In a study published in The Astrophysical Journal, Prof. Zhou Xia from the Xinjiang Astronomical Observatory (XAO) of the Chinese Academy of Sciences and collaborators have, for the first time, derived the dispersion relation for photons with nonzero mass propagating in plasma, and established a stringent upper limit for the photon mass at 9.52 × 10^-46 kg (5.34 × 10^-10 eV c^-2) using data collected by ultra-wideband (UWB) receivers from pulsar timing and fast radio bursts (FRBs).

Photons are typically considered massless particles, a hypothesis based on Maxwell’s electromagnetic theory and Einstein’s special relativity. However, if photons possess nonzero mass, it would have profound implications for existing physical theories.

Researchers in this study provided a novel theoretical framework for understanding the propagation characteristics of massive photons in plasma.

They used high-precision timing data from the Parkes Pulsar Timing Array (PPTA) and dedispersed pulse data from FRBs. Leveraging the wide frequency range covered by UWB receivers, they improved the signal-to-noise ratio and the accuracy of dispersion measurements.

The high time resolution of UWB technology allowed for precise determination of signal arrival times, effectively reducing the dispersion effects caused by the interstellar medium.

This study highlights the critical role of high-precision radio telescopes and advanced equipment in astronomical research.

With the deployment of the Five-hundred-meter Aperture Spherical radio Telescope (FAST) and the upcoming QiTai radio Telescope (QTT), along with the widespread application of UWB receivers, testing photon mass will become more precise and in-depth, which will contribute to a deeper understanding of the nature of photons and help uncover the fundamental laws of the universe.

Need a moment of levity? Try watching videos of astronauts falling on the moon. NASA’s outtakes of Apollo astronauts tripping and stumbling as they bounce in slow motion are delightfully relatable.

For MIT engineers, the lunar bloopers also highlight an opportunity to innovate.

“Astronauts are physically very capable, but they can struggle on the moon, where gravity is one-sixth that of Earth’s but their inertia is still the same. Furthermore, wearing a spacesuit is a significant burden and can constrict their movements,” says Harry Asada, professor of mechanical engineering at MIT. “We want to provide a safe way for astronauts to get back on their feet if they fall.”

Asada and his colleagues are designing a pair of wearable robotic limbs that can physically support an astronaut and lift them back on their feet after a fall. The system, which the researchers have dubbed Supernumerary Robotic Limbs or “SuperLimbs” is designed to extend from a backpack, which would also carry the astronaut’s life support system, along with the controller and motors to power the limbs.

The researchers have built a physical prototype, as well as a control system to direct the limbs, based on feedback from the astronaut using it. The team tested a preliminary version on healthy subjects who also volunteered to wear a constrictive garment similar to an astronaut’s spacesuit. When the volunteers attempted to get up from a sitting or lying position, they did so with less effort when assisted by SuperLimbs, compared to when they had to recover on their own.

The MIT team envisions that SuperLimbs can physically assist astronauts after a fall and, in the process, help them conserve their energy for other essential tasks. The design could prove especially useful in the coming years, with the launch of NASA’s Artemis mission, which plans to send astronauts back to the moon for the first time in more than 50 years.

Unlike the largely exploratory mission of Apollo, Artemis astronauts will endeavor to build the first permanent moon base—a physically demanding task that will require multiple extended extravehicular activities (EVAs).

“During the Apollo era, when astronauts would fall, 80% of the time it was when they were doing excavation or some sort of job with a tool,” says team member and MIT doctoral student Erik Ballesteros. “The Artemis missions will really focus on construction and excavation, so the risk of falling is much higher. We think that SuperLimbs can help them recover so they can be more productive, and extend their EVAs.”

Asada, Ballesteros, and their colleagues will present their design and study this week at the IEEE International Conference on Robotics and Automation (ICRA). Their co-authors include MIT postdoc Sang-Yoep Lee and Kalind Carpenter of the Jet Propulsion Laboratory.

Taking a stand

The team’s design is the latest application of SuperLimbs, which Asada first developed about a decade ago and has since adapted for a range of applications, including assisting workers in aircraft manufacturing, construction, and ship building.

Most recently, Asada and Ballesteros wondered whether SuperLimbs might assist astronauts, particularly as NASA plans to send astronauts back to the surface of the moon.

“In communications with NASA, we learned that this issue of falling on the moon is a serious risk,” Asada says. “We realized that we could make some modifications to our design to help astronauts recover from falls and carry on with their work.”

The team first took a step back, to study the ways in which humans naturally recover from a fall. In their new study, they asked several healthy volunteers to attempt to stand upright after lying on their side, front, and back.

The researchers then looked at how the volunteers’ attempts to stand changed when their movements were constricted, similar to the way astronauts’ movements are limited by the bulk of their spacesuits. The team built a suit to mimic the stiffness of traditional spacesuits, and had volunteers don the suit before again attempting to stand up from various fallen positions. The volunteers’ sequence of movements was similar, though required much more effort compared to their unencumbered attempts.

The team mapped the movements of each volunteer as they stood up, and found that they each carried out a common sequence of motions, moving from one pose, or “waypoint,” to the next, in a predictable order.

“Those ergonomic experiments helped us to model in a straightforward way, how a human stands up,” Ballesteros says. “We could postulate that about 80 percent of humans stand up in a similar way. Then we designed a controller around that trajectory.”

Helping hand

The team developed software to generate a trajectory for a robot, following a sequence that would help support a human and lift them back on their feet. They applied the controller to a heavy, fixed robotic arm, which they attached to a large backpack. The researchers then attached the backpack to the bulky suit and helped volunteers back into the suit. They asked the volunteers to again lie on their back, front, or side, and then had them attempt to stand as the robot sensed the person’s movements and adapted to help them to their feet.

Overall, the volunteers were able to stand stably with much less effort when assisted by the robot, compared to when they tried to stand alone while wearing the bulky suit.

“It feels kind of like an extra force moving with you,” says Ballesteros, who also tried out the suit and arm assist. “Imagine wearing a backpack and someone grabs the top and sort of pulls you up. Over time, it becomes sort of natural.”

The experiments confirmed that the control system can successfully direct a robot to help a person stand back up after a fall. The researchers plan to pair the control system with their latest version of SuperLimbs, which comprises two multijointed robotic arms that can extend out from a backpack. The backpack would also contain the robot’s battery and motors, along with an astronaut’s ventilation system.

“We designed these robotic arms based on an AI search and design optimization, to look for designs of classic robot manipulators with certain engineering constraints,” Ballesteros says. “We filtered through many designs and looked for the design that consumes the least amount of energy to lift a person up. This version of SuperLimbs is the product of that process.”

Over the summer, Ballesteros will build out the full SuperLimbs system at NASA’s Jet Propulsion Laboratory, where he plans to streamline the design and minimize the weight of its parts and motors using advanced, lightweight materials. Then, he hopes to pair the limbs with astronaut suits, and test them in low-gravity simulators, with the goal of someday assisting astronauts on future missions to the moon and Mars.

“Wearing a spacesuit can be a physical burden,” Asada notes. “Robotic systems can help ease that burden, and help astronauts be more productive during their missions.”

This story is republished courtesy of MIT News (web.mit.edu/newsoffice/), a popular site that covers news about MIT research, innovation and teaching.

At approximately 4:10 p.m. on January 1, 2024, the Noto region of Ishikawa Prefecture in Japan was hit by a large earthquake with a moment magnitude (Mw) of 7.5. This earthquake, known as the 2024 Noto Peninsula earthquake, registered a maximum seismic intensity of 7 on the Japanese scale and caused widespread damage, including numerous casualties.

Several active faults, primarily extending in a northeast-southwest direction, are known to exist in the Noto Peninsula and its surrounding areas.

For approximately three years prior to the earthquake, slow aseismic crustal deformation and active seismicity, which were believed to be associated with subsurface fluid movement, had been observed. Understanding how these active fault networks and crustal activities contribute to major earthquake ruptures is crucial for comprehending earthquake generation mechanisms and the production of intense shaking movements.

In a study, published in Geophysical Research Letters, researchers examined global seismic waveform data to estimate the rupture process of the 2024 Noto Peninsula earthquake.

Findings suggest that the earthquake comprised multiple rupture episodes. Notably, the initial rupture, which lasted approximately 10 s after the earthquake, coincided with the preceding active crustal activity zone. Moreover, the main rupture that followed the initial rupture was bifurcated into west and east ruptures across the initial rupture zone, where each zone had sequentially rupturing faults with varying orientations and inclinations.

This study highlights that the 2024 Noto Peninsula earthquake was governed by a network of faults with diverse geometries and that it was closely linked to the crustal activity observed in the initial rupture zone prior to the main shock.

This intricate rupture growth process is anticipated to provide valuable insights for gaining an improved understanding of earthquake mechanisms and assessing earthquake damage risks.

Black drivers in Chicago are significantly more likely than white drivers to be stopped by police regardless of where the drivers live or are going, according to a new study led by a Cornell city planning expert that maps the racial composition of roads by using mobile phone GPS data. The study confirms a racial bias in traffic stops that the researchers say is replacing stop and frisk as a new tactic for discrimination.

In addition to police stops, the researchers investigated ticketing by speed cameras deployed across the city, finding Black drivers were ticketed more—but roughly in proportion to the racial makeup of drivers in those locations. On a street where data showed half of drivers were Black, the researchers found a 54% probability of Black drivers being issued a camera ticket.

In comparison, police-initiated traffic stops showed a “strong overrepresentation” of Black motorists relative to the proportion on the roads—and the reverse for white drivers. On a street with 50% Black drivers, they comprised about 70% of the police stops, on average. Where half of drivers were white, fewer than 20% of stops involved white drivers.

“This is the first time that we’ve had such a granular, block-by-block understanding of a bias in traffic enforcement, showing that police disproportionately stop Black drivers at a higher rate,” said Wenfei Xu, assistant professor of city and regional planning in the College of Architecture, Art and Planning (AAP) and director of the Urban Data Research Lab.

Xu, a Chicago native, is the first author of the paper “The Racial Composition of Road Users, Traffic Citations, and Police Stops,” published June 3 in the Proceedings of the National Academy of Sciences with co-authors including Houpu Li, a master’s student in city and regional planning (AAP), and experts from Rutgers University; the University of Illinois, Chicago; and the University of Sydney in Australia.

While previous research has provided evidence of racial profiling in traffic stops, the demographics of the people stopped are often measured against the makeup of the adjacent neighborhood, rather than the demographics of drivers on the road. Xu’s team introduced a new level of detail by analyzing traffic stops and citations based on who is actually driving, down to the level of city blocks and intersections.

“Looking simply at the surrounding area is not the best approach for understanding what is happening across a city, because people who drive are often going through a neighborhood and not to it,” said David Levinson, professor of transportation in the University of Sydney’s School of Civil Engineering and a co-author of the research.

“There are a number of theories proposed to establish and understand the sources of police racial bias in traffic enforcement, but it is hard to deny that it exists.”

To conduct their analysis, the researchers obtained data from Replica, a mobility analytics platform, illustrating traffic patterns on a representative (pre-pandemic) day in 2020, encompassing 46 million trips in the Chicago metro area. Leveraging cellphones’ repeated signaling of their location, Replica’s anonymized models generate a “synthetic” population that reflects the racial composition of drivers throughout the day.

Through freedom of information requests, the research team then collected Chicago Police Department data for 2019 on nearly 650,000 traffic stops and more than 700,000 tickets issued by roughly 160 traffic cameras across the city. The scholars compared the demographics from those events to the roads’ racial composition.

“Regardless of where you are in the city and the makeup of drivers on the road,” said Xu, “Black drivers are always a higher proportion of those that are stopped.”

The justification for the stops—whose number have increased steadily over the past decade—seems questionable, Xu said, since a small fraction result in arrests, and a smaller percentage uncover illegal gun possession. But traffic stops can escalate into dangerous encounters that place Black Americans at higher risk—the 2016 police killing of Philando Castile in Minnesota being one high-profile example.

In disproportionately impacting minority residents, Xu said the traffic stops appear to mirror stop-and-frisk policies criticized for systemic racial bias. Cities and their police departments, she said, should consider prohibiting stops for minor offenses such as a broken taillight or expired registration.

When you receive a present on your birthday, you might be the kind of person who tears off the wrapping paper immediately to see what’s inside the box. Or maybe you like to examine the box, guessing the contents from its shape, size, weight or the sound it makes when you shake it.

When physicists at the Large Hadron Collider (LHC) analyze their datasets in search of new physics phenomena such as new particles, they usually take one of two different approaches. They either perform a direct search for a specific new kind of particle, equivalent to tearing off the wrapping paper immediately, or use an indirect strategy based on quantum mechanics and its subtle wonders, similar to shaking the box and guessing what’s inside.

At the annual LHCP conference that took place in Boston, the CMS collaboration reported how it used the second approach to look for new physics in a rare decay of a particle called B⁰ meson.

The physics process that drives the decay of a particle into lighter ones can be influenced by new, unknown particles, which might be too heavy to be produced at the LHC. This influence could change the decay process in ways that can be measured and compared to predictions of the Standard Model of particle physics.

In the same way as shaking the box containing your birthday present could give you a clue about what’s inside, any deviation from the Standard Model predictions could give physicists a hint of new physics.

The decay of the B⁰ meson, which is made up of a bottom quark and a down quark, into a K*⁰ meson (containing a strange quark and a down quark) and two muons is particularly suited to this approach. This is because it occurs via a rare penguin transition that is highly sensitive to possible contributions from new heavy particles.

In its new study, the CMS team used all the data collected by its detector between 2016 and 2018, during the second run of the LHC, to “shake” this B⁰ decay “box.” This box offers many ways to look for new physics. One is to weigh the box, i.e. measure the rate at which the decay occurs. Another is to take two twin boxes—for example, one corresponding to the decay into two muons and the other to the decay into two electrons—and check if they weigh the same.

In their new study, the CMS researchers looked at the shape of the box, i.e. they examined how the particles produced in the decay share the energy of the parent B⁰ meson and measured at what angles they fly away from each other. They then determined a set of parameters using these energies and angles, and compared the results with two sets of predictions from the Standard Model.

For most parameters, the results are in line with these two sets of Standard Model predictions. However, for two parameters, known as P₅‘ and P₂, and for specific energies of the two muons, the results are in tension with the two available predictions. Overall, the results are in agreement with the previous results from the ATLAS, LHCb and Belle experiments, while improving upon their level of precision.

Unfortunately, there is a charming, “naughty” kind of penguin that’s crashing the birthday party: a charm quark that participates in the rare penguin transition. This complicates the Standard Model predictions and makes it difficult to draw a conclusion. To advance, researchers need better predictions, more data and improved analysis techniques.