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Allegheny River Lock and Dam No. 9 is a historic lock and fixed-crest dam complex located at Madison Township and Washington Township in Armstrong County, Pennsylvania. It was built between 1935 and 1938 by the United States Army Corps of Engineers, and includes the lock, dam, steel miter gates, and Operations Building. The lock measures 56 feet by 360 feet, and has a lift of 22 feet. The dam measures approximately 60 feet high and 918 feet long. The Operations Building, or powerhouse, is a utilitarian two-story building in a vernacular early-20th century revival style. The lock and dam were built by the U.S. Army Corps of Engineers as a part of an extensive system of locks and dams to improve navigation along the Allegheny River.

Radio halos are large-scale sources of diffuse radio emission found in the center of some, but not all, galaxy clusters. There are two classes of radio halos: mini-halos and giant radio halos. The linear size of giant radio halos is about 700kpc-1Mpc, whereas mini-halos are typically less than 500kpc. Giant radio halos are more often observed in highly X-ray luminous cluster samples than less luminous X-ray clusters in complete samples. They have a very low surface brightness and do not have obvious galaxy counterparts. However, their morphologies typically follow the distribution of gas in the intra-cluster medium. Mini-halos however, while similar to giant halos, are found at the center of cooling core clusters but around a radio galaxy.