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Propfan
The propfan, also called an unducted fan or open rotor, is an aircraft engine combining turboprop fuel economy with turbofan speed, developed by NASA and flying by 1986.
Prophet's Mosque
The Prophet's Mosque (Al-Masjid an-Nabawi) is a mosque in Medina, Saudi Arabia, built by Muhammad in 622 and expanded under successive Islamic states into the second holiest site in Islam.
Propliner
A propliner is a large propeller-driven airliner, usually a piston-powered one from before the jet age; the best known is the Douglas DC-3, first flown in 1935.
Proportional control
Proportional control is a feedback method that adjusts a system's input in proportion to the error between setpoint and measured output, forming the core of PID control.
Proportional navigation
Proportional navigation (PN) is a guidance law commanding missile acceleration proportional to the line-of-sight rotation rate, the dominant terminal guidance for homing missiles since the 1950s.
Proportional valve
A proportional valve is an electro-hydraulic or electro-pneumatic valve whose control element moves continuously in proportion to an electrical input signal, allowing stepless flow and pressure regulation.
Proportional–integral–derivative controller
A proportional–integral–derivative (PID) controller, also known as a PID loop, is the most common feedback control algorithm in industry, correcting a process variable from present, past, and anticipated error.
Proposed merger between Union Pacific and Norfolk Southern
The proposed merger between Union Pacific and Norfolk Southern is a pending deal, announced in July 2025, that would create the first single-carrier freight railroad spanning the U.S. coasts.
Proposed subsea strait crossings
Proposed subsea strait crossings are road or rail tunnel megaprojects beneath sea straits that were seriously studied but mostly never built, covering Fehmarnbelt, Gibraltar, Messina, and Bering; only the Fehmarnbelt immersed tunnel is under construction.
Proposed tunnels in Africa
Proposed tunnels in Africa are tunnel schemes still at the study or concept stage, led by the Morocco–Spain rail tunnel under the Strait of Gibraltar, jointly studied since 1980.
Proprietary software
Proprietary software, also known as closed-source software, is software whose source code and redistribution rights are restricted by its owner, in contrast to free and open-source software.
Propulsive efficiency
Propulsive efficiency is the fraction of an engine's mechanical power that does useful work propelling a vehicle, rather than being wasted as kinetic energy in the exhaust.
Propulsive landing
A propulsive landing is one in which a spacecraft or rocket stage fires its own rocket engines against the direction of travel to slow down and touch down.
Propylene–propane separation
Propylene–propane separation is the industrial process of splitting mixed C3 hydrocarbon streams into pure propylene and propane, done almost exclusively by cryogenic distillation in tall, energy-intensive towers, with adsorption and membrane methods under study as alternatives.
ProQuest
ProQuest, formerly University Microfilms International, is an American information company based in Ann Arbor, Michigan, founded in 1938 and known for dissertation databases and digitized newspapers.
Prora
Prora, known as the "Colossus of Prora," is a 4.5-kilometer beach resort complex on Rügen's Baltic coast, built by the Nazi regime between 1936 and 1939.
Prosafe
Prosafe is a Stavanger-based Norwegian offshore services company that owns semi-submersible accommodation vessels housing workers next to oil and gas installations, listed on Euronext Oslo Børs.
Prosigns for Morse code
Prosigns for Morse code are one or two letters sent fused into a single character, carrying operating instructions like wait, end of message, and end of contact.
PROSPER (traffic engineering software)
PROSPER is a traffic signal optimization tool within the TRANSYT product line of TRL Software, used for designing signal timings from single junctions to large networks.
Prospera (agricultural technology company)
Prospera is an Israeli agricultural technology company founded in Tel Aviv in 2014 that applies machine learning and computer vision to crop production; Valmont Industries acquired it for $300 million in 2021.
Prosperity7 investment in Zhipu AI
The Prosperity7 investment in Zhipu AI was a 2024 minority stake by Saudi Aramco's venture arm in a $400 million round for the Chinese AI startup.
Protean eGov Technologies
Protean eGov Technologies, formerly NSDL e-Governance Infrastructure, is an Indian IT services company that processes PAN card applications and runs the National Pension System's recordkeeping.
Protected structure
A protected structure is an Irish building of special interest listed in a local authority's record of protected structures, protected under the Planning and Development Act 2000.
Protected Tactical SATCOM (PTES)
Protected Tactical SATCOM (PTES), or Protected Tactical Enterprise Service, is a United States Space Force ground system giving tactical warfighters jam-resistant satellite communications in contested environments.
Protected-permitted left turn
A protected-permitted left turn (PPLT) is a traffic signal phasing mode where left-turning drivers get a protected green-arrow phase plus a permissive interval requiring them to yield.
Protection of Personal Information Act (South Africa)
The Protection of Personal Information Act, known as POPIA, is South Africa's omnibus data protection law, signed in 2013 and fully in force since 1 July 2021.
Protection ring
A protection ring, also known as a hierarchical protection domain, is a privilege level in a computer's architecture, with inner rings accessing more resources than outer rings.
Protective Devices
Protective devices, including personal protective equipment (PPE), machine guards, light curtains, and guardrails, shield people from hazards; PPE is the final level of the hierarchy of controls, governed by OSHA, ANSI, NIOSH, and ISO standards.
Protective earth (ground)
A protective earth, or equipment ground, is a conductor connecting exposed metal parts of equipment to earth so an insulation fault cannot leave them at a dangerous voltage.
Protective relay
A protective relay, also called a protection relay, is a device that monitors current and voltage, detects faults, and trips circuit breakers to isolate the faulted section.