Archive for July 2007

Bouncing liquid jets

xantox, 19 July 2007 in News

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Physicists from the University of Texas at Austin found that “a liquid jet can bounce off a bath of the same liquid if the bath is moving horizontally with respect to the jet. Previous observations of jets rebounding off a bath (e.g. Kaye effect) have been reported only for non-Newtonian fluids, while we observe bouncing jets in a variety of Newtonian fluids, including mineral oil poured by hand. A thin layer of air separates the bouncing jet from the bath, and the relative motion replenishes the film of air. Jets with one or two bounces are stable for a range of viscosity, jet flow rate and velocity, and bath velocity. The bouncing phenomenon exhibits hysteresis and multiple steady states”.1

Bouncing liquid jets


  1. M. Thrasher, S. Jung, Y. Kwong Pang, C. Chuu, H. L. Swinney, “The Bouncing Jet: A Newtonian Liquid Rebounding off a Free Surface“, arXiv:0707.1721v1 [physics.flu-dyn] (2007). []
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Teleportation without shared entanglement

xantox, 14 July 2007 in News

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From ACQAO through The Quantum Pontiff: “Theorists from the UQ (Ashton Bradley, Simon Haine, Murray Olsen) and ANU Faculties (Joseph Hope) nodes of the ARC Centre of Excellence for Quantum-Atom Optics (ACQAO) have come up with a scheme to teleport quantum states of collections of atoms from one position to another by converting the quantum state to light and back again. The scheme relies on the sender and receiver each having a reservoir of extremely cold atoms, known as a Bose-Einstein condensate [and] it gets around the need for the sender and receiver to share entanglement, as the quantum state to be teleported is never actually measured“.1


  1. A. S. Bradley, M. K. Olsen, S. A. Haine, J. J. Hope, “Teleportation of massive particles without shared entanglement“, arXiv:0706.0062v1 [quant-ph] (2007). []
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Classical Molecules

xantox, 9 July 2007 in Gallery

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Animation showing the interaction of four charges of equal mass1, two positive and two negative, in the approximation of classical electromagnetism. The particles interact via the Coulomb force, mediated by the electric field represented in yellow. A repulsive “Pauli force” of quantum mechanical origin, which becomes very large at a critical distance of about the radius of the spheres shown in the animation, keeps the charges from collapsing into the same point. Additionally, the motion of the particles is damped by a term proportional to their velocity, allowing them to “settle down” into stable (or meta-stable) states.

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When the charges are allowed to evolve from the initial state, the first thing that happens (very quickly, since the Coulomb attraction between unbalanced charges is very large) is that they pair off into dipoles. Thereafter, there is still a (much weaker) interaction between neighboring dipoles (van der Waals force). Although in principle it can be either repulsive or attractive, there is a torque that rotates the dipoles so that it is attractive, eventually bringing the two dipoles together in a bound state. This mechanism binds the molecules of some substances into a solid.


  1. © 2004 MIT TEAL/Studio Physics Project, John Belcher []
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Axions not confirmed by PVLAS

xantox, 9 July 2007 in News

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From PhysicsWeb News: “The existence of a hypothetical particle called the axion has been put into further doubt now that the team that first claimed its discovery has failed to reproduce their results. Physicists working on the PVLAS experiment in Italy say that the tiny rotation in the polarization of laser light that they reported last year does not support the existence of axions, but rather is an artifact related to how the experiment had been performed”1.


  1. E. Zavattini et al., “New PVLAS results and limits on magnetically induced optical rotation and ellipticity in vacuum“, arXiv:0706.3419v1 (2007) []
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New limit placed on photon charge

xantox, 9 July 2007 in News

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From PhysicsWeb News: “A physicist in the US has analysed radio waves from distant galaxies to obtain a new upper bound on the electrical charge of the photon. Brett Altschul of Indiana University has found that the charge is no more than 10-46 times the charge of the electron — assuming the existence of photons with positive and negative charges. This is 13 orders of magnitude better than the previous direct bound on the charge of a particle that we normally assume to be neutral”1.


  1. Phys. Rev. Lett. 98 261801 []
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DNA replication

xantox, 3 July 2007 in Gallery

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Using computer animation1 based on molecular research2 it is possible to see how DNA is actually copied in living cells. This animation shows the “assembly line” of biochemical machines which pull apart the DNA double helix and output a copy of each strand. The DNA to be copied enters the whirling blue molecular machine, called helicase, which spins it as fast as a jet engine as it unwinds the double helix into two strands. One strand is copied continuously, and can be seen spooling off on the other side. Things are not so simple for the other strand, because it must be copied backwards, so it is drawn out repeatedly in loops and copied one section at a time. The end result is two new DNA molecules.

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  1. Drew Berry, “DNA animation”, The Walter and Eliza Hall Institute of Medical Research, Melbourne, Australia (courtesy of the author). © 2007 Howard Hughes Medical Institute []
  2. T. A. Baker, S. P. Bell, “Polymerases and the Replisome: Machines within Machines“, Cell, 92:295-305 (1998); K. P. Lemon, A. D. Grossman, “Movement of Replicating DNA through a Stationary Replisome“, Molecular Cell, 6, 6:1321-1330 (2000); M. R. Singleton, M. R. Sawaua, T. Ellenberger, D. B. Wigley, “Crystal structure of T7 gene 4 ring helicase indicates a mechanism for sequential hydrolysis of nucleotides“, Cell 101:589-600 (2000); D. S. Johnson, L. Bai, B. Y. Smith, S. S. Patel, M. D. Wang, “Single-Molecule Studies Reveal Dynamics of DNA Unwinding by the Ring-Shaped T7 Helicase“, Cell 129, 7:1299-1309 (2007). []
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