curve fitting. The dependence of flow duration, flow rate, and site density of BSA on binding kinetics was tested systematically, which further validated the feasibility and reliability of the new approach. Crown copyright (c) 2008 Published by Elsevier Inc. All rights reserved.

Two-Dimensional Kinetics Of Beta(2)-Integrin And Icam-1 Bindings Between Neutrophils And Melanoma Cells In A Shear Flow

Cell adhesion, mediated by specific receptor-ligand interactions, plays an important role in biological processes such as tumor metastasis and inflammatory cascade. For example, interactions between beta(2)-integrin ( lymphocyte function-associated antigen-1 and/or Mac-1) on polymorphonuclear neutrophils (PMNs) and ICAM-1 on melanoma cells initiate the bindings of melanoma cells to PMNs within the tumor microenvironment in blood flow, which in turn activate PMN-melanoma cell aggregation in a near-wall region of the vascular endothelium, therefore enhancing subsequent extravasation of melanoma cells in the microcirculations. Kinetics of integrin-ligand bindings in a shear flow is the determinant of such a process, which has not been well understood. In the present study, interactions of PMNs with WM9 melanoma cells were investigated to quantify the kinetics of beta(2)-integrin and ICAM-1 bindings using a cone-plate viscometer that generates a linear shear flow combined with a two-color flow cytometry technique. Aggregation fractions exhibited a transition phase where it first increased before 60 s and then decreased with shear durations. Melanoma-PMN aggregation was also found to be inversely correlated with the shear rate. A previously developed probabilistic model was modified to predict the time dependence of aggregation fractions at different shear rates and medium viscosities. Kinetic parameters of beta(2)-integrin and ICAM-1 bindings were obtained by individual or global fittings, which were comparable to respectively published values. These findings provide new quantitative understanding of the biophysical basis of leukocyte-tumor cell interactions mediated by specific receptor-ligand interactions under shear flow conditions.

Impact of carrier stiffness and microtopology on two-dimensional kinetics of P-selectin and P-selectin glycoprotein ligand-1 (PSGL-1) interactions

Mechanics and surface microtopology of the molecular carrier influence cell adhesion, but the mechanisms underlying these effects are not well understood. We used a micropipette adhesion frequency assay to quantify how the carrier stiffness and microtopology affected two-dimensional kinetics of interacting adhesion molecules on two apposing surfaces. Interactions of P-selectin with P-selectin glycoprotein ligand-1 (PSGL-1) were used to demonstrate such effects by presenting the molecules on three carrier systems: human red blood cells (RBCs), human promyelocytic leukemia HL-60 cells, and polystyrene beads. Stiffening the carrier alone or in cooperation with roughing the surface lowered the two-dimensional affinity of interacting molecules by reducing the forward rate but not the reverse rate, whereas softening the carrier and roughing the surface had opposing effects in affecting two-dimensional kinetics. In contrast, the soluble antibody bound with similar three-dimensional affinity to surface-anchored P-selectin or PSGL-1 constructs regardless of carrier stiffness and microtopology. These results demonstrate that the carrier stiffness and microtopology of a receptor influences its rate of encountering and binding a surface ligand but does not subsequently affect the stability of binding. This provides new insights into understanding the rolling and tethering mechanism of leukocytes onto endothelium in both physiological and pathological processes.