Rhinoceros is primarily a free form surface modeler that utilizes the NURBS mathematical model. Rhinoceros' application architecture and open SDK makes it modular and enables the user to customize the interface and create custom commands and menus.
Noun. 1. exigency-a pressing or urgent situation; the health-care exigency. crisis-an unstable situation of extreme danger or difficulty; they went bankrupt during the economic crisis.
The persistence of rhythms in the absence of a dark-light cycle or other exogenous time signal (i.e., a Zeitgeber) clearly seems to indicate the existence of some kind of internal timekeeping mechanism, or biological clock.