| CFDU | color-flow Doppler ultrasonography; color flow Doppler ultrasound |
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| FEF50/FIF50 | ratio of expiratory flow to inspiratory flow at 50% of forced vital capacity |
| FMF | familial Mediterranean fever; fetal movement felt; flow microfluorometry; forced midexpiratory flow |
| LBF | Lactobacillus bulgaricus factor; limb blood flow; liver blood flow |
| MEF | maximal expiratory flow; middle ear fluid; midexpiratory flow; migration enhancement factor; mouse e... |
| flow cytophotometry | <technique> Flow cytometry is an emerging technique which holds great promise for the separation, classification and quantitation of blood cells and antibodies which affect blood cells. Complex computerised instruments are used to pass a monocellular stream of cells, platelets or other microscopic particulate elements through a beam of laser light. The cells are categorised first by size and then computer analysed to sort the mixture of cellular elements into cell type by size. Cells are labelled with fluorescent dye and then passed, in suspending medium, through a narrow dropping nozzle so that each cell is in a small droplet. A laser based detector system is used to excite fluorescence and droplets with positively fluorescent cells are given an electric charge. Charged and uncharged droplets are separated as they fall between charged plates and so collect in different tubes. The machine can be used either as an analytical tool, counting the number of labelled cells in a population or to separate the cells for subsequent growth of the selected population. Further sophistication can be built into the system by using a second laser system at right angles to the first to look at a second fluorescent label or to gauge cell size on the basis of light scatter. The great strength of the system is that it looks at large numbers of individual cells and makes possible the separation of populations with, for example: particular surface properties. Tabulation of counted data in conjunction with size analysis enables determination of relative percentages of each specific cellular subset for which monoclonal antibody conjugates are utilised, even when the size of the cell is identical to other subset species. Flow cytometry is a slightly imprecise but common term for the use of the Fluorescence-activated Cell Sorter (FACS). (01 Dec 1998) |
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| flow injection analysis | The analysis of a chemical substance by inserting a sample into a carrier stream of reagent using a sample injection valve that propels the sample downstream where mixing occurs in a coiled tube, then passes into a flow-through detector and a recorder or other data handling device. (12 Dec 1998) |
| flow karyotyping | Use of flow cytometry toanalyse and/orseparate chromosomes on the basis of their DNA content. (09 Oct 1997) |
| flow-over vaporiser | A device for vaporization of a liquid anaesthetic by causing gases to pass over the anaesthetic or over material saturated with the anaesthetic. (05 Mar 2000) |
| flow rate | The amount of water that moves through an area (usually pipe) in a given period of time. (05 Dec 1998) |
| flow void | In magnetic resonance imaging, the absence of signal from blood whose activated protons leave a region before their magnetization is measured. See: signal void. (05 Mar 2000) |
| flow-volume curve | The graph produced by plotting the instantaneous flow of respiratory gas against the simultaneous lung volume, usually during maximal forced expiration. (05 Mar 2000) |
| laminar air flow unit | An air-filtering system used at some transplant facilities to remove particulate matter and fungi from the air. (16 Dec 1997) |
| laminar flow | The relative motion of elements of a fluid along smooth parallel paths, which occurs at lower values of Reynolds number. (05 Mar 2000) |
| forced expiratory flow | Expiratory flow during measurement of forced vital capacity; subscripts specify the exact parameter measured, e.g., peak instantaneous flow, the instantaneous flow at some specified point on the curve of volume expired versus time, or on the flow-volume curve, the mean flow between two expired volumes. (05 Mar 2000) |
| forced expiratory flow rates | Measurements of rates of airflow during a forced vital capacity determination. (12 Dec 1998) |
| frozen-in flow law | <radiobiology> In a perfect conductor, the total magnetic flux through any surface is a constant. In a plasma which is nearly perfectly conducting, the relevant surfaces move with the plasma, the result is that the plasma is tied to the magnetic field, and the field is tied to the plasma. Motion of the plasma thus deforms the magnetic field, and vice versa. The magnetic flux is said to be frozen into the plasma. (09 Oct 1997) |
| low flow principle | A principle based on the observation that animals can survive prolonged vena caval occlusion without sequelae: if blood from the azygos vein alone is permitted to enter the heart, patients are perfused during cardiac and pulmonary bypass at flows much less than the normal resting cardiac output. Synonym: low flow principle. (05 Mar 2000) |
| aperture for electron microscopy | <technique> Anode aperture: The opening in the accelerating voltage anode shield of the electron gun through which the electrons must pass to irradiate the specimen. Condenser aperture: An opening in the condenser lens controlling the number of electrons entering the lens and the angular aperture of the electron beam. The angular aperture can also be controlled by the condenser lens current. Physical objective aperture: A metallic diaphragm, with a small central hole, used to limit the cone of electrons accepted by the objective lens. This improves image-contrast since highly scattered electrons are prevented from arriving at the Gaussian image plane and therefore cannot contribute to background fog. Aplanatic. Free from spherical aberration and coma. (05 Aug 1998) |
| Auger electron | An electron ejected from a lower energy orbital after a photoelectric interaction of an X-ray photon with a K-shell electron by the characteristic radiation photon; the Auger electron recoils with energy equal to the characteristic radiation less the difference in shell binding energies. See: photoelectric effect. (05 Mar 2000) |