2000s in the music industry Inc.), who surpassed Wal-Mart to become the US’s largest music retailer in April 2008. Sector leaders include: Many hundreds more stores operate worldwide, often prominent only in particular countries or specialist genres. A third kind of operator never retails directly to the public, instead offering branded whitelabel stores and portals for organisations including bricks-and-mortar music stores, mobile telephony operators and ISPs. Some services which initially only offered streaming of tracks now also offer a-la-carte downloads, either through third parties (e.g. Spotify) or fully integrated (Deezer, Juno Digital, Rhapsody etc.). In 2009 "Rolling Stone" reported a price war between iTunes and
Tidal barrage pressure). When the water level outside of the basin or lagoon changes relative to the water level inside, the turbines are able to produce power. The basic elements of a barrage are caissons, embankments, sluices, turbines, and ship locks. Sluices, turbines, and ship locks are housed in caissons (very large concrete blocks). Embankments seal a basin where it is not sealed by caissons. The sluice gates applicable to tidal power are the flap gate, vertical rising gate, radial gate, and rising sector. Only a few such plants exist. The first was the Rance Tidal Power Station, on the Rance river,