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

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.

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.
References in periodicals archive ?
Chest CT (August 30, 2016) demonstrated a mass in posterior mediastinum with moderate pericardial effusion and bilateral pleural effusion [Figure 1]d.
The role of Abrams percutaneous pleural biopsy in the investigation of exudative pleural effusions.
In this study, ADA levels in non-tuberculous exudative pleural effusions rarely exceeded the cut-off set for tuberculous disease.
White arrow shows ultrasonographic visualization of a pleural effusion between the visceral and parietal pleura
Clinical and echocardiographic characteristics of significant pericardial effusions following cardiothoracic surgery and outcomes of echo-guided pericardiocentesis for management: Mayo Clinic experience, 1979-1998.
13 Cytology for cancer cells is positive in approximately 71% of patients who develop pleural effusions secondary to malignancy.
Subpulmonic effusions between the dome of the diaphragm and basal lung are suggested on frontal projection by elevation and lateralization of the hemidiaphragmatic peak, a paucity of vessels below the diaphragmatic margin, and increased distance between the left lung base and gastric bubble (Figure 1).
Since the patient immigrated to Israel from Ethiopia where TB is endemic and since she had hemorrhagic pericardial effusions with very low glucose levels and in the absence of a response to anti-inflammatory drugs, TB pericarditis was highly suspected and empiric antituberculous therapy was added to colchicine and prednisone.
3) However, pleural effusions rarely are clinical problems except in rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE), with an incidence of 20% and 50%, respectively.
Diagnosis of pericardial effusions in birds by ultrasound.