I’d like to flag a recent publication in Advances, which inverts the usual practice of growing LaAlO3 films on SrTiO3 substrates to produce fascinating oxide-interface systems. A team at the National University of Singapore has succeeded in growing SrTiO3 films on atomically flat LaAlO3 substrates. This methodological advance opens up avenues to produce new oxide interfaces, potentially with novel electronic or magnetic properties.
A rope of length L and mass m lies loosely coiled on frictionless ground. You starting pulling out one end at a constant velocity V. After time L/V, you have imparted a momentum mV, which implies that the force you applied was F = mV2/L (the force is constant, since at any given time the constant-velocity part of the rope is not relevant to the force). Of course you also impart a kinetic energy 1/2 mV2 from the work done by F over a distance L. So the force can also be written as F = 1/2 mV2/L. Ooops. Where did that factor of 1/2 come from?
The resistivity of a material is measured by attaching two or more contacts to the sample and measuring the voltage drop associated with a known current passing through the sample. Generally, one uses at least four contacts (two for measuring voltage, two more for applying the current), since this greatly reduces the sensitivity to the resistance of the contacts themselves. How can introducing a crack in a sample decrease the measured resistivity? Hint: there is more than one way to arrange the four contacts on a sample to measure resistivity.
A brief excerpt from Musings on Peer Review by one of the Advances editors, published in the SPS Observer:
“Although the individual researcher lost deep in thought or ensconced firmly in the lab is a compelling image in science, the pursuit of new knowledge about the natural world is intrinsically a social effort: new results gain meaning and impact through dissemination. Sharing results with peers is mediated by peers, through the (typically anonymous) peer review of new manuscripts within the venue of a journal. Although most researchers will enthusiastically convey stories of the frustrations and minor indignities they have suffered when their manuscripts were peer reviewed, they will also agree that peer review has overall improved their papers, both in the extra care that goes into preparing a manu- script that you know will be so judged and also by incorporat- ing the criticisms and suggestions of referees into the revised manuscript. New web-based tools are currently extending peer review in new directions, with online rating and commentary emerging as evolutionary enhancements to this time-honored process.”
Via the New Scientist, a link to a Chinese-language description of how to maximize one’s salad bar value under a “one bowl, one time” constraint (scroll down for photos). The use of carrot cantilevers and cucumber towers is particularly impressive. With proper technique, it appears possible to feed an entire banquet table with a single salad bowl.
A question for discussion: the most impressive bowls use walls of thin stacked cucumber slices. Is the thinness important? Could one be equally successful using much thicker, say half-cucumber-tall sections of cucumber for the outer walls?
Idle Speculations is a recurring series of … idle speculations. Speculations are the weakest of provisional explanations in science, those with only meager supporting evidence. Idle speculations are weaker still. Being motivated by the attractiveness of their conclusions rather than the persuasiveness of their supporting evidence (if they have any!), idle speculations are a dangerous model for doing science, but they can be an amusing diversion which might inspire some useful, non-idle thoughts.
Dark matter is frustratingly tantalizing: the dominant majority of the mass in the universe is hidden away in a gravitational ghetto, interacting with us creatures of light only in a boring, long-wavelength, single-parameter way. Compare the paucity of gravitational mechanisms in biology to the richness of electromagnetic phenomena in biochemistry to get a sense of what we’re missing. (Only birds and insects seems to have figured out anything useful to do with geodesics, while the fish flaunt their obliviousness. Damn fish.) Let’s try to rescue dark matter from this ghetto. What if dark matter does interact with regular matter in a non-gravitational manner, but mainly in a quantum incoherent fashion such that the net effect of one realm on the other (on long-enough scales) averages out to near-zero through destructive interference? And what if a suitable phase-coherent relation between the two realms could induce substantial net interactions between them? As a crude analogy, think of superconductivity: the phonon-mediated effective electron-electron interaction for typical (i.e. unpaired) many-body electronic states is incoherent, but within the pairing subspace the interaction sums coherently and thus lowers the overall free energy†. If some large kinetic barrier suppresses nature’s ability to access this putative coherent realm-crossing state, then dark will remain dark until some clever creature (of light or dark?) properly arranges the quantum degrees of freedom…
In the total absence of any supporting evidence, the probably that this idle speculation is correct is impossible to estimate: put a big weight on ‘zero’ and a tiny wisp on ‘just barely maybe’. But multiply that distribution by the huge payoff of accessing non-gravitationally the vast majority of our universe and perhaps the expected gain is not so idle.
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†Since only a tiny fraction of the electron Hilbert space is paired, the normal-state contribution of the electron-phonon interaction to the overall free energy is still larger than the portion assignable to superconductivity, it’s just that this incoherent component is present in both normal and superconducting states, so it doesn’t contribute to the difference in free energy between them.
What is this blog? Not just a site for the discussion of AIP Advances, our mission and your research articles, but also a forum for research ideas fully formed and nascent, puzzles practical and amusing, and issues of physics as applied broadly to the natural and built worlds. Let’s begin with one of each:
Don’t be shy – please jump in and join the discussion in the comments section. Click on the RSS button to receive auto-updates on future posts. I’ll try to make them worth your time and attention. Thanks, and until next time…
p.s. various of the Advances editors will be participating in this blog, but since it was my idea, I suspect that I’ll be the heaviest poster, at least at the beginning.
