Hello. I have a question regarding curvature and second derivatives. I have always been confused regarding what is concave/convex and what corresponds to negative/positive curvature, negative/positive second derivative. If we consider the profile shown in the following picture: https://www.princeton.edu/~asmits/Bicycle_web/pictures/vel_profile.GIF U(y) is the velocity plotted as a function of (y). We can see that the second derivative here is <0. DOes this correspond to negative curvature or positive and concave/convex?