One million dollars is waiting to be won by anyone who can solve one of the grand mathematical challenges of the 21st century. In the second of two articles, Chris Budd looks at the well-posedness of the Navier-Stokes equations.

Helen is a defence analyst with the MoD, using her maths skills to help defend the nation. Plus finds out about her career path.

Arguably, the exponential function crops up more than any other when using mathematics to describe the physical world. In the second of two articles on physical phenomena which obey exponential laws, Ian Garbett discusses radioactive decay.

Why can't human beings walk as fast as they run? And why do we prefer to break into a run rather than walk above a certain speed? Using mathematical modelling, R. McNeill Alexander finds some answers.

Arguably, the exponential function crops up more than any other when using mathematics to describe the physical world. In the first of two articles on physical phenomena which obey exponential laws, Ian Garbett discusses light attenuation - the way in which light decreases in intensity as it passes through a medium.

More than a century ago, an American astronomer named Seth Carlo Chandler discovered that, as the earth spun on its axis, it also wobbled. This wobble, now known as the Chandler wobble in honour of its discoverer, didn't disappear over time, as would have been expected if no further force reactivated it. The source of the continuing activating force has remained a mystery ever since - until now.

Jim McElwaine tells Plus how he combines his two loves - mathematics and mountaineering - in avalanche research.

Helen Thompson works for Sainsbury's Supermarkets as a Sales Forecasting Manager. The Plus team paid her a visit at Drury House on the banks of the Thames in London.

David Spaughton and Anton Merlushkin work for Credit Suisse First Boston, where they provide traders in the hectic dealing room with software based on complicated mathematical models of the financial markets. PASS Maths interviewed them at their offices in Canary Wharf in London.

In his second article, David Henwood explains the role of mathematics in the design of Hi-Fi loudspeakers.

New technology has provided us with some amazing images - satellite images, medical images, even images beamed back from Mars. Julian Stander tells us about the increasing role of statistics in interpreting them.