Is PayPal Stock a Buy?

PayPal stock trades at an all-time low valuation. If growth rates tick higher, shares could have plenty of upside.

How to upcycle low-energy light

To combine two low-energy photons into one high-energy photon efficiently, the energy must be able to hop freely, but not too quickly, between randomly oriented molecules of a solid. The discovery provides a much-needed design guideline for developing …