18. Niels Bohr

Niels Henrik David Bohr was a Danish physicist who made fundamental contributions to understanding atomic structure and quantum mechanics.

He was born in Denmark in 1885. His father was a professor of physiology at the University of Copenhagen. Bohr studied as an undergraduate, graduate and, under Christian Christiansen, as a doctoral student at Copenhagen University, receiving his doctorate in 1911. As a post-doctoral student, Bohr first conducted experiments under J. J. Thomson at Trinity College, Cambridge. He then went on to study under Ernest Rutherford at the University of Manchester in England. On the basis of Rutherford's theories, Bohr published his model of atomic structure in 1913, introducing the theory of electrons traveling in orbits around the atom's nucleus, the chemical properties of the element being largely determined by the number of electrons in the outer orbits. Bohr also introduced the idea that an electron could drop from a higher-energy orbit to a lower one, emitting a photon (light quantum) of discrete energy. This became a basis for quantum theory.

In 1922, Bohr was awarded the Nobel Prize in physics "for his services in the investigation of the structure of atoms and of the radiation emanating from them." After the war Bohr returned to Copenhagen, advocating the peaceful use of

nuclear energy. Bohr mentored and collaborated with many of the top physicists of the century at his institute in Copenhagen. He was also part of the team of physicists working on the Manhattan Project.

Much work was done on the interpretation of quantum mechanics. "Tube Alloys" was the code-name for the British nuclear weapon program. The British intelligence services inquired about Bohr's availability for work or insights of particular value. Bohr's reply made it clear that he could not help. This does not exclude the possibility that Bohr privately did make calculations going further than his work in 1939. He was evacuated from Stockholm in 1943. Bohr married Margrethe Nørlund in 1912, and one of their sons, Aage Niels Bohr, grew up to be

an important physicist who, like his father, received the Nobel prize, in 1975. Bohr has been described as one of the most influential physicists of the 20th.

In 1965, three years after Bohr's death, the Institute of Physics at the University of Copenhagen changed its name to the Niels Bohr Institute.

Answer the following questions:

1. Who was Niels Bohr?

2. Where did he study?

3. What theory did he introduce in 1913?

4. When and in what field of science was he awarded the Nobel Prize?

5. Which University is named after Niels Bohr?

19. Sikorsky Aircraft

In 1925 a Kiev-born Russian American aircraft engineer Igor Sikorsky developed the first stable, single-rotor, fully-controllable helicopter to enter large full-scale production in 1942, upon which the majority of subsequent helicopters were based. The company became a part of United Aircraft in 1929, now United Technologies Corporation (UTC), and remains one of the leading helicopter manufacturers, producing such well-known models as the UH-60 Black Hawk and SH-60 Seahawk, as well as experimental types like the Sikorsky X-Wing.

It is a leading defence contractor. Since 1957, Sikorsky has supplied the helicopter of the President of the United States, Marine One.

The company also acquired Helicopter Support Inc. (H.S.I) in 1998. This company handles all the after-market support for the Sikorsky product. The product lines of the two firms are complementary, and have very little overlap, as Sikorsky primarily concentrates on medium and large helicopters, while Schweizer produces small helicopters, gliders, and light planes.

Sikorsky's main plant and administrative offices are located in Stratford, Connecticut. Other Sikorsky facilities are in Shelton, and Bridgeport, Connecticut; West Palm Beach, Florida; and Troy, Alabama. Other Sikorsky-owned subsidiaries are in Trumbull, Connecticut; Coatesville, Pennsylvania; and Grand Prairie, Texas; and the company has branches around the world.