Showing papers by "Rakesh K. Jain published in 1979"

Blood Flow and Heat Transfer in Walker 256 Mammary Carcinoma

Abstract: True thermal conductivity of 13 Walker 256 mammary carcinomas in noninbred Sprague-Dawley rats averaged 3.2+/-0.9 mW/cm/degrees C under physiologic conditions. A comparison of the effective thermal conductivity in 4 tumors with and without blood flow revealed large differences ranging from 14 to 132%. When the blood supply to the tumor was doubled or reduced to one-half, the effective thermal conductivity varied proportionally to the square root of the perfusion rate. The values of thermal conductivity were obtained from a tumor preparation in which blood flow was monitored continuously during temperature changes. These changes were measured by thermistors and produced by thermal probes incorporated by the growing tumor, not surgically inserted within the tissue at the time of measurement. Inasmuch as tissue necrosis was not a dominant factor, the data are interpreted to reflect the degree of difference in local perfusion of the neoplastic tissue.

Pharmacokinetics of methotrexate in solid tumors.

Abstract: The transport of methotrexate (MTX) into Walker 256 carcinoma (W256) and hepatoma 5123 (H5123) transplanted in rats was investigated after a pulse injection and continuous infusion of the drug. A mathematical model was developed which adequately described the distribution and transport of MTX in both solid tumors. In H5123 the uptake was limited by the amount of drug carried by plasma (flow-limited transport), but in W256 MTX uptake was limited by the rate at which the drug crossed the tissue barriers (tissue-limited transport). Relative uptake by the solid tumors was almost eightfold more efficient with low than with high doses. MTX concentration in tumor interstitial fluid equilibrated with that of plasma in about 50 hr using a micropore chamber with a diffusion coefficient of 0.5 microm/min as sampling device. MTX concentration was higher in resistant than in responsive tumors.

The Role of Surfactants on the Coalescences of Emulsion Droplets

Abstract: The coalescence of droplets and their life-time are shown to depend strongly on the surfactant properties _aod concentration. The following more important effects are predicted: 1) With pure liquids the energy is mainly dissipated in the droplets and the velocity of thinning, V, sho~ld not depend on the film viscosity. 2) The surfactant partition coefficient should playa crucial role on the emulsion stability. When it is soluble in the continuous phase, the surface mobility and the rate of thinning should be small and the flow in the droplet(s) could be disregarded; When the surfactant is soluble in the droplet(s), it should have no effect on the surface mobility and hence on the rate of thinning which must be much higher than it would be in the former case. 3) While the rate of thinning virtually should not depend on the surface viscosity. even values as small as 10-7 kg. s-1 would be sufficient to consider the interfaces as tangentially immobile with respect to the wave motion. 4) The film profile and hence the critical thickness at which the rupture occurs, should not depend on factors affecting to the same extent both the thinning and the wave motion. 5) The effect of the surfactant on the lifetime of the droplets is mainly due to its influence on the velocity of thinning rather th~ on the critical thickness of rupture.