Shear ultrasound shaking found to lower friction between solids – Phys.org
When high-frequency shaking occurs at an interface between two solids, recent experiments have revealed that the frictional forces between the objects can be weakened. Through a simple new experiment detailed in The European Physical Journal E, Julien Léopoldès at Université Gustave Eiffel, Marne la Vallée (formerly at ESPCI Paris) has discovered that mechanical vibrations also enhance structural aging in these systems, and can sometimes trigger sudden, jerking motions.
The results could lead to a better understanding of how buildings are weakened by ambient vibrations, and may also help geologists to draw new insights into the mechanisms responsible for triggering earthquakes and landslides.
Elastic waves due to human activity and earthquakes can be found ambiently in the environment and are known to induce fracture. To learn more about their influence, Léopoldès constructed an experiment involving a plastic slider with a roughened surface. Using a spring, the slider was driven over a smooth glass slide at a carefully controlled velocity—ranging between 1 nanometer and 1 centimeter per second. The glass slide was itself attached to an ultrasound transducer—which produced shear vibrations, parallel to its interface with the slider.
In his experiment, Léopoldès measured the frictional forces experienced by the plastic slider as he varied the velocities applied by the spring. As he predicted, the high frequency shaking lowered the friction experienced by the slider—but at lower sliding velocities, he also found that the vibrations were enough to destabilize the entire system. In these jerky “stick-slip” motions, the slider remained static at first, but then moved suddenly as its stored energy was all released at once.
These discoveries could deepen our understanding of how the interfaces at the contact between solids are affected by traveling waves, and may also have important applications in fields including geology and structural engineering.
J. Léopoldès, Sliding friction perturbed by shear ultrasound vibrations: dynamic lubrication and overaging, The European Physical Journal E (2022). DOI: 10.1140/epje/s10189-022-00256-5
Shear ultrasound shaking found to lower friction between solids (2023, February 22)
retrieved 22 February 2023
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.
NASA’S JWST measures the temperature of a rocky exoplanet – Tech Explorist
An international team of researchers has used the NASA/ESA/CSA James Webb Space Telescope to measure the temperature of the rocky exoplanet TRAPPIST-1 b. The measurement is based on the planet’s thermal emission: heat energy given off in the form of infrared light detected by Webb’s Mid-Infrared Instrument (MIRI). The result indicates that the planet’s dayside has a temperature of about 500 kelvins (roughly 230°C), and suggests that it has no significant atmosphere. This is the first detection of any form of light emitted by an exoplanet as small and as cool as the rocky planets in our own solar system. The result marks an important step in determining whether planets orbiting small active stars like TRAPPIST-1 can sustain atmospheres needed to support life. It also bodes well for Webb’s ability to characterise temperate, Earth-sized exoplanets using MIRI.
“These observations really take advantage of Webb’s mid-infrared capability,” said Thomas Greene, an astrophysicist at NASA’s Ames Research Center and lead author on the study published today in the journal Nature. “No previous telescopes have had the sensitivity to measure such dim mid-infrared light.”
Rocky planets orbiting ultra cool red dwarfs
In early 2017, astronomers reported the discovery of seven rocky planets orbiting an ultracool red dwarf star (or M dwarf) 40 light-years from Earth. What is remarkable about the planets is their similarity in size and mass to the inner, rocky planets of our own solar system. Although they all orbit much closer to their star than any of our planets orbit the Sun – all could fit comfortably within the orbit of Mercury – they receive comparable amounts of energy from their tiny star.
TRAPPIST-1 b, the innermost planet, has an orbital distance about one hundredth that of Earth’s and receives about four times the amount of energy that Earth gets from the Sun. Although it is not within the system’s habitable zone, observations of the planet can provide important information about its sibling planets, as well as those of other M-dwarf systems.
“There are ten times as many of these stars in the Milky Way as there are stars like the Sun, and they are twice as likely to have rocky planets as stars like the Sun,” explained Greene. “But they are also very active – they are very bright when they’re young and they give off flares and X-rays that can wipe out an atmosphere.”
Co-author Elsa Ducrot from CEA in France, who was on the team that conducted the initial studies of the TRAPPIST-1 system, added, “It’s easier to characterise terrestrial planets around smaller, cooler stars. If we want to understand habitability around M stars, the TRAPPIST-1 system is a great laboratory. These are the best targets we have for looking at the atmospheres of rocky planets.”
Detecting an atmosphere (or not)
Previous observations of TRAPPIST-1 b with the NASA/ESA Hubble Space Telescope, as well as NASA’s Spitzer Space Telescope, found no evidence for a puffy atmosphere, but were not able to rule out a dense one.
One way to reduce the uncertainty is to measure the planet’s temperature. “This planet is tidally locked, with one side facing the star at all times and the other in permanent darkness,” said Pierre-Olivier Lagage from CEA, a co-author on the paper. “If it has an atmosphere to circulate and redistribute the heat, the dayside will be cooler than if there is no atmosphere.”
The team used a technique called secondary eclipse photometry, in which MIRI measured the change in brightness from the system as the planet moved behind the star. Although TRAPPIST-1 b is not hot enough to give off its own visible light, it does have an infrared glow. By subtracting the brightness of the star on its own (during the secondary eclipse) from the brightness of the star and planet combined, they were able to successfully calculate how much infrared light is being given off by the planet.
Measuring minuscule changes in brightness
Webb’s detection of a secondary eclipse is itself a major milestone. With the star more than 1,000 times brighter than the planet, the change in brightness is less than 0.1%.
“There was also some fear that we’d miss the eclipse. The planets all tug on each other, so the orbits are not perfect,” said Taylor Bell, the post-doctoral researcher at the Bay Area Environmental Research Institute who analysed the data. “But it was just amazing: The time of the eclipse that we saw in the data matched the predicted time within a couple of minutes.”
Analysis of data from five separate secondary eclipse observations indicates that TRAPPIST-1 b has a dayside temperature of about 500 kelvins, or roughly 230°C. The team thinks the most likely interpretation is that the planet does not have an atmosphere.
“We compared the results to computer models showing what the temperature should be in different scenarios,” explained Ducrot. “The results are almost perfectly consistent with a blackbody made of bare rock and no atmosphere to circulate the heat. We also didn’t see any signs of light being absorbed by carbon dioxide, which would be apparent in these measurements.”
This research was conducted as part of Guaranteed Time Observation (GTO) program 1177, which is one of eight approved GTO and General Observer (GO) programs designed to help fully characterise the TRAPPIST-1 system. Additional secondary eclipse observations of TRAPPIST-1 b are currently in progress, and now that they know how good the data can be, the team hopes to eventually capture a full phase curve showing the change in brightness over the entire orbit. This will allow them to see how the temperature changes from the day to the nightside and confirm if the planet has an atmosphere or not.
“There was one target that I dreamed of having,” said Lagage, who worked on the development of the MIRI instrument for more than two decades. “And it was this one. This is the first time we can detect the emission from a rocky, temperate planet. It’s a really important step in the story of discovering exoplanets.”
How to watch 5 planets in rare celestial event tonight – The Indian Express
This is not a true planetary alignment where they will appear in a straight line, but NASA scientist Bill Cooke told CBS News that the planets will be visible on March 28 and that the “alignment: will look “very pretty.”
How to watch the 5 planets
While the five planets should technically be visible along with the waxing crescent moon in most parts of the world, you will not be able to see it unless you are in a location with an unobstructed view of the horizon.
According to Rick Feinberg, senior contributing editor at Sky & Telescope magazine, Venus and Mars should be easy to spot. Venus is the brightest planet in the solar system and will be high in the sky, and Mars will shine brightly next to the waxing Moon. But on the other hand, Uranus, which will appear near Venus, will appear faint and will only be visible next.
“Wait until the sun has set and then go out and look low in that bright part of the sky where the sun has just set with binoculars, and you should see brighter Jupiter next to fainter Mercury,” said Fienberg to NPR.
In order to get the best view of this rare celestial event, go to a location with as little light pollution as possible and a clear horizon with not obstructions. Once there, you should be able to spot most planets, apart from Jupiter and Mercury, without the use of binoculars.
Is this a rare event?
While tonight is not an everyday event, it is not truly a five-planet alignment since the planets will not appear as if they form a single straight line.
If you were looking for an actual alignment of five planets, that time has passed. A true 5 planet alignment happened in June last year when Mercury, Venus, Mars, Jupiter and Saturn stretched across the sky from low in the east to higher in the south in the order of their distance from the Sun.
Even discounting the rare coincidence where they appeared in that particular order, the planetary alignment in June was the first one in nearly eighteen years, with the last time being on December 2004. Such an event is not expected to happen again until 2040, according to NPR.
Uncrewed Russian spacecraft that leaked coolant lands safely – CTV News
A Russian space capsule safely returned to Earth without a crew Tuesday, months after it suffered a coolant leak in orbit.
The Soyuz MS-22 leaked coolant in December while attached to the International Space Station. Russian space officials blamed the leak on a tiny meteoroid that punctured the craft’s external radiator. They launched an empty replacement capsule last month to serve as a lifeboat for the crew.
The damaged capsule safely landed Tuesday under a striped parachute in the steppes of Kazakhstan, touching down as scheduled at 5:45 p.m. (7:45 a.m. EDT) 147 kilometres (91 miles) southeast of Zhezkazgan under clear blue skies.
Space officials determined it would be too risky to bring NASA’s Frank Rubio and Russia’s Sergey Prokopyev and Dmitri Petelin back in the Soyuz in March as originally planned, as cabin temperatures would spike with no coolant, potentially damaging computers and other equipment, and exposing the suited-up crew to excessive heat.
The three launched in September for what should have been a six-month mission on the International Space Station. They now are scheduled to return to Earth in September in a new Soyuz that arrived at the space outpost last month with no one on board, meaning the trio will spend a year in orbit.
Also on the station are NASA astronauts Stephen Bowen and Woody Hoburg, the United Arab Emirates’ Sultan Alneyadi, and Russia’s Andrey Fedyaev.
A similar coolant leak was spotted in February on the Russian Progress MS-21 cargo ship docked at the space outpost, raising suspicions of a manufacturing flaw. Russian state space corporation Roscosmos ruled out any defects after a check and concluded that both incidents resulted from hits by meteoroids.
First Citizens acquires troubled Silicon Valley Bank – CP24
Player grades: Edmonton Oilers survive scrambly affair in Arizona, pull out 5-4 win – Edmonton Journal
iOS 16.4—Apple Just Gave iPhone Users 33 Reasons To Update Now – Forbes
Silver investment demand jumped 12% in 2019
Iran anticipates renewed protests amid social media shutdown
Search for life on Mars accelerates as new bodies of water found below planet’s surface
News15 hours ago
Grocery rebate coming in federal budget 2023
Tech12 hours ago
Is Shimano about to ditch derailleur hangers? Patent reveals direct-mount derailleur design
Health12 hours ago
Respiratory Outbreak Over: Jasper Place – Thunder Bay District Health Unit
Real eState16 hours ago
JPMorgan says commercial real estate decline is intensifying. Beware these exposed stocks
Sports13 hours ago
Maple Leafs clinch playoff berth with Panthers loss to Senators
Tech14 hours ago
Warner Bros brawler Multiversus to go offline in June 2023
Investment13 hours ago
Sen. Bob Casey oversaw Pa. pension investment in China-linked firm
Media14 hours ago
Gautam Adani acquires 49% in Quintillion Business Media for Rs 48 crore