common

common

[kom-uhn]
cold, common, acute viral infection of the mucous membranes of the nose and throat, often involving the sinuses. The typical sore throat, sneezing, and fatigue may be accompanied by body aches, headache, low fever, and chills. The congested and discharging mucous membrane may become a fertile ground for a secondary bacterial invasion that can spread to the larynx, bronchi, lungs, or ears. Uncomplicated infections usually last from three to ten days.

The cold is the most common human ailment. Most adult Americans suffer from one to four colds per year, but children ages one to five—who are the most susceptible—typically may contract as many as eight. Colds are spread by respiratory droplets or by contaminated hands or objects. Although the incidence of colds is higher in winter, exposure to chilling or dampness is considered to be of little significance.

Any one of up to 200 viruses (such as the rhinoviruses, coronaviruses, or respiratory syncytial virus [RSV]) can cause colds, to which it seems almost no one is immune. Infection with a viral strain confers only temporary immunity to that strain. Colds in infants and young children caused by RSV can progress to pneumonia and other complications, especially in those under a year old who were born prematurely or have chronic lung disease; RSV causes an estimated 4,500 deaths yearly in these groups in the United States.

There is no treatment for the common cold other than that aimed at relieving symptoms and keeping the body well-rested, -fed, and -hydrated. Because of the growing problem of drug resistance, doctors are being discouraged from prescribing antibiotics (which do not affect viruses) for colds unless secondary bacterial infection makes them necessary. There is no convincing evidence that vitamin C megadoses can prevent the common cold.

Researchers have reported reduction or prevention of cold symptoms in human tests of an experimental drug against rhinoviruses, which cause nearly half of all colds. The drug acts by imitating a molecule in the body called ICAM-1, to which the rhinovirus attaches to produce colds. As rhinoviruses attach to the decoy molecules instead, the likelihood or severity of infection is decreased.

In telecommunication, the term common-mode interference has the following meanings:

  1. Interference that appears on both signal leads (signal and circuit return), or the terminals of a measuring circuit, and ground.
  2. A form of coherent interference that affects two or more elements of a network in a similar manner (i.e., highly coupled) as distinct from locally generated noise or interference that is statistically independent between pairs of network elements.

Techniques for dealing with common-mode interference

Common mode noise may be isolated from the desired signal by various means:

  • Common mode noise may sensed and fed back negatively into object providing the signals (see Driven Right Leg).
  • Both signal and signal return may be applied to the primary of a transformer, with the signal taken from the secondary. As common mode interference will not cause current to be induced in the primary, no signal from this source will be seen in the secondary, while differential signals on the primary will cause current in the primary and so cause induced voltage in the secondary.
  • A signal transformer may have a center-tapped primary to ground, with the signal and signal return operating as a balanced line (push-pull technique). This is advantageous its resistance to signals raised on ground due to ground loop induction and ground circuit resistance.
  • The signal (line and return) may be used to drive the LED in an opto-isolator.

See also

Search another word or see commonon Dictionary | Thesaurus |Spanish
Copyright © 2015 Dictionary.com, LLC. All rights reserved.
  • Please Login or Sign Up to use the Recent Searches feature