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Oberwolfach Research Institute for Mathematics
The Oberwolfach Research Institute for Mathematics (MFO), German: Mathematisches Forschungsinstitut Oberwolfach, is a mathematics research institute in Oberwolfach in Germany's Black Forest, founded in 1944, hosting weekly invitation-only workshops for mathematicians.
Objective (optics)
An objective, also called an objective lens, is the lens or mirror in a telescope or microscope closest to the object, forming its first real image.
Objective-collapse theory
Objective-collapse theory, also known as spontaneous localization, is a family of modifications of quantum mechanics in which wave function collapse happens spontaneously, especially for macroscopic superpositions.
Oblate spheroidal coordinates
Oblate spheroidal coordinates are an orthogonal system of curvilinear coordinates whose constant-coordinate surfaces are oblate spheroids, adapted to flattened bodies like Earth and charged disks.
Oblique illumination
Oblique illumination is a light microscopy technique that illuminates the specimen at an angle rather than axially, enhancing contrast in transparent, unstained samples and giving images a shadowed, relief-like appearance.
Oblique plane microscopy
Oblique plane microscopy (OPM) is a fluorescence light-sheet microscopy technique in which a single objective both illuminates and images a tilted plane inside a specimen, first demonstrated in 2008.
Oblique projection
Oblique projection, or oblique view, is a parallel projection in technical drawing where the front face is shown true size and depth is drawn at an angle.
Oblique shock
An oblique shock is a shock wave in supersonic flow, inclined to the oncoming stream, across which pressure, temperature, and density rise and the flow turns toward the shock.
Observability
Observability is a property of dynamical systems, introduced by Rudolf Kalman in 1960, stating whether the full internal state can be inferred from measured outputs.
Observable
In quantum mechanics, an observable is a measurable physical quantity, such as position, momentum, energy, or spin, represented by a self-adjoint operator whose eigenvalues are the possible measurement results.
Observable universe
The observable universe, also called the visible universe, is the sphere of space about 46 billion light-years in radius from which light has reached Earth.
Observation
Observation, in science, is the gathering of empirical information about the world through sensing, often aided by instruments such as telescopes and microscopes, used as evidence in describing phenomena and testing theories.
Observational error
Observational error, also called measurement error, is the difference between a measured value of a quantity and its true value, divided into systematic and random components.
Observational study
An observational study, as defined by William G. Cochran in 1965, investigates cause and effect without assigning exposures, making it possible where randomized trials would be unethical but leaving it vulnerable to bias.
Observer effect (physics)
The observer effect in physics is the disturbance of a measured system by measurement itself; in quantum mechanics even an ideal measurement changes the state.
Observer-expectancy effect
The observer-expectancy effect, also called experimenter bias or the Clever Hans effect, is a research bias in which researchers' expectations unintentionally shape results, without conscious fraud, by cueing subjects.
Obsidian
Obsidian, also called obsidian rock or dragonglass, is a volcanic glass formed when silica-rich lava cools so fast that crystals cannot form, long prized for razor-sharp tools.
Obsolete and proposed metric prefixes
Obsolete and proposed metric prefixes are the former metric prefixes, such as myria- (10^4) and myrio- (10^-4), made obsolete in 1960, and proposals never adopted.
Obstacle problem
The obstacle problem is a constrained variational problem in partial differential equations, modeling an elastic membrane resting on an obstacle, the prototype of free boundary problems.
Obstructed atomic limit
An obstructed atomic limit (OAL) is a band-insulator phase in which Wannier charge centers sit at empty Wyckoff positions, blocking a symmetric connection to an ordinary atomic insulator.
Obstruction theory
Obstruction theory is a family of methods in algebraic topology, codified by Samuel Eilenberg around 1940, that tests whether a partial map or section can be extended.
Obukhov length
The Obukhov length, also called the Monin–Obukhov length, is a length scale characterizing stability of the atmospheric surface layer by comparing shear and buoyancy effects on turbulence.
Occluded front
An occluded front, or front occlusion, forms when a faster-moving cold front overtakes a warm front in an extratropical cyclone, signaling the low has reached its mature, decaying stage.
Occultation
An occultation is the passage of one celestial body in front of a more distant one, hiding it from view, used to probe planetary atmospheres and discover rings.
Occultation observer networks
Occultation observer networks are organized groups of telescopes, often run by volunteers, spread along a predicted occultation path to measure asteroid and Kuiper Belt object shadows.
Occultation observing techniques
Occultation observing techniques are the methods used to record a star's light being blocked by the Moon or an asteroid, using high-resolution detectors and accurate GPS timing.
Occultation prediction
Occultation prediction is the computation of when and where a star's light will be blocked by the Moon, an asteroid, or another Solar System body.
Occultations by planets and satellites
An occultation by a planet or satellite occurs when the body passes in front of a star, briefly blocking its light; the dimming reveals atmospheres and rings.
Occultations in the history of astronomy
Occultations in the history of astronomy traces discoveries made when one celestial body hides another: six of eight known dense ring systems, Pluto's 1985 atmosphere discovery, and ancient Chinese records.
Occultations of stars by asteroids
Occultations of stars by asteroids occur when an asteroid briefly blocks a star's light. Observers along the shadow path measure asteroid sizes and shapes with kilometric precision.