the energy of a discrete-time signal x(t) is defined as
Relationship to energy in physics
Energy in this context is not, strictly speaking, the same as the conventional notion of energy in physics and the other sciences. The two concepts are, however, closely related, and it is possible to convert from one to the other:
For example, if x(t) represents the potential (in volts) of an electrical signal propagating across a transmission line, then Z would represent the characteristic impedance (in ohms) of the transmission line. The units of measure for the signal energy would appear as volt2·seconds, which is not dimensionally correct for energy in the sense of the physical sciences. After dividing by Z, however, the dimensions of E would become volt2·seconds per ohm, which is equivalent to joules, the SI unit for energy as defined in the physical sciences.
On September 18, 2001, Collective Soul released their greatest hits compilation Seven Year Itch: Greatest Hits, 1994-2001 (stylized as 7even Year Itch). The compilation includes songs recorded from 1994 to 2001 and included two new tracks; "Next Homecoming" and "Energy". Seven Year Itch received decent reviews and was relatively successful It sold 225,000 copies in the first year after its release and reached number fifty on the Billboard 200; in Canada, it reached number nine on its albums chart and went platinum. All the songs in Seven Year Itch had charted in the US on the Billboard Hot 100, Mainstream Rock Tracks, or the Modern Rock Tracks chart, except for "Energy", which debuted in this compilation.
The compilation has sold over 500,000 copies. It saw a resurgence in sales after Collective Soul began putting out albums on their own independent label, El Music Group, beginning in 2004.
Seven Year Itch was the last album Collective Soul released through Atlantic Records and their last album to feature guitarist Ross Childress, who had been with the band since its 1993/1994 debut.
Following the Russo-Persian Wars of 1804–13 and 1826–28, the territories of the Iranian Qajar dynasty in the Caucasus were forcefully ceded to the Russian Empire and the Treaty of Gulistan in 1813 and the Treaty of Turkmenchay in 1828 finalized the borders between the Russian Empire and Qajar Iran. The areas to the north of the river Aras, including the territory of the contemporary Republic of Azerbaijan, were Iranian territory until they were occupied by Russia over the course of the 19th century. The Russo-Persian Wars of the 19th century settled the modern-day boundary of Iran, stripping it of all its Caucasian territories and incorporating them into the Russian Empire. The eventual formation of the Azerbaijan Democratic Republic in 1918 established the territory of modern Azerbaijan.