Why charge density of moving dipole is dependent on time?

[Lokesh]

TL;DR Summary

Here is the link to the paper: https://doi.org/10.1119/1.4712308

This paper aims to resolve the inconsistency between different transformation equations by expressing the electric current created by a moving electric dipole as the sum of polarization and magnetization currents and calculating the resulting magnetic field. Here they take
charge density to be dependent on time. Why?

 

[BvU]

I don't want to spend $ 40 to purchase access to the article. Is it perhaps the same as this one ?

In that case equation $(5)$ answers your question:$$\rho_b({\bf r},t)=-{\bf\nabla\cdot P}({\bf r},t)=-{\bf p}_0{\bf \nabla}\delta({\bf r}-{\bf r}_0(t))$$the dipole is moving, so the charge distribution in space is not constant in time.

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[berkeman]

And why is the author of that paper from NIOSH? That's weird...

 

[Frabjous]

And why is the author of that paper from NIOSH? That's weird...