The United States of America (USA), commonly referred to as the United States (U.S.) or America, is a federal republic composed of 50 states, the federal district and five territories. It is a superpower, and some argue that currently the US is the only superpower in the world. It has great influence over world finance, trade, culture, military, politics, and technology. The United States is located on the North American Continent. The United States of America is bordered by the Pacific Ocean, the Atlantic Ocean, Canada to the north, and Mexico to the south.
The geographical sense, is the contiguous United States, the state of Alaska, the island state of Hawaii, the five insular territories of Puerto Rico, Northern Mariana Islands, U.S. Virgin Islands, Guam, and American Samoa, and minor outlying possessions. The United States shares land borders with Canada and Mexico and maritime borders with Russia, Cuba, and the Bahamas in addition to Canada and Mexico.
The United States is the world's largest national economy in nominal terms and second largest according to purchasing power parity (PPP), representing 22% of nominal global GDP and 17% of gross world product (GWP). The relative increase in R&D and basic research of foreign nations as compared to the U.S. can (in some ways) work to the advantage of U.S. industry. The U.S. trading position in technology-oriented services remains strong as evidenced by the continued surplus in trade of computer software and manufacturing.
In Physics, Medicine, Chemistry etc including all fields this island nation produced 357 Nobel laureates so far, in which mostly are for Chemistry and Physiology or Medicine. Paul Lawrence Modrich is an American biochemist is awarded Nobel Prize in Chemistry in 2015. William Cecil Campbell is an Irish-American biologist is awarded Nobel Prize in Physiology or Medicine in 2015. USA is ranked number 1 suceeded by Japan in publishing highest number of articles related to Clinical Sciences. Numerous clinical journals are published from USA with good reputation as well.