Automatic
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Automatic
What Is Automatic Revalidation?The Department of Homeland Security (DHS) U.S. Customs and Border Protection (CBP) has the authority and the responsibility over the admission of travelers to the United States. Under the automatic revalidation provision of immigration law, certain temporary visitors holding expired nonimmigrant visas who seek to return to the U.S. may be admitted at a U.S. port-of-entry by CBP, if they meet certain requirements, including, but not limited to the following:
Many nonimmigrants will need to reapply and be reissued visas to reenter the U.S. when their existing visas have expired, even if they are in possession of valid admission stamp or paper Form I-94, because automatic revalidation applies to limited categories of travelers. Refer to the Automatic Revalidation Fact Sheet on the CBP website. The following temporary visitors whose nonimmigrant visas have expired, but who have a valid admission stamp or paper Form I-94, must reapply for and be issued nonimmigrant visas prior to their reentry to the United States, if one or more of the following situations exists (this is not a complete listing):
An automatic transmission (sometimes abbreviated AT) is a multi-speed transmission used in motor vehicles that does not require any input from the driver to change forward gears under normal driving conditions.
The most common type of automatic transmission is the hydraulic automatic, which uses a planetary gearset, hydraulic controls, and a torque converter. Other types of automatic transmissions include continuously variable transmissions (CVT), automated manual transmissions (AMT), and dual-clutch transmissions (DCT).
The 1904 Sturtevant "horseless carriage gearbox" is often considered to be the first true automatic transmission.[1][2] The first mass-produced automatic transmission is the General Motors Hydramatic four-speed hydraulic automatic, which was introduced in 1939.
Globally, 43% of new cars produced in 2015 were manual transmission, falling to 37% by 2020.[3] Automatic transmissions have long been prevalent in the United States, but have only started to become common in Europe much more recently. In Europe in 1997, only 10-12% of cars had automatic transmission.[4]
In the United States, over 80% of new cars had automatic transmission by 1957.[3] Automatic transmission has been standard in large cars since at least 1974.[5] By 2020 only 2.4% of new cars had manual transmission.[6] Historically, automatic transmissions were less efficient, but lower fuel prices in the US made this less of a problem than in Europe.[7]
In the United Kingdom, a majority of new cars have had automatic transmission since 2020. Several manufacturers including Mercedes and Volvo no longer sell manual transmission cars. The growing prevalence of automatic transmission is attributed to the increasing number of electric and hybrid cars, and the ease of integrating it with safety systems like Autonomous Emergency Braking.[8][9]
The most common design of automatic transmissions is the hydraulic automatic, which typically uses planetary gearsets that are operated using hydraulics.[10][11] The transmission is connected to the engine via a torque converter (or a fluid coupling prior to the 1960s), instead of the friction clutch used by most manual transmissions.[12]
A hydraulic automatic transmission uses planetary (epicyclic) gearsets instead of the manual transmission's design of gears lined up along input, output and intermediate shafts. To change gears, the hydraulic automatic uses a combination of internal clutches, friction bands or brake packs. These devices are used to lock certain gears, thus setting which gear ratio is in use at the time.[13]
A sprag clutch (a ratchet-like device which can freewheel and transmits torque in only one direction) is often used for routine gear shifts. The advantage of a sprag clutch is that it eliminates the sensitivity of timing a simultaneous clutch release/apply on two