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Effusion
In physics and chemistry, effusion is the process in which a gas escapes from a container through a hole of diameter considerably smaller than the mean free path of the molecules. Such a hole is often described as a ''pinhole'' and the escape of the gas is due to the pressure difference between the container and the exterior. Under these conditions, essentially all molecules which arrive at the hole continue and pass through the hole, since collisions between molecules in the region of the hole are negligible. Conversely, when the diameter is larger than the mean free path of the gas, flow obeys the Sampson flow law. In medical terminology, an effusion refers to accumulation of fluid in an anatomic space, usually without locule, loculation. Specific examples include Subdural hematoma, subdural, otitis media with effusion, mastoid, pericardial effusion, pericardial and pleural effusions. Etymology The word effusion derives from the Latin word, effundo, which means "shed", " ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Pleural Effusion
A pleural effusion is accumulation of excessive fluid in the pleural space, the potential space that surrounds each lung. Under normal conditions, pleural fluid is secreted by the parietal pleural capillaries at a rate of 0.6 millilitre per kilogram weight per hour, and is cleared by lymphatic absorption leaving behind only 5–15 millilitres of fluid, which helps to maintain a functional vacuum between the parietal and visceral pleurae. Excess fluid within the pleural space can impair inhalation, inspiration by upsetting the functional vacuum and hydrostatically increasing the resistance against lung expansion, resulting in a fully or partially collapsed lung. Various kinds of fluid can accumulate in the pleural space, such as serous fluid (hydrothorax), blood (hemothorax), pus (pyothorax, more commonly known as pleural empyema), chyle (chylothorax), or very rarely urine (urinothorax) or feces (coprothorax). When unspecified, the term "pleural effusion" normally refers to hydro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Pericardial Effusion
A pericardial effusion is an abnormal accumulation of fluid in the pericardial cavity. The pericardium is a two-part membrane surrounding the heart: the outer fibrous Connective tissue, connective membrane and an inner two-layered serous membrane. The two layers of the serous membrane enclose the pericardial cavity (the potential space) between them. This pericardial space contains a small amount of pericardial fluid, normally 15-50 mL in volume. The pericardium, specifically the pericardial fluid provides lubrication, maintains the anatomic position of the heart in the chest (levocardia), and also serves as a barrier to protect the heart from infection and inflammation in adjacent tissues and organs. By definition, a pericardial effusion occurs when the volume of fluid in the cavity exceeds the normal limit. If large enough, it can compress the heart, causing cardiac tamponade and obstructive shock. Some of the presenting symptoms are shortness of breath, chest pain, chest pressu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Otitis Media With Effusion
Otitis media is a group of inflammatory diseases of the middle ear. One of the two main types is acute otitis media (AOM), an infection of rapid onset that usually presents with ear pain. In young children this may result in pulling at the ear, increased crying, and poor sleep. Decreased eating and a fever may also be present. The other main type is otitis media with effusion (OME), typically not associated with symptoms, although occasionally a feeling of fullness is described; it is defined as the presence of non-infectious fluid in the middle ear which may persist for weeks or months often after an episode of acute otitis media. Chronic suppurative otitis media (CSOM) is middle ear inflammation that results in a perforated tympanic membrane with discharge from the ear for more than six weeks. It may be a complication of acute otitis media. Pain is rarely present. All three types of otitis media may be associated with hearing loss. If children with hearing loss due to OME ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Effusion
In physics and chemistry, effusion is the process in which a gas escapes from a container through a hole of diameter considerably smaller than the mean free path of the molecules. Such a hole is often described as a ''pinhole'' and the escape of the gas is due to the pressure difference between the container and the exterior. Under these conditions, essentially all molecules which arrive at the hole continue and pass through the hole, since collisions between molecules in the region of the hole are negligible. Conversely, when the diameter is larger than the mean free path of the gas, flow obeys the Sampson flow law. In medical terminology, an effusion refers to accumulation of fluid in an anatomic space, usually without locule, loculation. Specific examples include Subdural hematoma, subdural, otitis media with effusion, mastoid, pericardial effusion, pericardial and pleural effusions. Etymology The word effusion derives from the Latin word, effundo, which means "shed", " ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Graham's Law
Graham's law of effusion (also called Graham's law of diffusion) was formulated by Scottish physical chemist Thomas Graham in 1848. Keith J. Laidler and John M. Meiser, ''Physical Chemistry'' (Benjamin/Cummings 1982), pp. 18–19 Graham found experimentally that the rate of effusion of a gas is inversely proportional to the square root of the molar mass of its particles. This formula is stated as: :=\sqrt, where: :Rate1 is the rate of effusion for the first gas. (volume or number of moles per unit time). :Rate2 is the rate of effusion for the second gas. :''M1'' is the molar mass of gas 1 :''M2'' is the molar mass of gas 2. Graham's law states that the rate of diffusion or of effusion of a gas is inversely proportional to the square root of its molecular weight. Thus, if the molecular weight of one gas is four times that of another, it would diffuse through a porous plug or escape through a small pinhole in a vessel at half the rate of the other (heavier gases diffuse mor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Thomas Graham (chemist)
Thomas Graham (20 December 1805 – 11 September 1869) was a Scottish chemist known for his pioneering work in dialysis and the diffusion of gases. He is regarded as one of the founders of colloid chemistry. Life Graham was born in Glasgow, Scotland and was educated at the High School of Glasgow. Graham's father was a successful textile manufacturer, and wanted his son to enter into the Church of Scotland. Instead, defying his father's wishes, Graham became a student at the University of Glasgow in 1819. There he developed a strong interest in chemistry, studying under Professor Thomas Thomson, who was impressed and influenced by the young man. He left the university after receiving his MA in 1824. He later studied medicine at the University of Edinburgh and then briefly taught chemistry at the Glasgow University Portland Street Medical School. In 1828 he was elected a Fellow of the Royal Society of Edinburgh, his proposer was Edward Turner. He won the Society's Keith Med ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Knudsen Cell
In crystal growth, a Knudsen cell is an effusion evaporator source for relatively low partial pressure elementary sources (e.g. Ga, Al, Hg, As). Because it is easy to control the temperature of the evaporating material in Knudsen cells, they are commonly used in molecular-beam epitaxy. Development The Knudsen effusion cell was developed by Martin Knudsen (1871–1949). A typical Knudsen cell contains a crucible (made of pyrolytic boron nitride, quartz, tungsten or graphite), heating filaments (often made of metal tantalum), water cooling system, heat shields, and an orifice shutter. Vapor pressure measurement The Knudsen cell is used to measure the vapor pressures of a solid with very low vapor pressure. Such a solid forms a vapor at low pressure by sublimation. The vapor slowly effuses through the pinhole, and the loss of mass is proportional to the vapor pressure and can be used to determine this pressure.Peter Atkins and Julio de Paula, ''Physical Chemistry'' (8th ed., W.H.F ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Kinetic Theory Of Gases
The kinetic theory of gases is a simple classical model of the thermodynamic behavior of gases. Its introduction allowed many principal concepts of thermodynamics to be established. It treats a gas as composed of numerous particles, too small to be seen with a microscope, in constant, random motion. These particles are now known to be the atoms or molecules of the gas. The kinetic theory of gases uses their collisions with each other and with the walls of their container to explain the relationship between the macroscopic properties of gases, such as volume, pressure, and temperature, as well as transport properties such as viscosity, thermal conductivity and mass diffusivity. The basic version of the model describes an ideal gas. It treats the collisions as perfectly elastic and as the only interaction between the particles, which are additionally assumed to be much smaller than their average distance apart. Due to the time reversibility of microscopic dynamics ( microsco ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Sampson Flow
Sampson flow is defined as fluid flow through an infinitely thin orifice in the viscous flow regime for low Reynolds number. It is derived from an analytical solution to the Navier-Stokes equations. The below equation can be used to calculate the total volumetric flowrate through such an orifice: :Q_S=\Delta P d^3 / 24 \mu Here, Q_S is the volumetric flowrate in m^3/sec, \Delta P is the pressure difference in Pa, d is the pore diameter in m, and \mu is the fluid's dynamic viscosity in Pa·s. The flow can also be expressed as a molecular flux as: :J_S=P_ \Delta P d/6\pi\mu k_BT Here, J_S is the molecular flux in atoms/m2·sec, P_ is the average of the pressures on either side of the orifice, k_B is the Boltzmann constant, (1.38\times10^ J/K), and T is the absolute temperature in K. Sampson flow is the macroscopic analog of effusion flow, which describes stochastic diffusion of molecules through an orifice much smaller than the mean-free-path of the gas molecules. For pore diamete ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Vapor Pressure
Vapor pressure or equilibrium vapor pressure is the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases (solid or liquid) at a given temperature in a closed system. The equilibrium vapor pressure is an indication of a liquid's thermodynamic tendency to evaporate. It relates to the balance of particles escaping from the liquid (or solid) in equilibrium with those in a coexisting vapor phase. A substance with a high vapor pressure at normal temperatures is often referred to as '' volatile''. The pressure exhibited by vapor present above a liquid surface is known as vapor pressure. As the temperature of a liquid increases, the attractive interactions between liquid molecules become less significant in comparison to the entropy of those molecules in the gas phase, increasing the vapor pressure. Thus, liquids with strong intermolecular interactions are likely to have smaller vapor pressures, with the reverse true for weaker interactions. The vapor p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Anatomic Space
{{set index article In anatomy, a spatium or anatomic space is a space (cavity or gap). Anatomic spaces are often landmarks to find other important structures. When they fill with gases (such as air) or liquids (such as blood) in pathological ways, they can suffer conditions such as pneumothorax, edema, or pericardial effusion. Many anatomic spaces are potential spaces, which means that they are potential rather than realized (with their realization being dynamic according to physiologic or pathophysiologic events). In other words, they are like an empty plastic bag that has not been opened (two walls collapsed against each other; no interior volume until opened) or a balloon that has not been inflated. Examples of anatomic spaces (or potential spaces) include: * Axillary space * Buccal space * Canine space * Cystohepatic triangle * Deep perineal space * Deep temporal space *Epidural space * Extraperitoneal space * Fascial spaces of the head and neck * Infratemporal space *Interco ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
