搜尋結果
TSMC was founded in Taiwan in 1987 by Morris Chang as the world's first dedicated semiconductor foundry. It has long been the leading company in its field. [15] [16] When Chang retired in 2018, after 31 years of TSMC leadership, Mark Liu became chairman and C. C. Wei became Chief Executive.
- 73,090 (2022)
- US$73.67 billion (2022)
Christopher Columbus[b] (/kəˈlʌmbəs/;[2] between 25 August and 31 October 1451 – 20 May 1506) was an Italian[3][c] explorer and navigator from the Republic of Genoa who completed four Spanish-based voyages across the Atlantic Ocean sponsored by the Catholic Monarchs, opening the way for the widespread European exploration and European ...
Taiwan,[II][k] officially the Republic of China (ROC),[I][l] is a country[27] in East Asia.[o] It is located at the junction of the East and South China Seas in the northwestern Pacific Ocean, with the People's Republic of China (PRC) to the northwest, Japan to the northeast, and the Philippines to the south. The territories controlled by the ...
It was formed approximately 4.5 billion years ago, is a terrestrial planet and is the second smallest of the Solar System 's planets with a diameter of 6,779 km (4,212 mi). A Martian solar day ( sol) is 24.5 hours and a Martian solar year is 1.88 Earth years (687 Earth days). Mars has two small and irregular natural satellites: Phobos and Deimos.
Water is an inorganic compound with the chemical formula H2O. It is a transparent, tasteless, odorless,[c] and nearly colorless chemical substance, and it is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a solvent[19]). It is vital for all known forms of life, despite not ...
- Background
- Construction
- Operation
- Environmental Impact
- Naming Controversy
- Recognition
- See Also
- Bibliography
- External Links
Search for resources
As the United States developed the Southwest, the Colorado River was seen as a potential source of irrigation water. An initial attempt at diverting the river for irrigation purposes occurred in the late 1890s, when land speculator William Beatty built the Alamo Canal just north of the Mexican border; the canal dipped into Mexico before running to a desolate area Beatty named the Imperial Valley. Though water from the Alamo Canal allowed for the widespread settlement of the valley, the canal...
Planning and agreements
In 1922, the Reclamation Service presented a report calling for the development of a dam on the Colorado River for flood control and electric power generation. The report was principally authored by Davis and was called the Fall-Davis report after Interior Secretary Albert Fall. The Fall-Davis report cited use of the Colorado River as a federal concern because the river's basin covered several states, and the river eventually entered Mexico. Though the Fall-Davis report called for a dam "at o...
Design, preparation and contracting
Even before Congress approved the Boulder Canyon Project, the Bureau of Reclamation was considering what kind of dam should be used. Officials eventually decided on a massive concrete arch-gravity dam, the design of which was overseen by the Bureau's chief design engineer John L. Savage. The monolithic dam would be thick at the bottom and thin near the top and would present a convex face towards the water above the dam. The curving arch of the dam would transmit the water's force into the abu...
Labor force
Soon after the dam was authorized, increasing numbers of unemployed people converged on southern Nevada. Las Vegas, then a small city of some 5,000, saw between 10,000 and 20,000 unemployed descend on it. A government camp was established for surveyors and other personnel near the dam site; this soon became surrounded by a squatters' camp. Known as McKeeversville, the camp was home to men hoping for work on the project, together with their families. Another camp, on the flats along the Colora...
River diversion
Before the dam could be built, the Colorado River needed to be diverted away from the construction site. To accomplish this, four diversion tunnels were driven through the canyon walls, two on the Nevada side and two on the Arizona side. These tunnels were 56 ft (17 m) in diameter. Their combined length was nearly 16,000 ft, or more than 3 miles (5 km).The contract required these tunnels to be completed by October 1, 1933, with a $3,000-per-day fine to be assessed for any delay. To meet the d...
Groundworks, rock clearance and grout curtain
To protect the construction site from the Colorado River and to facilitate the river's diversion, two cofferdams were constructed. Work on the upper cofferdam began in September 1932, even though the river had not yet been diverted. The cofferdams were designed to protect against the possibility of the river's flooding a site at which two thousand men might be at work, and their specifications were covered in the bid documents in nearly as much detail as the dam itself. The upper cofferdam wa...
Power plant and water demands
Excavation for the powerhouse was carried out simultaneously with the excavation for the dam foundation and abutments. The excavation of this U-shaped structure located at the downstream toe of the dam was completed in late 1933 with the first concrete placed in November 1933. Filling of Lake Mead began February 1, 1935, even before the last of the concrete was poured that May. The powerhouse was one of the projects uncompleted at the time of the formal dedication on September 30, 1935; a cre...
Spillways
The dam is protected against over-topping by two spillways. The spillway entrances are located behind each dam abutment, running roughly parallel to the canyon walls. The spillway entrance arrangement forms a classic side-flow weirwith each spillway containing four 100-foot-long (30 m) and 16-foot-wide (4.9 m) steel-drum gates. Each gate weighs 5,000,000 pounds (2,300 metric tons) and can be operated manually or automatically. Gates are raised and lowered depending on water levels in the rese...
Roadway and tourism
There are two lanes for automobile traffic across the top of the dam, which formerly served as the Colorado River crossing for U.S. Route 93. In the wake of the September 11 terrorist attacks, authorities expressed security concerns and the Hoover Dam Bypass project was expedited. Pending the completion of the bypass, restricted traffic was permitted over Hoover Dam. Some types of vehicles were inspected prior to crossing the dam while semi-trailer trucks, buses carrying luggage, and enclosed...
The changes in water flow and use caused by Hoover Dam's construction and operation have had a large impact on the Colorado River Delta. The construction of the dam has been implicated in causing the decline of this estuarine ecosystem. For six years after the construction of the dam, while Lake Mead filled, virtually no water reached the mouth of ...
During the years of lobbying leading up to the passage of legislation authorizing the dam in 1928, the press generally referred to the dam as "Boulder Dam" or as "Boulder Canyon Dam", even though the proposed site had shifted to Black Canyon.The Boulder Canyon Project Act of 1928 (BCPA) never mentioned a proposed name or title for the dam. The BCPA...
Hoover Dam was recognized as a National Historic Civil Engineering Landmark in 1984. It was listed on the National Register of Historic Places in 1981 and was designated a National Historic Landmarkin 1985, cited for its engineering innovations.
Cited works
1. Bureau of Reclamation (2006). Reclamation: Managing Water in the West: Hoover Dam. US Department of the Interior. 2. Cummings, Homer (1939). Selected Papers of Homer Cummings. New York: Scribners. 3. Dunar, Andrew J.; McBride, Dennis (2001) [1993]. Building Hoover Dam: An Oral History of the Great Depression. Reno, Nev.: University of Nevada Press. ISBN 978-0-87417-489-2. 4. Hiltzik, Michael A. (2010). Colossus: Hoover Dam and the Making of the American Century. New York: Free Press. ISBN...
Other sources
1. Arrigo, Anthony F. (2014). Imaging Hoover Dam: The Making of a Cultural Icon. Reno, NV: University of Nevada Press. 2. Bartojay, Katie; Joy, Westin (October 21–22, 2010). Wiltshire, Richard L.; Gilbert, David R.; Rogers, Jerry R. (eds.). Long-Term Properties of Hoover Dam Mass Concrete. Hoover Dam 75th Anniversary History Symposium. Las Vegas, Nevada: American Society of Civil Engineers. pp. 74–84. ISBN 978-0-7844-1141-4. 3. Cohn, Jeffrey P. (December 2001). "Resurrecting the Dammed: A Loo...
Wikipedia[note 3] is a free content online encyclopedia written and maintained by a community of volunteers, known as Wikipedians, through open collaboration and the use of the wiki-based editing system MediaWiki. Wikipedia is the largest and most-read reference work in history.[3][4] It is consistently ranked as one of the ten most popular ...
