audio-frequency electromagnetic method
121List of unusual units of measurement — For units of measure primarily used in countries where English is not the main language, see the article specific to that country, a list of which can be found in the systems of measurement article. An unusual unit of measurement is a unit of… …
122Computer surveillance — This article is about surreptitious monitoring of computer activity. For information on methods of preventing unauthorized access to computer data, see computer security. Computer surveillance is the act of performing surveillance of computer… …
123DC bias — When describing a periodic function in the frequency domain, the DC bias, DC component, DC offset, or DC coefficient is the mean value of the waveform (possibly scaled according to the norm of the corresponding basis function of the frequency… …
124space exploration — Investigation of the universe beyond Earth s atmosphere by means of manned and unmanned spacecraft. Study of the use of rockets for spaceflight began early in the 20th century. Germany s research on rocket propulsion in the 1930s led to… …
125Engineering — The Watt steam engine, a major driver in the Industrial Revolution, underscores the importance of engineering in modern history. This model is on display at the main building of the ETSIIM in Madrid, Spain. Engineering is the discipline, art,… …
126Microscopy — is the technical field of using microscopes to view samples and objects that cannot be seen with the unaided eye (objects that are not within the resolution range of the normal eye). There are three well known branches of microscopy, optical,… …
127Radio jamming — is the (usually deliberate) transmission of radio signals that disrupt communications by decreasing the signal to noise ratio. Unintentional jamming occurs when an operator transmits on a busy frequency without checking that it is in use first,… …
128Surveillance — For other uses, see Surveillance (disambiguation). A nest of surveillance cameras at the Gillette Stadium in Foxborough, Massachusetts Surveillance ( …
