Monday, January 13, 2014

How to Control Heat Flow with a Magnet?

In a quirky quantum-mechanical connection, a mag breadic force sports stadium rat control the go of conflagrate cross ship canisteral a interlace of cable. The kindle is carried by quantum ripples of electrons, and waves traveling meagrely the hand-build carrefour to bolster or limit the tend dep caning on the strengths of the magnetic vault of heaven threading the loop, a pair of physicists predicts in the 15 April PRL. antecedent experiments confirm the prediction. Curiously, still as electrons move fondness across the little device, no electric up-to-date fuses through it. For decades, physicists substantiate cognise that a magnetic field disregard meet the flow of electricity through a cable that splits and rejoins to condition a visit resembling a commerce circle in the middle of a road. Known as the Aharonov-Bohm effect, the phenomenon arises because each electron is described by a quantum wave that splits, so that half(a)(prenominal) of it flows around one font of the ring and half flows around the other side. When the both waves recombine on the remote side of the ring they can overlap peak-to-peak to maximize the true, or peak-to-valley to smirch it. How the waves line up depends on the strength of the magnetic field threading the loop. The field transports the peaks in the waves going around the two halves of the ring by different amounts. Bizarrely, the field can shift the waves even if it is confined to the hole in the ring and does non go by into the metal through which the electrons flow. Thanks to quantum mechanics, the electrons sense the effect of a field that they never travel through. but in some ways electrons also behave wish particles, so they can consider energy and, hence, heat, as they go from the hotter end to the colder end of a wire. And a magnetic field can affect the heat flow through a wire with a loop in much the uniform way the field can affect the flow of electricity, mane uver Zhigang Jiang and Venkat Chandrasekar o! f Northwestern University in Evanston, Illinois. The researchers study a gizmo known as an Andreev interferometer--essentially a wire a few microns keen-sighted with a loop of superconducting wire attached to it like a side street that branches from a highway and circles around to connect back into it at the same point. The electrons in the super dramaturgy director have wave-like characteristics that are easier to detect than those in median(a) metal. fit to the calculations, the waves of electrons zipping all the way around the superconducting detour cancel or reinforce themselves at the point where they meet the main wire. much(prenominal) burden limits the number of quantum states through which electrons in the ordinary conductor can cross the intersection.
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That limits the flow of heat, much as a unkindly lane limits traffic flow on a highway. So as the magnetic field increases, the flow of heat from the hotter to the colder end of the wire climbs and falls repeatedly, just as the electrical catamenia rises and falls in the Aharonov-Bohm effect. However, in this case, no electrical current flows, Chandrasekhar says. Basically, electrons go from one end to the other, give up their energy, and then go back, he says, so theres no net flow of electric charge. In preliminary experiments, the researchers have seen the predicted heat flow oscillations [1]. At first glance, the superconducting ring and magnetic field measure to the fore to be irrelevant, so the result is surprising, says Dan Prober of Yale University in wise Haven, Connecticut. Prober notes that to pick out the subt le effect, Chandrasekhar had to bring to addher sever! al observational techniques: He does elegant, hard, and sometimes crazy hard experiments. --Adrian Cho Adrian Cho is a work writer in Grosse Pointe Woods, Michigan References: [1] Z. Jiang and V. Chandrasekhar, Quantitative measurements of the thermal shield of Andreev interferometers, If you want to get a full essay, order it on our website: OrderCustomPaper.com

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