Iterative reconstructionIterative reconstruction refers to iterative algorithms used to reconstruct 2D and 3D images in certain imaging techniques. For example, in computed tomography an image must be reconstructed from projections of an object. Here, iterative reconstruction techniques are usually a better, but computationally more expensive alternative to the common filtered back projection (FBP) method, which directly calculates the image in a single reconstruction step.
Pulse-density modulationPulse-density modulation, or PDM, is a form of modulation used to represent an analog signal with a binary signal. In a PDM signal, specific amplitude values are not encoded into codewords of pulses of different weight as they would be in pulse-code modulation (PCM); rather, the relative density of the pulses corresponds to the analog signal's amplitude. The output of a 1-bit DAC is the same as the PDM encoding of the signal. In a pulse-density modulation bitstream, a 1 corresponds to a pulse of positive polarity (+A), and a 0 corresponds to a pulse of negative polarity (−A).
Radiocommande de modélismevignette|Un servomoteur ou servo. Une radiocommande de modélisme est un instrument permettant de commander un modèle réduit à distance. Elle est généralement équipée de deux leviers permettant le contrôle de la puissance du moteur et de la direction. On trouve également des modèles avec molette et une gâchette pour les modèles réduits de voitures. Elles peuvent être très simples (levier de profondeur et de direction et celle des gaz pour les avions) ou très complexes (changement de canaux et de modes).
Cable television headendA cable television headend is a master facility for receiving television signals for processing and distribution over a cable television system. A headend facility may be staffed or unstaffed and is typically surrounded by some type of security fencing. The building is typically sturdy and purpose-built to provide security, cooling, and easy access for the electronic equipment used to receive and re-transmit video over the local cable infrastructure. One can also find head ends in power-line communication (PLC) substations and Internet communications networks.
Cable television in the United StatesCable television first became available in the United States in 1948. By 1989, 53 million U.S. households received cable television subscriptions, with 60 percent of all U.S. households doing so in 1992. Most cable viewers in the U.S. reside in the suburbs and tend to be middle class; cable television is less common in low income, urban, and rural areas. According to reports released by the Federal Communications Commission, traditional cable television subscriptions in the US peaked around the year 2000, at 68.
