Question: What number, representing a dimensionless quantity, is named after the winner of the 1983 Nobel Prize for Physics

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Gravitational coupling constant: In physics, a gravitational coupling constant is a constant characterizing the gravitational attraction between a given pair of elementary particles.  The electron mass is typically used, and the associated constant typically denoted "α" .  It is a dimensionless quantity, with the result that its numerical value does not vary with the choice of units of measurement, only with the choice of particle.

Particle number: The particle number (or number of particles) of a thermodynamic system, conventionally indicated with the letter "N", is the number of constituent particles in that system.  The particle number is a fundamental parameter in thermodynamics which is conjugate to the chemical potential.  Unlike most physical quantities, particle number is a dimensionless quantity.  It is an extensive parameter, as it is directly proportional to the size of the system under consideration, and thus meaningful only for closed systems.

Subrahmanyan Chandrasekhar: Subrahmanyan Chandrasekhar, FRS (Tamil: சுப்பிரமணியன் சந்திரசேகர் ; ; 19 October 1910 – 21 August 1995), was an Indian American astrophysicist who was awarded the 1983 Nobel Prize for Physics with William A. Fowler "for his theoretical studies of the physical processes of importance to the structure and evolution of the stars".  His mathematical treatment of stellar evolution yielded many of the best current theoretical models of the later evolutionary stages of massive stars and black holes.  The Chandrasekhar limit is named after him.

G-factor (physics): A g"-factor (also called g" value or dimensionless magnetic moment) is a dimensionless quantity that characterizes the magnetic moment and gyromagnetic ratio of an atom, a particle or nucleus.  It is essentially a proportionality constant that relates the observed magnetic moment "μ" of a particle to its angular momentum quantum number and a unit of magnetic moment, usually the Bohr magneton or nuclear magneton.

Proton-to-electron mass ratio: In physics, the proton-to-electron mass ratio, μ or β, is simply the rest mass of the proton divided by that of the electron.  Because this is a ratio of like-dimensioned physical quantities, it is a dimensionless quantity, a function of the dimensionless physical constants, and has numerical value independent of the system of units, namely:

Dimensionless quantity: In dimensional analysis, a dimensionless quantity is a quantity to which no physical dimension is applicable.  It is also known as a bare number or a quantity of dimension one.  Dimensionless quantities are widely used in many fields, such as mathematics, physics, engineering, and economics.  By contrast, examples of quantities with dimensions are length, time, and speed, which are measured in dimensional units, such as metre, second and metre per second.

Fine-structure constant: In physics, the fine-structure constant, also known as Sommerfeld's constant, commonly denoted "α" (the Greek letter "alpha"), is a fundamental physical constant characterizing the strength of the electromagnetic interaction between elementary charged particles.  It is related to the elementary charge "e", which characterizes the strength of the coupling of an elementary charged particle with the electromagnetic field, by the formula 4π"ε""ħcα" = "e" .  Being a dimensionless quantity, it has the same numerical value of about in all systems of units.  Arnold Sommerfeld introduced the fine-structure constant in 1916.

Mach number: In fluid dynamics, the Mach number (M or Ma) ( ; ] ) is a dimensionless quantity representing the ratio of flow velocity past a boundary to the local speed of sound.

Chandrasekhar number: The Chandrasekhar number is a dimensionless quantity used in magnetic convection to represent ratio of the Lorentz force to the viscosity.  It is named after the Indian astrophysicist Subrahmanyan Chandrasekhar.

Saturation vapor density: Saturation vapor density (SVD) is a concept closely tied with saturation vapor pressure (SVP).  It is useful for getting an exact quantity of water vapor in the air from a relative humidity (RH = % local air humidity measured / local total air humidity possible ) Given an RH percentage, the density of water in the air is given by RH × SVD = Actual Vapor Density .  Alternatively, RH can be found by RH = Actual Vapor Density ∕ SVD .  As relative humidity is a dimensionless quantity (often expressed in terms of a percentage), vapor density can be stated in units of grams or kilograms per cubic meter.

Supporting paragraphs: Chandrasekhar number Subrahmanyan Chandrasekhar
Answer: Chandrasekhar number