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Biomedical subjects

A Borhan

Publications and source records attributed to A Borhan.

6 recordsLinked to original sources
PubMed2000

Stability of the Shape of a Viscous Drop under Buoyancy-Driven Translation in a Hele-Shaw Cell.

It has been shown (N. R. Gupta, A. Nadim, H. Haj-Hariri, and A. Borhan, J. Colloid Interface Sci. 218, 338 1999) that a circular drop translating in a Hele-Shaw cell under the action of gravity is linearly stable for nonzero interfacial tension. In this paper, we use the boundary integral method to examine the nonlinear evolution of the shape of initially noncircular drops translating in a Hele-Shaw cell. For prolate initial deformations, it is found that the drop reverts to a circular shape for all finite Bond numbers considered. Initially oblate drops, on the other hand, are found to become unstable and break up if the initial shape perturbation is of sufficiently large magnitude. The critical conditions for the onset of drop breakup are examined in terms of the magnitude of the initial deformation as a function of Bond number. Two branches of marginal stability are identified and the effects of viscosity ratio and asymmetric initial perturbations on the stability diagram are discussed. Copyright 2000 Academic Press.

Journal Article↗
PubMed1999

On the Linear Stability of a Circular Drop Translating in a Hele-Shaw Cell.

For the buoyancy-driven motion of a drop in a Hele-Shaw cell, a circle is an exact solution for the shape of the drop. The stability of the shape of a circular drop translating in a Hele-Shaw cell under the action of gravity is investigated. It is shown that for nonzero interfacial tension, the circular shape is linearly stable. Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

Effect of Insoluble Surfactants on the Pressure-Driven Motion of a Drop in a Tube in the Limit of High Surface Coverage.

The effect of surfactants on the axisymmetric pressure-driven motion of a droplet in a tube is investigated under low Reynolds number conditions. In the presence of surface-active impurities, the motion of the drop results in constant redistribution of the adsorbed surfactant along the interface by convection and diffusion, leading to nonuniformities in interfacial tension (i.e., Marangoni stresses) which modify the viscous stress balance at the interface. These, in turn, affect the mobility of the drop and its steady or transient shape deformations. In this study, the steady-state behavior of such a drop is examined in the presence of nondilute concentrations of bulk-insoluble surfactants on the surface of the drop. The boundary integral method is used in conjunction with a finite-difference scheme to solve the unsteady surface convective-diffusion equation for surfactant transport. The Frumkin adsorption framework is used to explore the effects of monolayer saturation and nonideal surfactant interactions on the steady drop shape and speed in the limit of high surface coverage. It is found that for surfactants with strong cohesive interactions, the drop mobility increases with increasing surface coverage, attaining maximum mobility at about 50% initial coverage. Furthermore, surface-convection-dominated systems with strong cohesive interactions exhibit surface flow patterns corresponding to the formation of a stagnant cap at the trailing end of the drop. All other systems exhibit surface flow patterns corresponding to uniform retardation of interface mobility as a fully immobilized interface is approached with increasing surface convection. Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

Upper ureteral reconstructive surgery.

Upper ureteral reconstructive surgery encompasses a wide variety of procedures directed at the correction of abnormal processes and structural defects in the proximal ureter. Although some of these techniques have strict indications for specific causes, technical innovations have led to development of numerous alternatives in upper ureteral reconstructive surgery. These innovations provide the practicing urologist with various options from which to choose for the management of upper ureteral disease.

Adult↗
PubMed1989

Anatomical basis of latissimus dorsi myocutaneous flap: clinical applications.

The anatomical study was carried out using 40 preserved cadaveric specimens of latissimus dorsi myocutaneous flaps. It included dissections, angiographies and tissue clearing after arterial injection with latex. The results proved that the dominant vascular supply, the thoracodorsal a., has an almost constant pattern of intramuscular distribution. In addition, there are two sets of segmental pedicles, from the intercostal and lumbar vessels, supplying the medial third of the muscle. The accurate localization of the intramuscular distribution of the thoracodorsal a. permitted the proper design of several island flaps with competent vascularity. The designed flaps were successfully applied in 10 cases for reconstruction of breast, axilla, neck and chest wall.

Arteries↗