Articles

I still remember my first fountain pen. It was a beautiful thing, green and blue, nice to touch, that would caress the paper when you wrote. To this day, holding a fountain pen in my hand puts me in writing mood, in thinking mood. It opens my mind, as Paul Erdös would say. I became conscious of this not long ago when, as I was reading Daniel Kahneman’s wonderful Thinking, Fast and Slow, I understood for the first time how prevalent this effect is, and how important it probably is in my life. ...

We cannot predict how the development of something large and complex is going to play out. We are not sure about what the right product architecture is, nor where the snags are hidden. In most cases we don’t even know what we’ll actually want by the time the product is done, when the compromises that reality will inevitably impose on us are bought off. Nor whether anybody will actually want what we envision today. ...

During the last three years I have managed a team of engineers doing ink-jet printer design at HP’s R&D lab in Barcelona. The excellent org-mode emacs package has helped me keep up-to-date with the work of the 12 engineers in my team, working in four different projects, without an obvious impact in my sanity. During this time some work-flows have evolved, and I have written helper functions for org-mode to support them. This is an account of the steady state at which I have arrived. Please let me know if any of what follows could be done or written in a simpler or more idiomatic way. ...

By Juan Reyero, Jaime Fernández and Utpal Sarkar. What is the maximum slope that a unicycle can climb? Trying to answer this question leads to some elegant results, and sheds some light on the dynamics of unicycle riding. Assumptions We shall assume the rotational inertia of the wheel, pedals and legs to be negligible. A further simplifying assumption is that the rider is putting all his weight into the pedal throughout its trajectory as it is going down, and that this is the only impulsion force. Which implies that the rider is not pulling up from the saddle, nor accelerating the body upwards with respect to the unicycle, nor making a horizontal force in the pedals. We know this assumption to be too stringent for expert unicyclists, who will typically be able to do all these things, but we hold it to be a reasonable approximation to what a unicyclist of normal skill would do when pressed to climb a slope at the limit of the unicycle’s possiblities. ...

This is a very rough attempt at deriving useful conclusions from the equations of motion of a unicycle. It was inspired by my brother’s desire to buy one: my brother is large (almost 2 m tall, and around 100 Kg) and I wanted to know how the usual recommendations for beginners (a 20" unicycle) would work for him. Does a large fellow need a large wheel? The equations have turned out to be too complex of me to be able to make much sense out of them. But I haven’t lost hope. ...