linkstream2 microblog

http://link.springer.com/article/10.1007%2Fs11214-014-0054-6

http://www.wsj.com/articles/bridging-the-generation-gap-with-chess-1432167354?KEYWORDS=Zach&alg=y

http://www.nytimes.com/2015/08/02/nyregion/sunday-at-grey-gardens-with-liz-lange-fashion-designer.html?smprod=nytcore-iphone&smid=nytcore-iphone-share

http://journals.aps.org/pre/abstract/10.1103/PhysRevE.51.1020

refers to
B. Josephson, Letter to the Guardian, June 14, 2000.

http://journals.aps.org/pre/pdf/10.1103/PhysRevE.75.021110

QT:{{”

The bridge’s movements were caused by a ‘positive feedback’
phenomenon, known as synchronous lateral excitation. The natural sway motion of people walking caused small sideways oscillations in the bridge, which in turn caused people on the bridge to sway in step, increasing the amplitude of the bridge oscillations and continually reinforcing the effect.[6] On the day of opening, the bridge was crossed by 90,000 people, with up to 2,000 on the bridge at any one time.

Resonant vibrational modes due to vertical loads (such as trains, traffic, pedestrians) and wind loads are well understood in bridge design. In the case of the Millennium Bridge, because the lateral motion caused the pedestrians loading the bridge to directly participate with the bridge, the vibrational modes had not been anticipated by the designers. The crucial point is that when the bridge lurches to one side, the pedestrians must adjust to keep from falling over, and they all do this at exactly the same time. Hence, the situation is similar to soldiers marching in lockstep, but horizontal instead of vertical.

The lateral vibration problems of the Millennium Bridge are very unusual, but not entirely unique.[7] Any bridge with lateral frequency modes of less than 1.3 Hz, and sufficiently low mass, could witness the same phenomenon with sufficient pedestrian loading. The greater the number of people, the greater the amplitude of the vibrations. For example, Albert Bridge in London has a sign dating from 1873 warning marching ranks of soldiers to break step while crossing.[8] Other bridges which have seen similar problems are:
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https://en.wikipedia.org/wiki/Millennium_Bridge,_London

https://www.youtube.com/watch?v=eAXVa__XWZ8

https://en.wikipedia.org/wiki/SQUID

http://www.macrumors.com/2015/10/23/ipad-pro-hands-on-productivity/

QT:{{”
In 1665, Christiaan Huygens [Huygens, 1673] noted “When we suspended two clocks so constructed from two hooks imbedded in the same wooden beam, the motions of each pendulum on opposite swings were so much in agreement that they never receded the least bit from each other and the sound of each was always heard simultaneously. Further, if this agreement was disturbed by some interference, it reestablished itself in a short time. For a long time I was amazed at this unexpected result, but after a careful examination finally found that the cause of this is due to the motion of the beam, even though this is hardly perceptible. The cause is that the oscillations of the pendula, in proportion to their weight, communicate some motion to the clocks. This motion, impressed onto the beam, necessarily has the effect of making the pendula come to a state of exactly contrary swings if it happened that they moved otherwise at first, and from this finally the motion of the beam completely ceases.” The study of coupled
oscillators has since become an active branch of mathematics, with applications in physics, biology, and chemistry. In physics, one encounters coupled oscillators in arrays of Josephson junctions [Chung et al., 1989, Blackburn et al., 1994], in modelling molecules [Sage, 1994], and in coupled lasers [Dente et al., 1990]. Coupled oscillators are also prevalent in biological systems. Most organisms appear to be coupled to various periodicities extant in our surroundings, such as the rotation of the earth about the sun, the alternation of night and day, or the tides. Not only do organisms exhibit periodicities due to their environment, but they also exhibit innate periodic behavior. Breathing, pumping blood, chewing, and galloping are examples of rhythmic patterns of motion…
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http://web.cse.ohio-state.edu/pnl/theses/campbell/Ch1.pdf