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Messages - saikat07

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EEE / Re: Hypertension: Causes, Symptoms and Treatments
« on: February 28, 2020, 09:27:29 PM »
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EEE / Re: Metamaterials: The Next Photonics Revolution
« on: February 28, 2020, 09:27:21 PM »
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EEE / Re: Crystals
« on: February 28, 2020, 09:27:09 PM »
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EEE / Re: Butterflies and metamaterials with Professor Roy Sambles
« on: February 28, 2020, 09:26:55 PM »
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EEE / Re: গ্রাফিন নিয়ে গবেষণা
« on: February 28, 2020, 09:26:44 PM »
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EEE / Re: Metamaterials: What They Are and Why They're Important
« on: February 28, 2020, 09:26:35 PM »
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EEE / Re: Seismic activity on Mars confirmed by Insight lander
« on: February 28, 2020, 09:26:17 PM »
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EEE / Re: Application of Transducers in Biomedical Instrumentation
« on: February 28, 2020, 09:26:10 PM »
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EEE / Re: Application of Transducers in Biomedical Instrumentation
« on: February 28, 2020, 09:26:03 PM »
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EEE / Re: Action Potential and Resting Potential
« on: February 28, 2020, 09:25:55 PM »
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EEE / Re: Bio Electrode Potential
« on: February 28, 2020, 09:25:47 PM »
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EEE / Re: Work Function and Threshold Frequency
« on: February 28, 2020, 09:25:37 PM »
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EEE / A new kind of spray is loaded with microscopic electronic sensors
« on: February 28, 2020, 09:24:20 PM »
alk about cloud-connected devices.

Using tiny 2-D materials, researchers have built microscopic chemical sensors that can be sprayed in an aerosol mist. Spritzes of such minuscule electronic chips, described online July 23 in Nature Nanotechnology, could one day help monitor environmental pollution or diagnose diseases.

Each sensor comprises a polymer chip about 1 micrometer thick and 100 micrometers across (about as wide as a human hair) overlaid with a circuit made with atomically thin semiconducting materials (SN Online: 2/13/18). This superflat circuit includes a photodiode, which converts ambient light into electric current, and a chemical detector. This chemical detector is composed of a 2-D material that conducts electric current more easily if the material binds with a specific chemical in its environment.
Researchers can choose from a vast menu of 2-D materials to fashion detectors that are sensitive to different chemicals, says study coauthor Volodymyr Koman, a chemical engineer at MIT (SN Online: 1/17/18). In lab experiments, Koman and colleagues created a sensor spray that detected toxic ammonia vapor inside a sealed section of piping, as well as a spray that ID’d soot particles sprinkled across a flat surface.

Right now, researchers can determine whether their sensors have come in contact with certain particles only after the fact — by collecting the chips and hooking them up to electrodes. These electrodes test how easily electric current flows through a chip’s chemical detector, which reveals whether it touched a particular chemical after it was sprayed. But future sensors could emit light signals when in contact with target particles, says study coauthor Michael Strano, a chemical engineer at MIT.

The team is also investigating ways to power the circuits without ambient light and to integrate multiple chemical detectors onto a single chip. The simpler, single-chemical detection systems tested so far are “only the beginning,” Koman says.

“It’s very exciting,” says Kourosh Kalantar-Zadeh, an electrical and chemical engineer at the University of New South Wales in Sydney whose commentary on the study appears in the same issue of Nature Nanotechnology. Sprayable sensors could someday detect gas leaks, pollution from power plants, volatile organic compounds and other air and water contaminants (SN: 3/17/18, p. 12).

Being so tiny, the devices could also be injected into a person’s bloodstream to monitor its chemical composition for medical purposes — like a blood test that wouldn’t require drawing any blood, Kalantar-Zadeh says. Or chemical sensors could be taken as nasal spray or swallowed to track digestive health (SN Online: 1/8/18). Unlike silicon-based devices that might pose environmental or health hazards, the polymers and the minute amounts of 2-D materials used to make the new devices are expected to be more biofriendly, he says.

EEE / Strange metals are even weirder than scientists thought
« on: February 28, 2020, 09:23:50 PM »
Curiouser and curiouser: Strange metals are getting a little stranger.

Normal metals such as copper and aluminum are old hat — physicists have a strong grasp on the behavior of the electrons within. But strange metals behave in mysterious ways, and researchers have now uncovered an additional oddity. A type of strange metal called a cuprate behaves unexpectedly when inside a strong magnetic field, the team reports in the Aug. 3 Science.

Strange metals are “really one of the most interesting things to happen in physics” in recent decades, says theoretical physicist Chandra Varma of the University of California, Riverside, who was not involved with the research. The theory that explains the behavior of standard metals can’t account for strange metals, so “a completely new kind of fundamental physics” is needed.
The metallic curios’ idiosyncrasies relate to their resistivity — how difficult it is for electric current to flow through them. As scientists crank up a strange metal’s temperature, its resistivity increases in lockstep: Double the temperature and you double the resistivity. That’s unusual: In most metals, the change in resistivity is more complex. For example, at low temperatures, the resistivity of a normal metal like copper would hardly change as the temperature inched up.

Strange metals’ behavior flouted the norms of physics, attracting scientists’ attention. The materials were “poking in our eye much more than other materials,” says physicist Arkady Shekhter of the National High Magnetic Field Laboratory in Tallahassee, Fla. So he and colleagues studied how the cuprate behaved in extremely strong magnetic fields, up to almost 2 million times the strength of Earth’s magnetic field.

The researchers showed that when the magnetic field is ramped up, the strange metal exhibits similarly weird behavior as it does with temperature. As the magnetic field grows, resistivity in the cuprate increases apace. It’s what’s known as a linear relationship, because it looks like a diagonal straight line when plotted on a graph showing resistivity versus magnetic field. In a normal metal, the change in resistance with the increasing magnetic field would be smaller, and would not be a straight line, instead curving.

Besides being strange metals, cuprates have another claim to fame: Under certain conditions, cuprates become superconducting, transmitting electricity without resistance (SN: 1/20/18, p. 11). While most superconductors have to be cooled to nearly absolute zero, cuprates operate at significantly higher temperatures. That makes the superconductors easier to use in technological applications, where the elimination of resistance could allow for more efficient, better performing electronics. Studying strange metals could help scientists better understand how cuprates superconduct at higher temperatures.

The result is “a really amazing discovery,” says physicist Jiun-Haw Chu of the University of Washington in Seattle, who was not involved with the research. “There’s a symmetric role that is played by temperature and field, and that is really new.”

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