November « 2009 « Equilibrium Networks

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5 November 2009

5 November 2009

³He shortage impacting experiments requiring dilution refrigerators…more than a few quantum computing groups use this technology to get to millikelvin temperatures and I remember seeing such a fridge at LPS nearly a decade ago. If it ever became a problem for QC research I imagine NSA and the gang would talk to DoE to get the stuff pipelined to favored (US?) groups, and indeed the government is prioritizing the stuff already, with a lot going towards neutron counters to detect radioactive materials under the DHS umbrella. Good alternatives apparently do not exist for QC work: note that magnetic refrigeration is fundamentally contraindicated for a lot of QC experiments because of, e.g. the big magnetic fields and stuff like the Zeeman effect, even apart from the issue of what temperatures you can reach. And while I have no idea about the capabilities or applicability of dry dilution fridges, in the Physics Today article you can reach via the first link, Bob Richardson is quoted as saying ³He “is irreplaceable. If you want to create temperatures on the order of magnitude of 10 mK, there is no substitute.” (As a more general disclaimer: being on the abstract side even for a theorist when I wear a physics hat means that I don’t claim to say anything correct about experimental physics, but informed comments are always welcome.)

Oxford scientists describe “a new coarse-grained model of DNA which reproduces its thermodynamic and structural properties, representing single-stranded stacking, duplex and hairpin transitions consistently for the first time”. Models taking these ideas further will eventually answer a lot of fundamental questions about the kinetics of oligomeric DNA hybridization that are necessary to tackle in order to fully realize DNA nanotechnology. For example, it’s possible (but quite complicated if you want to do it all classy-like) to enumerate all the oligomeric sequences that fit a prescribed thermodynamical profile in silico. But the actual kinetics (versus the equilibrium situation) cannot yet be modeled, and different plausible theories of oligomeric hybridization lead to dramatically different results on the timescales required to reach thermodynamic equilibrium–i.e., to achieve the desired self-assembly–as a function of the particular sequences chosen for the purpose, and therefore could suggest radically different sorts of sequences to arrive at a typical end result. I’ve been convinced for eight years or so that this is one of the reasons why DNA computing never lived up to its own (admittedly limited) potential–the fundamental biophysical process was too poorly understood.