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Cracking the mystery of egg shape - 2 views

vis.sciencemag.org/eggs BIO fun
shared by Marcus Maertens on 07 Mar 19 - No Cached
LeopoldS and microno95 liked it
  • Marcus Maertens on 07 Mar 19
     
    In preparation of Easter...
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On the extraordinary strength of Prince Rupert's drops - 1 views

aip.scitation.org/...1.4971339
shared by Alexander Wittig on 10 May 17 - No Cached
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  • Alexander Wittig on 10 May 17
     
    Prince Rupert's drops (PRDs), also known as Batavian tears, have been in existence since the early 17th century. They are made of a silicate glass of a high thermal expansion coefficient and have the shape of a tadpole. Typically, the diameter of the head of a PRD is in the range of 5-15 mm and that of the tail is 0.5 to 3.0 mm. PRDs have exceptional strength properties: the head of a PRD can withstand impact with a small hammer, or compression between tungsten carbide platens to high loads of ∼15 000 N, but the tail can be broken with just finger pressure leading to catastrophic disintegration of the PRD. We show here that the high strength of a PRD comes from large surface compressive stresses in the range of 400-700 MPa, determined using techniques of integrated photoelasticity. The surface compressive stresses can suppress Hertzian cone cracking during impact with a small hammer or compression between platens. Finally, it is argued that when the compressive force on a PRD is very high, plasticity in the PRD occurs, which leads to its eventual destruction with increasing load.
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[1107.0167] Nonlinear transformation optics and engineering of the Kerr effect - 9 views

arxiv.org/1107.0167 PHY nan optics metamaterials
shared by Luzi Bergamin on 04 Jul 11 - No Cached
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  • Luzi Bergamin on 04 Jul 11
     
    The best paper on transformation optics written ever :-)
  • ...2 more comments...
  • jmlloren on 05 Jul 11
     
    Finally something worth to read in the MM field!. The idea is excellent, congratullations. However, I think there is a typo or mistake in the definition of l=3x10-13 m, the "waist" of the laser beam. Seems clear that 0.3 pm is too small for being a waist of any laser beam.
  • Luzi Bergamin on 05 Jul 11
     
    Thanks for your commendation. Of course, the problem with nonlinear transformation optics is the same as with linear: it's very easy to come up with theoretical descriptions of devices that have the most absurd properties, but it will be extremely hard to fabricate them. But if you have any good suggestion, please shoot! About the laser beam: Pekka made the simulations, since I am not a "Comsolist", but still I think the numbers are correct. You are right that we should not call this a laser beam. Our problem was the following: we need to have a very simple model that can be simulated exactly (full Maxwell equations) but naturally exhibits self focusing. The Gaussian beam was the simplest solution. Since our model is purely classical and moreover we do not take into account diffraction effects, the parameter "l" is of minor importance. Taking "l" much larger gives almost the same picture but requires much more computer power to simulate. I guess that's why Pekka chose an unnaturally small number.
  • jmlloren on 05 Jul 11
     
    Concerning the fabrication... as usual, no idea. I agree that this is the main drawback of MM, and certainly difficult to overcome. I would double check that number, because its value is related with the beam shape of Fig. 1 A. I believe that the simulations are correct, it's just a detail.
  • LeopoldS on 06 Jul 11
     
    wow ... still publishing despite babysitting and new job!!

Observation : this month, four planets aligned in the early morning sky. - 9 views

started by Marion Nachon on 11 May 11 no follow-up yet
LeopoldS liked it
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