This month Kronos Quartet will spend a weeklong residency at the UI, including two concerts at Krannert Center for the Performing Arts. The first, at 8 p.m. Sept. 23 in the Colwell Playhouse, features George Crumb's "Black Angels," a musical portrait of the Vietnam War. At 8 p.m. Sept. 24 in the Foellinger Great Hall, the quartet performs with Hamza El Din, a Nubian musician who was featured on the group's popular "Pieces of Africa" album. Din replaces Foday Musa Suso, who was originally scheduled for the performance. During their residency, Kronos Quartet and Hamza El Din will work with students in the UI School of Music, including those in composition, string performance and musicology. Kronos also will offer an informal concert/discussion as part of the Frances P. Rohlen Visiting Artist and Lecture Series. The event is free and open to the public, and will be held at 3 p.m. Sept. 21 in the Foellinger Great Hall. Since its inception in 1973, Kronos Quartet has revolutionized the chamber music repertoire by combining a unique musical vision with a fearless dedication to experimentation. Its extensive repertoire ranges from Dimitri Shostakovich, Anton von Webern and Charles Ives to Astor Piazzolla, John Cage and Howlin' Wolf. In addition to working closely with such modern artists as Terry Riley, John Zorn and H.M. Gorecki, Kronos commissions new works from today's most innovative composers around the world, extending its reach as far as Zimbabwe, Australia, Japan, Argentina and Azerbaijan. The work "Black Angels" holds special significance for the group: When violinist David Harrington first heard the work in 1973, he was fascinated by it and felt driven to perform the work someday. He founded the Kronos Quartet with that goal in mind. Composed by Crumb in 1970, "Black Angels" uses an arsenal of sounds including shouting, whistling, whispering, gongs, maracas and crystal glasses to depict the Vietnam War. It was recorded by Kronos in 1990 and will be performed with special lighting effects in this concert. With its 1992 album "Pieces of Africa," Kronos Quartet hit the top of both the classical music and world music charts. The album features works written for the quartet by African composers, merging African sounds and rhythms with the string quartet idiom. Hamza El Din, whose work "Escalay" ("Waterwheel") is included on the album, introduced the oud, a lute-like instrument, to Western audiences in the 1960s. A virtuosic musician, El Din also plays the tar, a hand-held circular drum. Tickets for the Sept. 23 performance are $21($20 for students and senior citizens); for the Sept. 24 concert, $21, $20 and $19 ($19, $18 and $17 for students and senior citizens). UI students are eligible for a $5 discount for both performance.