Tagged: Seoul National University Toggle Comment Threads | Keyboard Shortcuts

  • richardmitnick 11:15 am on November 6, 2019 Permalink | Reply
    Tags: "Chemists observe “spooky” quantum tunneling", , , , , Seoul National University   

    From MIT News: “Chemists observe “spooky” quantum tunneling” 

    MIT News

    From MIT News

    November 4, 2019
    Anne Trafton

    1
    MIT chemists have observed, for the first time, inversion of the umbrella-like ammonia molecule by quantum tunneling. Image: Chelsea Turner, MIT.

    Extremely large electric fields can prevent umbrella-shaped ammonia molecules from inverting.

    A molecule of ammonia, NH3, typically exists as an umbrella shape, with three hydrogen atoms fanned out in a nonplanar arrangement around a central nitrogen atom. This umbrella structure is very stable and would normally be expected to require a large amount of energy to be inverted.

    However, a quantum mechanical phenomenon called tunneling allows ammonia and other molecules to simultaneously inhabit geometric structures that are separated by a prohibitively high energy barrier. A team of chemists that includes Robert Field, the Robert T. Haslam and Bradley Dewey Professor of Chemistry at MIT, has examined this phenomenon by using a very large electric field to suppress the simultaneous occupation of ammonia molecules in the normal and inverted states.

    “It’s a beautiful example of the tunneling phenomenon, and it reveals a wonderful strangeness of quantum mechanics,” says Field, who is one of the senior authors of the study.

    Heon Kang, a professor of chemistry at Seoul National University, is also a senior author of the study, which appears this week in the Proceedings of the National Academy of Sciences. Youngwook Park and Hani Kang of Seoul National University are also authors of the paper.

    Suppressing inversion

    The experiments, performed at Seoul National University, were enabled by the researchers’ new method for applying a very large electric field (up to 200,000,000 volts per meter) to a sample sandwiched between two electrodes.

    3

    This assembly is only a few hundred nanometers thick, and the electric field applied to it generates forces nearly as strong as the interactions between adjacent molecules.

    “We can apply these huge fields, which are almost the same magnitude as the fields that two molecules experience when they approach each other,” Field says. “That means we’re using an external means to operate on an equal playing field with what the molecules can do themselves.”

    This allowed the researchers to explore quantum tunneling, a phenomenon often used in undergraduate chemistry courses to demonstrate one of the “spookinesses” of quantum mechanics, Field says.

    As an analogy, imagine you are hiking in a valley. To reach the next valley, you need to climb a large mountain, which requires a lot of work. Now, imagine that you could tunnel through the mountain to get to the next valley, with no real effort required. This is what quantum mechanics allows, under certain conditions. In fact, if the two valleys have exactly the same shape, you would be simultaneously located in both valleys.

    In the case of ammonia, the first valley is the low-energy, stable umbrella state. For the molecule to reach the other valley — the inverted state, which has exactly the same low-energy — classically it would need to ascend into a very high-energy state. However, quantum mechanically, the isolated molecule exists with equal probability in both valleys.

    Under quantum mechanics, the possible states of a molecule, such as ammonia, are described in terms of a characteristic energy level pattern. The molecule initially exists in either the normal or inverted structure, but it can tunnel spontaneously to the other structure. The amount of time required for that tunneling to occur is encoded in the energy level pattern. If the barrier between the two structures is high, the tunneling time is long. Under certain circumstances, such as application of a strong electric field, tunneling between the regular and inverted structures can be suppressed.

    For ammonia, exposure to a strong electric field lowers the energy of one structure and raises the energy of the other (inverted) structure. As a result, all of the ammonia molecules can be found in the lower energy state. The researchers demonstrated this by creating a layered argon-ammonia-argon structure at 10 kelvins. Argon is an inert gas which is solid at 10 K, but the ammonia molecules can rotate freely in the argon solid. As the electric field is increased, the energy states of the ammonia molecules change in such a way that the probabilities of finding the molecules in the normal and inverted states become increasingly far apart, and tunneling can no longer occur.

    This effect is completely reversible and nondestructive: As the electric field is decreased, the ammonia molecules return to their normal state of being simultaneously in both wells.

    “This manuscript describes a burgeoning frontier in our ability to tame molecules and control their underlying dynamics,” says Patrick Vaccaro, a professor of chemistry at Yale University who was not involved in the study. “The experimental approach set forth in this paper is unique, and it has enormous ramifications for future efforts to interrogate molecular structure and dynamics, with the present application affording fundamental insights into the nature of tunneling-mediated phenomena.”

    Lowering the barriers

    For many molecules, the barrier to tunneling is so high that tunneling would never happen during the lifespan of the universe, Field says. However, there are molecules other than ammonia that can be induced to tunnel by careful tuning of the applied electric field. His colleagues are now working on exploiting this approach with some of those molecules.

    “Ammonia is special because of its high symmetry and the fact that it’s probably the first example anybody would ever discuss from a chemical point of view of tunneling,” Field says. “However, there are many examples where this could be exploited. The electric field, because it’s so large, is capable of acting on the same scale as the actual chemical interactions,” offering a powerful way of externally manipulating molecular dynamics.

    The research was funded by the Samsung Science and Technology Foundation and the National Science Foundation.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.


    Stem Education Coalition

    MIT Seal

    The mission of MIT is to advance knowledge and educate students in science, technology, and other areas of scholarship that will best serve the nation and the world in the twenty-first century. We seek to develop in each member of the MIT community the ability and passion to work wisely, creatively, and effectively for the betterment of humankind.

    MIT Campus

     
  • richardmitnick 8:46 am on August 27, 2018 Permalink | Reply
    Tags: A touch sensor that can detect even minuscule forces, An artificial nerve system aims to give prosthetics a sense of touch, , Artificial nerve technology remains in its infancy, Restore sensation to amputees, Seoul National University, , Transmit sensations to the brain   

    From Stanford University – Engineering: “An artificial nerve system aims to give prosthetics a sense of touch” 

    Stanford University Name
    From Stanford University – Engineering

    May 31, 2018
    Tom Abate

    While still in its infancy, the new technology represents a first step in creating skin coverings to restore sensation to amputees.

    1
    The development has the potential to mimic how skin can stretch, repair itself and transmit sensations to the brain. | Illustration by Kevin Craft

    Stanford and Seoul National University researchers have developed an artificial sensory nerve system that can activate the twitch reflex in a cockroach and identify letters in the Braille alphabet.

    The work, reported May 31 in Science, is a step toward creating artificial skin for prosthetic limbs, to restore sensation to amputees and, perhaps, one day give robots some type of reflex capability.

    “We take skin for granted but it’s a complex sensing, signaling and decision-making system,” said Zhenan Bao, professor of chemical engineering and one of the senior authors.

    “This artificial sensory nerve system is a step toward making skin-like sensory neural networks for all sorts of applications.”

    Building blocks

    This milestone is part of Bao’s quest to mimic how skin can stretch, repair itself and, most remarkably, act like a smart sensory network that knows not only how to transmit pleasant sensations to the brain, but also when to order the muscles to react reflexively to make prompt decisions.

    The new Science paper describes how the researchers constructed an artificial sensory nerve circuit that could be embedded in a future skin-like covering for neuro-prosthetic devices and soft robotics. This rudimentary artificial nerve circuit integrates three previously described components.

    The first is a touch sensor that can detect even minuscule forces. This sensor sends signals through the second component — a flexible electronic neuron. The touch sensor and electronic neuron are improved versions of inventions previously reported by the Bao lab.

    Sensory signals from these components stimulate the third component, an artificial synaptic transistor modeled after human synapses. The synaptic transistor is the brainchild of Tae-Woo Lee of Seoul National University, who spent his sabbatical year in Bao’s Stanford lab to initiate the collaborative work.

    “Biological synapses can relay signals, and also store information to make simple decisions,” said Lee, who was a second senior author on the paper. “The synaptic transistor performs these functions in the artificial nerve circuit.”

    Lee used a knee reflex as an example of how more-advanced artificial nerve circuits might one day be part of an artificial skin that would give prosthetic devices or robots both senses and reflexes.

    In humans, when a sudden tap causes the knee muscles to stretch, certain sensors in those muscles send an impulse through a neuron. The neuron, in turn, sends a series of signals to the relevant synapses. The synaptic network recognizes the pattern of the sudden stretch and emits two signals simultaneously, one causing the knee muscles to contract reflexively and a second, less urgent signal to register the sensation in the brain.

    Making it work

    The new work has a long way to go before it reaches that level of complexity. But in the Science paper, the group describes how the electronic neuron delivered signals to the synaptic transistor, which was engineered in such a way that it learned to recognize and react to sensory inputs based on the intensity and frequency of low-power signals, just like a biological synapse.

    The group members tested the ability of the system to both generate reflexes and sense touch.

    In one test they hooked up their artificial nerve to a cockroach leg and applied tiny increments of pressure to their touch sensor. The electronic neuron converted the sensor signal into digital signals and relayed them through the synaptic transistor, causing the leg to twitch more or less vigorously as the pressure on the touch sensor increased or decreased.

    They also showed that the artificial nerve could detect various touch sensations. In one experiment the artificial nerve was able to differentiate Braille letters. In another, they rolled a cylinder over the sensor in different directions and accurately detected the direction of the motion.

    Bao’s graduate students Yeongin Kim and Alex Chortos, plus Wentao Xu, a researcher from Lee’s own lab, were also central to integrating the components into the functional artificial sensory nervous system.

    The researchers say For instance, creating artificial skin coverings for prosthetic devices will require new devices to detect heat and other sensations, the ability to embed them into flexible circuits and then a way to interface all of this to the brain.

    The group also hopes to create low-power, artificial sensor nets to cover robots, the idea being to make them more agile by providing some of the same feedback that humans derive from their skin.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Leland and Jane Stanford founded the University to “promote the public welfare by exercising an influence on behalf of humanity and civilization.” Stanford opened its doors in 1891, and more than a century later, it remains dedicated to finding solutions to the great challenges of the day and to preparing our students for leadership in today’s complex world. Stanford, is an American private research university located in Stanford, California on an 8,180-acre (3,310 ha) campus near Palo Alto. Since 1952, more than 54 Stanford faculty, staff, and alumni have won the Nobel Prize, including 19 current faculty members

    Stanford University Seal

     
c
Compose new post
j
Next post/Next comment
k
Previous post/Previous comment
r
Reply
e
Edit
o
Show/Hide comments
t
Go to top
l
Go to login
h
Show/Hide help
shift + esc
Cancel
%d bloggers like this: