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Second Severn Crossing
The Second Severn Crossing, officially the M4 Prince of Wales Bridge, is a road bridge carrying the M4 motorway across the River Severn between England and Wales.
Second Temple (בית המקדש השני)
The Second Temple (בית המקדש השני), known as Zerubbabel's Temple, was the Jewish temple in Jerusalem, dedicated in 516 BCE and rebuilt by Herod the Great.
Second voyage of HMS Beagle
The second voyage of HMS Beagle was a Royal Navy hydrographic survey that circumnavigated the globe from 1831 to 1836, commanded by Captain Robert FitzRoy and carrying naturalist Charles Darwin.
Second-generation biofuels
Second-generation biofuels are liquid transport fuels made from non-food biomass like crop and forest residues and switchgrass, in contrast to first-generation corn or sugarcane ethanol.
Second-life battery
A second-life battery is a lithium-ion pack retired from electric-vehicle service, usually below 70% to 80% of original capacity, and reused in less demanding applications like grid and solar energy storage.
Second-order analysis (structural)
Second-order analysis is structural analysis formulated on a structure's deformed geometry, so axial loads on displaced or deflected members produce additional P-delta forces required by design codes like AISC.
Second-system effect
The second-system effect, or second system syndrome, is the tendency of engineers to over-engineer a successful system's successor with deferred features, named by Frederick Brooks in his 1975 book The Mythical Man-Month.
Secondary Security Screening Selection
Secondary Security Screening Selection, or SSSS, is a TSA code printed on boarding passes, primarily on US flights, that selects passengers for enhanced checks like pat-downs, luggage searches, and explosive-trace swabs.
Secondary surveillance radar
Secondary surveillance radar (SSR) is an air traffic control system that interrogates aircraft transponders on 1030 MHz and receives replies on 1090 MHz, providing identity and altitude.
Secondary treatment
Secondary treatment is the stage of wastewater treatment that uses biological processes, usually aerobic microorganisms, to remove dissolved and finely suspended organic matter left after primary settling, chiefly by activated sludge and trickling filters.
Secrecy capacity
Secrecy capacity is the maximum rate at which a message can be sent reliably to a receiver while an eavesdropper learns nothing, defined for the wiretap channel.
Secrecy coding for fading wiretap channels
Secrecy coding for fading wiretap channels designs codes that send a message reliably to a receiver while keeping it secret from an eavesdropper over fluctuating wireless links.
Secret sharing
Secret sharing, also called secret splitting or a threshold scheme, is a cryptographic method splitting a secret into shares, invented by Shamir and Blakley in 1979.
Secretaría de Infraestructura, Comunicaciones y Transportes
The Secretaría de Infraestructura, Comunicaciones y Transportes (SICT) is Mexico's federal ministry for highways, railways, airports, and telecommunications; created in 1891, it took its current name in 2021.
Secretariat Building, New Delhi
The Secretariat Building in New Delhi, designed by Sir Herbert Baker, consists of North Block and South Block, the main office buildings of the Government of India.
Secretariat of Energy (Mexico)
The Secretariat of Energy (Secretaría de Energía, SENER) is the Mexican federal ministry responsible for national energy policy, exercising the nation's rights over hydrocarbons and electricity.
Secretary Bird Optimization Algorithm
The Secretary Bird Optimization Algorithm is a population-based metaheuristic introduced in 2024 that mimics secretary birds hunting snakes and evading predators to solve numerical optimization and engineering design problems.
Secretary of State for Employment v Associated Society of Locomotive Engineers and Firemen (No 2)
Secretary of State for Employment v ASLEF (No 2) was a 1972 Court of Appeal decision on a ballot of railway workers during Britain's national work-to-rule dispute.
Section 4(f) of the Department of Transportation Act
Section 4(f) of the Department of Transportation Act is a 1966 US law barring DOT agencies from approving projects that use parks, refuges, or historic sites when prudent alternatives exist.
Section 45Q
Section 45Q is a provision of the U.S. Internal Revenue Code providing a production tax credit for carbon oxides captured at industrial facilities, power plants, or from the air.
Section 45X tax credit
The Section 45X tax credit, formally the Advanced Manufacturing Production Credit, is a US federal tax credit for clean energy components and critical minerals produced in America.
Section control
Section control, also called point-to-point or average speed enforcement, measures a vehicle's average speed between two cameras several kilometers apart and prosecutes drivers exceeding the limit.
Sectional density (ballistics)
Sectional density is a ballistics figure of merit for a projectile: bullet weight divided by diameter squared, used in ballistic coefficients and as a rough gauge of penetration.
Sectional overhead door
A sectional overhead door is a door made of hinged horizontal panels that rises in side tracks and runs back along ceiling tracks, standard on garages and warehouses.
Sectionalizer
A sectionalizer is an automatic switching device on medium-voltage distribution feeders that isolates faulted line sections by counting the interruption operations of an upstream recloser or breaker.
Sector coupling
Sector coupling, also called sector integration, is the interlinking of the electricity, heat, transport, and industry sectors so renewable electricity can replace fossil fuels and add flexibility.
Sectra
Sectra is a Swedish medical imaging IT and cybersecurity company founded in 1978 at Linköping University, developing PACS for hospitals and encryption for defense customers.
Secunda CTL
Secunda CTL is a commercial coal-to-liquids facility operated by Sasol in South Africa. It converts low-grade coal and natural gas into liquid fuels, meeting about 28% of the country's annual needs.
Secunderabad Junction railway station
Secunderabad Junction railway station is one of the principal rail terminals serving Hyderabad in Secunderabad, Telangana, India. Opened in 1874 under the Nizam, it is among South India's oldest stations.
Secure aggregation
Secure aggregation is a cryptographic protocol letting a server compute the sum of vectors from many clients, such as model updates, while learning nothing about any individual input.