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# Questions tagged [notation]

This tag is for questions on the meaning, history, and usage of various symbols and notation that are used to denote different quantities in physics. Don't forget to mention the reference, where you encountered those notations.

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### What does an upside down delta mean - covariant vectors? [duplicate]

I was scrolling through a wiki article on terminal velocity when I spotted an upside down delta. What does this symbol mean? How is it applied in other contexts? EDIT: If possible could someone expand ...
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### What is the name and notation given to the inverse of the inertial resistivity $\beta$ (aka non-Darcy factor or Forchhiemer factor)?

The viscous resistivity $\alpha$ is the reciprocal of permeability $k$. That is, $\alpha=1/k$. Considering the 1D isotropic non-Darcy equation, $$\tag{1} -\frac{dp}{dx}=\alpha \mu q+ \beta \rho q^2,$$...
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### Units inside square brackets [closed]

As a physics teacher, I often see students writing a physical quantity with a numerical value followed by its unit (sometimes not...) placed inside square brackets. We can argue about the meaning of ...
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### Explanation of name Cobimaximal Matrix

Cobimaximal matrix is a modified form of the neutrino mixing matrices and it is consistent with neutrino oscillation data. It predicts atmospheric mixing angle to be 45 (degree) but new oscillation ...
How do I find $<x|p|\psi>$ in terms of $\psi (x) = <x|\psi>$ And again for $<x|H|\psi>$, where $H$ is the hamiltonian?