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Topic: Brownian ratchet

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	Brownian motion - Wikipedia, the free encyclopedia
		In the end, the Brownian motion of particles in a liquid, is due to the instantaneous unbalance in the force exerted by the small liquid molecules on the particle.
		Brownian motion is related to the random walk problem and it is generic in the sense that many different stochastic processes reduce to Brownian motion in suitable limits.
		For a particle experiencing a brownian motion corresponding to the mathematical definition, the equation governing the time evolution of the probability density function associated to the position of the Brownian particle is the diffusion equation, a partial differential equation.
	en.wikipedia.org /wiki/Brownian_motion (1507 words)

	Highlight:Listeria steps (Site not responding. Last check: 2007-10-08)
		Called the "Brownian ratchet" by George Oster and colleagues, this type of model is very elegant and amenable to analytical exploration with a minimum of parameters (Peskin, Odell and Oster 1993, Biophys J 65:316-324).
		This floppiness is the fundamental mechanism that allows the elastic Brownian ratchet to generate a gap large enough for monomers to insert between the ends of the filaments and the bacterium.
		However, the physics behind the elastic Brownian ratchet model must occur, but the published calculations assume that the ends of filaments are free to 'wiggle' to allow intercalation (Mogilner and Oster 1996, Biophys J 71: 3030-3045).
	www.bme.jhu.edu /~skuo/emph_ListSteps.html (2242 words)

	Stanford scientists use noise to sort proteins
		The array is a realization of a theoretical device called a Brownian ratchet, popularized by Nobel physicist Richard Feynman, who used it to illustrate the inviolability of the second law of thermodynamics, the law that explains why it is always easier to make a mess than it is to clean it up.
		An analogy for the operation of the membrane ratchet is a bar filled with drunken sailors (a common term for random motion is a drunken sailor's walk).
		Brownian motion is an example of what scientists call a random walk, a movement whose steps are determined at random.
	www.eurekalert.org /pub_releases/1999-08/SU-Ssun-130899.php (1322 words)

	Playing both sides, Erica Klarreich (Site not responding. Last check: 2007-10-08)
		Thus even when the ratchet is subject to forces that would move the wheel back and forth, the action of the pawl and the teeth allows the wheel to move in only one direction.
		Brownian ratchets do not provide energy for free; like all motors, they merely convert one form of order, such as chemical or electromagnetic energy, into another form: directed motion.
		Brownian motion makes it drift a little to the right or left, so that when the momentary burst of energy subsides, the kinesin molecule may slide down into the nearest neighboring trough—say, to the right.
	www.nasw.org /users/klarreich/parrondo.htm (3800 words)

	Brownian motion Article, Brownianmotion Information (Site not responding. Last check: 2007-10-08)
		Brownian motion is the simplest stochastic process on acontinuous domain, and it is a limit of both simpler (see random walk) and more complicated stochastic processes.
		Mathematically, Brownian motion is a Wiener process in which theconditional probability distribution of the particle's position at time t+dt, given that its position at timet is p, is a normal distribution with a mean of p+μ dt and a variance of σ
		Brownian motion is related to the random walk problem and it is generic in the sense that many different stochasticprocesses reduce to Brownian motion in suitable limits.
	www.anoca.org /random/mathematical/brownian_motion.html (590 words)

	Brownian Ratchets in Biophysics: from Diffusing Phospholipids to Polymerizing Actin Filaments (Site not responding. Last check: 2007-10-08)
		Brownian Ratchets in Biophysics: from Diffusing Phospholipids to Polymerizing Actin Filaments
		This ratchet consists of a two-dimensional microfabricated periodic array of asymmetric diffusion barriers.
		I will demonstrate that the geometrical Brownian ratchet can be used as a molecular sieve to separate mixtures of membrane molecules without the need to extract them from the membrane.
	flux.aps.org /meetings/YR00/MAR00/abs/S2020004.html (312 words)

	The Ultimate Brownian motion - American History Information Guide and Reference
		Brownian motion was discovered by the biologist Robert Brown in 1827.
		The first to give a theory of Brownian motion was Louis Bachelier in 1900 in his PhD thesis "The theory of speculation".
		Mathematically, Brownian motion is a Wiener process in which the conditional probability distribution of the particle's position at time t+dt, given that its position at time t is p, is a normal distribution with a mean of p+μ dt and a variance of σ
	www.historymania.com /american_history/Brownian_motion (799 words)

	Brownian ratchet - Wikipedia, the free encyclopedia
		One simplistic way to visualize how the machine might fail is to remember that the ratchet itself will undergo Brownian motion as well.
		In fact, the ratchet will be a comparable size to the gear and undergo similar size motions.
		So as often as the machine ratchets forward, it slips due to the ratchet's Brownian motion.
	en.wikipedia.org /wiki/Brownian_ratchet (338 words)

	The Official Parrondo's Paradox Page - Research Links
		A ratchet and pawl device, shown in Figure 1, was first discussed around 1900 by the French physicist Lippmann—the open question at the time was: can a microscopic version of this device harness the thermal Brownian fluctuations of gas molecules, by a process of rectification?
		One of the problems that face scientists and translators that deal with Brownian ratchets and Parrondo's paradox, in other languages, is that "ratchet" and "pawl" are rather strange uncommon words.
		For example when we say "ratchet," in English, we sometimes use it to mean the "ratchet wheel" and we sometimes use it to refer to the whole ratchet wheel and pawl mechanism.
	www.eleceng.adelaide.edu.au /Groups/parrondo/ratchet.html (853 words)

	[No title]
		Basically, Brownian Ratchets are a way of filtering things which are moving around according to Brownian motion - molecules bouncing around due to random collisions.
		The Brownian Ratchet inserts an asymetrical obstacle into this movement, making it easier for certain molecules to pass through the sieve, kind of like a tiny Pachinko machine.
		Since Brownian motion displaces small particles more than large ones, the ratchet can be used for filtering viruses by their size, or polluting particles from water.
	www.omidyar.net /group/netchange/news/15/text (628 words)

	Biophysical Journal: A chemically reversible Brownian motor: Application to Kinesin and Ncd (Site not responding. Last check: 2007-10-08)
		Here we present another possibility, based on a Brownian ratchet, in which the direction of motion of the motor is controlled by the chemical mechanism of ATP hydrolysis and is an inherent property of a single head.
		Here we present a model, based on a Brownian ratchet (Huxley, 1957; Hanggi and Bartussek, 1996; Astumian, 1997; Julicher et al., 1997) where the direction of motion is controlled by the chemical mechanism of ATP hydrolysis.
		These fluctuating-force ratchets (Magnasco, 1993), although possibly technologically relevant (Lee et al., 1999), are inconsistent with transport driven by a chemical reaction such as ATP hydrolysis, because the fluctuating driving force is long range, and chemical reactions only act.locally.
	www.findarticles.com /p/articles/mi_qa3938/is_199908/ai_n8855634 (1068 words)

	Abstracts (Site not responding. Last check: 2007-10-08)
		A Brownian donkey is a small nonequilibrium system subjected to thermal fluctuations that displays the remarkable property of absolute negative mobility, i.e., it moves always opposite to the direction of an applied (small) force.
		This novel effect is due to a thermal ratchet mechanism in the space of orientations of the ferromagnetic particles, which we investigate theoretically, numerically, and experimentally.
		We discuss the optimization of the ratchet under deterministic operation; we show that both irreversible and reversible modes of operation are possible, and discuss the possibility of achieving high efficiencies under irreversible operation.
	www.algarcia.org /Bmotor/abstracts.html (2366 words)

	Brownian Motion Ratchet effect (Site not responding. Last check: 2007-10-08)
		Here are some pages I've collected while surfing for Brownian Ratchet effect, along with some notes of ways to apply the concepts to waves of uplift.
		However, the ratchet with a force exhibits a curious property: when the potential is permanently on or off, the Brownian particles move in the same direction as the force, whereas they move in the opposite direction when the potential is switched on and off.
		We study the probability current of the Brownian particles in a tilted periodic piecewise linear ``saw-tooth'' potential.
	omidyar.net /group/netchange/ws/brownian_motion_ratchet_effect/check (872 words)

	DNA transport by a micromachined Brownian ratchet device -- Bader et al. 96 (23): 13165 -- Proceedings of the National ...
		We have micromachined a silicon-chip device that transports DNA with a Brownian ratchet that rectifies the Brownian motion
		Brownian ratchets have been demonstrated to transport micrometer- to millimeter-sized particles in experiments with ratchets
		In conclusion, we have fabricated a Brownian ratchet device that is capable of transporting small DNA molecules in aqueous
	www.pnas.org /cgi/content/full/96/23/13165 (2657 words)

	Reference.com/Encyclopedia/Brownian ratchet
		One simplistic way to visualize how the machine might fail is to remember that the rachet itself will undergo Brownian motion as well.
		In fact, the rachet will be a comparable size to the gear and undergo similar size motions.
		So as often as the machine rachets forward, it slips due to the rachet's Brownian motion.
	www.reference.com /browse/wiki/Brownian_ratchet (307 words)

	Science News: Maze-like ratchet sorts biomolecules - new device would transform Brownian motion - Brief Article (Site not responding. Last check: 2007-10-08)
		The device is a novel type of Brownian ratchet, a tiny machine that harnesses the energy of random jiggles to produce a one-way particle flow.
		Although a Brownian ratchet powered only by erratic particle motion violates the second law of thermodynamics, researchers have come up with workable ratchets in recent years that use oscillating electric fields.
		The shape and placement of the 25-nanometer-high barriers enable Brownian motion to nudge the proteins along in one direction, while a constant electric field gently pushes them along a perpendicular course.
	www.findarticles.com /p/articles/mi_m1200/is_12_156/ai_56183565 (442 words)

	Directed Motion From Brownian Fluctuations in Non-Equilibrium Steady State: The Brownian Ratchet Revisited (Site not responding. Last check: 2007-10-08)
		A recent model referred to as the "Brownian ratchet" was developed by Peskin, et al that showed how Brownian fluctuations can lead to directed motion.
		However, it is believed that the disagreement of the experimental data to the theory stems from two considerations: (1) misconceptions of the model's fundamental principles, and (2) the model lacks the crucial, realistic feature of ATP hydrolysis-driven polymerization.
		Using principles of macromolecular mechanics, a new model of the Brownian ratchet augmented with nucleotide hydrolysis is developed.
	flux.aps.org /meetings/YR01/NWS01/abs/S100007.html (210 words)

	Brownian Motor
		Due to the fluctuating force caused by the pushing molecules of the surrounding fluid or gas the Brownian particle may overcome the potential barrier moving to the left or to the right.
		But the ratchet can be turned into a so-called a Brownian motor that seems to violate the second law of thermodynamics.
		When the ratchet potential is switched on, the particle gets trapped in one of the potential minima.
	monet.physik.unibas.ch /~elmer/bm (724 words)

	Stochastic Analysis of Particle-Pair Transport in Brownian Ratchet Device...
		Stochastic Analysis of Particle-Pair Transport in Brownian Ratchet Device...
		The motion of particle pairs in a Brownian ratchet device is studied using Langevin simulations.
		The effects of such interaction upon a recent model for Brownian motors [3] is investigated, with emphasis on the steady-state current.
	www.x-cd.com /nano2004/html/prof255.html (88 words)

	The protein import motor of mitochondria: a targeted molecular ratchet driving unfolding and translocation (Site not responding. Last check: 2007-10-08)
		In the 'Brownian ratchet' model, import of folded domains is explained by their ability to undergo spontaneous reversible local unfolding due to thermal breathing.
		A representation of the two models that have been proposed, the 'power stroke' (or 'pulling') model and the 'Brownian ratchet' (or 'trapping') model, is given in Figure 8.
		Notably, a Brownian ratchet mechanism has been proposed for the post-translational translocation of proteins into the ER (Matlack et al., 1999).
	www.nature.com /emboj/journal/v21/n14/full/7594578a.html (8131 words)

	Showing the way to DNA
		The researchers say that their pump, just two thousandths of a millimetre wide, could form part of a laboratory-on-a-chip, in which pieces of DNA are sorted, moved around and sequenced on a single chip, all under computer control.
		A molecular thermal ratchet is like this, except that the aimless swimming corresponds to random Brownian motion owing to the molecules' thermal energy, and the ramped landscape corresponds to an underlying 'field', such as an electric field, with a sawtooth shape.
		In the Brownian DNA ratchet proposed by Bader's group, the sawtooth field is provided by tiny electrodes engraved into the silicon wafer, in alternating positive-and-negative pairs.
	www.mindswap.org /2002/nature/991202-3.xml (572 words)

	Optimal modulation of a Brownian ratchet and enhanced sensitivity to a weak external force -- Tarlie and Astumian 95 ...
		Optimal modulation of a Brownian ratchet and enhanced sensitivity to a weak external force -- Tarlie and Astumian 95 (5): 2039 -- Proceedings of the National Academy of Sciences
		Optimal modulation of a Brownian ratchet and enhanced sensitivity to a weak external force
		We studied the dynamics of a Brownian particle moving in a spatially anisotropic potential acted on by multiplicative temporal
	www.pnas.org /cgi/content/full/95/5/2039 (2778 words)

	Math Biology Seminar Abstracts (Site not responding. Last check: 2007-10-08)
		This analysis reveals that translocation involves a single rate-limiting step, which is postulated to be the release of the signal sequence from the translocation channel.
		Next, the Brownian ratchet and power stroke models of translocation are compared against the data.
		A likelihood-ratio test reveals that the optimal fit of the Brownian ratchet model, which contains one fewer free parameter, does not differ significantly from that of the power stroke model.
	www.math.utah.edu /~keener/mathbio/abstracts/Elston.html (159 words)

	[No title]
		He suggested that we could build a tiny device that consists of a vane (on the right) and a ratcheted wheel (on the left) that is attached by an axel from which we could suspend something (perhaps a flea).
		It turns out that if you start looking at the mechanisms by which DNA makes copies of itself or the way proteins are folded as they are created, there is pretty convincing data to suggest that nature has engineered Brownian ratchets to assist in these fundamental biological processes.
		While a Brownian ratchet is not the means to a free energy lunch, it may be core to the creation of all the foods that go into your lunch.
	www.eprairie.com /printer/article.asp?newsletterID=4574 (731 words)

	分子細胞学I (Site not responding. Last check: 2007-10-08)
		of a "ratchet and pawl" device shrunk to microscopic size (4).
		1B), a Brownian particle moves along a lattice of electric dipoles arranged head to tail (7).
		ratchet such as a car jack or ratchetting screwdriver.
	www.sci.saitama-u.ac.jp /~ohnishi/Lec/BrownianMotor.htm (4535 words)

	SIAP Volume 60 Issue 3
		Since biomolecular motors typically transport cargo that are much larger than themselves, one would expect the speed of such a motor to be severely limited by the small diffusion coefficient of its enormous cargo.
		This paper evaluates the influence of the elasticity of the tether on the speed of an imperfect Brownian ratchet.
		In both cases, the speed of the motor is an increasing function of the elasticity of the tether.
	epubs.siam.org /sam-bin/dbq/article/34534 (283 words)

	Physics 4710 Homework #6
		Consider an ideal Brownian Ratchet device for the separation of DNA.
		(c) The Brownian Ratchet seems like a 'free lunch' -- a violation of the 2nd Law of thermodynamics -- although in fact the ratchet is doing work.
		Since the particle in our Brownian ratchet cannot move to the left, the ratchet is actually better described by a different distribution, in which the particle has a probability p of moving to the right, and a probability 1-p of not moving at all with any step.
	www.phys.ufl.edu /~hagen/phz4710/spring02/homework6.html (1175 words)

	Cellular motions and thermal fluctuations: The Brownian ratchet - Peskin, Odell, Oster (ResearchIndex)
		Cellular motions and thermal fluctuations: The Brownian ratchet (1993)
		We shall call these machines "Brownian Ratchets" (BR) because rectified Brownian motion is fundamental to their operation.
		Cellular motions and thermal fluctuations: the Brownian ratchet.
	citeseer.ist.psu.edu /284220.html (689 words)

	Brownian ratchet - TheBestLinks.com - Brownian motion, California Institute of Technology, May 11, Physics, ... (Site not responding. Last check: 2007-10-08)
		Brownian ratchet - TheBestLinks.com - Brownian motion, California Institute of Technology, May 11, Physics,...
		Brownian ratchet, Brownian motion, California Institute of Technology, May 11...
		You can add this article to your own "watchlist" and receive e-mail notification about all changes in this page.
	www.thebestlinks.com /Brownian_ratchet.html (298 words)

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