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Accurate torsional potentials and torsional barriers are derived for the 1, 3-butadiene molecule using state-of-the-art coupled-cluster (CC) methods. The basis set effect, and the performance of different ab initio methodologies with respect to the CC calculations, have been carefully addressed. The CC results obtained here provide an excellent compromise between accuracy and computational cost, which can be extended to other systems. [ABSTRACT FROM AUTHOR]

The article reports on three cases of West Nile Virus infections that were reported to health officials in Puerto Rico and were investigated by members of the U.S. Centers for Disease Control and Prevention. A discussion of the infections, and of surveillance which has been conducted by the centers in an effort to determine the extent of the disease's transmission in Puerto Rico, is presented. Blood donor screenings which were put into place in the United States and Puerto Rico to prevent the transmission of the disease are discussed. The many ways the disease can be transmitted are discussed.