Maxwells demons may drive some biological systems

first_imgConventionally, the switching mechanism was thought to operate in equilibrium, where the switch changes between clockwise and counterclockwise motor rotations in a balanced way. An earlier experiment showed that the time interval a flagllear motor spends in a given state (either clockwise or counterclockwise) follows a peaked distribution. Based on Tu’s work, this peaked interval time distribution indicates that the switch operates out of equilibrium. In order to achieve this fast and accurate switching, the switch must be extremely sensitive to the CheY-P concentration. In the non-equilibrium model, Tu shows that this high sensitivity can be explained by the presence of two Maxwell’s demons, which act as the switch’s sensors for the CheY-P. “The easiest way to explain the work of these two Maxwell’s demons is that they are two coincidence counters,” he said. “Each switch can have up to 34 CheY-P regulators bind to it. One of the demons will count the number of bound CheY-P, and if the number is greater than some threshold, say 22, it will switch the motor from CCW to CW; another demon works the opposite way with a low threshold, say 12. If the number of CheY-P bound is less than 12, this demon will switch the motor from CW to CCW.”These “demons” consume energy to do their work, in accordance with the second law of thermodynamics. The more energy the demons use, the more sensitive the switch is. Tu determined the exact amount of energy used per switch cycle, and discovered that it is roughly equal to the work done by one or two protons moving through the membrane near the flagellar motor. Based on this finding, he predicts that the switch may be powered by protons passing through the membrane. This possibility would agree with earlier observations that the average switching frequency depends on the proton flux.As Tu explains, viewing the flagellar motor switch in the framework of a non-equilibrium model could help scientists understand the switching mechanism as an integrated part of the motor system. In biology, many systems operate out of equilibrium, and Tu’s model could help scientists detect interesting non-equilibrium effects. Besides the flagellar motor, he predicts that a similar non-equilibrium mechanism, driven by Maxwell’s demons, could be responsible for a variety of other cellular processes.More information: Tu, Yuhai. “The nonequilibrium mechanism for ultrasensitivity in a biological switch: Sensing by Maxwell’s demons.” PNAS, August 19, 2008, vol. 105, no. 33, 11737-11741.Copyright 2008 PhysOrg.com. All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of PhysOrg.com. (PhysOrg.com) — According to the second law of thermodynamics, entropy always increases. For example, two bodies of different temperatures, when brought into contact, will eventually mix together to result in a uniform temperature. This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. But, as the physicist James Clerk Maxwell famously suggested in 1871, what would happen if a theoretical demon could stand at a doorway between the two bodies, and only allow high-temperature particles to pass through one way, and only low-temperature particles to pass through the other? The tiny doorman would prevent the two temperatures from mixing, and theoretically prevent entropy. Of course, the demon would use energy to do this job, thus creating entropy itself, and so the second law would not be violated.While Maxwell’s demon was originally considered a thought experiment, similar mechanisms have been discovered for various applications. One example is a Ranque-Hilsch vortex tube, which is a pneumatic device that separates hot and cold air by spinning hot and cold molecules in different directions.Now, a recent study shows that a similar mechanism may drive a motor switch in the bacteria Escherichia coli, and may be responsible for many other signaling systems in biology. Researcher Yuhai Tu at IBM’s T.J. Watson Research Center in Yorktown Heights, New York, explains how E. coli’s Maxwell’s demons work in a recent issue of the Proceedings of the National Academy of Sciences.“There are two related contributions made in this paper,” Tu told PhysOrg.com. “First, a general non-equilibrium mechanism for making a highly sensitive switch (i.e., how Maxwell’s demons can be used to increase sensitivity). Second, a general result on dwell-time statistics (how long a system should stay in a given state before it switches to other states). This result can be used as a diagnostic tool to detect the existence of these demons (or non-equilibrium effects) in an unknown system.”The bacterium contains flagellar motors that drive its motion. A flagellar motor has a switch (a shift gear) whose job is to sense the concentration of a regulator called CheY-P, and then control the rotational direction of the motor to be either clockwise (CW) or counterclockwise (CCW), accordingly. “The purpose of the CW and CCW switch is to control the motion of the cell,” Tu said. “The CheY-P level is the signal (red/yellow/green light) which affects the switch (stop/slow/move). In a very loose sense, CCW results in movement and CW results in switching direction. The bacterium cell needs to control these two types of motions to navigate towards (away from) favorable (toxic) environments.” Video games are a ‘great equalizer’ for people with disabilities Citation: Maxwell’s demons may drive some biological systems (2008, September 10) retrieved 18 August 2019 from https://phys.org/news/2008-09-maxwell-demons-biological.html Explore furtherlast_img read more

New evidence for a preferred direction in spacetime challenges the cosmological principle

first_imgThe hemisphere with the “preferred” direction on the left, in contrast to the opposite hemisphere on the right. The color of the dots represents the sign and magnitude of the anisotropy level. Image credit: Cai, et al. Statistical modeling could help us understand cosmic acceleration But a few recent studies have found the possible existence of cosmological anisotropy: specifically, that the universe’s expansion is accelerating at a faster rate in one direction than another. In the most recent study, scientists have analyzed data from 557 Type 1a supernovae and found, in agreement with some previous studies, that the universe’s expansion seems to be accelerating faster in the direction of a small part of the northern galactic hemisphere.The researchers, Rong-Gen Cai and Zhong-Liang Tuo from the Chinese Academy of Sciences in Beijing, have posted their study at arXiv.org. A valuable tool for cosmologists, Type 1a supernovae serve as “standard candles” due to their consistent peak luminosity, allowing researchers to measure their distance with high accuracy. Observations of these supernovae famously revealed in 1998 that the universe is not only expanding, but is doing so at an accelerating rate. And now, some observations of Type 1a supernovae at different locations in the sky hint that the acceleration is not uniform in all directions.In their analysis, Cai and Tuo looked at the deceleration parameter, q0, to quantify the anisotropy level of the northern galactic and southern galactic hemispheres. As the scientists explain in their study, the direction with the smaller value of q0 is expanding faster than the direction with the larger value. The researchers analyzed the data using both a dynamical dark energy model and a standard model without dark energy, and found that both models revealed similar results: an anisotropy deviation of 0.76 and 0.79, respectively, and a preferred direction of (309°, 21°) and (314°, 28°), respectively. As noted by the Physics arXiv Blog, this direction of greatest acceleration is in the faint constellation of Vulpecula in the northern hemisphere.But as Cai and Tuo note in their study, the case is far from closed. In contrast with the current results, some previous analyses of Type 1a supernovae data have not found any statistically significant evidence for anisotropies. And many other data – such as that for the cosmic microwave background radiation, galaxy statistics, and dark matter haloes – strongly support the assumption of homogeneity and isotropy on the cosmic scale. Yet considering that the cosmological principle is one of the pillars of modern cosmology whose fundamental importance is difficult to exaggerate, threats to its credibility won’t be taken lightly. If the cosmological principle turns out to be wrong, it would dramatically change the way we look at the world. (PhysOrg.com) — According to the cosmological principle, there is no special place or direction in the universe when viewed on the cosmic scale. The assumption enabled Copernicus to propose that Earth was not the center of the universe and modern scientists to assume that the laws of physics are the same everywhere. Due to the cosmological principle, scientists also assume that the universe is “homogeneous” – having a uniform structure throughout – and “isotropic” – having uniform properties throughout. More information: Rong-Gen Cai, et al. “Direction dependence of the acceleration in type Ia supernovae.” arXiv:1109.0941v2 [astro-ph.CO]via: Physics arXiv Blog This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. © 2011 PhysOrg.com Explore further Citation: New evidence for a preferred direction in spacetime challenges the cosmological principle (2011, September 7) retrieved 18 August 2019 from https://phys.org/news/2011-09-evidence-spacetime-cosmological-principle.htmllast_img read more