Effusion


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effusion

1. the flow of a gas through a small aperture under pressure, esp when the density is such that the mean distance between molecules is large compared to the diameter of the aperture
2. Med
a. the escape of blood or other fluid into a body cavity or tissue
b. the fluid that has escaped
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Effusion

 

the slow leakage of gas through a small aperture. Two cases of effusion are distinguished. In the first case, the diameter of the opening is small compared with the mean free path of the molecules (the pressure in the vessel is very low). In such a case, molecular effusion occurs in which collisions between molecules play no part, and the overall volume of gas escaping per unit time is Effusion, where S is the area of the aperture, μ is the molecular mass of the gas, R is the universal gas constant, T is the absolute temperature of the gas, and p1 and p2 are the gas pressures on the two sides of the aperture. The effusion method of measuring very low pressures (about 10–3–10–4 mm Hg) is based on this case.

In the second case, where the gas pressure is so high that the mean free path is smaller than the diameter of the aperture, the leakage of gas obeys the laws of hydrodynamics. The molecules escape from the aperture in the form of a jet, and the volume of gas discharged per unit time is inversely proportional to the square root of the density of the gas. This law underlies a method of determining the density of gases from the time of their discharge through small apertures (0.10–0.01 mm). However, if the pressure within the vessel is considerably greater than the external pressure, the amount of gas escaping is proportional to the pressure in the vessel.


Effusion

 

the process of lava (magma) pouring out onto the earth’s surface. When the lava cools, effusive rocks are formed, bedded in the form of lava flows and lava sheets. Effusion, one of the manifestations of volcanic activity, is usually accompanied by an explosion, with discharges of small fragments (volcanic ash, sand, or tuff) or large chunks (volcanic bombs and slags). Viscous acidic lava sometimes will not flow, but rather is extended, forming volcanic domes.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

effusion

[e′fyü·zhən]
(medicine)
A pouring out of any fluid into a body cavity or tissue.
(physical chemistry)
The movement of a gas through an opening which is small as compared with the average distance which the gas molecules travel between collisions.
(science and technology)
The act or process of leaking or pouring out.
Any material that is effused.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
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However, pericardial effusion is not a common complication.
On echocardiography, pericardial effusion surrounding the heart circumferentially with a wideness up to 1 cm was detected (Figure 1).
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Diagnostic accuracy of interleukin 27 for tuberculous pleural effusion: Two prospective studies and one meta-analysis.
Whenever the effusion is rich in mesothelial cells or is suspicious for malignancy, the possibility of a MM should be explored by ancillary diagnostic measures.
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This study had been carried to find out the clinical profile and various etiological causes of pleural effusion in a teaching hospital located in Eastern part of India.
The diagnosis of OME was based on the amber color of effusion fluid, the air-fluid level, air bubbles, or opacity of the tympanic membrane and B- or C-type tympanograms.