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Informally, a permutation of a set of objects is an arrangement of those objects into a particular order. The notion of permutation relates to the act of ... more

In probability theory, a probability distribution assigns a probability to each measurable subset of the possible outcomes of a random experiment, survey, ... more

The mass number (A), also called atomic mass number or nucleon number, is the total number of protons and neutrons (together known as nucleons) in an ... more

Auger electron spectroscopy is a common analytical technique used specifically in the study of surfaces and, more generally, in the area of materials ... more

An achromatic lens or achromat is a lens that is designed to limit the effects of chromatic and spherical aberration. Achromatic lenses are corrected to ... more

A lens is a transmissive optical device which affects the focusing of a light beam through refraction. A simple lens consists of a single piece of ... more

Adsorption is usually described through isotherms, that is, the amount of adsorbate on the adsorbent as a function of its pressure (if gas) or ... more

Adsorption is usually described through isotherms, that is, the amount of adsorbate on the adsorbent as a function of its pressure (if gas) or ... more

A quantity is said to be subject to exponential decay if it decreases at a rate proportional to its value. If the decaying quantity, N(t), is the number of ... more

Capacitance is the ability of a body to store an electrical charge. Any object that can be electrically charged exhibits capacitance. The capacitance is a ... more

A stepper motor or step motor or stepping motor is a brushless DC electric motor that divides a full rotation into a number of equal steps. The ... more

The weighted mean is similar to an arithmetic mean (the most common type of average), where instead of each of the data points contributing equally to the ... more

Abbe number , is a measure of the material’s dispersion in relation to the refractive index, with high values of V indicating low dispersion (low ... more

Trapezoid is a convex quadrilateral with only one pair of parallel sides. The parallel sides are called the bases of the trapezoid and the other two sides ... more

Wind-chill or windchill, (popularly wind chill factor) is the perceived decrease in air temperature felt by the body on exposed skin due to the flow of ... more

The Sagnac effect (also called Sagnac interference), named after French physicist Georges Sagnac, is a phenomenon encountered in interferometry that is ... more

In optics, the numerical aperture (NA) of an optical system is a dimensionless number that characterizes the range of angles over which the system can ... more

Temperature difference – I-nodes model of an Earth spacecraft

Log-polar coordinates in the plane consist of a pair of real numbers (ρ,θ), where ρ is the logarithm of the distance between a given point and the origin ... more

Youden’s J statistic (also called Youden’s index) is a single statistic that captures the performance of a diagnostic test. Its value ranges ... more

In electrical and electronic systems, reactance is the opposition of a circuit element to a change of electric current or voltage, due to that ... more

In finance, the net present value or net present worth of a time series of cash flows, both incoming and outgoing, is defined as the sum of the present ... more

The normalized difference vegetation index (NDVI) is a simple graphical indicator that can be used to analyze remote sensing ... more

The Earth Similarity Index, ESI or “easy scale” is a measure of how physically similar a planetary-mass object is to ... more

Binoculars, field glasses or binocular telescopes are a pair of identical or mirror-symmetrical telescopes mounted side-by-side and aligned to point ... more

Stiffness is the rigidity of an object — the extent to which it resists deformation in response to an applied force. In general, stiffness is not the same ... more

Tortuosity is a property of curve being tortuous (twisted; having many turns). There have been several attempts to quantify this property. ... more

Rhombus is a simple (non-self-intersecting) quadrilateral whose four sides all have the same length. Every rhombus is a parallelogram, and a rhombus with ... more

In electrical and electronic systems, reactance is the opposition of a circuit element to a change of electric current or voltage, due to that ... more

Snell’s law (also known as the Snell–Descartes law and the law of refraction) is a formula used to describe the relationship between the angles of ... more