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Graduate Center of the City University of New York

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Papers by DASH JAMES

Physical Review B, 1975

Nonuniformity of substrate properties can be detected in the physical adsorption of common molecu... more Nonuniformity of substrate properties can be detected in the physical adsorption of common molecular gases including helium. Effects due to binding-energy variation extend beyond the first adsorbed layer, usually to thicknesses of many layers. We qualitatively describe reasons for this persistence and show how its form and range are related to the spatial variation of the binding energy. Heterogeneity can play an important role in the appearance of superfluidity in thin films of He4. It is argued that heterogeneity has been a more serious perturbation in superfluid-onset experiments than is generally recognized; that heterogeneity can account for the lack of agreement between experiments which use different techniques and/or substrates; that the experimental disagreements have hindered development of a satisfactory theory of superfluidity in thin films. We derive a thermodynamic formula relating the shifts of onset temperature with thickness to the lateral scale of the thickness variations caused by substrate heterogeneity, and illustrate its application in simple examples. The sensitivity of superfluid onset to heterogeneity might be exploited for surface characterization, yielding important information that is not presently obtainable by other methods. As a separate benefit, it can lead to a clearer understanding of superfluidity. Specific experimental tests are suggested.

Annals of Biomedical Engineering, 2010

New mathematical model equations for O2 and CO2 saturations of hemoglobin ( \( S_{{{\text{HbO}}_{... more New mathematical model equations for O2 and CO2 saturations of hemoglobin ( \( S_{{{\text{HbO}}_{ 2} }} \) and \( S_{{{\text{HbCO}}_{ 2} }} \) ) are developed here from the equilibrium binding of O2 and CO2 with hemoglobin inside RBCs. They are in the form of an invertible Hill-type equation with the apparent Hill coefficients \( K_{{{\text{HbO}}_{ 2} }} \) and \( K_{{{\text{HbCO}}_{ 2} }} \) in the expressions for \( S_{{{\text{HbO}}_{ 2} }} \) and \( S_{{{\text{HbCO}}_{ 2} }} \) dependent on the levels of O2 and CO2 partial pressures ( \( P_{{{\text{O}}_{ 2} }} \) and \( P_{{{\text{CO}}_{ 2} }} \) ), pH, 2,3-DPG concentration, and temperature in blood. The invertibility of these new equations allows \( P_{{{\text{O}}_{ 2} }} \) and \( P_{{{\text{CO}}_{ 2} }} \) to be computed efficiently from \( S_{{{\text{HbO}}_{ 2} }} \) and \( S_{{{\text{HbCO}}_{ 2} }} \) and vice versa. The oxyhemoglobin (HbO2) and carbamino-hemoglobin (HbCO2) dissociation curves computed from these equations are in good agreement with the published experimental and theoretical curves in the literature. The model solutions describe that, at standard physiological conditions, the hemoglobin is about 97.2% saturated by O2 and the amino group of hemoglobin is about 13.1% saturated by CO2. The O2 and CO2 content in whole blood are also calculated here from the gas solubilities, hematocrits, and the new formulas for \( S_{{{\text{HbO}}_{ 2} }} \) and \( S_{{{\text{HbCO}}_{ 2} }} \) . Because of the mathematical simplicity and invertibility, these new formulas can be conveniently used in the modeling of simultaneous transport and exchange of O2 and CO2 in the alveoli–blood and blood–tissue exchange systems.

Cheminform, 2009