摘要:

We have developed certain new technology for the encapsulation of various biological materials, including living cells. Submillimeter‐size droplets bearing the encapsulant are given a biocompatible membrane covering by immersion into a bath containing a reactant. We present in this paper a brief description of the methods and materials of the process, and emphasize the results of a photographic study of the droplet deformation during submersion and of the concurrent membrane formation.

ISSN:0094-243X    

DOI:10.1063/1.38947

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The motion of a thin liquid sheet subjected to the effects of surface tension and external gaseous pressure is studied. Equations of motion are constructed by essentially ignoring the interal flow of the liquid in the layer. For an axisymmetric case, for example, the system is reduced to a set of coupled nonlinear partial differential equations depending on time and only one spatial variable, which can be solved numerically as an initial‐boundary‐value problem. Here, a review of the application of this approach to two different problems is presented. The first is the instability of an annular jet, in which a cylindrical liquid sheet emanating from an annular nozzle and enclosing a gas stream breaks up into liquid shells downstream. The second is the centering mechanism of such a liquid shell under capillary oscillations. Reasonable results have been obtained from the numerical studies of these problems.

ISSN:0094-243X    

DOI:10.1063/1.38948

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The thickness of water films between an inclined Lucite plate submerged in water and air bubbles moving beneath it was measured with a small impedance probe. The instrument was calibrated with a laser interferometer built for this purpose. The bubbles released beneath the plate varied in size from 10 cc to 100 cc. At a plate inclination angle of 0.98°, and in tap water, an uninterrupted water film covered most of the bubbles. Some bubbles, however, dewetted the plate, and the water film covered only a forward part of the bubble. When the film was uninterrupted, its thickness was very uniform from front to rear. When the bubble dewetted the plate, a large forward section of the film had the same uniform thickness, but this was followed by a hump on the film the rear slope of which ended at the plate surface. For some of the experiments, the surface tension of the water was reduced by admixing a detergent. In these experiments, dewetting was not observed. In a second set of experiments, a hand held transparent container filled with water and a 1.3 cm3 air bubble was used to observe visually the behavior of the moving bubble and its associated water film.

ISSN:0094-243X    

DOI:10.1063/1.38950

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A capability to quantify the size of bubbles has been developed using time delay spectrometry. This signal processing technique uses swept frequenceis and matched filter detection. It can provide either ranging or frequency response data based upon fundamental or second harmonic signal processing. This system has been tested using bubbles in the 1–50 micron range. The use of this signal processing provides a technique that is both quantitative and capable of uniquely characterizing bubbles and their size distributions.

ISSN:0094-243X    

DOI:10.1063/1.38951

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The effect of surface tension on the determinatin of shape and velocity of a steadily translating bubble in a Hele‐Shaw cell as well as its linear stability are presented in this paper. For zero surface tension, there is a continuum of steady bubble solutions for which the bubble velocity and the distance of the bubble centroid from the channel centerline are arbitrary. However, for arbitrarily small surface tension, only a discrete set of bubble solutions are possible with the bubble being symmetric about the channel centerline. Of this discrete set, only branch of the solution for which the bubble velocity is the largest is linearly stable in accordance with similar results for the finger. Transcendentally small terms in surface tension play a crucial role in the determination of bubble velocity, symmetry as well as linear stability. The discrepancy of experimental observations with these theoretical results based on a simplified set of boundary conditions are pointed out. Recent theoretical development that may account for a part of the discrepancy is discussed and open problems pointed out.

ISSN:0094-243X    

DOI:10.1063/1.38952

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

This paper reviews the effect of surface tension on three different free surface flow problems. Each flow is characterized by a continuum of solutions when surface tension is neglected. When surface tension is taken into account there is a discrete set of solutions. As the surface tension approaches zero all these solutions reduce to a unique solution. The corresponding free surface profiles are found to be in good agreement with experimental data.

ISSN:0094-243X    

DOI:10.1063/1.38953

出版商:AIP    

年代:1990

数据来源: AIP