Archive for May 2009

A recent trick floating around the xda-developers forums involves using UnionFS to layer the microSD storage on top of the existing data partition, effectively allowing the microSD storage to be used for data. This technique originated from MarcusMaximus04 and has made its way into the firmware builds of TheDudeOfLife and JesusFreke.

While most users were playing around with the easy “apps2SD” feature, I decided to explore a different aspect of UnionFS — stackable snapshots. The goal was to be able to make snapshots of the filesystem that could be rolled back at any time, undoing any changes. While this may sound like server-oriented technology, it could be useful on a mobile platform that is collecting a sizable hacker community.

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I encountered a most awesome function today; it’s called OK.

OK accepts no arguments and returns either true or false. When a program needs to make a decision, it could ask if it’s OK or not. Interesting? You bet. But this is only half of the story. How does OK work?

When OK is called, it saves a snapshot of the current program execution state and returns true; it also installs a hook so that it is called at the end of the program. If the program ends successfully, OK does nothing. If the program fails, on the other hand, OK recalls the saved state and returns false.

Hmm…

On the way to class I passed by a confused-looking male who was besieged by a group of girls. “What’s goin’ on?” he asked.

Girl: We need a boyfriend.
Guy: Wait, what?
Girl: We need a boyfriend, now.
Guy: I don’t understand; I can’t be your boyfriend.
Girl: Why not? You look single.
Guy: Uh, yeah… but there’re so many of you.
Girl: Yeah, so?

The guy happened to look my way for a second, so I could not help winking and giving him a thumbs-up.

Girl: See! This guy agrees.
Guy: Okay, okay, I get it; there’s plenty of me to go ’round.

As hilarity ensued, I found my way into molecular biology class.

I’d designed few alcohol burners in the past, and they’d all depended on using metal rods or shims to vaporize the fuel. One end of the metal would be submerged in fuel while the other end would be in contact with the flame, thus conducting heat back into the fuel and generating combustible gas in situ. A benefit of this approach is that much more power is generated due to the pressure and mixing with air. Because of this, the alcohol burner has become a useful part of my toolkit.

Recently I spent an hour or so reading up on Bunsen’s design of his gas burner. Though a Bunsen burner relies on pressure from the gas line rather than generating its own pressure, some of the concepts are nonetheless helpful in improving my own design. Incorporating some of Bunsen’s ideas, I came up with yet another alcohol burner design: this one allows fresh air to be drawn into the flame by the Venturi effect, thereby improving efficiency and power output. The result is a clean and non-luminous flame.

Here are a couple of pictures of the burner in action. In the first, it is burning 70% ethanol available at most pharmacies; in the second, it is burning 100% acetone. I also tried 100% ethanol, but the flame is barely visible; it works very well, but it is not worth photographing…

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