Posts Tagged ‘Brownian motion

Albert Einstein: The Size and Existence of Atoms

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Written by physicsgg

March 16, 2012 at 7:00 am


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New twist on Brownian motion seen for the first time

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An artist's impression of a tiny sphere (centre) held by optical tweezers and subjected to random kicks from a surrounding fluid

An important aspect of Brownian motion predicted decades ago has been observed for the first time by researchers in Europe. The team has measured how micrometre-sized spheres interact with a surrounding fluid and have shown that the spheres “remember” their previous motion. Their experimental technique, the researchers claim, could be used as a biophysical sensor.
Famously explained by Albert Einstein in 1905, Brownian motion describes the erratic motion of a tiny particle in a fluid. It is caused by the many small “kicks” that the particle receives as a result of the thermal motion of the fluid. Initially, Einstein and other physicists believed these kicks to be independent of the motion of the particle and to be characterized by white noise….. Read the rest of this entry »

Written by physicsgg

October 11, 2011 at 3:44 pm

Magnetic joystick

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Regulating Brownian Fluctuations with Tunable Microscopic Magnetic Traps
A. Chen, G. Vieira, T. Henighan, M. Howdyshell, J. A. North, A. J. Hauser, F. Y. Yang, M. G. Poirier, C. Jayaprakash, and R. Sooryakumar
Phys. Rev. Lett. 107, 087206 (Published August 18, 2011)

The zigzagging nanowire with magnetic traps at each vortex, which can pin down magnetic beads

Magnetic particles can be guided with external fields through small-scale fluidic environments, bringing with them a biological molecule hitching a ride. A paper appearing in Physical Review Letters presents a two-dimensional magnetic trap that uses this type of magnetic remote control to guide the thermal motion of submicron magnetic beads.
Following a magnetic trap design from their earlier work, Aaron Chen at The Ohio State University in Columbus and his colleagues deposit a 2-micron-wide magnetic wire in the shape of a zigzag on a silicon surface. Chen et al. apply a one-time, large, in-plane magnetic field of 1000 oersted to polarize the legs of the zigzag shape, resulting in a sequence of head-to-head and tail-to-tail magnetic domain walls which meet at the kinks in the wire. Embedding the trap in a solution of magnetic beads, the team coaxes the beads to the large magnetic trapping gradients near the kinks using fairly weak (less than 100 oersted) external magnetic fields. The key control parameter is the strength of the external field perpendicular to the trap.
This setup allows exploration between two types of particle motion: one where the beads are tightly confined near a wire kink and another where the motion, driven by thermal fluctuations, spreads out around the kink. A magnetic trap such as this has the additional benefit that it does not rely on strong fields to move the particles or generate heat, both of which could perturb the environment studied.
Read also: Zigzag nanowire regulates Brownian motion

Written by physicsgg

August 29, 2011 at 11:18 am