Analysis of the internal ventilation for a motorcycle helmet. Development and analysis of a CFD-based methodology for the numerical simulation of the internal airflow as well as sweat-related heat transfer

By the time you have ten groups of ten (a hundred), you can introduce another symbol, for instance +. Ten hun dreds, or a thousand, can become = and so on. In that case, the number "four thousand six hundred seventy-five" can be written - ++++++ To make such a set of symbols more easily graspable, we can take advantage of the ability of the eye to form a pattern. (You know how you can tell the numbers displayed by a pack of cards or a pair of dice by the pattern itself.) We could therefore write "four thousand six hundred sev enty-five" as And, as a matter of fact, the ancient Babylonians used just this system of writing numbers, but they used cunei form wedges to express it. The Greeks, in the earlier stages of their development, used a system similar to that of the Babylonians, but in later times an alternate method grew popular. They made use of another ordered system-that of the letters of the alphabet. It is natural to correlate the alphabet and the number system. We are taught both about the same time in child hood, and the two ordered systems of objects naturally tend to match up ...»