Let G(xr − xe) be the causal Green function for the wave equation in four spacetime dimensions, representing the signal received at the spacetime point xr due to an impulse emitted at the spacetime point xe. Such emission and reception processes are highly idealized, since no signal can be emitted or received at a single (mathematical) point in space and time. We present a simple model for exte...

Great thanks are due to Khan et al1 for nicely addressing in their study the beneficial metabolic effects of Ramadan fasting (RF) in patients with type 2 diabetes mellitus (DM). Though no studies assessing similar effects in patients with type 1 DM are yet present, the available data pointed out that RF is not harmful, and has no adverse effects on the heart, lung, liver, kidneys, eyes, hematol...

The degree of surface roughness and clarity with which a surface in a brittle material can be formed via fracture is known to be related to the speed of the propagating crack. Cracks traversing a brittle material at low speed produce very smooth surfaces, while those propagating faster create less reflective and rough surfaces (Buehler MJ, Gao H. 2006 Nature 439, 307-310 (doi:10.1038/nature0440...