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The United States of America (USA), commonly referred to as the United States (U.S.) or America, is a federal republiccomposed of 50 states, the federal district of Washington, D.C., five major territories, and various possessions.[fn 1] The 48 contiguous states and Washington, D.C., are in central North America between Canada and Mexico. The state of Alaska is in the northwestern part of North America and the state of Hawaii is an archipelago in the mid-Pacific. The territories are scattered about the Pacific Ocean and the Caribbean Sea. At 3.8 million square miles (9.9 million km2) and with over 320 million people, the country is the world's third largest by total area (fourth largest by land area) and the third most populous. It is one of the world's most ethnically diverse and multicultural nations, the product of large-scale immigration from many countries.

The geography and climate of the United States are also extremely diverse, and the country is home to a wide variety of wildlife. The term "United States", when used in 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, andminor 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. From 1989 through 1996, the total area of the US was listed as 9,372,610 km2 (3,618,780 sq mi) (land + inland water only). The listed total area changed to 9,629,091 km2 (3,717,813 sq mi) in 1997 (Great Lakes area and coastal waters added), to 9,631,418 km2 (3,718,711 sq mi) in 2004, to 9,631,420 km2 (3,718,710 sq mi) in 2006, and to 9,826,630 km2 (3,794,080 sq mi) in 2007 (territorial waters added). Currently, the CIA World Factbook gives 9,826,675 km2 (3,794,100 sq mi), the United Nations Statistics Division gives 9,629,091 km2 (3,717,813 sq mi), and the Encyclopædia Britannica gives 9,522,055 km2(3,676,486 sq mi)(Great Lakes area included but not coastal waters).These source consider only the 50 states and the Federal District, and exclude overseas territories.

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 United States' GDP was estimated to be $17.914 trillion as of Q2 2015. The U.S. dollar is the currency most used in international transactions and is the world's foremost reserve currency Over the same period, the three heavyweights, the European Union, USA and Japan, have registered a decrease. In 2002, almost 83% of research and development was carried out in developed countries; by 2007 this share had dropped to 76%. This trend is even clearer when industry’s contribution to GERD is considered. Between 2000 and 2007, the private sector share of R&D spending, as a proportion of GDP, saw a sharp increase in Japan, China, Singapore and especially the Republic of Korea, while it remained stable in Germany, France, and the United Kingdom and even saw a slight decrease in the Russian Federation and the USA.

The clinical nursing specialist (CNS) is an expert who applies an expanded range of practical, theoretical, and research-based competencies to the care of patients within in a specialty clinical area within the larger discipline of nursing. A large number of studies consistently conclude that the CNS is a valuable healthcare resource that provides high-quality clinical and evidence-based nursing practice and improves patient outcome. The CNS has been involved in healthcare practices for many years, with an increasingly diverse role.

The United States Constitution itself reflects the desire to encourage scientific creativity. It gives the United States Congress the power "to promote the progress of science and useful arts, by securing for limited times to authors and inventors the exclusive right to their respective writings and discoveries. Research conducted by universities, hospitals, and corporations also contributes to improvement in diagnosis and treatment of disease. According to updated United States nursing journals list there are different nursing journals in United States in which American Journal of Nursing is one of excellent nursing journals and it publishes about nursing research in USA. The other list of nursing journals in united states includes American Journal of Nursing .