October 06, 2016 at 04:01AM

Today I Learned: 1) There is a limit, called the diffraction limit, on how small a thing you can see using light of a given wavelength. Today I learned that the diffraction limit only applies at focal distances greater than a couple of wavelengths. So if you could build a lens and camera less than a few hundred nanometers across, you could, in principle, build an optical microscope that could see things below the diffraction limit for visible light. Except not really, because to do so would require materials with negative and/or imaginary refractive indices, for reasons I do not understand. But you *can* build metamaterial lenses for longer wavelengths, like radio. 2) DNA bases, in the usual narrative, pair beacuse of hydrogen bonding between bases that sort of fit together. That's not really true, exactly -- most (order of magnitude 50%) of the energy in a base pair is actually in stacking bonds between adjacent bases (they have some sort of favorable shared pi-bond between aromatic rings). The base pairing works largely because when two bases don't sort of fit together, they physically bump into each other and mess up the structure required to get the benefit of base stacking. Something I'd idly wondered about was why you can't get relatively good bonding between pyrimidines (Ts, Cs, and, in RNA, Us), which are much smaller than purines (As and Gs). They're small, so they shouldn't clash with each other, right? Today I learned a plausible explanation, which is that pyrimidines don't actually contribute much, if at all, to base stacking -- it's the second aromatic ring on the larger purines that actually makes the base stacking interaction, so every base pair needs a purine to "work". 3) One of the well-known (in the business world) places where growing businesses fail is the so-called "Chasm". The chasm is the gap between a company that can produce a product in small volume for early adopters and a company that sells to the mass market. Apparently it's quite common for a product to get really enthusiastic support early on from a small pool of early adopters, only to be completely ignored by the vast majority of consumers once the company tries to scale up. On a similar note, economy of scale doesn't always apply. Service-oriented industries, or other industries where a large amount of human intervention is required, are a good example.